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PCAT Study guide

by: Jisun Ban

PCAT Study guide PCAT

Jisun Ban
GPA 3.5

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These are some MUST KNOW for your Pharmacy college admission test! PCAT I hope these helps you! I am done with these and now in the process of interview with schools I applied to 10 schools and...
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Date Created: 10/10/16
COMPLETE BIOLOGY Table of contents  I. Chemistry  II. Cells III. Cellular Respiration IV. Photosynthesis V. Cell Division VI. Heredity VII. Molecular Genetics VIII. Evolution IX. Biological Diversity X. Plants XI. Animal Forms and Function (Physiology) XII. Animal Reproduction and Development  XIII. Animal Behavior XIV. Ecology I. Chemistry Atoms, Molecules, Ions, Bonds –  Atom is made up of neutrons, protons, and electrons. Molecules are groups of 2 or more atoms held together by chemical bonds. Chemical bonds are due to electron interactions  Electronegativity = ability of an atom to attract electrons  Bond Types: o Ionic – transfer of electrons from one atom to another (different electronegativities) o Covalent – electrons are shared between atoms (similar electronegativities) – can be single, double, triple  Nonpolar = equal sharing of electrons (identical electronegativity)  Polar = unequal sharing of electrons (different electronegativity and formation of a dipole) o Hydrogen – weak bond between molecules with a hydrogen attached to a highly electronegative atom and is attracted to a negative charge on another molecule (F, O, N) * Properties of Water: 1. Excellent solvent: dipoles o2 H O break up charged ionic molecules. 2. High Heat Capacity: heat capacity is the degree in which a substance changes temp in response to gain/loss of  heat. The temp of large water body are very stable in response to temp changes of surrounding air; must add large amount  of energy to warm up water. High heat of vaporization as well.  3. Ice Floats: water expands as it freezes, becomes less dense than its liquid form (H­bonds become rigid and form a  crystal that keeps molecules separated). 4. Cohesion/Surface tension: attraction between like substances due to H­bonds; the strong cohesion bet2een H O  molecules produces a high surface tension. 5. Adhesion: attraction of unlike substances. (wet finger and flip pages); capillary action: ability of liquid to flow  without external forces (e.g. against gravity) Organic Molecules –  Have carbon atoms. Macromolecules form monomers (1 unit) which form polymers (series of repeating monomers) o 4 of carbon’s 6 electrons are available to form bonds with other atoms 1  Functional group = particular cluster of atoms, give molecules unique properties o Hydroxyl (OH): polar and hydrophilic o Carboxyl (COOH): polar, hydrophilic, weak acid o Amino (NH )2 polar, hydrophilic, weak base o Phosphate (PO )3 polar, hydrophilic, acid (sometimes shows as PO 4) (y acidic?) o Carbonyl (C=O): polar and hydrophilic  Aldehyde (H-C=O)  Ketone (R-C=O) o Methyl (CH3): nonpolar and hydrophobic Carbohydrates:  Monosaccharide = single sugar molecule (e.g. glucose and fructose) o Alpha or beta based on position of H and OH on first (anomeric) carbon (down=alpha, up=beta)  Disaccharide = two sugar molecules joined by a glycosidic linkage (joined by dehydration) o E.g. sucrose (glu+fru), lactose (glu+gal), maltose (glu+glu)  Polysaccharide = series of connected monosaccharides; polymer o Bond via dehydration synthesis, breakdown via hydrolysis ­ Starch: a polymer of α­glucose molecules; store energy in plant cells. ­ Glycogen: a polymer of α­glucose molecules; store energy in animal cells. (differ in polymer branching). ­ Cellulose: a polymer of β­glucose; structural molecules for walls of plant cells and wood. ­ Chitin: polymer similar to cellulose; but each β­glucose has a nitrogen­containing group attached to ring. Structural  molecule in fungal cell walls (also exoskeleton of insects, etc) Lipids –  Hydrophobic molecules. Fxns: Insulation, energy storage, structural (cholesterol and phoslipids in membrane), endocrine  Triglycerides (triacylglycerols) = three fatty acid chains attached to a glycerol backbone o Saturated: no double bonds (bad for health, saturated = straight chain = stack densely and form fat plaques) o Unsaturated: double bonds (better for health, unsaturated = double bonds cause branching = stack less dense)  Phospholipid: two fatty acids and a phosphate group (+R) attached to a glycerol backbone o Amphipathic = both hydrophilic and hydrophobic properties  Steroids = three 6 membered rings and one 5 membered ring –hormones and cholesterol (membrane component)  Lipid Derivatives: o Phospholipids (covered above) o Waxes – esters of fatty acids and monohydroxylic alcohols. Used as protective coating or exoskeleton (lanolin) o Steroids (sex hormones, cholesterol, corticosteroids) – 4 ringed structure o Carotenoids – fatty acid carbon chains w/ conjugated double bounds and six membered C- rings at each end. Pigments which produce colors in plants and animals.  Carotenes and xanthophylls (subgroups) o Porphyrins (tetrapyrroles) – 4 joined pyrrole rings. Often complex w/ metal (e.g. porphyrin heme complexes with Fe in hemoglobin, chlorophyll w/ Mg) 2 Adipocytes (img) are specialized fat cells – white fat cells contain a large lipid droplet composed primarily of triglycerides with a small layer of cytoplasm around it, while brown fat cells have considerable cytoplasm, lipid droplets scattered throughout, and lots of mitochondria Glycolipids are like phospholipids but w/ carb group instead of phos. Note: lipids are insoluble so they are transported in blood via lipoproteins (lipid core surrounded by phospholipids and apolipoproteins). Note on lipids in membranes: Cell membranes need to maintain a certain degree of fluidity and are capable of changing membrane fatty acid composition to do so. In cold weather, to avoid rigidity, cells incorporate more mono and polyunsaturated fatty acids into the membrane (lower melting points and are kinked to increase fluidity). Warm weather climates show the opposite trend. Unsaturated fatty acids have lower melting point compared to saturated fatty acids – there are increased "kinks" in packing of the molecules as a result of the double bonds, which decrease the melting point due to less efficient packing (you can look at this two ways; freezing point: harder to pack into crystal/solid form with kinks so temp has to be lowered more, or