First Midterm in Molecular Cell Biology
First Midterm in Molecular Cell Biology Molecular Cell Biology
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This 18 page Study Guide was uploaded by Kien Tran on Sunday January 31, 2016. The Study Guide belongs to Molecular Cell Biology at University of North Florida taught by Dr. Orchrietor in Winter 2016. Since its upload, it has received 109 views. For similar materials see PCB3023 in Biology at University of North Florida.
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Molecular and Cell Biology Questions – Exam 1 concepts August 27 Chapter 1 1. What is a cell? Cell is the fundamental, smallest unit of life. They come in a variety of sizes and shapes and function differently. 2. Why are present day cells thought to have derived from one common ancestor? Despite all cells come from different structures and functions, they share certain structural features and carry out complicated processes in basically the same way. By inherited the genetic information from parents through sexual reproduction, over billions of years, species became more diverged and adaptive to individual environments from ancestors those who could survive and reproduce. 3. What is a genome? Genome is an entire sequence of nucleotides in an organism’s DNA. It provides a genetic program that instructs the cell how to behave. Since the sequence of genes/ nucleotides made the genetic information we all carry even all cells come from mitochondria. 4. What are the principles of the Cell Theory? Who is/are credited with the Cell Theory? All cells grow and produce from other cells All organisms come from one or more cells Cells are the basic unit of life, a universal building block of all living tissues. The theory was credited to Matthias Scleiden 1838 and Theodor Schwann 1839. 5. What common structures are shared by all cells? All cells have: a. plasma membrane (converts resources to ATP) b. ribosome (except virus) c. DNA Cytoplasm, where all organelles are located, is enclosed by a plasma membrane DNA as a store of genetic information and are used to synthesize RNA and proteins All plant cells contain choloblasts to convert sunlight into engery; all animals and protists contain mitochondria to convert food into ATP 6. What feature(s) distinguish prokaryotes from eukaryotes? Prokaryotes: cells have no nucleus, no internal membranes, unicellular, generally smaller in size Eukaryotes: Cells have nucleus and membraneenclosed organelles, multicellular, and are generally bigger than prokaryotes. Plans, animals, fungi, and protists Most important organelles: nucleus containing DNA, mitochondria generate usable energy from food to power the cell. 7. What are the two domains of prokaryotes? Bacteria and Archae that are usually small and have spherical, rodlike, or corkscrew shaped Bacteria: most are familiar to everyday life and also cause illness Archae: live in any imaginable environments, harsh environments, such as too acidic, extremely hot or cold, salty, high pH that bacteria cannot live in. 8. What kind of microscopes do you use in MoCell lab? Light microscope Phase contrast microscope (live cells) ((((Confocal microscope (3D) (scanning: see only outside, transmission: see organelles) Fluorescent microscope (uses mercury or laser to excite the cell to emit different colors in terms of florescence)))) September 1 Chapter 2 1. What element is the key to chemistry of life? Living creatures are merely chemical systems that they are so diverse in forms, purposeful behaviors, and the ability to grow and reproduce. First, living forms are made of carbon compounds known as organic chemistry Second, it depends exclusively on chemical reactions that take place in aqueous solutions in a relatively narrow range of temperatures on Earth. Third, it is enormously complex: even the simplest cell is vastly more complicated in its chemistry than any other chemical system known Fourth, it is dominated and coordinated by collections of enormous polymeric molecules that enable organisms to grow and reproduce and to do other functions that are characteristic of life Fifth, it is tightly regulated: cells deploy a variety of mechanisms to make sure that all their chemical reactions occur at the proper place and time. 2. What is an atom? Describe its components. An atom consists of a nucleus and the cloud of electrons. The nucleus carries positivecharged protons and neutral neutrons, the nucleus contains the most mass as its atomic mass. The electrons carry negative charge and are much lighter in weight. They always move around, so their positions can’t be located at a certain time. They create the electron cloud 3. What is a valence shell? How many electrons make up a stable valence shell? How many electrons are found on the valence shell of carbon? Valence shell is the outermost shell of an atom. 8 electrons make up the most stable valence shell, except H (1 valence electron), and He (2 valence electrons). 