Other Metabolic Processes - GRE Subject Test: Biochemistry, Cell, and Molecular Biology

Phosphorylases are enzymes that attach phosphate groups to acceptors by breaking a chemical bond. Phosphatases are enzymes that remove phosphate groups.

Glycogen catabolism occurs by activation of glycogen phosphorylase, which then catalyzes the reaction of glycogen into glucose-1-phosphate (and a glycogen chain that is one glucose shorter).

Carnitine is ultimately responsible for helping fatty acids enter into the mitochondrial matrix. Acyl-CoA is actually the activated fatty acid that is being transferred. Carnitine reacts with acyl-CoA, and the newly formed acyl carnitine is moved into the mitochondrial matrix by a translocase.

Biotin is a vitamin that has many functions, including aiding in fatty acid synthesis. There is no protein that is actually called fatty acid transferase.

Macromolecules, such as peptides, polysaccharides, lipids, and proteins can be broken down to provide energy as well as operate in reverse through anabolic pathways. Anabolic and catabolic processes can occur simultaneously. All of the other answers are true.

A catabolic reaction is defined as a reaction in which a large molecule is broken down into smaller subunits. Of the following options, all listed are anabolic except for glycolysis. Glycolysis is the process of converting a glucose molecule into 2 pyruvate molecules, which classifies it as catabolic in nature.

When blood glucose levels are low, the obvious bodily response is to create more free glucose. Glycogen phosphorylase is an enzyme that is responsible for freeing glucose monomers from glycogen (thus creating more free glucose and raising the blood glucose concentration). Phosphorylation of glycogen phosphorylase activates the enzyme to create more free glucose. Thus, statement I should appear in our answer.

Glycogen synthase is an enzyme that does just the opposite; it traps free-floating glucose monomers by adding them to glycogen chains. Phosphorylation of glycogen synthase inhibits the enzyme's function to create more free glucose. Thus, statement II should also appear in our answer.

Increasing the production of insulin would lower blood glucose levels even further (glucagon, another hormone, would help raise them). Thus, statement III should not appear in our answer.

The final answer is statements I and II.

Antidiuretic hormone (ADH) binds the ADH receptors in the basolateral membrane of the collecting duct, which, through an ATP-dependent signaling cascade, synthesizes and relocates aquaporin-2 to the apical membrane of the collecting duct epithelial cells. The increase of aquaporin-2 at this membrane location facilitates increased water reabsorbtion into the bloodstream.

Insulin is a hormone that can often be associated with post-meal metabolism. The body has just eaten a meal, and is sequestering all of the nutrients and vitamins in the food. As a result, insulin is often associated with anabolic processes: glycogenesis, cholesterol and protein synthesis, and lipogenesis. Lipolysis, or the breaking down of fatty acids, is observed in periods of starvation, and therefore would not be stimulated by insulin.

After eating a carbohydrate-heavy meal, the body is not going to have any problem getting access to glucose. As a result, the body is going to activate enzymes needed for bringing glucose into cells and storing/using it. This includes glucokinase, PFK-1, and glycogen synthase. Fructose-1,6-bisphosphatase is an enzyme used in gluconeogenesis. Since the body does not need to create glucose following the meal, this enzyme is inhibited.

The primary purpose of fermentation is to regenerate the NAD+ that was reduced to NADH during glycolysis. This is essential because the cell will need that NAD+ to be able to go through glycolysis. In anaerobic environments, the Krebs cycle and electron transport chain cease to function, leaving glycolysis as the primary metabolic process for the cell to generate ATP. NAD+ is an essential reactant for glycolysis, but is rapidly consumed when the electron transport chain is not running. Fermentation takes place in order to replenish this reactant and allow glycolysis to continue.

Ethanol and lactic acid can be products of fermentation, but are not the primary purpose for fermentation. No oxygen or ATP is generated during this process.

During aerobic metabolism, a single glucose molecule produces significantly more ATP molecules than during anaerobic metabolism. The exact number depends on a number of things, including the organism, cell type, and NADH shuttle. Aerobic metabolism of glucose produces more reduced coenzymes, which drop off their electrons at the electron transport chain in the mitochondria. Electron transport provides energy to pump protons from the mitochondrial matrix into the intermembrane space. Both processes produce pyruvate.