melting point: less efficient packing means less intermolecular interactions, so less heat is needed to melt the solid liquid form). Cholesterol also has a role (see below). Remember: the above trends are relevant for fatty acids as a group, not necessarily molecules in general. Random chemistry note: double/triple bonds tend to have decreased polarity vs single bonds in the same (already polar) bond. Proteins –  Polymers of amino acids joined by peptide bonds o Amino acid structure: H, NH2, COOH bonded to a central carbon and then a variable R group  Structural, storage, transport, defensive (antibodies), enzymes o Storage protein: casein in milk, ovalbumin in egg whites, and zein  in corn seeds. o Transport protein: Hemoglobin carries oxygen, cytochromes carry electrons o Enzymes: ATP contains ribose instead of deoxy­ ribose (ATP isn’t an enzyme, why is this here?). ­ amylase catalyzes the rxn that breaks the α­ glycosidic bonds  in starch. ­ catalyzes a reaction in both forward and reverse directions based on [substrate]. ­ efficiency is determined by temp and pH. ­ cannot change spontaneity of a rxn  Random note: enzymes are almost always considered to be proteins, but sometimes RNA can act as an enzyme (e.g. ribozymes)  ­ Cofactors are nonprotein molecules that assist enzymes. Holoenzyme is the union of the cofactor and  the enzyme (the enzyme is called apoenzyme/apoprotein when NOT combined w/ cofactor); can be  3 organic (called coenzymes e.g. vitamin) or inorganic (metal ions like Fe 2+ and Mg 2+). If cofactor strongly  covalent bonds to enzyme = prosthetic group  Protein structure: o Classifications: simple (entirely amino acids), albumins + globulins (functional and act as carriers or enzymes), scleroproteins (fibrous, structural e.g. collagen), conjugated (simple protein + nonprotein), lipoprotein (bound to lipid), mucoprotein (bound to carb), chromoprotein (bound to pigmented molecule), metalloprotein (complexed around metal ion), nucleoprotein (contain histone or protamine, bound to nucleic acid). o Primary structure = sequence of amino acids o Secondary structure = 3d shape resulting from hydrogen bonding between amino and carboxyl groups of adjacent amino acids (e.g. alpha helix, beta sheet) o Tertiary structure = 3d structure due to noncovalent interactions between amino acid R groups (subunit interaction) (factors: H-bonds, ionic bonds, hydrophobic effect [R groups push away from water center], disulfide bonds, van der waals) o Quaternary structure = 3d shape of a protein that is a grouping of two or more separate peptide chains Note:All proteins have a primary structure, and most have a secondary structure. Larger proteins can have a tertiary and quarternary structure. There are three main protein categories: globular proteins (somewhat water soluble, many fxns: enzymes, hormones, inter and intracellular storage and transport, osmotic regulation, immune response, etc., mostly dominated by 3ary structure), fibrous/structural proteins (not water soluble, made from long polymers, maintain + add strength to cellular and matrix structure, mostly dominated by 2ndary structure), and membrane proteins (membrane pumps/channels/receptors) Note: Protein denaturation means the (secondary onward) structure of the protein is basically removed, not necessarily that the protein itself is broken down into individual amino acids. Denaturation is usually irreversible, but in some cases it can be reversed with the removal of the denaturing agent (implies all info needed for protein to assume its native state is encoded in the primary structure) Nucleic Acids –  DNA is a polymer of nucleotides o Nucleotide: nitrogen base, five carbon sugar deoxyribose, phosphate group  Purines (2 rings) – adenine, guanine (double ring)—2 H bonds (AT2, GC3)  Pyrimidines (1 ring): thymine, cytosine (singe ring) – 3 H bonds (to remember: CUT the PYE)  A nucleoside is just the sugar+base o Two antiparallel strands of a double helix  RNA is a polymer of nucleotides that contain ribose, not deoxyribose o Thymine is replaced by uracil (which pairs with adenine) o Usually single stranded Cell doctrine/theory: 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of structure, function, and organization in all organisms. 3. All cells come from preexisting, living cells. 4. Cells carry hereditary information RNA world hypothesis proposes that self-replicating ribonucleic acid (RNA) molecules were precursors to current life (based on deoxyribonucleic acid (DNA), RNA and proteins). RNA stores genetic information like DNA + catalyzes chemical reactions like an enzyme protein may have played a major step in the evolution of cellular life. RNA is unstable compared to DNA, so more likely to participate in chemical rxns (due to its extra hydroxyl group). Central dogma of genetics: biological information cannot be transferred back from protein to either protein or nucleic acid; DNA  RNA  proteins Know basic microscopy: -Stereomicroscope (light): Visible light for surface of sample. Can look at living samples, but low resolution vs compound light micro. -Compound microscope (light): Visible light for thin section of sample. Can look at some living samples (single cell layer). May require staining for good visibility. -Phase-contrast: Uses light phases and contrast. Allows for detailed observation of living organisms (including internal structures) if thin. Good resolution/contrast, but not good for thick samples and produces “Halo effect” around perimeter of samples. -Confocal laser scanning + fluorescence: Can look at thin slices while keeping sample intact; can look at specific parts of cell via fluorescent tagging. Can look at living cells, but only fluorescently tagged parts. Fluorescence can cause 4 artifacts. Used to observe chromosomes during mitosis. Note: confocal laser scanning microscope can be w/out fluorescence as well. Uses laser light to scan dyed specimen, then displays the image digitally. -Scanning elctron microscope (SEM): Look at surface of (3D) objects with high resolution. Can’t use on living: preparation is extensive (sample needs to be dried and coated). Costly. -CryoSEM: Like SEM but no dehydration so you can look at samples in more “natural” form. Can’t use on living: samples frozen for prep, which can cause artifacts. -Transmission electron microscope (TEM): look at very thin cross-sections in high detail. Can look at internal structures, very high resolution, but can’t be used on living things (preparation is extensive). Costly. -Electron