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BSC2010 Week 4 Lecture Notes

by: Madison Pacheco

BSC2010 Week 4 Lecture Notes BSC2010

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Madison Pacheco

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Cells, signaling. Professor: Sixue Chen
Biology I
Sixue Chen
Class Notes
biology BSC BSC2010 Bio Bio1




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This 9 page Class Notes was uploaded by Madison Pacheco on Friday January 29, 2016. The Class Notes belongs to BSC2010 at a university taught by Sixue Chen in Fall 2016. Since its upload, it has received 10 views.


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Date Created: 01/29/16
StudySoup 1 BSC2010 Week 4 Lecture Notes Sixue Chen Monday, January 25, 2016 Review: Prokaryotic, Eukaryotic: both have cell membrane, cytoplasm, DNA Difference: pros don’t have organelles Plant vs animal: cell wall, large central vacuole, choloroplasts, plasmodesmata, glyoxisome Organelles: nucleus, membrane, rough/smooth ER, Golgi, lysosome Ribosomes are made up of: RNA and proteins Organelle generated by golgi body that contains digestive enzymes: lysosome (not phagosome, doesn’t contain digestive enzyme) Chapter 4: Cells: the Working Unit of Life Cells Provide Compartments for Biochemical Reactions  Plant Cell o Plant and algae contain plastids that can differentiate into organelles: some are used for storage o Chloroplast contains chlorophyll and is the site of photosynthesis  Photosynthesis converts light energy into chemical energy  Enclosed within two membranes, series of internal membranes called thylakoids  Granum is a stack of thylakoids  Light energy is converted to chemical energy on the thylakoid membranes  Carbohydrate synthesis occurs in the stroma: the aqueous fluid surrounding the thylakoid o Chromoplasts make and store pigments in flowers and fruits o Leucoplasts store macromolecules such as starch  **plastids can come in many different forms StudySoup 2 o Peroxisomes collect and break down toxic by-products of metabolism, such as H2O2, using specialized enzymes o Glyoxysomes (found only in plants) are where lipids are converted to carbohydrates for growth o Vacuoles occur in some eukaryotes (yeast) but mainly in plants and fungi  Functions:  Storage of waste products and toxic compounds; some may deter herbivores (toxic)  Structure for plant cells: water enter the vacuole by osmosis, creating turgor pressure  Reproduction: vacuoles in flowers and fruits contain pigments whose colors attract pollinators and aid seed dispersal  Catabolism: digestive enzymes in seeds’ vacuoles hydrolyze stored food for early growth  Contractile vacuoles in freshwater protests get ride of excess water entering the cell due to solute imbalance  Enlarges as water enters, then quickly contracts to force water out through special pores  Genes that code for all the proteins found in a chloroplast are located in the: nuclear and chloroplast DNA  **only human cell with flagella: sperm cell The Cytoskeleton Provides Strength and Movement  The Cytoskeleton: o Supports and maintains cell shape o Holds organelles in position o Moves organelles o Involved in cytoplasmic streaming o Interacts with extracellular structures to anchor cell in place  Microtubules o Largest cytoskeletal structures o Form rigid external skeleton for some cells or regions o Act as framework for motor proteins to move structures in the cell o Composed of alpha and beta tubulin o Protect cell from collapse o Hollow o Also transport system o Pull chromosomes apart during cell division StudySoup 3 o Found in flagella (sperm) and cilia (line respiratory tract)  Microfilaments o Smallest cytoskeletal structures o Help a cell or parts of a cell to move o Determine cell shape o Microfilaments are polymers made from the protein (monomer) actin o Microfilaments are dynamic and often change organization and length in a cell o Don’t form external structures, but can help cell move by changing shape  Pseudopodia, push and deform cell to form a foot  Also within cell, chloroplast current pushes chloroplasts to optimal areas of photosynthesis  Intermediate filaments o At least 50 different kinds in six molecular classes o Have tough, ropelike protein assemblages, more permanent than other filaments and do not show dynamic instability o Anchor cell structures in place o Resist tension, maintain rigidity o Less dynamic, change shape less quickly and less often, more stable Extracellular structures allow Cells to Communicate with the External Environment  Plant cell wall: semi-rigid structure outside plasma membrane  Fibrous component is the polysaccharide cellulose  Gel-like matrix contains cross-linked polysaccharides  3 major roles of cell wall: o support for the cell and limits volume by remaining rigid o acts as a barrier to infection o contributes to form during growth and development  Animal cells o Surrounded by extracellular matrix o Fibrous components is the protein collagen o Gel-like matrix consists of proteoglycans o Third group of proteins links the collagen and the matrix together o Roles of