4 electrons are in the valence shell of carbon Noble gas are nonreactive 4. What is a chemical bond? Bonds are the attraction between 2 atoms through valence electrons Ionic bonds are stronger than covalent bonds in terms of energy, but less stable and less numerous than covalent bonds. Chemical bonds are formed by interactions between valence electrons of two atoms of the same element or different elements to help individual atom reach the most stable state of its outermost shell (8 electrons). These interactions can be in terms of sharing valence electrons or donating/accepting (transferring) electrons. There are covalent bonds and noncovalent bonds Noncovalent bonds include ionic bonds/electrostatic interactions (only intermolecular interactions, no transferring of electrons) and hydrogen bonds (between hydrogen and more electronegative elements, only when H is bonded to S, O, N) 5. What is a covalent bond? Covalence bond is formed from shared pair (s) of valence electrons between two of the same element or two different elements, so both atoms can reach the octet rule. 6. What is an ionic bond? Ionic bond is the transferring one or more valence electrons between one metal (cation) and one nonmetal (anion) elements. One atom gives up one or more pairs of valence electrons to another, so both atoms can reach octet rule. Ionic bond is the strongest bond in all types of chemical bonds, but much weaker than covalent bonds in aqueous solutions. 7. What is a polar covalent bond? Polar Covalence bond is a type of covalent bond, but between two different elements. One element is more electronegative than the other, so the shared pair (s) of valence electron will be more shifted towards the more negative element. 8. What is a hydrogen bond? Hydrogen bond is a type of intermolecular forces between two or more molecules, in which the bond in a molecule is formed between hydrogen atom and one of N, O, F, or S elements. Hydrogen bonds are formed when there are a positive charged H held in one molecule by a polar covalent linkage comes close to a negatively changed atomtypically N or O belonging to another molecule. Water cohesion results from hydrogen bonds (water attach to skin, or water tension phenomenon) 9. Why is water a good universal solvent? What are shells of hydration???? Because water is polar, it can dissolve other polar molecules, which includes lots of organic compounds containing oxygen and halogens. Water makes up 70% of a cell’s weight, facilitating the most intracellular reactions occurring in an aqueous environment. Hydrogen bonds create very strong force from many molecules exist in a solution at the same time. IN each molecule of H2O, the two H atoms are linked to the O atom by covalent bonds. The two HO bonds are highly polar with O strongly negative and H strongly positive. Therefore, this big difference in electronegativity drives more interactions of hydrogen with other more negative elements in other molecules, thus increases intermolecular forces and increasing the stability of the molecules in water solvent, meaning increasing solubility of the pola\r molecules. 10. What does the term hydrophobic mean? What does the term hydrophilic mean? Hydrophobic mean not waterfearing molecules, meaning these molecules do not dissolve in water by being uncharged or forming few or no hydrogen bonds. Hydrophilic mean waterloving molecules, meaning these molecules readily dissolve in water, such as sugars, DNA, RNA, and most proteins, by being polar or carrying positive and negative charges like ions that can dissociate well in water. 11. Are nonpolar molecules hydrophobic or hydrophilic? Are polar molecules hydrophobic or hydrophilic? Nonpolar molecules are hydrophobic Polar molecules are hydrophilic September 3 1. What are the four types of macromolecules within a cell? Proteins (amino acids) Nucleic acids (nucleotides) Large polysaccharides/glycogen/starch (sugars) Fats and membrane lipids (fatty acids). 2. What subunits are found within polysaccharides? Sugars – monosaccharides – (CH O)n n23,4,5,6 Condensation reaction: dehydration reaction to join two monosaccharides. Hydrolysis reaction: water comes in to reform –OH groups for monosaccharides. 