Ch 9: Carbohydrate Metabolism 1

Question 1

GLUT 2

Answer 1

low affinity transporter in hepatocytes and pancreatic cells; found in the liver (for glucose storage) and pancreatic B-islet cells (as part of the glucose sensor); has a high Km

Question 2

GLUT 4

Answer 2

glucose transport; found in adipose tissue and muscle and is stimulated by insulin; has a low Km

Question 3

Glycolysis

Answer 3

occurs in cytoplasm of all cells, and does not require oxygen; it yields 2 ATP per molecule of glucose

Question 4

Glucokinase

Answer 4

important glycolysis enzyme which converts glucose to glucose 6-phosphate. present in the pancreatic B-islet cells as part of the glucose sensor and is responsive to insulin in the liver

Question 5

Hexokinase

Answer 5

important glycolysis enzyme converts glucose to glucose 6-phosphate in peripheral tissues

Question 6

Phosphofructokinase-1 (PFK-1)

Answer 6

important glycolysis enzyme that 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-biphosphate (F2,6-BP) and is inhibited by ATP and citrate

Question 7

Phosphofructokinase-2 (PFK-2)

Answer 7

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

Question 8

Glyceraldehyde-3-phosphate dehydrogenase

Answer 8

important glycolysis enzyme produces NADH, which can feed into the electron transport chain

Question 9

3-phosphoglycerate kinase & pyruvate kinase perform

Answer 9

important glycolysis enzyme that performs substrate-level phosphorylation

Question 10

substrate-level phosphorylation

Answer 10

placing an inorganic phosphate (Pi) onto ADP to form ATP

Question 11

4 enzymes that catalyze irreversible reactions in glycolysis are

Answer 11

glucokinase
hexokinase
PFK-1
pyruvate kinase

Question 12

when oxygen/mitochondia are present, NADH produced in glycolysis is

Answer 12

oxidized by mitochondrial electron transport chain

Question 13

when oxygen/mitochondia are NOT present, NADH produced in glycolysis is

Answer 13

oxidized by cytoplasmic lactate dehydrogenase

examples: red blood cells, skeletal muscle (during short, intense bursts of exercise), and any cell deprived oxygen

Question 14

Galactose

Answer 14

comes from lactose in milk; trapped in cell by galactokinase and converted to glucose 1-phosphate via galactose-1-phosphate uridyltransferase and epimerase

Question 15

galactose-1-phosphate uridyltransferase

Answer 15

converts galactose to glucose 1-phosphate

Question 16

Fructose

Answer 16

comes from honey, fruit, and sucrose (table sugar); trapped in cell by fructokinase, and cleaved by aldolase B to form glyceraldehyde and DHAP

Question 17

Pyruvate dehydrogenase

Answer 17

refers to a complex of enzymes that converts pyruvate to acetyl-CoA; stimulated by insulin and inhibited by acetyl-CoA

Question 18

Glycogenesis (glycogen synthesis)

Answer 18

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

Question 19

Glycogen synthase

Answer 19

enzyme in glycogenesis that creates alpha-1,4 glycosidic linkages between glucose molecules. it is activated by insulin in 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

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

Question 22

Glycogen phosphorylase

Answer 22

enzyme in glycogenolysis which 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 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

Answer 24

liver maintains glucose levels in blood during fasting through this (or glycogenolysis); occurs in both the cytoplasm and mitochondria, predominantly in the liver; small contribution from the kidneys

Question 25

Gluconeogenesis is the reverse of

Answer 25

glycolysis

Question 26

Gluconeogenesis must surpass the 3 irreversible steps of glycolysis with these different enzymes:

Answer 26

pyruvate carboxylase & phosphoenolpyruvate carboxykinase (PEPCK) fructose-1,6-bisphosphatase glucose-6-phosphatase

Question 27

Pyruvate carboxylase | & PEPCK

Answer 27

converts pyruvate into oxaloacetate, which is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase (PEPCK); together these 2 enzymes bypass pyruvate kinase Pyruvate carboxylase is activated by acetyl-CoA from B-oxidation PEPCK 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. this is the rate limiting step of gluconeogenesis; is activated by ATP directly and glucagon indirectly (via decreased levels of fructose 2,6-bisphosphate) and 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. it is found only in the endoplasmic reticulum of the liver

Question 30

Pentose Phosphate Pathway (PPP)

Answer 30

also known as the hexose monophosphate (HMP) shunt occurs in the cytoplasm of most cells, two main functions: generating NA-DPH and sugars for biosynthesis (derived from ribulose 5-phosphate- PPP is the source of this)

Question 31

Glucose-6-phosphate dehydrogenase

Answer 31

rate-limiting enzyme which is activated by NADP+ and inhibited by NADPH and insulin in the PPP

Question 32

Rate-limiting enzyme of Glycolysis

Answer 32

phosphofructokinase-1

Question 33

Rate-limiting enzyme of Fermentation

Answer 33

lactate dehydrogenase

Question 34

Rate-limiting enzyme of Glycogenesis

Answer 34

glycogen synthase

Question 35

Rate-limiting enzyme of Glycogenolysis

Answer 35

glycogen phosphorylase

Question 36

Rate-limiting enzyme of Gluconeogenesis

Answer 36

fructose-1,6-bisphosphatase

Question 37

Rate-limiting enzyme of Pentose Phosphate Pathway

Answer 37

glucose-6-phosphate dehydrogenase

Question 38

Glycogenesis

Answer 38

synthesis of glycogen granules, beginning with core protein called glycogenin

Question 39

NADPH

Answer 39

primary functions are lipid biosynthesis, bacterial bleach formation in white blood cells, and maintenance of glutathione stores to protect against reactive oxygen species

Question 40

How Glycolysis Pushes Forward the Process: Kinases | is a mnemonic for

Answer 40

Irreversible steps of glycolysis Hexokinase Glucokinase PFK-1 Pyruvate Kinase