Biochemistry Ch 9. Carbohydrate Metabolism

Question 1

Glucose transporters

Answer 1

GLUT 2 and GLUT 4

Question 2

GLUT 2

Answer 2

Found in the liver (for glucose storage) and pancreatic beta cells (as part of the glucose sensor), has a high Km

Question 3

GLUT 4

Answer 3

Found in adipose tissue and muscle and is stimulated by insulin, has a low Km

Question 4

Glycolosis

Answer 4

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

Question 5

Glucokinase

Answer 5

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 6

Hexokinase

Answer 6

Converts glucose to glucose 6-phophase in peripheral tissues

Question 7

Phosphofructokinase-1

Answer 7

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

Question 8

Phosphofructokinase-2

Answer 8

PFK-2 - produces the F2,6-BP that activates PFK-1, activated by glucose and inhibited by glucagon

Question 9

Glyceradehyde-3-phosphate dehydrogenase

Answer 9

Produces NADH which can feed into the electron transport chain

Question 10

3 - phosphoglycerate kinase

Answer 10

Performs substrate level phosphorylation, placing an inorganic phosphate (Pi) onto ADP to form ATP

Question 11

Pyruvate kinase

Answer 11

Performs substrate level phosphorylation, placing an inorganic phosphate (Pi) onto ADP to form ATP

Question 12

Substrate-level phosphorylation

Answer 12

When an inorganic phosphate (Pi) in placed onto ADP to form ATP

Question 13

NADH product of glycolysis

Answer 13

Oxidized by the mitochondrial electron transport chain when oxygen is present, if oxygen absent, the NADH is oxidized by cytoplasmic lactate dehydrogenase

Question 14

Enzymes that catalyze irreversible reactions of glycolysis??

Answer 14

Glucokinase/hexokinase, PFK-1, and pyruvate kinase

Question 15

Lactate dehydrogenase

Answer 15

Will oxidize NADH if oxygen is absent

Question 16

Galactose

Answer 16

Comes from lactose in milk, trapped in the cell by galactokinase and converted to glucose 1-phosphate via galactose-1-phosphate uridyltransferase and an epimerase

Question 17

Fructose

Answer 17

Comes from honey, fruit, and sucrose (common table sugar), it is trapped in the cell by fructokinase and cleaved by aldolase B to form glyceraldehyde and dHAP

Question 18

Pyruvate dehydrogenase

Answer 18

Refers to a complex of enzymes that convert pyruvate to acetyl-CoA, stimulated by insulin and inhibited by acetyl-CaoA

Question 19

Glycogenesis

Answer 19

Glycogen synthesis, the production of glycogen using two main enzymes: glycogen synthase and branching enzyme

Question 20

Glycogen synthase

Answer 20

Creates alpha-1,4 glycosidic links between glucose molecules, activated by insulin in liver and muscle

Question 21

Branching enzyme

Answer 21

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 22

Glycogenolysis

Answer 22

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

Question 23

Glycogen phosphorylase

Answer 23

Removes single glucose 1-phosphate molecules by breaking alpha-1,4 glycosidic links, in the liver 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 24

Debranching enzyme

Answer 24

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 branch point, which is connected via an alpha-1,6 glycosidic link, releasing a free glucose molecule

Question 25

Gluconeogenesis

Answer 25

Occurs in both the cytoplasm and mitochondria predominantly in the liver, there is a small contribution from the kidneys, most of it is simply the reverse of glycolysis using the same enzymes, three irreversible steps bypassed by enzymes: pyruvate carboxylase, fructose-1,6-bisphosphatase, and glucose-6-phosphate

Question 26

Pyruvate carboxylase

Answer 26

Converts pyruvate into oxaloacetate, which is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase (PEPCK), these to enzymes bypass pyruvate kinase, activated by acetyl-CoA from beta-oxidation

Question 27

Phosphoenolpyruvate carboxykinase

Answer 27

PEPCK - converts oxaloaetate to phosphoenolpyruvate, works with pyruvate cacrboxylase to bypass pyruvate kinase, activated by glucagon and cortisol

Question 28

Fructose-1,6-bisphosphatase

Answer 28

Converts fructose 1,6-bisphosphate to fructose 6-phosphate, bypassing phosphofructokinase-1, rate limiting step of gluconeogenesis, activated by ATP directly and glucagon indirectly (via decreased levels of fructose 2,6-bisphosphate), inhibited by AMP directly and insulin indirectly (via increased levels of fructose 2,6-bisphosphate)

Question 29

Glucose-6-phosphatase

Answer 29

Converts glucose 6-phosphate to free glucose, bypassing glucokinase, found only in the endoplasmic reticulum of the liver

Question 30

Pentose phosphate pathway

Answer 30

PPP - aka hexose monophosphate shunt, occurs in the cytoplasm of most cells, generating NADPH and sugars for biosynthesis (derived from ribulose 5-phosphate), rate limiting enzyme is glucose-6-phosphate dehydrogenase

Question 31

Glucose-6-phosphate dehydrogenase

Answer 31

Rate limiting enzyme in pentose phosphate pathway, activated by NADP+ and insulin and inhibited by NADPH