Lecture 27 Flashcards
What are the main points about glycolysis?
Glycolysis is the splitting of glucose (6 carbon) into pyruvate (3 carbons). Its a ubiquitous pathway (all cells in body can do it), and is done cytoplasmically in animals. In mammals this is essential for some cells (blood cells due to no mitochondria) and is a major fuel for some cells (e.g brain). The energy is conserved in ATP and NADH and the pyruvate may be further metabolised either aerobically or anaerobically.
What are the two phases in glycolysis and what products do they lead to?
Glycolysis has an energy input phase (2 ATP used to activate the glucose in two seperate reactions, one ATP for each reaction leading to glucose being split into glyceraldehyde free phosphate and dihydroxyacetone phosphate (which is then converted to glyceraldehyde free phosphate) at the end), this then converts the (glucose to two pyruvate + 2 H2O) and (2 NAD+ to 2 NADH + 2H+) and (2 ADP + 2P to 2 ATP), this is the energy payoff phase.
What occurs in the energy input phase? What are the end products and how do they both become the needed form?
Glucose goes to glucose-6-phosphate via coupling with ATP hydrolysis, a small amount of energy is then used to rearrange it into fructose-6-phosphate (no coupling needed). The third step is addition of a phosphate to fructose-6-phosphate to make it fructose-1-phosphate via coupling with ATP). This molecule is then split via the aldelase enzyme. The dihydroxyacetone phosphate is in equilibrium with glyceraldehyde-3-phosphate, as this is used up the dihydroxyactone phosphate will be converted.
How is substrate level phosphorylation done?
Substrate level phosphorylation is when the energy to put the phosphate onto ADP is coupled with something with a negative delta G value.
What are the steps in the energy payoff stage?
Glyceraldehyde-3-phosphate is oxidised to 1,3-BPG using NAD+ as a coenzyme. This adds a phosphate without requiring ATP. This carbon 1 phosphate is removed, releasing energy and moving the phosphate to ADP to make ATP. The 3-phosphoglycerate is then rearranged to phosphoenolpyruvate and the phosphate bond can then be cleaved by pyruvate kinase (should be a phosphatase but is named a kinase). This happens twice for every glucose. this process can be interrupted by arsenic, the arsenic substitutes for phosphate, the resulting compound is unstable but ATP is not synthesised by phosphoglycerate kinase.
What occurs to pyruvate in further metabolising?
under aerobic conditions pyruvate is converted into acetyl-CoA in the mitochondrial matrix involving several cofactors. It is an oxidative decarboxylation (pyruvate is oxidised and carboxyl group is lost), it has a negative delta G. Under anaerobic conditions pyruvate is converted into lactate (NADH to NAD+, an oxidation, pyruvate is reduced). Anearobic metabolism of glucose to pyruvate converts NAD+ to NADH (reduction), this allows the refueling of the NAD+. In anaerobic alcoholic fermentation its converted to ethanol and CO2 via oxidation of NADH to NAD+.