3. What bonds are found between subunits of polysaccharides? Monosaccharides are linked via covalent bonds, called glycosidic bonds 4. What is the difference between a structural polysaccharide and a storage polysaccharide? Storage polysaccharides: more complex in branches from connecting to other molecules. And these branches can be broken down into smaller molecules to release energy. Energy is stored in chemical bonds as glucose Animals store energy as glycogen (Glycogen has space in their structure that they help the body store lots of water) Plants store energy as starch => They are both potential energy (α-glycosidic bonds) (Alpha: OH groups of two monosaccharides are on same side Beta: OH groups of two monosaccharides are on different sides) Structural polysaccharides: formed from linear polymer of a sugar derivative called N acetylglucosamine that creates more stable, rigid structures to provide supports for the body. => Cellulose and chitin are made of β-glycosidic bonds (bacteria help break down cellulose, other organisms cannot do it) 5. What is the difference between a saturated fatty acid and an unsaturated fatty acid? Saturated fatty acids: stay in solid state at RT (fat), contain no double bonds between carbon atoms and contain maximum number of hydrogens, their tails packed closely together) Unsaturated fatty acids: stay in liquid form at RT (oil), have at least one C=C double bonds and have the ability to take in more hydrogens, or can be said double bonds are kinks in the hydrocarbon tails, their tails do not pack together The presence or absence of these double bonds that accounts for the difference between hard (saturated) and soft (polyunsaturated) margarine. 6. Why are fatty acids amphipathic? Fatty acids contain both hydrophobic heads (no polarity > waterfearing > nonreactive) and hydrophilic tails (bc of polarity > waterloving > reactive) regions. 7. What is a triacylglycerol? The compounds exist in cytoplasm of many cells in animal fats and are made of three fatty acid chains covalently jointed to a glycerol molecule 8. What is a phospholipid? How are phospholipids oriented within a membrane? Phospholipids are fatty acids that contain a polar head of phosphate group and two nonpolar tails of carbohydrates. The phospholipids are constructed mainly from glycerol and fatty acids with the glycerol joining to two fatty acid chains. The OH group on the glycerol is linked to hydrophilic phosphate group, which in turn is attached to a small hydrophilic compound. With two hydrophobic fatty acid tails and a hydrophilic, phosphatecontain head, phospholipids are strongly amphipathic, which helps them form membrane in water. These lipids spread over the surface of water to form monolayer. With their hydrophobic tails facing the air and their hydrophilic heads in contact with water. Two such molecular layers can readily combine tailto tail in water to form phospholipid sandwich that is the lipid bilayer, where their hydrophobic tails fear water together and their hydrophilic heads face water. 9. What is a steroid? Small molecule that contains multiple aromatic rings, and belong to lipids family. Cholesterols and testosteron 10. What are the subunits of nucleic acids? Nucleotides bonded by phosphodiester bonds. Each nucleotide includes nitrogen base, ribose (3’ OH), and phosphate (5’). DNA Deoxyribonucleis acid (OH’s are trans) RNA Ribonucleic acid (OH’s are cis) 11. What are the subunits of proteins? Amino acids are linked by peptides bonds. Each contain amino group NH2, a carboxyl group (COOH), and a side chain R attached to their alphacarbon. 12. What bonds are found between subunits of proteins? Covalent bonds, called peptides. 13. What is the difference between a protein and a polypeptide? Protein include two or more polypeptide chains that function together for a specific role 1 : sequence 2 : alpha helixes/ beta sheets 3 : 3D structure o 4 : associations between different polypeptides, including the other three structures, usually have no functions (such as hemoglobin just carrying oxygen) Polypeptide is just a chain of amino acid, function individually, and do not have functions that proteins have September 8 Chapter 11 1. What is the fluid mosaic model of the plasma membrane? Fluid: movement, not stiff Mosaic: mixture of phospholipids, cholesterols, and proteins. The formation of two layers of phospholipids, which contain hydrophilic heads and hydrophobic tails that form phospholipid bilayer to separate the cell from the surrounding, import and export materials from and to the environment. 2. Why do phospholipids form bilayers and sealed compartments? The bilayer of phospholipids contains hydrophilic heads and hydrophobic tails. This formation reduces the interactions of the fearingtails with water, which is favorable in water with no cost of energy. The phospholipid bilayer serves as a barrier to prevent the contents of the cells from escaping and mixing with the cytoplasm. It also serves to exchange products between different compartments together as supplies such as nutrients, and also secret waste to help the cell survive. 