Carbohydrate Metabolism Flashcards
Glycolysis?
occurs in the cytoplasm of all cells, does not require oxygen, yields 2 ATP per glucose
Glucokinase?
present in the pancreatic beta islet cells as part of the glucose sensor and is responsive to insulin in the liver, irreversible
Hexokinase?
traps glucose, irreversible
Phosphofructokinase-1 (PFK-1)?
rate limiting step, irreversible
Phosphofructokinase-2 (PFK-2)?
produces F2, 6-BP which activates PFK-1
Glyceraldehyde-3-phosphate dehydrogenase?
produces NADH
3-phosphoglycerate kinase and pyruvate kinase?
perform substrate level phosphorylation, irreversible (pyruvate kinase)
NADH produced glycolysis is oxidized aerobically by the _______ ______ _______ ______ and anaerobically by cytoplasmic _______ ______.
mitochondrial electron transport chain
lactate dehydrogenase
Pyruvate dehydrogenase?
converts pyruvate to acetyl CoA, stimulated by insulin and inhibited by acetyl CoA
Where does the citric acid cycle take place?
mitochondrial matrix
What is the main purpose of the citric acid cycle?
oxidize acetyl CoA and generate high energy electron carriers (NADH, FADH2) and GTP
Where does the electron transport chain take place?
matrix facing surface of the inner mitochondrial membrane
What happens in the electron transport chain?
- NADH donates electrons to the chain, which are passed from one complex to the next
- reduction potentials increase down the chain, until the electrons end up on oxygen, which has the highest reduction potential
- NADH cannot cross the inner mitochondrial membrane, so must use one of two shuttle mechanisms to transfer its electrons to energy carriers in the matrix: glycerol 3-phosphate shuttle or malate aspartate shuttle
What is the proton motive force?
electrochemical gradient generated by the electron transport chain across the inner mitochondrial membrane
The intermembrane space has a _____ concentration of protons than the matrix.
higher
-this gradient stores energy which can be used to form ATP via chemiosmotic coupling
ATP synthase?
the enzyme responsible for generating ATP from ADP and an inorganic phosphate (Pi)
Energy yield of glycolysis?
2 NADH and 2 ATP
Energy yield of pyruvate dehydrogenase?
1 NADH (2 NADH per molecule of glucose b/c each glucose forms two molecules of pyruvate)
Energy yield of citric acid cycle?
3 NADH, 1 FADH2, 1 GTP (x2 per molecule of glucose)
Energy yield of each NADH?
2.5 ATP
Energy yield of each FADH2?
1.5 ATP
GTP are converted to ____.
ATP
Total energy yield per molecule of glucose?
30-32 ATP
Glycogenesis?
building of glycogen using glycogen synthase and branching enzyme
Glycogen synthase?
creates alpha-1,4 glycosidic links between glucose molecules, it is activated by insulin in the liver and muscles
Branching enzyme?
moves a block of oligoglucose from one chain and connects it as a branch using an alpha 1,6 glycosidic link
Glycogenolysis?
breakdown of glycogen using glycogen phosphorylase and debranching enzyme
Glycogen phosphorylase?
removes single glucose 1-phosphate molecules by breaking alpha 1,4 glycosidic links.
- in the liver it is activated by glucagon to prevent low blood sugar
- in exercising skeletal muscle it is activated by epinephrine and AMP to provide glucose for the muscle itself
Debranching enzyme?
moves a block of oligoglucose from one branch and connects it to the chain using an alpha 1,4 glycosidic link
Gluconeogenesis?
occurs in both the cytoplasm and mitochondria, predominantly in the liver. most of the time it is just the reverse of glycolysis, using the same enzymes
What bypasses pyruvate kinase?
pyruvate carboxylase and PEP carboxykinase
What bypasses PFK 1?
Fructose-1,6 bisphosphatase
What bypasses hexokinase/glucokinase?
Glucose-6-phosphatase
What is the pentose phosphate pathway?
occurs in the cytoplasm of most cells, generating NADPH and sugars for biosynthesis
What is the rate limiting enzyme in the pentose phosphate pathway?
glucose-6-phosphate dehydrogenase, which is activated by NADP+ and inhibited by NADPH and insulin
