Ch. 9: Carbohydrate Metabolism I

Question 1

what drives glucose entry into the cells

Answer 1

concentration

Question 2

where is GLUT 2 located

Answer 2

hepatocytes and pancreatic cells

Question 3

what does GLUT 2 do

Answer 3

captures excess glucose from the digestive tract primarily for storage

Question 4

when does GLUT 2 function

Answer 4

when blood glucose levels are high until the concentration drops below the Km T (which is high) for the transporter

Question 5

where is GLUT 4 located

Answer 5

adipose tissue and muscle

Question 6

how does GLUT 4 function with insulin

Answer 6

when insulin is high, transporters move from inside cell to membrane

Question 7

how high is the Km of GLUT 4 in relationship to nl blood glucose levels

Answer 7

Km is slightly higher than normal blood glucose

Question 8

what does GLUT 4 do

Answer 8

captures excess blood glucose for for storage in muscles (as glycogen) and adipose tissue (DHAP)

Question 9

what occurs (big picture) during glycolysis

Answer 9

• glucose is converted into two pyruvate molecules
• which release energy that
• is captured in two substrate level phosphorylations and
• one oxidation reaction

Question 10

how are the products of glycolysis used by the body (big picture)

Answer 10

if oxygen + mitochondria, NADH feeds into aerobic respiratory pathway

if no oxygen or mitochondria, anaerobic energy

sometimes, intermediates for other pathways

Question 11

what do hexokinase and glucokinase do

Answer 11

phosphorylate glucose inside the cell to prevent it from leaving the cell via the transporter

Question 12

where is hexokinase located

Answer 12

most tissues (GLUT 4)

Question 13

where is glucokinase located

Answer 13

hepatocytes and pancreas cells (GLUT 2)

Question 14

what does phosphofructokinase-1 do

Answer 14

rate-limiting enzyme and main control point in glycolysis

phosphorylates fructose

activated (turns on glycolysis) by AMP and citrate and inhibited (turns off glycolysis) by ATP

Question 15

what does phosphofructokinase-2 do

Answer 15

phosphorylates F6P to F26P, which activated PFK-1

Question 16

what does glyceraldehyde-3-phosphate dehydrogenase do

Answer 16

catalyzes an oxidation and addition of inorganic phosphate to its substrate –> high energy intermediate: 1,3 - biphosphoglycerate

reduces NAD+ to NADH

Question 17

what does 3-phosphoglycerate kinase do

Answer 17

transfers the high-energy phosphate from 1,3 - biphosphoglycerate to ADP –> ATP

substrate-level phosphorylation

Question 18

what occurs during substrate-level phosphorylation

Answer 18

ADP is directly phosphorylated to ATP using high energy intermediate

not oxygen dependent, like oxidative phosphorylation

Question 19

what does pyruvate kinase do

Answer 19

catalyzes substrate-level phosphorylation of ADP –> ATP and pyruvate

Question 20

what occurs during fermentation

Answer 20

anaerobic ATP production

lactate dehydrogenase reduces pyruvate to lactate and oxidizes NADH to NAD+

Question 21

what is dihydroxyacetone phosphate (DHAP)

Answer 21

intermediate of glycolysis

used in hepatic and adipose tissue for tracylglycerol synthesis

Question 22

what are the irreversible enzymes of glycolysis

Answer 22

hexokinase, glucokinase, PFK-1, pyruvate kinase

Question 23

how is ATP produced in erythrocytes

Answer 23

anaerobic glycolysis

Question 24

what is the disaccharide precursor to galactose

Answer 24

lactose (glucose + galactose)

Question 25

what is the disaccharide precursor to fructose

Answer 25

sucrose

Question 26

what enzyme phosphorylates fructose

Answer 26

fructokinase

Question 27

what enzyme phosphorylates galactose

Answer 27

galactokinase

Question 28

what can pyruvate be converted to in the mitochondria

Answer 28

acetyl coA -->citric acid cycle (makes ATP) | OR --> fatty acid synthesis (when enough ATP)

Question 29

what enzyme converts pyruvate to acetyl coA

Answer 29

pyruvate dehydrogenase enzyme (PDH)

Question 30

what is glycogen

Answer 30

a branched polymer of glucose, glucose in its storage form

Question 31

where is glycogen stored

Answer 31

the cytoplasm as a granule

Question 32

where is glycogen synthesized

Answer 32

the liver and skeletal muscle

Question 33

what occurs during glycogenesis (big picture)

Answer 33

glycogen granules are synthesized

Question 34

what is glycogenin

Answer 34

the core protein of a glycogen granule

Question 35

what is glycogen synthase

Answer 35

- rate-limiting enzyme of glycogenesis - forms alpha 1,4 glycosidic bond - stimulated by insulin, inhibited by epinephrine

Question 36

what does branching enzyme do

Answer 36

introduces alpha 1,6 linkages to glycogen, creating branches 1,4 goes 4ward...1,6 puts a branch in the mix

Question 37

what occurs during glycogenolysis (big picture)

Answer 37

glycogen is broken down

Question 38

what is the rate limiting enzyme of glycogenolysis

Answer 38

glycogen phosphorylase --> breaks alpha 1,4 bonds, stops when reaching branches

Question 39

what does debranching enzyme do

Answer 39

deconstructs branches in glycogen by - breaking adjacent 1,4 bonds, - moving the oligoglucose chain to the exposed end of the other chain, - hydrolyzing the 1,6 bond

Question 40

glycogen storage diseases

Answer 40

genetic deficiencies that result in the accumulation/lack of glycogen in the tissues

Question 41

what occurs during glyconeogenesis (big picture)

Answer 41

the liver produces glucose during times of fasting to maintain blood glucose levels by essentially reversing glycolysis

Question 42

what can glycogenic amino acids (except leucine and lysine) be converted into

Answer 42

intermediates that feed into gluconeogenesis

Question 43

what can ketogenic amino acids be converted into

Answer 43

ketone bodies which are used for alternative fuels during prolonged starvation

Question 44

what does pyruvate carboxylase do

Answer 44

mitochondrial enzyme activated by acetyl co-A (from fatty acids) to produce oxaloacetate

Question 45

what does phosphoenolpyruvate carboxykinase (PEPCK)

Answer 45

converts OAA to PEP in the cytoplasm with GTP

Question 46

what does fructose 1,6 bisphosphatase do

Answer 46

key control enzyme of gluconeogenesis reverses action of PFK-1, removing phosphate from biphosphorylated fructose, in the cytoplasm

Question 47

what does glucose-6-phosphatase do

Answer 47

circumvents gucokinase and hexokinase, allowing free glucose to be transported out of the cell

Question 48

what are the major functions of the pentose phosphate pathway/hexose monophosphate shunt

Answer 48

- produce NADPH | - source of ribose phosphate for nucleotide synthesis

Question 49

what is the rate limiting enzyme of PPP

Answer 49

glucose-6-phosphate dehydrogenase (G6PD) produces NADPH