tomography: 3D model buildup using TEM data. Can look at objects in 3D and see objects relative to one another. Can’t be used on living things (see TEM above). Centrifugation (spins + seperates liquified cell homogenates separate into layers based on density: (most dense/fastest to pellet out/the bottom is nuclei layer, spin faster then mitochondria/chloroplasts/lysosome/peroxisomes, spin faster  then microsomes [internal membranes from ER]/small vesicles, spin faster  then ribosomes/viruses/larger macromolecules). Centrifugation can be differential centrifugation or density centrifugation, the former is density + shape factor based on speed the macromolecule travels at whereas density is just density based. The above described spin pattern is differential centrifugation, we spin and take the dense pellet and then spin again repeat. Density centrifugation is continuous layers of sediment. Chemical Reactions in Metabolic Processes –  Catalysts lower activation energy, accelerating the rate of the rxn  Metabolism = catabolism + anabolism + energy transfer  Characteristics of chemical reactions o Concentration of reactants and products determines which way a rxn will go  Equilibrium: rate of forward and reverse rxns is the same = 0 net production o Enzymes are globular proteins that act as catalysts  Substrate specific, unchanged during rxn, catalyzes in both forward and reverse directions, temperature and pH affect enzyme function, active site and induced fit is how enzymes bind o Cofactors are nonprotein molecules that assist enzymes usually by donating or accepting some component of a rxn like electrons  Coenzyme are organic cofactors , usually donate or accept electrons  Vitamins  Inorganic cofactors are usually metal ions (Fe 2+ and Mg 2+)  If binds tightly/covalently, prosthetic group o ATP – common source of activation energy. New ATP formed via phosphorylation (ADP + phosphate using energy from energy rich molecule like glucose). Note that ATP contains, but is not itself, potential energy.  Regulation (more here): o Allosteric enzymes – have both an active site for substrate binding and an allosteric site for binding of an allosteric effector (activator, inhibitor) o Competitive inhibition – substance that mimics the substrate inhibits the enzyme by binding at the active site. Can be overcome by increasing substrate cxn. Km changed (raised) but Vmax is not o Noncompetetive inhibition – substance inhibits enzyme by binding elsewhere than active site, substrate still binds but reaction is prevented from completing. Km unchanged but Vmax is not. o Uncompetitive/anti-competitive inhibition: enzyme inhibitor binds only to the formed E-S complex, preventing formation of product (Vmax lowered). Km is also lowered (Le Chetalier’s principle: the equilibrium between E-S complexes and ESI (inhibitor attached) complexes is disrupted by this type of inhibition, as it favors the ESI: so ES complexes are depleted. E+S  ES complex is subsequently shifted forward, so the enzyme’s apparent affinity for the substrate is raised = lower Km). 5 o Cooperativity – enzyme becomes more receptive to additional substrate molecules after one substrate molecule attaches to an active site (e.g enzymes w/ multiple subunits that each have active site [quaternary structure])  Example of process: hemoglobin binding additional oxygen (although hemoglobin ≠ enzyme!) o Km is the Michaelis constant. It represents the substrate cxn at which the rate is half of Vmax. In a way it indirectly represents binding affinity, inversely: small Km indicates that the enzyme requires only a small amount of substrate to become saturated. Hence, the maximum velocity is reached at relatively low substrate concentrations. A large Km indicates the need for high substrate concentrations to achieve maximum reaction velocity. So raised Km = substrate is binding worse, lowered Km = substrate is binding better. ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ II. Cells  Membrane proteins: peripheral (loosely attached to one side surface), integral (embeds inside membrane), transmembrane (all the way through, both sides – this is a TYPE of integral)  Phospholipid membrane permeability – small, uncharged, nonpolar molecules (polar can only if small and uncharged) and hydrophobic molecules can freely pass across the membrane. Everything else requires transporter (large, polar, charged molecules). Another way of saying impermeable is “resistant to”.  Note: peripheral membrane proteins are generally hydrophilic; held in place by H-bonding and electrostatic interaction. Disrupt/detach by changing salt cxn or pH to disrupt these interactions. Integral proteins are hydrophobic; use detergent to destroy membrane and expose these proteins. * Proteins: ­ Channel proteins: provide passageway through membrane for hydrophilic (water­soluble) substances (polar, and charged). **­ Recognition proteins: such as major­histocompatibility complex on macrophage to distinguish between self and foreign; they are glycoproteins due to oligosaccharides attached. ­ Ion channels: passage of ions across membrane. Called gated channels in nerve and muscle cells, respond to stimuli. Note  that these can be voltage­gated (respond to difference in membrane potential), ligand­gated (chemical binds and opens  channel), or mechanically­gated (respond to pressure, vibration, temperature, etc).  **­ Porins: allow passage of certain ions + small polar molecules. Aquaporins increase rate of H2O passing (kidney and  plant root cells). These tend not to be specific, they’re just large passages, if you can fit you’d go through. ­ Carrier proteins: bind to specific molecules, protein changes shape, molecule passed across. E.g. glucose into cell.(this is a type of transport protein). Carrier seems to be specific to movement across membrane via integral membrane protein. ­ Transport proteins: can use ATP to transport materials across (not all transport use ATP). Active transport. E.g. Na+­K+  pump to maintain gradients. Facilitated diffusion as well. Transport protein is a broad category that encompasses many of  the above.Chad’s quiz says transport use ATP but other sources contradict: transport can by facilitated diffusion.  **­ Adhesion proteins: attach cells to neighboring cells, provide anchors for internal filaments and tubules  (stability) ­ Receptor proteins: binding site for hormones + other trigger molecules ­ Cholesterol: adds rigidity to membrane of animal cells under normal conditions (but at low temperatures it maintains its  fluidity); sterols provide similar function in plant cells. Prokaryotes do not have cholesterol in their membranes (use  hopanoids instead) **­ Glycocalyx: a carbohydrate coat that covers outer face of cell wall of some bacteria and outer face of plasma membrane  (some animal cells). It consists of glycolipids (attached to plasma membrane) and glycoproteins (such as recognition  proteins). It may provide adhesive capabilities, a barrier to infection, or markers for cell­cell recognition. * Organelles 6 ­ Nucleus: chromatin is the general packaging structure of DNA around proteins in eukaryotes, the tightness of the  packaging varies depending on cell stage; chromosomes is tightly condensed chromatin when the cell is ready to divide;  histones serve to organize DNA which coil around it into bundle nucleosomes (8 histones); nucleolus inside the nucleus  are the maker of ribosomes (rRNA).  rRNA is synth’d in nucleolus + ribosomal proteins imported from cytoplasm = ribosomal subunits form; these  subunits are exported to the cytoplasm for final assembly into comp. Nucleus bound by double layer nuclear envelope w/ nuclear  pores for transport (mRNA, ribosome subunits, dNTPs, proteins like RNA polymerase + histones, etc) in/out. Note there is  no “cytoplasm” in nucleus, there’s a nucleoplasm instead. **­ Nuclear Lamina: dense fibrillar network inside nucleus of eukaryotic cells (Intermediate filaments + membrane assoc.  proteins). Provides mechanical support; also helps regulate DNA replication, cell division, chromatin organization.  ­ Nucleoid: irregular shaped region within the cell of prokaryote that contains all/most generic material  ­ Cytoplasm: this is an area, not a structure! metabolic activity and transport occur here. Cyclosis is streaming movement  within cell. Doesn’t include nucleus, but does included cytosol, organelles, everything suspended w/in cytosol but nucleus ­ Cytosol: difference vs cytoplasm here (cytosol doesn’t include the stuff suspended within the gel­like substance, it is JUST the gel­like stuff. Think jello vs veggie stew.) (the cytosol is also known as cytoplasmic matrix) ­ Ribosomes: 60S + 40S = 80S, prokaryote (50S + 30S = 70S); the two subunits produced inside the nucloleus moved into  the cytoplasm where they assembled into a single 80S ribosomes (larger S value indicates heavier molecule). Made of  rRNA+protein, function to make proteins. **­ ER: rough ER (with ribosomes) creates glycoproteins by attaching polysaccharides to polypeptides as they are  assembled by ribosomes. In eukaryotes the rough ER is continuous with the outer nuclear membrane. Smooth ER (no  ribosomes) synthesizes lipids and steroid hormones for export. In liver cells, smooth ER has functions in breakdown toxins,  drugs, and toxic by­products from cellular rxn. Smooth and striated muscle have smooth ER’s called sarcoplasmic  reticulums that store and release ions, e.g. Ca 2+ **­ Lysosomes: vesicles produced from Golgi that contain digestive enzymes (low pH for function); break down  nutrients/bacteria/cell debris. Any enzyme that escape from lysosomes remains inactive in the neutral pH of cytosol (other  source says autolysis) (lysosomes in plant cell – maybe, but generally taught as none). Functions in apoptosis (releases  contents into cell).  ­ Golgi: transport of various substances in vesicles (cis face is for incoming vesicles, trans face for secretory vesicles). Has  flattened sacs known as cisternae.  **­ Peroxisomes: break down substances (H O  +RH 2> 2 + 2H2 ), fatty ac2d, and amino acid; common in liver and  kidney where they break toxic substances. In plant cell, peroxisomes modify by­products of photorespiration. In  germinating seeds, it is called glyoxysomes break down stored fatty acids to help generate energy for growth. Peroxisome  produce H O 2w2ich they then use to oxidize substrates, they can also break down H O  if nece2s2ry (H O  => H O + 2 2 2 2 **­ Microtubules: made up of protein tubulin, provide support and motility for cellular activities; spindle apparatus which  guide chromosomes during division; in flagella and cilia (9+2 array; 9 pairs + 2 singlets in center) in all animal cells and  lower plants (mosses, ferns). **­ Intermediate filaments: provide support for maintaining cell shape. E.g. keratin.  ­ Microfilament: made up of actin and involved in cell motility. (skeletal muscle, amoeba pseudopod, cleavage furrow) **­ Microtubules organizing centers (MTOCs): include centrioles and basal bodies (are at the base of each flagellum and  cilium and organize their development). 9x3 array. Plant cells lack centrioles and its division is by cell plate instead of  cleavage furrow – note that plants DO have MTOC’s.  ­ Transport vacuoles: move materials between organelles or organelles and the plasma membrane ­ Food vacuoles: temporary receptacles of nutrients; merge with lysosomes which break down food. ­ Central vacuoles: large, occupy most of plant cell interior, exert turgor when fully filled to maintain rigidity. Also store  nutrients, carry out functions performed by lysosomes in animal cells. Have a specialized membrane (tonoplast) **­ Storage vacuoles: plants store starch, pigments, and toxic substances (nicotine). **­ Contractile vacuoles: in single­celled organisms that collect and pump excess water out of the cells (prevent bursting).  Active transport. Found in Protista like amoeba and paramecia, organisms live in hypotonic environment. 7 ­ Cell walls: found in plants, fungi, protists, and bacteria (cellulose in plants; chitin in fungi; peptidoglycans in bacteria,  polysaccharides in archea). Provides support. Sometimes a secondary cell wall develops beneath the primary one. **­ Extracellular matrix: found in animals, in area between adjacent cells (beyond plasma membrane and glycocalyx);  occupied by fibrous structural proteins, adhesion proteins, and polysaccharides secreted by cells; provide mechanical  support and helps bind adjacent cells (collagen is most common here, we also see integrin+fibronectin; network of collagen  and proteoglycans connected to integrins in the cell membrane via fibronectin). Laminin can be seen as well (acts similar to  fibronectin). Images here. Note that cells adhere to the ECM in two ways: focal adhesions (connection of ECM to actin  filaments in the cell) and hemidesmosomes (connection of ECM to intermediate filaments e.g. keratin).   ­ Plastids: found in plant cells. Chloroplasts (site of photosynthesis), leucoplasts (can specialize to store starch/lipid/protein  as amyloplasts/elaioplasts/proteinoplasts respectively, or serve general biosynthetic fxns), chromoplasts (store carotenoids) Mitochondria: make ATP, also fatty acid catabolism (B­oxidation)! (fatty acids are made in cytosol). Also have their own  circular DNA and ribosomes (gives rise to endosymbiotic theory!). Have a double layered membrane.  **Cytoskeleton: microtubules (ex. flagella & cilia), microfilaments, intermediate filaments. In eukaryotic cells, aids in cell division, cell crawling, and the movement of cytoplasm and organelles. Note on plant cells: in a hypotonic solution (their normal state), vacuole swells  turgid. In isotonic, the plant cell is flaccid. In hypertonic, the cell is plasmolyzed – cytoplasm is pulled away from the cell wall. Fungal cells also remain turgid due to cell wall, but animal cells will burst (cytolysis). The endomembrane system is the network of organelles and structures, either directly or indirectly connected, that function in the transport of proteins and other macromolecules into or out of the cell.Includes plasma membrane, endoplasmic reticulum, golgi apparatus, nuclear envelope, lysosomes, vacuoles, vesicles, endosomes but not the mitochondria or chloroplasts. * Circulation:   Intracellular Circulation o Brownian movement (particles move due to kinetic energy, spreads small suspended particles throughout cytoplasm) o Cyclosis/streaming: circular motion of cytoplasm around cell transport molecules o Endoplasmic Reticulum: Provides channel through cytoplasm, provides direct continuous passageway from plasma membrane to nuclear membrane  Extracellular Circulation o Diffusion: If cells in close contact with external environment, can suffice for food and respiration needs. Also used for transport of materials between cells and interstitial fluid around cells in more complex animals o Circulatory system: complex animals w/ cell too far from external environment require one. Use vessels. * Junctions: **­ Anchoring junctions: desmosome (keratin filaments inside attach to adhesion plaques which bind adjacent cells  together via connecting adhesion proteins, providing mechanical stability, hold cellular structures together). In animal cells.  Present in tissues with mechanical stress – skin epithelium, cervix/uterus. img ­ Tight junctions: completely encircles each cell, producing a seal that prevents the passage of materials between cells;  characteristic of cells lining the digestive tract where materials are required to pass through cells into blood (They prevent  the passage of molecules and ions through the space between cells. So materials must actually enter the cells (by diffusion  or active transport) in order to pass through the tissue). In animal cells. img ­ Gap junction: narrow tunnels between animal cells (connexins); prevent cytoplasms of each cell from mixing, but allow  passage of ions and small molecules; essentially channel proteins of two adjacent cells that are closely aligned (smooth  muscle single of spreading action potential). In animal cells. Tissue like heart have these to pass electrical impulses. img  ­ Plasmodesmata: narrow tunnels between plant cells (narrow tube of endoplasmic reticulum­desmotubule; but exchange  material through cytoplasms surrounding the desmotubule). img * Prokaryotes and Eukaryotes: **Eukaryotes include all organisms except for bacteria, cyanobacteria, and archaebacteria. Prokaryotes have a  plasma membrane, DNA molecule, ribosomes, cytoplasm, and cell wall. In prokaryotes:  1. No nucleus. 4. Cell walls (peptidoglycan); archea (polysaccharides) – many have sticky capsules on wall 8 2. Single (circular) naked ds DNA (no chromatin). 3. Prokaryote (50S + 30S = 70S); 5. Flagella are constructed from flagellin not microtubules in prokaryotes.  Substance Movement: o Hypertonic (higher solute concentration), hypotonic (lower solute concentration), isotonic (equal solute concentration) o Bulk Flow = collective movement of substances in the same direction in response to a force or pressure (e.g. blood) o Passive Transport –  Simple diffusion, osmosis, dialysis (diffusion of different solutes across a selectively permeable membrane), plasmolysis (movement of water out of a cell that results in its collapse), facilitated diffusion, countercurrent exchange (diffusion by bulk flow in opposite directions – blood and water in fish gills). Note: diffusion is net, some few particles still move against the gradient because molecule movement is random, but net diffusion is generally what we talk about. o Active Transport – movement of transports against their concentration gradients requiring energy. Usually solutes like small ions, amino acids, monosaccharides * Endocytosis: uses ATP (active process) (exocytosis is also active process) (Cliff’s FC says bulk flow is active too…?) ­ Phagocytosis: undissolved material (solid) enters cell; white blood cell engulfs. Plasma membrane wraps outward around. ­ Pinocytosis: dissolved material (liquid). Plasma membrane invaginates. ­ Receptor­mediated: a form of pinocytosis; specific molecules (ligand) bind to receptors; proteins that transport cholesterol  in blood (LDL) and hormones target specific cells by this. ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ Interlude: Biothermodynamics Recall Gibbs Free Energy, which tells us whether a given chemical rxn can occur spontane(H is enthalpy, T is temperature, S is entropy. If ∆G is negative, the reaction can occur spontaneously. Likewise, if ∆G is positive, the reaction is nonspontaneous. How  does this apply to biology? Chemical reactions can be “coupled” together if they share intermediates. In this case, the overall Gibbs  Free Energy change is the sum of the ∆G values for each reaction. Therefore, an unfavorable reaction (positive ∆G1) can be driven by a second, highly favorable reaction (negative ∆G2 where the magnitude of ∆G2 > magnitude of ∆G1). Example: the reaction of  glucose with fructose to form sucrose has a ∆G value of +5.5 kcal/mole (will not occur spontaneously). The breakdown of ATP to form  ADP and inorganic phosphate has a ∆G value of ­7.3 kcal/mole. These two reactions can be coupled together, so that glucose binds  with ATP to form glucose­1­phosphate and ADP. The glucose­1­phosphate is then able to bond with fructose yielding sucrose and  inorganic phosphate. The ∆G value of the coupled reaction is ­1.8 kcal/mole, indicating that the reaction will occur spontaneously. This  principle of coupling reactions to alter the