3. What determines membrane fluidity? The length of carbon chain and the number of double bonds in the lipids, the shorter the carbon chain, the more fluid the compound is (1424 C); more double bonds, the more fluid; more cholesterol, less fluid and less permeable. Fluidity is measured using FRAP – Florescence Recovery After Photo bleaching Region of bleach is called region of interest: “roi” 4. Can phospholipids (and proteins) move within the membrane? What experiments/techniques demonstrate/test this? Flipflop movements need energy by enzyme flippase Flexation and rotation do not cost energy Plasma membrane is made from the ER Phospholipids can move laterally within the membrane. There are four types of membrane proteins: a. Trans membrane proteins b. Monolayerassociated alphahelix: attached to membrane via an amphipathic alpha helix c. Lipidanchored membrane proteins: anchor to the membrane via a lipid molecule d. Peripheral proteins, called attached proteins: connect to membrane by binding to other weak membrane proteins. => All except d are integral proteins (This was tested by and experiment of fusing a mouse cell with human cell to form double sized hybrid cell and then monitor the distribution of certain mouse and human plasma membrane proteins. At first the mouse and human proteins are confined to their own halves of the newly formed hybrid cells, but within half and hour, the two sets of proteins become evenly mixed over the entire cell surface). 5. How does cholesterol affect the plasma membrane? Cholesterol presents in large amount in plasma membrane. Because cholesterol is hard and rigid, they fill spaces between neighboring phospholipid molecules left in the kinks in their unsaturated HC tails. In this way, cholesterol tends to stiffen the bilayer, making it less flexible, less permeable, thus less fluid. The more unsaturated fats > the more cholesterol, less fluid membrane. 6. How/where are membranes synthesized? The membrane is synthesized the ER. The ER membrane produces new phospholipids from free fatty acids and inserts them into the cytosolic monolayer. Then scramblases enzymes then randomly transfer phospholipid molecules from one monolayer to another, allowing the membrane to grow as bilayer. When the membrane leave the ER and are incorporated in the Golgi, they encounter the flippase enzymes that selectively remove some specific phospholipids from the noncytosolic monolayer to the flip them over in the cytosolic monolayer, resulting the curvature of the membrane. 7. How do proteins interact with the plasma membrane? Protein can play roles as transporters, ion channels, anchors, receptors, or enzymes. There are four types of membrane proteins: a. Trans membrane proteins b. Monolayerassociated alphahelix: attached to membrane via an amphipathic alpha helix c. Lipidanchored membrane proteins: anchor to the membrane via a lipid molecule d. Peripheral proteins, called attached proteins: connect to membrane by binding to other weak membrane proteins. => All except d are integral proteins 8. Why are most transmembrane proteins made up of ahelices? Are bsheets found within transmembrane proteins? Because the water is absent to the interior of the bilayer, atoms forming the backbone are driven to form hydrogen bonds with one another. Hbonding is maximized if the polypeptide chain forms a regular alphahelix, and so great majority of membranespanning segments of polypeptide chains traverse the bilayer as alphahelix. In these membranespanning alpha helices, the hydrophobic side chains are exposed on the outside of the helix, where they contact with the hydrophobic lipids tails, while atoms in the polypeptide backbone from hydrogen bonds with one another on the inside of the helix. 9. What is the cell cortex? How does it interact with the plasma membrane? Cell cortex is a framework of proteins attached to the underneath of the cell membrane as a mesh via transmembrane proteins, and they are used to strengthen the cell membrane, which is very thin and fragile. Mostly, cell cortex is composed of protein spectrin dimer, or some other proteins similar to spectrin, a long thin flexible rod, with its associated attachment proteins forming a meshwork. 