extracellular matrices in animal cells  Hold cells together in tissues  Contribute to physical properties of cartilage, skin, and other tissues  Filter materials StudySoup 4  Orient cell movement during growth and repair  Cell junctions: specialized structures that protrude from adjacent cells and “glue” them together – often in epithelial cells o Tight junctions prevent substances from moving through spaces between cells o Desmosomes hold cells together but allow materials to move in the matrix; allows for stretching (stomach, bladder) o Gap junctions are channels that run between membrane pores in adjacent cells, allowing substances to pass between the cells (heart muscle) o Prevent passage of unwanted materials Wednesday, January 27, 2016 Review: Microfiliaments = smallest Cell wall and plasmodesmata Tight junctions: nothing can pass in between Plasmosomes aka anchoring junctions Gap junctions (most similar to plasmodesmata) The presence of gap and tight junctions means that substances must pass through, rather than between, the epithelial cells that form the lining of the small intestines **know differences between membrane junctions Biological Membranes Have a Common Structure and Are Fluid  A membrane’s structure and functions are determined by its constituents: lipids, proteins, and carbohydrates o No DNA or RNA  The general structure of membranes is known as the fluid mosaic model  Phospholipids form a bilayer which is like a lake in which a variety of proteins float  Lipids form the hydrophobic core of the membrane o Most lipid molecules are phospholipids with two regions:  Hydrophilic regions = electrically charged “heads” that associate with water molecules  Hydrophobic regions: nonpolar fatty acid tails that do not dissolve in water Two important factors in membrane fluidity: StudySoup 5 o Lipid composition: types of fatty acids can increase or decrease fluidity (saturated = saturated with Hydrogen) o Temperature: membrane fluidity decreases in older conditions  Want more unsaturated during colder times, can pack more fats  Biological membranes contain proteins, with varying ratios of phospholipids o Peripheral membrane proteins lack hydrophobic groups and are not embedded in the bilayer; “on the side”  Imbedded proteins are hydrophobic (so can sit within phospholipid bilayer) and the ends are hydrophilic (so it can interact with outer part) o Integral membrane proteins are partly embedded in the phosopholipid bilayer Cell membrane carbohydrates play a role in cell communication and cell adhesion o Modified by sugars o Glycolipid: fats with sugars attached o Glycoprotein: protein with sugars attached o Proteoglycan: protein with a lot of sugars attached  How to cross the membrane? o Biological membranes allow some substances, and not others, to pass. This is known as selective permeability o 3 ways of transport:  passive transport does not require metabolic energy (small molecules)  simple diffusion  facilitated diffusion: channel or carrier proteins  active transport requires input of metabolic energy (small molecules)  vesicles for transport of large molecules o Diffusion (passive transport)  Process of random movement toward equilibrium  Diameter of the molecules  Temperature of the solution  The concentration gradient in the system  Higher concentration inside the cell causes the solute to diffuse out and a higher concentration outside causes the solute to diffuse in, for many molecules  Small nonpolar and uncharged molecules can pass trough the membrane (ie carbon dioxide, o2 gases) o Osmosis (passive transport)  Diffusion of water across membranes StudySoup 6  Depends on the concentration of solute molecules on either side of the membrane  Water passes through special membrane channels (aquaporins)  Isotonic solution: solution has equivalent solute concentration  Hypertonic solution: solution (outside of cell) has a higher solute concentration than other solution  Water moves out  Hypotonic solution: has a lower solute concentration than the other solution  Water moves in  Animal cells explode, plant cells just get very turgid o Facilitated Diffusion  Polar or charged substances (water, amino acids, sugars, and ions)  Channel proteins: ions, water  Carrier proteins: sugars, amino acids  Stimulus protein allows channel to open, flow is from high to low concentration, so still diffusion that just requires a protein; does not require energy  Glucose carrier protein moves glucose down concentration gradient o Active transport  2 types of active transport:  primary active transport involves the direct hydrolysis of ATP for energy  Secondary active transport does not use ATP directly. Instead, its energy is supplied by an ion concentration gradient, or an electrical gradient; energy of ATP is for setting up the gradient o indirect o Passive transport: simple diffusion Large molecules cross membrane via vesicles  Macromolecuels are too large or too charged to pass through biological membranes and instead pass through vesicles  To take up or secrete molecules, cells must use endocytosis or exocytosis o Endocytosis: molecules are engulfed o