Biochemistry Chapter 9: Carbohydrate Metabolism I

Question 1

GLUT 2

Answer 1

found in the liver (for glucose storage) and pancreatic beta-islet cells (as part of the glucose sensor). Has a high Km

Question 2

GLUT 4

Answer 2

found in adipose tissue and muscle and is stimulated by insulin. Has a low Km

Question 3

Where does glycolysis take place?

Answer 3

in the cytoplasm

Question 4

Does glycolysis require oxygen?

Answer 4

No

Question 5

What does glycolysis yield?

Answer 5

2 ATP

Question 6

Glucokinase

Answer 6

converts glucose to glucose 6-phosphate. present in the pancreatic beta-islet cells as part of the glucose sensor and is responsive to insulin in the liver

Question 7

Hexokinase

Answer 7

converts glucose to glucose 6-phosphate in peripheral tissues.

Question 8

Phosphofructokinase-1

Answer 8

phosphorylates fructose 6-phosphate to fructose 1,6-biphosphate in the rate-limiting step of glycolysis. PFK-1 is activated by AMP and fructose 2,6-bisphosphate and is inhibited by ATP and citrate

Question 9

Phosphofructokinase-2

Answer 9

produces the F2,6 - BP that activates PFK-1. It is activated by insulin and inhibited by glucagon

Question 10

Glyceraldehyde-3-phosphate dehydrogenase

Answer 10

produces NADH, which can feed into the electron transport chain.

Question 11

3-phosphoglycerate kinase / pyruvate kinase

Answer 11

substrate-level phosphorylation - placing an inorganic phosphate onto ADP to form ATP.

Question 12

Which enzyme perform irreversible reactions?

Answer 12

glucokinase/hexokinase, PFK-1, pyruvate kinase

Question 13

Where is the NADH from gylcolysis oxidized?

Answer 13

The mitochondrial electron transport chain

Question 14

If oxygen or mitochondria are absent, then the NADH produced in glycolysis…

Answer 14

is oxidized by cytoplasmic lactate dehydrogenase. ex. red blood cells, skeletal muscle, and any cell deprived of oxygen.

Question 15

Galactose

Answer 15

Comes from lactose in milk - trapped by galactokinase and converted to glucose 1-phosphate via galactose-1-phosphate uridyl-transferase and an epimerase

Question 16

fructose

Answer 16

comes from honey, fruit, sucrose. It is trapped in the cell by fructokinase and then cleaved by aldolase B to form glyceraldehyde and DHAP.

Question 17

Pyruvate dehydrogenase

Answer 17

a complex of enzymes that convert pyruvate to acetyl-CoA. It is stimulated by insulin and inhibited by acetyl-CoA

Question 18

Glycogenesis

Answer 18

production of glycogen using two main enzymes: glycogen synthase and branching enzyme

Question 19

glycogen synthase

Answer 19

creates a alpha-1,4 glycosidic link between glucose molecules. Activated by insulin in the liver and muscle.

Question 20

Branching enzyme

Answer 20

moves a block of oligoglucose from one chain and adds it to the growing glycogen as a new branch using an alpha-1,6 glycosidic link.

Question 21

Glycogenolysis

Answer 21

a breakdown of glycogen using two main enzymes: glycogen phosphorylase and debranching enzyme

Question 22

Glycogen phosphorylase

Answer 22

removes single glucose 1-phosphate molevules 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 23

Debranching enzyme

Answer 23

Moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link. It also removes the branchpoint, which is connected via an alpha 1,6 glycosidic link, releasing a free glucose molecule.

Question 24

Gluconeogenesis occurs in..

Answer 24

occurs in both the cytoplasm and mitochondria, predominantly in the liver. There is a small contribution from the kidneys.

Question 25

What is gluconeogenesis?

Answer 25

the reverse of glycolysis.

Question 26

What are the three irreversible steps of gluconeogenesis?

Answer 26

Pyruvate carboxylase, fructose 1, 6 BP, glucose-6-phosphatase

Question 27

Pyruvate carboxylase

Answer 27

• converts pyruvate into oxaloacetate which is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase.
• activated by acetyl-CoA from beta-oxidation
• PEPCK is activated by glucagon and cortisol

Question 28

Fructose-1,6-bisphosphatase

Answer 28

• converts fructose 1,6 bisphosphate to fructose 6-phosphate
• It is activated by ATP directly and glucagon indirectly
• inhibited by AMP directly and insulin indirectly

Question 29

Glucose - 6- phosphatase

Answer 29

converts glucose 6-phosphate to free glucose bypassing glucokinase. It is found only in the endoplasmic reticulum of the liver.

Question 30

Pentose phosphate pathway (PPP)

Answer 30

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

Question 31

Rate limiting enzyme for PPP

Answer 31

glucose-6-phosphate dehydrogenase (activated by NADP+ and inhibited by NADPH and insulin