10. What limits protein movement within the plasma membrane? a. The tight junction (barrier) was created by the asymmetric distribution of the membrane proteins. The tight junction proteins form a continuous belt around the cell where the cell contacts its neighbors, creating a seal between adjacent plasma membranes, so membrane proteins cannot diffuse past the junction. b. Attach to protein: tethered to cell cortex inside the cell c. Attach to the ECM molecule outside the cell d. Attach to cytoskeleton 12. Where are sugars found on transmembrane proteins? What do the sugar moieties do? Sugars exist in the outermost layer of the plasma membrane (in the extracellular space). All of the carbohydrates on oligosaccharides from glycoproteins and polysaccharides from proteoglycans of membrane proteins form a sugar coating called glycocalyx, which protect the cell surface from mechanical damage also give the cell a slimy surface for motile cells and also play a role as a recognition September 10 Chapter 17 Cytoskeleton 1. What are intermediate filaments? How do they assemble? What is their function? Where are they found? Intermediate filaments are the proteins and have ropelike structure in which many long strands of proteins twisted together to provide tensile strength. Each strain is an intermediate filament proteins rod. These two rods twist around each other to form a dimer with coiledcoil configuration. These two dimers run in opposite directions forming staggered tetramer. These tetramers interact associate with each other side by side, assembling to generate the final ropelike intermediate filament. They exist in cytoplasm or nucleus in most animals that strengthen the cell’ structure to withstand mechanical stress when stretching but do not degrade easily. Their size is in between of thinner actin filament and thicker myosin filaments. Four types: Cytoplasmic: keratin filaments, vimentin and vimentinrelated filament, and neurofilaments. Nuclear: nuclear lamins 2. What are microtubules? Microtubules are hollow cylinders made of 13 protofilaments. There are alpha (minus end) and beta (plus end) protein tubulin that bound together by noncovalent interactions to create dimers. These primers stack together to create a protofilament. Each microtubule is a long and straight and typical have one end attached to a single microtubuleorganizing center called a centrosome. Microtubules are a part of cytoskeleton mainly responsible, more rigid than actin filaments and intermediate filaments, but they break when stretch; so they are responsible for transporting and positioning membrane enclosed organelles within the cell or guiding intracellular transport of various cytosolic macromolecules. 3. What is dynamic instability? The switching back and forth between polymerization and depolomerization Tubulin dimers carrying GTP bind more tightly to one another than do tubulin dimers carrying GDP. Therefore, rapidly growing plus ends of microtubules, which have freshly added tubulin dimers with GTP bound, tend to keep growing > polymerization. If microtubule growth is slow, the dimers in this GTP cap will hydrolyze their GTP to GDP before fresh dimers loaded with GTP have time to bind. The GTP cap therefore lost. Because the GDP carrying dimers are less tightly bound in the polymer, the protofilaments peel away from the plus end, and the dimers are released, causing the microtubule to shrink > depolarization. 4. What is a microtubule organizing center? Centrosome 5. How do microtubules contribute to mitosis? Only during mitosis, there are two microtubules in the cytoplasmic microtubules, they disassemble and then reassemble into mitotic spindle, which provides a machinery structure that will segregate the chromosomes equally into two daughter cells before cell divides. Four stages of mitosis: Prophase, Metaphase (spindle forms), Anaphase, and Telophase 6. How do microtubules contribute to cytokinesis in plants?????? Cell wall has cellulose that is from gogi complex. The vesicles come to the center and fuse together to form new cell wall for two new plant cells. 7. What are cilia and flagella? How do they work? What kind of structures do they have? Cilia and Flagella are hairlike structures that extend from the surface of many eukaryotic cells. Their structures consist of a highly organized and stable bundle of microtubules. Each cillium contains a core of stable microtubules, arranged in a bundle and grow from the organizing center. Cillia beat in a whiplike fashion, either to move fluid over the surface of a cell or to propel single cells through fluid. Flagella are structured like cillia but much longer. They are designed to move entire cell, rather than moving fluid across the cell surface. Flagella propagate regular waves along their length, propelling the attached cell along. 