change in Gibbs Free Energy is the basic principle behind all enzymatic action in biological  organisms. III. Cellular Respiration: review page 46 in Cliffs. CELLULAR RESPIRATION – overall an oxidative, exergonic process ( ∆G = ­686 kcal/mole)  External respiration is entry of air into lungs and gas exchange between alveoli and blood; internal respiration is exchange of gas between blood and the cells + intracellular respiration processes  During respiration, high energy H atoms removed from organic molecules (dehydrogenation)  C H6O 1266  6CO2+6H O +2energy2  Aerobic respiration = in the presence of O (glyc2lysis, pyruvate decarb, krebs cycle, oxidative phosphorylation); water is the final product  Glycolysis – decomposition of glucose into pyruvate in cytosol o 2ATP added, 2NADH produced, 4 ATP produced, 2 pyruvate formed  NET: 2 ATP + 2 NADH + 2 pyruvate (+2 H O + 2 H2) o ATP produced here via substrate level phosphorylation  Direct enzymatic transfer of a phosphate to ADP, no extraneous carriers needed o Hexokinase phos’s glucose, important because then it can’t diffuse out + tricks the gradient nd o PFK (enzyme) adds 2 phosphate, makes fructose 1,6-biphosphate – this is irreversible and commits to glycolysis, major regulatory point! 9  Pyruvate Decarboxylation o At this point we are in the mitochondrial matrix o Pyruvate to Acetyl CoA, producing 1 NADH and 1 CO 2  NET: 2 NADH + 2 CO 2 o Catalyzed by PDC enzyme (pyruvate dehydrogenase complex)  Krebs Cycle/Citric Acid Cycle/Tricarboxylic Acid Cycle - fate of pyruvate that is produced in glycolysis o **In the Krebs cycle, Acetyl CoA merges with oxaloacetate to form citrate, cycle goes w/ 7 intermediates o 3 NADH, 1 FADH2, 1 ATP (via sub phos), and 2 CO ar2 produced per turn o x2 for glucose because 2 pyruvate are made from 1 glucose in glycolysis so two rounds of TCA cycle occur  Total 6 NADH, 2 FADH ,22 ATP (technically GTP), 4 CO 2  These ATP produced via substrate level phos o takes place in mitochondria matrix (likewise with pyruvate decarbox) o CO 2roduced here is the CO an2mals exhale when they breathe  ETC (electron transport chain) o Takes place at the inner membrane/cristae (folds which increase SA for more ETC action)  Oxidative Phosphorylation – process of ADP  ATP from NADH and FADH via pa2sing of electrons through various carrier proteins; energy doesn’t accompany the phosphate group but comes from the electrons in the ETC establishing an H+ gradient that supplies energy to ATP synthase o NADH makes more energy than FADH , mor2 H+ is pumped across per NADH (both are coenzymes) (3:2 yield) o Final electron acceptor is oxygen – combines with native H+ to form water (H2O) o Random note: oxidizing agent causes something else to get oxidized; the oxidizing agent itself is reduced; vice versa for reducing agents o Carriers extract energy from NADH and FADH2 while pumping protons into the intermembrane space – atp synthase uses this gradient (which is a pH and electrical gradient) to make atp as it shuttles H+ back into the inner matrix o Coenzyme Q (CoQ)/Ubiquinone is a soluble carrier dissolved in the membrane that can be fully reduced/oxidized, it passes electrons as seen in diagram o Cytochrome C is a protein carrier in the ETF, common in many living organisms, used for genetic relation  Cytochromes have nonprotein parts like iron (donate/accept electrons, for redox!) o Couples exergonic flow of electrons with endergonic pumping of protons across cristae membrane  TOTAL energy from 1 glucose is ~36 ATP, but in prokaryotes 38 ATP (not actual yield, mitochondrial efficacy varies) o Difference because prokaryotes have no mitochondria so they (unlike eukaryotes) don’t need to transfer pyruvate into the mitochondrial matrix (which is done via active transport thus costing ATP), they use cell membrane for respiration. 10  Mitochondria – outer membrane, intermembrane space (H+), inner membrane (ox phosp.), mitochondrial matrix (krebs)  Chemiosmosis in mitochondria: o Mechanism of atp generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane o Krebs produces NADH/FADH , 2hey are oxidized (lose electrons), H+ transported from matrix to intermembrane space, pH and electric charge gradient is created, ATP synthase uses the energy in this gradient to create ATP by letting the protons flow through the channel o Common question topic is about pH changes from these processes; remember that H+ cxn up means pH down! ATP (adenosine triphosphate) – an RNA nucleotide (due to its ribose sugar)  Unstable molecule because the 3 phosphates in ATP are negatively charged and repel one another o When one phosphate group removed via hydrolysis, more stable molecule ADP results o The change from less stable molecule to more stable always releases energy  Provides energy for all cells by transferring phosphate from ATP to another molecule Anaerobic Respiration (cytosol) –  Includes glycolysis + fermentation  Aerobic respiration regenerates NAD+ via O , 2hich is required for continuation of glycolysis, without O2, there would be no replenishing – NADH accumulates, cell would die w/ no new ATP, so fermentation occurs…  **Alcohol Fermentation o Occurs in plants, fungi (e.g. yeasts), and bacteria (e.g. botulinum) o Pyruvate  acetaldehyde + CO , then acetaldehyde ethanol (and NADH  NAD+). o Acetaldehyde is the final electron acceptor! The final molecule isn’t the final acceptor; acetaldehyde is the final acceptor of the electrons thus forming ethanol! Same with O2 being the final electron acceptor of cellular respiration; thus forming H2O!  **Lactic Acid Fermentation o Occurs in human muscle cells, other microorganisms o Pyruvate  lactate (and NADH  NAD+) o Lactate is transported to liver for conversion back to glucose once surplus ATP available  Facultative anaerobes can use oxygen when it’s present (more efficient) but switch to fermentation/anaerobic respiration if it isn’t; obligate anaerobes cannot live in presence of oxygen Alternate energy sources:  When glucose supply is low, body uses other energy sources, in the priority order of: other carbs, fats, and proteins. First converted to glucose or glucose intermediates, then degraded in glycolysis or CAC.  