MCAT Metabolism Flashcards
Describe each step of glycolysis
- Glucose is converted to glucuose-6- phosphate via hexokinase. ATP to ADP.
- Glucose- 6- phosphate is converted to fructose- 6- phosphate via phosphohexose isomerase.
- Fructose- 6- phosphate is converted to fructose- 1,6- phosphate via phosphofructokinase. ATP to ADP.
- Fructokinase- 1,6- phosphate is converted to glyceraldehyde-3- phosphate via aldolase. G3P can be isomerized to dihydroxyacetone phosphate.
- G3P is converted to 1,3- bisphosphoglycerate via G3P dehydrogenase. 2NAD+ is converted to 2 NADH.
- 1,3- BPG is converted to 3-phosphoglycerate via phosphoglycerate. kinase. 2 ADP to 2 ATP.
- 3- Phosphoglycerate is converted to 2- phosphoglycerate via phosphoglycerate mutase.
- 2- phosphoglycerate is converted to phosphoenolpyruvate via enolase. H20 is released.
- phosphoenolpyruvate is converted pyruvate via pyruvate kinase. 2 ADP to 2 ATP.
What are the two glucose receptors?
Glut 2 has a high Km and is found in the liver (for glucose storage) and beta islet of cells of the pancreas (for sensing glucose).
Glut 4 has a low Km and is found in muscle and adipose tissue and is stimulated by insulin.
What is the process of glycolysis?
Carbohydrate metabolism. Occurs in the cytoplasm of all cells and yields 2 ATP per glucose.
What are the net products of glycolysis?
2 NADH
2 ATP
2 Pyruvate
Glucokinase v. Hexokinase
Glucokinase is present in beta islet cells in is part of the glucose sensor and responds to insulin.
Hexokinase is present in peripheral tissues.
Phosphofructokinase -1 v. phosphofructokinase-2
Phosphofructokinase -1 - converts fructose -6- phosphate to fructose- 1,6- bisphosphate. It’s the rate limiting step pf glycolysis. Enzyme is inhibited by ATP and citrate but activated by AMP and fructose- 2,6- bisphosphate.
Phosphofructokinase -2 - creates fuctose-2,6- bisphosphate which activates phospfructokinase-1. Enzyme activated by insulin but inhibited by glucagon.
Which steps of glycolysis are irreversible?
Glucokinase/ Hexokinase, PFK-1, and pyruvate kinase.
Which enzymes participates in substrate level phosphorylation?
Phosphoglycerate kinase and pyruvate kinase.
Substrate level phosphorylation
When we transfer a phosphate from a high energy compound to create ATP or GTP.
What happens to the NADH that’s made during glycolysis?
If oxygen is present NADH enters the electron transport chain where it’s oxidized.
When oxygen is absent it’s oxidized by lactate dehydrogenase in the cytoplasm.
What is glycogenesis and which enzymes play a role in it?
Glycogenesis is the creation of glycogen. The storage form of carbohydrates in the body.
The process is the reverse of glycolysis, once it’s done the glucose that’s created is used by glycogen synthase and branching enzyme.
- glycogen synthase creates a chain of glucose monomers linked via alpha-1,4 linkages.
- Branching enzyme creates branches off the chain of glucose monomers linked via alpha- 1,6 linkages.
Role of pyruvate dehydrogenase?
Converts pyruvate into acetyl- coA. It’s activated by insulin by inhibited by acetyl-coA.
What is glycogenolysis and which enzymes are play a role in it?
The process of breaking down glycogen when we have low blood sugar.
- Glycogen phosphorylase- breaks glucose monomers apart from the chain to create a glucose- 1- phosphate that’s released into the bloodstream.
In liver it’s activated by glucagon. while in exercising muscle it’s activated by AMP and norepinephrine. - Debranching enzyme - moves oligonucleotides from branch and add it to the chain via alpha- 1,4 linkages and removes the branch point which exhibits alpha- 1,6 linkages.
Describe the enzymes of glycogenolysis needed to bypass steps in glycolysis?
1st. Pyruvate carboxylase converts pyruvate to oxaloacetate. Phosphoenolpyruvate carboxykinase converts oxaloacetate into phosphenolpyruvate. Both enzymes serve to bypass pyruvate kinase.
Pyruvate carboxylase is activated by acetyl- coA from beta oxidation.
Phosphenopyruvate carboxykinase is activated by glucagon and cortisol.
2nd. Fructose-1, 6- bisphosphatase converts fructose-1,6- bisphosphate to fructose- 6- phosphate. Bypasses phosphofructokinase - 1.
Fructose- 1,6- bisphosphatase activated by ATP and glucagon while it’s inhibited by ATP and Insulin.
- Glucose- 6- phosphatase converts glucose- 6- phosphate into glucose which is added to the glycogen chain.
Enzyme only present in the ER of the liver.
What is the pentose phosphate pathway?
Takes some glucose from glycolysis and makes ribulose-5-phosphate (important in making DNA and RNA) and NADPH.