8. What are actin filaments? Actin filaments are helical polymers of actin monomers called protein actins and are present in all eukaryotic cells. They are more flexible, thinner, and shorter, but more numerous than microtubules. They have plus and minus ends like in microtubules. They are essential for many of cells’ movements and contraction and cell shape, especially those involving surface, most concentrated in the cortex. 9. What is treadmilling A behavior that an individual monomers moves through the actin filament from the plus to the minus end, meaning the monomers gain at the plus end and loss at the minus end, it the rates of addition and loss are equal, the filament remains the same size => microtubules undergo more drastic changes than do actin filaments – either growing rapidly or collapsing rapidly. Actin monomers add to the plus end at a rate faster than the bound ATP can be hydrolyzed, so the plus end grows. At the minus end, ATP is hydrolyzed faster than new monomers can be added; because ADPactin destabilizes the structure, the monomers are lost at the minus end. 10. How do cells migrate? Eukaryotic cells can crawl over surfaces, rather than by swimming via beating cilia and flagella. Three processes include: a. The cell pushes out protrusions at its “front” or leading edge by actin polimerization b. These protrusions adhere to the surface over which the cell is crawling, making the new anchorage between the cell and the surface. c. The rest of the cell drags itself forward by traction on these anchorage points. New anchorage point is established at the front and the old one is released at back, as the cell moving forward. The cycle is repeated the same => All of these three processes involve actin filament in different ways 11. What is the difference between lamellipodia and filapodia? In the first step, the pushing forward of the cell surface, is driven by actin polymerization. The leading edge of a crawling fibroblast in culture regularly extend thin, sheetlike lamellipodia, which contain meshwork of actin filaments, oriented so that the filaments have their plus ends close to the plasma membrane so the monomers can be added on to elongate the surface of membrane without tearing it. Many cells go extend think, stiff protrusions called flipodia, both at leading edge and elsewhere on their surface. September 15 Chapter 20 1. What types of tissues do animals possess? Four basic types: connective, epithelial, nervous, and muscular tissues. Connective tissue is different from the rest of those tissue types 2. What is the extracellular matrix? It is what cells secrete around themselves to give supportive tissues such as bones or wood their strength. EM contains collagen for extra support 3. Do plants have an extracellular matrix? Yes, it is their doublelayer cell wall, boxlike structure, made of cellulose that encloses, protects, and constrains the shape of each of its cells. 4. What is collagen? Collagen is made of polypeptides > triplestranded collagen molecules > collagen fibril > many fibrils come in bundle make collagen fibers. Fibroblast secret collagen and other EM components in to the EM Collagen is synthesized as a procollagen molecule that has unstructure peptides at either end. These peptides prevent collagen from assembling into a fibril inside the fibroblast. When the procollagen is secreted outside cell, an enzyme removes its terminal peptides, producing an active collagen molecule which can selfassemble into ordered collagen fibril. 5. What is fibronectin? Fibronectin is found in cell membrane on the outside. They are an extracellular protein that provides a linkage between collagen and the cell to help cell crawl because cell does not attach well to bare collagen. 6. What role do integrins play? Cell attaches itself to fibronectin via integrin. Integrin, a receptor protein, spans the cells’ plasma membrane of the cell, helping to bind its EM to cytokeleton. When the extracellular domain of the integrin binds to fibronectin, the intracellular domain binds to an actin filament inside the cell. The existence of integrins helps the plasma membrane of the cell not to be ripped off as the cell attempted to pull itself along the matrix. 7. What are glycosaminoglycans? What are proteoglycans? Where do you find them? GAGs are negatively charged chains made of repeating disaccharide units. GAGs are strongly hydrophilic, thus can adopt highly extended conformation > space fillers in the EM of connective tissues. GAGs are usually covalently linked to core proteins to form proteoglycans, which are extremely diverse in size, shape, and chemistry. They can be found in extracellular matrix in connective tissues and play a role as resisting compression. 