Other carbohydrates o Unrelated: remember we don’t just break down glucose, we can produce it (gluconeogenesis)  Occurs in liver and kidney (liver is responsible for maintaining glucose cxn in blood) o Also: glycogen is a glucose polymer, stored 2/3 in liver and 1/3 in muscles, storage of glucose o **Insulin after large meals stores glucose as glycogen, glucagon is the opposite effect and turns on glycogen degradation. Insulin activates PFK enzyme, glucagon inhibits it (think about this: insulin means ‘hey, we’ve got a lot of glucose around, so let’s chew it up’ whereas glucagon says ‘uhoh, not enough glucose around, don’t chew it up – we need it for the brain, other tissues can use other energy sources’). o Disaccharides are hydrolyzed into monosaccharides, most of which can be converted to glucose or glycolytic intermediates o **All cells capable of producing and storing glycogen but only muscle cells and especially liver cells have large amts  Fats 11 o Store more energy than carbohydrates per C, their carbons are in a more reduced state  Hence why fats are 10 cals/g, whereas carbs and protein are 4 **^ What’s going on above: triglycerides, in the lumen of the small intestine (the tube itself) are broken down via lipases into monoacylglycerides + fatty acids, which are then absorbed into the enterocytes (cell lining of the small intestine). There, they are reassembled into triglycerides, and then (along w/ cholesterol/proteins/phospholipids) packaged into chylomicrons which move on to the lymph capillary for transport to the rest of the body where they are stored as adipose tissue. o Lipases in adipose tissue are hormone sensitive (e.g. to glucagon) o Glycerol  PGAL, enters glycolysis o When fatty acid  Acetyl CoA, every 2 carbon from fatty acid chain makes an Acetyl CoA  ** Fatty acids in blood combine with albumin which carries them o **Fatty acids are broken down for energy via beta oxidation (takes place in mitochondrial matrix)  2 ATP spent activating the (entire) chain  Saturated fatty acids produce 1 NADH and 1 FADH for every 2ut into 2 carbons  NOT the same as for every 2 carbons – e.g. 18C chain is 9 2C pieces but only cut 8 times, each cut is the beta oxidation step  Unsaturated fatty acids produce 1 less FADH2 for each double bond (can’t use double bond forming step)  Results in BIG yield of ATP, yields more ATP per carbon than carbohydrates, more energy in fats than sugars  Protein o Least desirable source of energy, only when carbs and fat unavailable o **Most amino acids are deaminated in liver, then converted to pyruvate or acetyl CoA or other CAC intermediates, enter cellular respiration at these various points (varies by AA)  Oxidative deamination removes ammonia molecule directly from AA. Ammonia is toxic to vertebrates: fish excrete, insects and birds convert to uric acid, mammals convert to urea for excretion. ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ IV. Photosynthesis: overall 6CO  2 6H O 2 C H O6 1266 (some2 ay 6CO  + 12H 2  C H 2  + 6O6+12H 6) 2  2 ­ Photosynthesis begins with light­absorbing pigments in plant cells; able to absorb energy from light; chlorophyll a, b, and  carotenoids (red, orange, yellow). Light is incorporated into electrons => excited electrons are unstable and re­emit  absorbed energy; energy is then reabsorbed by electrons of nearby pigment molecule. The process ends when energy is  absorbed by one of two special chlorophyll a molecules (P 680P ).700 fo700 pigment cluster (PSI) and P  for680 pigment cluster (PSII). Antenna pigments (chlorophyll b, carotenoids, phycobilins [red algae pigment], xanthophylls)  capture wavelegnths that chlorophyll a does not, passes energy to chlorophyll a where direct light rxn occurs. Chlorophyll a  has porphyrin ring (alternating double and single bonds, double bonds critical for light rxns) complexed w/ Mg atom inside. 12 A.  Noncyclic Photophosphorylation  (ADP + P + light ­> ATP):ilight­dependent reaction.    1. Photosystem II: electrons trapped by P  in PSII 680 energized by light. ­ ­ ­    2.  Primary e     acceptor: two excited e passed to primary e acceptor; primary because it is the first in chain of acceptor.    3.      transport chain: consists of a plastoquinone complex (PSII) which contains proteins like cytochrome and cofactor  Fe ; analogous to oxidative phosphorylation. ­    4. Phosphorylation: 2e move down chain => lose energy (energy used to phosphorylate about 1.5ATP).    5. Photosystem I: e transport chain terminates with PSI (P ); they are ag700 energized by sunlight and passed on to  ­ another primary e acceptor. From this point forward it can go to cyclic or noncyclic path. If noncyclic… + +    6. NADPH: 2e­ then pass down a short electron transport chain (with proteins like ferrodoxin) to combine NADP  + H  + 2e => NADPH (coenzyme) (only in noncyclic?). ­ ­ +    7. Splitting of Water (photolysis): the loss of 2e from PSII (initially) is replaced when H O splits into 2e, 22 , and ½O . 2 (H  goes for NADPH formation and ½ O  that contribut2s to release as oxygen gas). This occurs at PSII.  {  H 2 + ADP + P + NADPi + light => ATP + NADPH + O  + H 2 + } Note on photosystems: few hundred in each thylakoid, have a rxn center containing chlorophyll a surrounded by antenna pigments that  funnel energy to it. Also note Cliff page 58 diagrams this well.   B. Cyclic Photophosphorylation: this replenishes ATP when Calvin cycle consumes it ­ ­ When excited 2e from PSI join with protein carriers in the first electron transport chain and generate 1ATP as they pass  through; these 2e are recycled into PSI and can take either cyclic or noncyclic path. C. Calvin Cycle: fixes CO , repeat26 times, uses 6CO  to produce C H2O  (glucose). C  6ho12sy6thesis (dark rea3tion)    1. Carboxylation: 6CO  + 6Ru2P => 12PGA, RuBisCo (most common protein in the world, aka RuBP carboxylase)  catalyzes this reaction. (so named because PGA is 3C). +    2. Reduction: 12ATP + 12NADPH converts 12PGA => 12G3P or 12PGAL; energy is incorporated; by­products (NADP   and ADP) go into noncyclic photophosphorylation.    3. Regeneration: 6ATP convert 10G3P => 6RuBP (allows cycle to repeat).    4. Carbohydrate synthesis: 2 remaining G3P are used to build glucose. 6CO  +218ATP + 12NADPH + H  => 18ADP + 18P + 12NADP  + 1glucose (2i3P) +    5. This is the “dark reaction”, but it cannot occur w/out light because it is dependent on the high energy molecules  produced from the light rxn (ATP and NADPH)  Note: Bootcamp says that the energy used to drive the light­independent rxns comes from light (photons). Light energy is what drives  photosynthesis! And the energy in glucose traces back to light that gets stored in the form of glucose chemical bonds! Remember, plants do  have mitochondria that make ATP, BUT: the ATP from photosynthesis comes from the chloroplast (not mitochondria) and is used to drive  photosynthesis further (Calvin cycle). Photosynthesis primarily makes glucose for the plant’s own mitochondria to use as energy! Still need  mitochondria for plant tissues but they don’t make the ATP for photosynthesis, and photosynthesis ATP isn’t used for general cell fxn!  