Exocytosis: molecules leave cell StudySoup 7  Pinocytosis: “cellular drinking” Friday, January 29, 2016 In which pair cell membranes most likely to be similar in their molecular composition? Cis face of golgi apparatus and endoplasmic reticulum The Membrane Plays a Key Role in a Cell’s Response to Environmental Signals  Cells can respond to many signals if they have a specific receptor for that signal  A signal transduction pathway is a sequence of molecular events and chemical reactions that lead to a cellular response, following the receptor’s activation by a signal  Cells are exposed to many signals that may have diff responses: o Autocrine signals affect the same cells that release them (tumor) o Paracrine signals diffuse to and affect nearby cells (neurotransmitter) o Hormones travel to distant cells  Only cells with necessary receptors can respond to a signal, the target cell must be able to sense it and respond to it  Signal transduction pathway involves a signal, receptor, response (on/off switch)  A common mechanism of signal transduction is allosteric regulation o Protein can change shape from protein binding to it and then respond  Signal transduction pathway may produce short or long term responses  A signal molecule, or ligand, fits into a three-D site on the receptor proteins o Not generally metabolized further, but their binding may expose an active site on the receptor o Binding is reversible and the ligand can be released, to end stimulation o An inhibitor, or antagonist, can bind in place of the normal ligand o Ex: coffee  Receptors can be classified by their location in cell; determined whether their ligand can diffuse through the membrane StudySoup 8 o Cytoplasmic receptors have ligands, such as estrogen that are small or nonpolar and can diffuse across membrane o Membrane receptors have large or polar ligands, such as insulin, cannot diffuse and must bind to a transmembrane receptor at an extracellular site Receptors also classified by their activity o Ion channel o Protein kinase o G protein-linked receptors  Ion channel receptors o Aka gated ion channels o Change their 3D shape when a ligand binds o The actylcholine receptor, a ligand-gated Na+ channel, binds it to open the channel and allow Na+ to diffuse into the cell, resulting in muscle contraction  Protein kinase receptors o Change their shape when a ligand binds o The new shape exposes or activates a cytoplasmic domain that has catalytic (protein kinase) activity o ATP + protein -> ADP + phosporylated protein o Each protein kinase has a specific target protein whose activity is change when it is phosphorylated **Universal feature of receptors: o Undergo structural changes when the signal molecule is bound o Not always present in plasma membrane  G-protien-linked receptors o Expose a site that can bind to a membrane protein, a G protein o G protein is partially inserted in the lipid bilayer and partially exposed on the cytoplasmic surface o Many G proteins have 3 subunits to bind  The receptor  GDP and GTP  An effector protein to cause an effect in the cell o The activated protein-linked receptor exchanges GDP nucleotide bound to the G protein for GTP  GDP releases RAS and then it binds to GTP, brief stimulation of cell division; then hydrolizes and rebinds to GDP  Cancer: some form of RAS can’t hydrolyze GTP into GDP  Amplification effect: one stimulation can cause many others o Aids in “fight or flight” StudySoup 9  We have lots of stored energy, so quick burning of glycogen gives us more energy o A second messenger is an intermediary between the receptor and the cascade of responses  Located inside cell, not outside of it  In fight or flight response, epinephrine (adrenaline) activates the liver enzyme glycogen phosphorylase  the enzyme catalyzes the breakdown of glycogen stored in liver to glucose for quick energy  researchers found that the cytoplasmic enzyme could be activated by the membrane-bound epinephrine in broken cells, as long as all parts were present  they discovered that another molecule delivered the message from epinephrine to the enzyme  second messenger = cyclic AMP  allow cell to respond to a single membrane event with many events inside the cell – they distribute the signal  they amplify the signal by activating more than one enzyme target  activation: phosphorylase kinase is activated by phosphorylation and is part of a cascade that results in the liberation of glucose molecules  **know basic concept of the steps, don’t necessarily have to know every single step  inhibition inactivates glycogen o protein kinase phosphorylates active glycogen synthase, which makes it become inactive Signal transduction regulatory mechanisms  signal transduction ends after the cell responds – enzymes convert each transducer back to its inactive precursor  cells can alter the balance of enzymes in two ways: o synthesis or breakdown of the enzyme o activation or inhibition of the enzymes by other molecules  cell functions change in response to environmental signals o opening ion channels o alterations in gene expression


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