Carbohydrate Metabolism

Question 1

Glycolysis?

Answer 1

occurs in the cytoplasm of all cells, does not require oxygen, yields 2 ATP per glucose

Question 2

Glucokinase?

Answer 2

present in the pancreatic beta islet cells as part of the glucose sensor and is responsive to insulin in the liver, irreversible

Question 3

Hexokinase?

Answer 3

traps glucose, irreversible

Question 4

Phosphofructokinase-1 (PFK-1)?

Answer 4

rate limiting step, irreversible

Question 5

Phosphofructokinase-2 (PFK-2)?

Answer 5

produces F2, 6-BP which activates PFK-1

Question 6

Glyceraldehyde-3-phosphate dehydrogenase?

Answer 6

produces NADH

Question 7

3-phosphoglycerate kinase and pyruvate kinase?

Answer 7

perform substrate level phosphorylation, irreversible (pyruvate kinase)

Question 8

NADH produced glycolysis is oxidized aerobically by the _______ ______ _______ ______ and anaerobically by cytoplasmic _______ ______.

Answer 8

mitochondrial electron transport chain

lactate dehydrogenase

Question 9

Pyruvate dehydrogenase?

Answer 9

converts pyruvate to acetyl CoA, stimulated by insulin and inhibited by acetyl CoA

Question 10

Where does the citric acid cycle take place?

Answer 10

mitochondrial matrix

Question 11

What is the main purpose of the citric acid cycle?

Answer 11

oxidize acetyl CoA and generate high energy electron carriers (NADH, FADH2) and GTP

Question 12

Where does the electron transport chain take place?

Answer 12

matrix facing surface of the inner mitochondrial membrane

Question 13

What happens in the electron transport chain?

Answer 13

• 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

Question 14

What is the proton motive force?

Answer 14

electrochemical gradient generated by the electron transport chain across the inner mitochondrial membrane

Question 15

The intermembrane space has a _____ concentration of protons than the matrix.

Answer 15

higher

-this gradient stores energy which can be used to form ATP via chemiosmotic coupling

Question 16

ATP synthase?

Answer 16

the enzyme responsible for generating ATP from ADP and an inorganic phosphate (Pi)

Question 17

Energy yield of glycolysis?

Answer 17

2 NADH and 2 ATP

Question 18

Energy yield of pyruvate dehydrogenase?

Answer 18

1 NADH (2 NADH per molecule of glucose b/c each glucose forms two molecules of pyruvate)

Question 19

Energy yield of citric acid cycle?

Answer 19

3 NADH, 1 FADH2, 1 GTP (x2 per molecule of glucose)

Question 20

Energy yield of each NADH?

Answer 20

2.5 ATP

Question 21

Energy yield of each FADH2?

Answer 21

1.5 ATP

Question 22

GTP are converted to ____.

Answer 22

ATP

Question 23

Total energy yield per molecule of glucose?

Answer 23

30-32 ATP

Question 24

Glycogenesis?

Answer 24

building of glycogen using glycogen synthase and branching enzyme

Question 25

Glycogen synthase?

Answer 25

creates alpha-1,4 glycosidic links between glucose molecules, it is activated by insulin in the liver and muscles

Question 26

Branching enzyme?

Answer 26

moves a block of oligoglucose from one chain and connects it as a branch using an alpha 1,6 glycosidic link

Question 27

Glycogenolysis?

Answer 27

breakdown of glycogen using glycogen phosphorylase and debranching enzyme

Question 28

Glycogen phosphorylase?

Answer 28

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

Question 29

Debranching enzyme?

Answer 29

moves a block of oligoglucose from one branch and connects it to the chain using an alpha 1,4 glycosidic link

Question 30

Gluconeogenesis?

Answer 30

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

Question 31

What bypasses pyruvate kinase?

Answer 31

pyruvate carboxylase and PEP carboxykinase

Question 32

What bypasses PFK 1?

Answer 32

Fructose-1,6 bisphosphatase

Question 33

What bypasses hexokinase/glucokinase?

Answer 33

Glucose-6-phosphatase

Question 34

What is the pentose phosphate pathway?

Answer 34

occurs in the cytoplasm of most cells, generating NADPH and sugars for biosynthesis

Question 35

What is the rate limiting enzyme in the pentose phosphate pathway?

Answer 35

glucose-6-phosphate dehydrogenase, which is activated by NADP+ and inhibited by NADPH and insulin