CONCEPT 11. Regulation of metabolic pathways

• What is gluconeogenesis?

  The process of synthesizing glucose from non-carbohydrate sources.
• Why doesn't gluconeogenesis occur all the time?

  7 out of the 10 steps from glycolysis are used but in reverse. The 3 that are not reversible regulate rates of gluconeogenesis.
• Where are carbohydrates stored?

  In liver and muscle cells, as glycogen
• Where is fat stored?

  In fat deposits
• Lipids store more energy than glucose but require more time to be broken down as they are more complex
• Glycerol is a lipid that can be fed into the glycolysis pathway
• Fatty acids can undergo beta oxidation to become acetyl-CoA and be used in the Krebs cycle
• There is no storage form of proteins, therefore, amino acids must be regularly ingested in our diet so proteins can be built and replaced
• When does protein metabolism occur?

  When there is an excess of amino acids
• What are the stages of protein metabolism?

  Transamination, oxidative deamination and the urea cycle
• How is the rate of reactions measured?

  By measuring the decreasing concentration of the substrate or the increasing concentration of the products
• What is the Michaelis-Menton model?

  explains how the rate of an enzyme-catalysed reaction depends on the concentration of the enzyme and its substrate
• What is the Michaelis constant?

  Describes an enzymes affinity for its substrate. Small Km = high substrate affinity / High Km = low substrate affinity
• How does temperature affect enzyme activity?

  Temperature affects enzyme activity by increasing the rate of reaction as temperature increases, up to an optimal temperature, after which the enzyme denatures and activity decreases.
• How does pH affect enzyme activity?

  pH affects enzyme activity by altering the enzyme's shape and charge, which can either enhance or inhibit its ability to catalyze a reaction.
• What are cofactors?

  Cofactors are non-protein molecules that assist enzymes in carrying out their catalytic functions.
• What are coenzymes?

  Organic molecules which transfer chemicals from one active site to another
• What are prosthetic groups?

  A type of coenzyme that is permanently bound to an enzyme and is required for the enzyme to be active.
• What affect to enzyme inhibitors have on enzyme activity?

  Reduces the activity of an enzyme or inactivates it
• What are competitive inhibitors?

  Molecules that bind to the active site of an enzyme, blocking the substrate. To reverse this effect, substrate concentration should be increased over inhibitor concentration.
• What are non-competitive inhibitors?

  Molecules that bind to an enzyme away from the active site, triggering a change in enzyme shape so that the active site is no longer complementary to its substrate. Type of allosteric regulation.
• What are irreversible inhibitors?

  Irreversible inhibitors are molecules that covalently bond to the side chains in the active site, permanently inactivating the enzyme.
• What are examples of irreversible inhibitors?

  Often toxic substances including insecticides, antibiotics and aspirin
• How does allosteric regulation affect enzymes?

  Allosteric regulation causes changes to the enzyme's shape, either activating or inactivating it. Most allosteric enzymes are proteins with quaternary structure.
• Why can't allosteric regulation be classified as non-competitive regulation?

  Certain forms of allosteric inhibition can prevent the substrate from binding to the active site thus allosteric inhibition can be noncompetitive or competitive
• What is cooperativity?

  A type of allosteric activation where the binding of one substrate molecule to the active site of one subunit unlocks all subunits in active confirmation.
• What is the role of allosteric activators and inhibitors?

  The activators or inhibitors will bind to an allosteric enzyme with multiple subunits and stabilise it in either its active or inactive form. The activators and inhibitors bind to allosteric sites, and the enzyme will oscillate between forms until equilibrium is achieved.
• How does allosteric regulation regulate metabolism?

  At certain points of the metabolic pathway, allosteric enzymes will be present and the activation or inactivation of these enzymes set the pace of glycolysis and the citric acid cycle. The excess or absence of the pathway's products create feedback regulation which adjusts rates of respiration as the cell's needs change
• What is feedback inhibition?

  Regulation of a process by its end product.