D. Chloroplast: light­dependent and light­independent reactions occur. (double membrane like mito + nucleus)    1. Outer membrane: plasma membrane (phospholipid bilayer)        2. Intermembrane space    3. Inner membrane: also phospholipid bilayer.    4. Stroma: fluid material that fills area inside inner membrane; Calvin cycle occurs here (fixing CO  => G3P) 2    5. Thylakoids: suspended within stroma (stacks); individual membrane layers are thylakoids; entire stack is granum  membrane of thylakoids contain (PSI + PSII), cytochromes, and other e  carriers. Also phospholipid bilayer. +    6. Thylakoid lumen: interior of the thylakoid; H  accumulates here. Note: Gradient uses ATP synthase to move the accumulated H+ from thylakoid lumen to stroma; H+ move from in to out to generate ATP via  synthase, whereas in ox­phos we build up H+ outside and then shuttle it back in to mitochondria to generate ATP via synthase Locations: noncyclic photophos takes place in thylakoid membranes. Cyclic phos takes place on stroma lamellae (pieces connecting the thylakoids). Photolysis takes  place inside the thylakoid lumen (passes e­ to the membrane for noncyclic photophos). Calvin Cycle takes place in the stroma. Chemiosmosis takes place across the  thylakoid membrane. All of these take place inside the chloroplast! Remember that is the thylakoid membrane, not the outer/inner chloroplast membranes,  that absorb light! 13 E.  Chemiosmosis   in Chloroplasts: uses H  gradient to generate ATP. (p. 61) +    1. H+ ions accumulate inside thylakoids: H+ are released into lumen when H2O is split by PSII. H  is also carried into  lumen from stroma by cytochrome between PSII and PSI.    2. A pH and electrical gradient is created: about pH5.    3. ATP synthase generates ATP: phosphorylate ADP + P => ATP. (3Hi is required for 1ATP). ­ ­    4. Calvin cycle produces 2G3P using NADPH & CO  & ATP: at t2e end of e transport chain following PSI, 2e produces  NADPH. F. Photorespiration: fixation of oxygen by rubisco (can also fix CO ) => produ2es no ATP or sugar. Rubisco is not  “efficient” or fast because it will fix both CO  and 2xygen at the same time if both are present. Probably arose because  early earth atmosphere didn’t have much O  so it 2idn’t matter. Peroxisomes breakdown the products of this process.  G. C4 Photosynthesis: evolved from C , when C3  enters lea2; absorbed by mesophyll cells (then moved to bundle sheath  cells);  instead of being fixed by rubisco into PGA, CO  combin2s with PEP to form OAA by PEP carboxylase  (in mesophyll) ­ OAA has 4C => C4 photosynthesis. 1 ATP  AMP required ­ OAA => malate and then transported through plasmodesmata into bundle sheath cell. ­ Malate => pyruvate + CO . (CO2 can b2 used into Calvin cycle) (Pyruvate moved back to mesophyll then => PEP)     ­ Overall purpose is to move CO  fro2 mesophyll to bundle sheath cell (structure = Kranz anatomy, process = Hatch­ Slack pathway (little O  p2esence reduces competition while rubisco is fixing). Minimize photorespiration and H2O loss  from stomata (leaf pores); found in hot, dry climates (faster fixation speed and more efficient). Requires one additional ATP (which becomes AMP). C  typica3ly occurs in mesophyll cells, but in C  it occurs 4n bundle­sheath cells. Corn, sugarcane H. CAM Photosynthesis: ­ Another add­on to C3, crassulacean acid metabolism; almost identical to C . 4    1. PEP carboxylase fixes CO  + P2P to OAA; OAA => malic acid.    2. Malic acid is shuttled into vacuole of cell.    3. At night, stomata are open (opposite of normal), PEP carboxylase is active, malic acid accumulates in vacuole.    4. During day, stomata are closed. Malic acid is out of vacuole and converted back to OAA (require 1ATP), releasing CO 2 (moved onto Calvin cycle with rubisco) and PEP.    ­ Overall advantages are can proceed during day while stomata are closed (reduce H O loss). Cac2i, crassulacea plants,       2+    ­ As leaves age, chlorophyll breaks down to extract valuable components like Mg , carotenoids are visible.    ­ Splitting of H2O provides 2e­ for noncyclic photophosphorylation; incorporated into NADPH and Calvin cycle.    ­ Calvin cycle is light­independent, but it requires ATP and NADPH produced from light­dependent rxn. ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ V. Cell Division: nuclear division (karyokinesis) followed by cytokinesis ­ In diploid cells, there are two copies of every chromosome, forming a pair (homologous chromosome). Human have 46  chromosomes, 23 homologous pair, a total of 92 chromatids (depending on stage of division1). ­ MTOCs: Microtubule organizing centers aka centrosomes. Pair of these lay outside nucleus. In animal cells, each MTOC  contains a pair of centrioles.  Recall that plants do have MTOC’s called centrosomes, but they aren’t composed of centrioles.   A. Mitosis:     1. Prophase: nucleus disassembles: nucleolus disappear, chromatin condenses into chromosomes, and nuclear envelope  breaks down. Mitotic spindle is formed and microtubules (composed of tubulin) begin connecting to kinetochores.    2. Metaphase: chromosomes line up single file at center, each chromatid is complete with a centromere and a kinetochore, once separated, it is a chromosome (to keep track of total: count centromeres!). Centrosomes at opposite ends of cell. (note:  once separated that’s the end of metaphase, so to be precise the chromosome # doubles at anaphase). Karyotyping  performed here.    3. Anaphase: microtubules shorten, each chromosome is pulled apart into two chromatids (once separated it is a  chromosome; chromosome # doubles), pulls the chromosomes to opposite poles (disjunction); at the end of this phase, each  pole has a complete set of chromosome, same as original cell before replication.     4. Telophase: nuclear division, nuclear envelop develops, chromosomes => chromatin, nucleoli reappear. 14  Cytokinesis: Actually begins during the later stages of mitosis (most sources indicate it begins towards the end of  anaphase). Division of cytoplasm to form 2 cells. ­ Cleavage furrow: actin and myosin microfilaments shorten, pull plasma membrane into center (animal)  Note: begins formation during anaphase? ­?


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