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5 Written questions

5 Matching questions

  1. Autophagy
  2. Cadherin
  3. Clathrin
  4. cis-unsaturated fatty acid
  5. Pinocytosis
  1. a
    Also known as autophagocytosis,this is a catabolic process involving the degradation of a cell's own components through the lysosomal machinery. It is a tightly regulated process that plays a normal part in cell growth, development, and homeostasis, helping to maintain a balance between the synthesis, degradation, and subsequent recycling of cellular products. It is a major mechanism by which a starving cell reallocates nutrients from unnecessary processes to more-essential processes.
  2. b
    Also known as "cell-drinking", "bulk-phase pinocytosis", "non-specific, non-absorptive pinocytosis", "fluid endocytosis" is a form of endocytosis in which small particles are brought into the cell - forming an invagination, and then suspended within small vesicles that subsequently fuse with lysosomes to hydrolyze, or to break down, the particles. This process requires a lot of energy via ATP. It is used primarily for the absorption of extracellular fluids (ECF), and, in contrast to phagocytosis, generates very small vesicles. Unlike receptor-mediated endocytosis, pinocytosis is nonspecific in the substances that it transports. The cell takes in surrounding fluids, including all solutes present. Pinocytosis also works as phagocytosis, the only difference being that phagocytosis is specific in the substances it transports. Phagocytosis actually engulfs whole particles, which are later broken down by enzymes, such as lysosomes, and absorbed into the cells. Pinocytosis, on the other hand, is when the cell engulfs already-dissolved or broken-down food.
  3. c
    A cis configuration means that adjacent hydrogen atoms are on the same side of the double bond. The rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has. When a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. Alpha-linolenic acid, with three double bonds, favors a hooked shape. The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be closely packed, and therefore could affect the melting temperature of the membrane or of the fat.
  4. d
    Cadherins (named for "calcium-dependent adhesion") are a class of type-1 transmembrane proteins. They play important roles in cell adhesion, ensuring that cells within tissues are bound together. They are dependent on calcium (Ca2+) ions to function, hence their name. The extra cellular domains on cadherins interact with their counterparts in other cell membranes and their intracellular domains interact intracellular proteins. The intracellular proteins are then bound to cytoskeleton intermediate filaments known as keratin.
  5. e
    This protein plays a major role in the formation of coated vesicles. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice that surrounds the vesicle. Coat-proteins, like clathrin, are used to build small vesicles in order to safely transport molecules between cells. The endocytosis and exocytosis of vesicles allows cells to transfer nutrients, to import signaling receptors, to mediate an immune response after sampling the extracellular world, and to clean up the cell debris left by tissue inflammation. On occasion, this mechanism also provides a pathway for raiding pathogens or toxins.

5 Multiple choice questions

  1. Cells are broken up by a homogeniser (blender). This releases the organelles from the cell. The resultant fluid is known as the homogenate, which is then filtered to remove any complete cells and large pieces of debris.
  2. The release of substances from a cell membrane only when specific conditions exist. A good example is the release of gastrointestinal hormones and digestive enzymes in response to food.

  3. Also known as actin filaments,one of three protein sub units that make up the eukaryote cytoskeleton. Found in highest concentration around the edges of the cell just below the cell membrane, they tend to form bundles. Actin polymers have the ability to disassemble and re-assemble meaning they are particulary useful for cell locomotion and in the microvilli of absorptive epithelial cells.

  4. The process by which substances or pathogens are taken in to a cell by engulfment by a vesicular structure surrounded by cell membrane.
  5. When electron carriers of the ETC 'sense' the slowing down of ATP synthase, due to full sotkc of ATP in the mitochondria, they too slow down the transfer of electrons, thus automatically conserving fuel when ATP is plentiful.

5 True/False questions

  1. Chaperone Protein
    In molecular biology, these are proteins that assist the non-covalent folding or unfolding and the assembly or disassembly of other macromolecular structures, but do not occur in these structures when the structures are performing their normal biological functions having completed the processes of folding and/or assembly. The common perception that they are concerned primarily with protein folding is incorrect. The first protein to be called a chaperone assists the assembly of nucleosomes from folded histones and DNA and such assembly chaperones, especially in the nucleus,are concerned with the assembly of folded subunits into oligomeric structures.

    One major function of chaperones is to prevent both newly synthesised polypeptide chains and assembled subunits from aggregating into nonfunctional structures. It is for this reason that many chaperones, but by no means all, are also heat shock proteins because the tendency to aggregate increases as proteins are denatured by stress. However, 'steric chaperones' directly assist in the folding of specific proteins by providing essential steric information, e.g. prodomains of bacterial proteases, lipase-specific foldases, or chaperones in fimbrial adhesion systems.


  2. SNARE hypothesis
    The hypothesis that t- SNARE and v-SNARE proteins are embedded in vessicles to ensure that they only fuse with the correct destination organnele or membrane.


  3. Anchoring Junction
    Junctions present in many types of animal tissue which serve to hold the constituentcells to each other and to the surrounding extra cellular matrix. They all have a common general structure consisting of transmembrane protein molecules known as cadhedrins.


  4. Plasmalemma
    Proteasomes are very large protein complexes inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm.The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that carry out such reactions are called proteases. Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. The degradation process yields peptides of about seven to eight amino acids long, which can then be further degraded into amino acids and used in synthesizing new proteins. Proteins to be destroyed are labelled by ubiquitin.


  5. α HelixThe protein of which the microtubules of the eukaryote cytoskeleton are formed.


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