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Biochem > Glycolysis, Glycogen, Gluconeogenesis, etc > Flashcards

Glycolysis, Glycogen, Gluconeogenesis, etc Flashcards

1
Q

What are the glucose transporters?

A

GLUT 1- 4

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2
Q

What is GLUT 2?

A

low-affinity transporter in hepatocytes and pancreatic cells; capture excess glucose primarily for storage (picks up excess glucose and stores it preferentially after a meal)

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3
Q

What is GLUT 4?

A

in adipose tissue and muscle and responds to glucose concentration in peripheral blood

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4
Q

What is glycolysis?

A

a cytoplasmic pathway that converts glucose into two pyruvate molecules, releasing a modest amount of energy captured in two substrate-level phosphorylations and one oxidation reaction

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5
Q

What is the Km of GLUT 2?

A

~15 mM (high)

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6
Q

What is the Km of GLUT 4?

A

~5 mM (low)

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7
Q

Can GLUT 2 be saturated under normal glucose levels?

A

No; not at normal physiological conditions

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8
Q

Can GLUT 4 be saturated under normal glucose levels?

A

Yes; saturated when glucose levels are only slightly above 5 mM

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9
Q

How does glucose enter the cell?

A

facilitated diffusion or active transport

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10
Q

What do kinases do in general?

A

attach a phosphate group from ATP to their substrates

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11
Q

What are two kinases involved in glycolysis?

A

hexokinase and glucokinase

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12
Q

What do kinases in glycolysis do?

A

convert glucose to glucose 6-phosphate

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13
Q

What prevents glucose from leaving the cell?

A

GLUT transporters that move glucose in and out of the cell are specific to glucose and not Phosphorylated glucose so it cannot leave the cell

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14
Q

Describe hexokinase

A

widely distributed in tissues and is inhibited by its product, glucose 6-phosphate

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15
Q

Describe glucokinase

A

found only in liver cells and pancreatic beta-islet cells; induced by insulin in liver

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16
Q

What are liver cells called?

A

hepatocytes

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17
Q

What is the Km of hexokinase?

A

low; reaches maximum velocity at low glucose

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18
Q

What is the Km of glucokinase?

A

high; acts on glucose proportionally to its concentrations

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19
Q

What is phosphofructosekinase-1 (PFK-1)?

A

rate-limiting enzyme and main control point of glycolysis; phosphorylates fructose 6-phosphate to fructose 1,6-biphosphate

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20
Q

PFK-1 is inhibited by _____ and _____ and turned on by _____

A

ATP and citrate; AMP

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21
Q

How does insulin stimulate PFK-1?

A

Insulin activates phosphofructokinase-2 (PFK-2) which converts a tiny amount of fructose 6-phosphate to fructose 2,6- biphosphate (F2,6-BP) which activates PFK-1

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22
Q

How does glucagon inhibit PFK-1?

A

it inhibits PFK-2 which lowers F2,6-BP and inhibits PFK-1

23
Q

Where is PFK-2 found?

A

mainly in the liver

24
Q

Why is PFK-2 useful?

A

it activates PFK-1 and overrides PFK-1’s need for ATP, allowing the cell to continue glycolysis even when energetically satisfied and can be put into storage molecules

25
Q

What does glyceraldehyde-3-phosphate dehydrogenase do?

A

catalyzes an oxidation and addition of inorganic phosphate (Pi) to its substrate, glyceraldehyde 3-phosphate; results in the production of a high-energy intermediate 1,3-biphosphoglycerate and the reduction of NAD+ to NADH

26
Q

What does 3-phosphoglycerate kinase do?

A

transfers the high-energy phosphate from 1,3-biphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate

27
Q

What is substrate-level phosphorylation?

A

when ADP is directly phosphorylated to ATP using a high-energy intermediate

28
Q

What does pyruvate kinase do?

A

catalyzes a substrate-level phosphorylation of ADP using the high-energy substrate phosphoenolpyruvate (PEP); activated by fructose 1,6-biphosphate from the PFK-1 reaction

29
Q

What is feed-forward activation?

A

the product of an earlier reaction of glycolysis stimulates a later reaction

30
Q

What is lactase dehydrogenase?

A

oxidizes NADH to NAD+; reduces pyruvate to lactase

31
Q

What is dihydroxyacetone phosphate (DHAP)?

A

used in hepatic and adipose tissue for triacylglycerol synthesis; formed from fructose 1,6-biphosphate

32
Q

What is 1,3-biphosophoglycerate (1,3-BPG)?

A

a high energy intermediate used to generate ATP by substrate-level phosphorylation

33
Q

What is phosphoenolpyruvate (PEP)?

A

a high energy intermediate used to generate ATP by substrate-level phosphorylation

34
Q

What are three enzymes used for irreversible reactions in glycolysis?

A

glucokinase/hexokinase
PFK-1
Pyruvate kinase

35
Q

What is biphosphoglycerate mutase?

A

produces 2,3-biphosphoglycerate (2,3-BPG) from 1,3-BPG in glycolysis

36
Q

What are mutases?

A

enzymes that move a functional group from one place in a molecule to another

37
Q

What does 2,3-biphosphoglycerate do?

A

binds allosterically to the beta-chains of hemoglobin A (HbA) and decreases its affinity for oxygen

38
Q

What does galactokinase do?

A

phosphorylates galatose

39
Q

What does galactose-1-phosphate uridyltransferase do?

A

converts galactose 1-phosphate to glucose 1-phosphate

40
Q

What does fructokinase do?

A

phosphorylates fructose

41
Q

What does the pyruvate dehydrogensase complex reaction do?

A

converts pyruvate to acetyl-CoA

42
Q

What is glycogen?

A

a branched polymer of glucose that acts as a storage form

43
Q

What is starch?

A

long alpha-linked chains of glucose

44
Q

What is glycogenesis?

A

synthesis of glycogen granules

45
Q

What does glycogen synthase do?

A

forms the alpha-1,4 glycosidic bond found in the linear glucose chains of the granule; rate limiting enzyme of glycogen synthesis

46
Q

What is glycogen synthase inhibited and stimulated by?

A

stimulated by glucose 6-phosphate and insulin; inhibited by epinephrine and glucagon

47
Q

What does branching enzyme/glycosyl alpha 1,4:alpha-1,6 transferase do?

A

responsible for introducing alpha-1,6-linked branched into the granule as it grows

48
Q

What does glycogen phosphorylase do?

A

breaks alpha-1,4 glycosidic bonds, releasing glucose 1-phosphate from the periphery of the granule; the rate-limiting enzyme of glycogenesis

49
Q

What does debranching enzyme do?

A

two-enzyme complex that deconstructs the branches in glycogen that have been exposed by glycogen phosphorylase

50
Q

What are isoforms?

A

slightly different versions of the same protein

51
Q

What are glycogen storage diseases?

A

diseases that are caused by the accumulation or lack of glycogen in one or more tissues

52
Q

Which organ maintains gluconeogenesis?

A

liver; kidney to a lesser degree

53
Q

what is pyruvate carboxylase?

A

a mitochondrial enzyme that is activated by acetyl-CoA (from beta-oxidation)

54
Q

What is phosphoenolpyruvate carboxykinase (PEPCK)?

A

induced by glucagon and cortisol, which generally act to raise blood sugar levels`(used in glucogenesis)

Biochem (8 decks)

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