8. How are epithelia organized? Epithelia contain multiple sheets of cells in which the cells are joined together side to side, and can take many forms. In some cases, the sheet is many cells thick as in the epidermis. In other cases, it is one cell thick as in lining of gut. Five types: a. Simple b. Stratified c. Columnar d. Cuboidal e. Squamous 9. What is the basal lamina? Basal lamina is a surface of the epithelial sheet that is attached to the sheet of connective tissue in the EM The apical surface is free and exposed to air or to watery fluid. 10. What are tight junctions? Tight junctions are a type of epithelial cell junction, and have the sealing function. They seal neighbored cells together so that watersoluble molecules cannot easily leak between them. 11. What are adherens junctions? Desmosomes? Hemidesmosomes? Adherens junctions and desmosomes bind one epithelial cell to another, and are both built around the transmembrane proteins that belong to the Ca2+ cadherin family. At the adherens junction, each cadherin molecule is tied inside its cell to actin filaments At a desmosome, a different set of cadherin molecules connects to keratin filaments, the intermediate filaments found in epithelial cells, and stronger than adhesive junction. Hemidesmosomes binds epithelial cells to the basal lamina. 12. How/why do epithelial sheets form round structures? Depending on the contraction of the epithelial sheet is oriented along one axis, or is equal in all directions, the epithelium will either roll up into tubed shape or invaginate to form vesicle. The contraction of the apical bundles of actin filaments linked cell to cell via adherens junctions creating adhesion belt. The invagination of epithelial sheet caused by an organized tightening along adhesion belts in selected regions of cell sheet. Then epithelial tube pinches off fro overlying sheet of cells. This process is driven by an apical narrowing of epithelial cells in all directions. 13. What are gap junctions? Gap junctions are where chemical signaling occurs, and are a type of epithelial cell junction, and appears as a region where the membranes of two cells lie close together and exactly parallel, with a very narrow gap filled with transmembrane protein complexes for cells to communicate. 14. What are plasmodesmata? Since plant tissue lack all the types of cell junction that animals have since their cells are connected by cell wall. They have plasmodesmata, which are cytoplasmic channels lined with plasma membrane to keep the continuity of one cell to another by spanning the intervening cell wall September 17 Chapter 20 1. What are stem cells? Stem cells are undifferentiated cells and can divide without limit for at least or the lifetime of the animal Embryonic Resident Induced pluripotent 2. What are differentiated cells? Differentiated cells are cells that need continual replacement bc they are unable to divide 3. How are gut epithelia renewed? The single layered, simple epithelium covering the surfaces of the fingerlike villi that projects from the gut lumen. This epithelium is continuous with the epithelium lining the crypts. The stem cells lie near the bottom of the crypts, where they give rise mostly to proliferating precursor cells, which move upward in the plane of the epithelial sheet. As they move upward, the precursor cells terminatelly differentiate into absorptive or secretory cells, which are shed into gut lumen and die when they are reach the tips of the villi. 4. How are skin cells renewed? The epidermis are proliferating stem cells and precursor cells are confined to the basal layer, adhering to the basal lamina. The differentiating cells travel outward from their site in a direction perpendicular to the plane of the cell sheet; terminally differentiated cells and their corpses are eventually shed from the skin surface. 5. What are embryonic stem cells? Embryonic stem cells or ES cells are cells taken from embryos and can be kept proliferating indefinitely in culture and yet retain unrestricted developmental potential and are thus said to be pluripotent. The ES cells can intergrade perfectly into whatever site they come to occupy, adopting the characteristic and behavior that normal cells would show at that cite. 6. What are induced pluripotent stem cells? Cells are taken from an adult tissue, grown in culture, and reprogramed into an ESlike state by artificially driving the expression of a set of three transcription regulators called Oct3/4, Sox2, and Klf4. This treatment is sufficient to convert fibroblasts into cells with practically all the properties of ES cells.
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