5 Written questions
5 Matching questions
- Raft hypothesis
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.
- b The hypothesis that small 'rafts', semi rigid microdomains, dense in glycosphingolipids containing saturated fatty acids, cholesterols and various GPI anchored proteins exist in cell membranes. This has been supported by a number of fluorescence studies and it has been siggested that they may be hot spots for signalling.
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.
Latin for little caves, singular: caveola, which are a special type of lipid raft, are small (50-100 nanometer) invaginations of the plasma membrane in many vertebrate cell types, especially in endothelial cells and adipocytes.These flask-shaped structures are rich in proteins as well as lipids such as cholesterol and sphingolipids and have several functions in signal transduction.They are also believed to play a role in endocytosis, oncogenesis, and the uptake of pathogenic bacteria and certain viruses.They are one source of clathrin-independent endocytosis involved in turnover of adhesive complexes.
- e Any compound that increases the proton permiability of the inner mitochondrial membrane and hence severes the link between electron transport and ATP synthesis. Two example are thyroxine and brown adipose tissue.
5 Multiple choice questions
Saturated fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms and have no double bonds. Thus, saturated fatty acids are saturated with hydrogen (since double bonds reduce the number of hydrogens on each carbon). Because saturated fatty acids have only single bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega carbon at the end that has 3 hydrogens).
- Cellular compartments in cell biology comprise all closed parts within a cell, usually surrounded by a single or double lipid layer membrane. Most organelles are compartments like mitochondria, chloroplasts (in photosynthetic organisms), peroxisomes, lysosomes, the endoplasmic reticulum, the cell nucleus or the Golgi apparatus. Smaller elements like vesicles, and sometimes even microtubules can also be counted as compartments.
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.
A membrane protein, involved in passive and active transport, that binds to a solute molecule or ion and releases it on the other side of the membrane. An example of this is the glucose carrier protein in mammalian cells which responds only to glucose and not other sugars and moves glucose down a concentration gradient from the outside to the inside of the cell.
Also known as a nuclear localisation sequence (NLS) this is an amino acid sequence which 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal, which targets proteins out of the nucleus.
5 True/False questions
Glycolysis (from glycose, an older term for glucose + -lysis degradation) is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).
Pyruvate dehydrogenase complex →
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.
Hofstee-Eadie plot →
A plot used to obtain a more accurate indication of Km and Vmax. Simplified - v/[S] so the figures used to plot the original hyperbolic rectangle are used dviding the enzyme byt hte substrate. These new figures are then plotted on along the horizontal axis and a best fit line drawn along them. The point at which the line crosses the vertical axis is the Vmax, the point at which it crosses the horizontal axis is the Km.
Irreversible Inhibitors → Usually not of biological origins, these act by forming strong covalent bonds with the enzyme, poisoning them. The bond is so strong it is irreversible and example of this would be heavy metal toxicity.
Substrate level phosphorylations → Cellular compartments in cell biology comprise all closed parts within a cell, usually surrounded by a single or double lipid layer membrane. Most organelles are compartments like mitochondria, chloroplasts (in photosynthetic organisms), peroxisomes, lysosomes, the endoplasmic reticulum, the cell nucleus or the Golgi apparatus. Smaller elements like vesicles, and sometimes even microtubules can also be counted as compartments.