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Kaplan MCAT > BIOCHEM Chp.9 Glycolysis, PDH, Glycogenesis, Glycogenolysis, Gluconeogenesis, & PPP > Flashcards

BIOCHEM Chp.9 Glycolysis, PDH, Glycogenesis, Glycogenolysis, Gluconeogenesis, & PPP Flashcards

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MCAT flashcards
1
Q

What is Km?

A

the concentration of substrate when an enzyme is active at half of its maximum velocity. the lower the Km, the higher the enzyme affinity for the substrate

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2
Q

What is GLUT2?

A

a low-affinity, high Km transporter in hepatocytes and pancreatic cells that captures excess glucose for storage after a meal.

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3
Q

What are the glucose sensors for insulin release?

A

B-islet cells in the pancreas, GLUT2, and glucokinase

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4
Q

What is GLUT4?

A

a high affinity, low Km glucose transporter in adipose tissue and muscle that responds to [glucose] in peripheral blood

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5
Q

What is glucose stored in muscles and the liver?

A

muscle - glycogen
liver - FA

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6
Q

What is glycoslysis?

A

a pathway that converts glucose into 2 pyruvate molecules and 2 ATP. occurs in the cytoplasm and does not require oxygen

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7
Q

How do kinases operate?

A

they attach a phosphate group from ATP to their substrates

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8
Q

What is the function of Hexokinase?

A

glucose enters the cell by facilitated diffusion or active transport, then hexokinase phosphorylates the glucose to glucose 6-phosphate

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9
Q

What inhibits Hexokinase?

A

glucose 6-phosphate

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10
Q

What is the function of Glucokinase?

A

phosphorylates glucose to Glose-6-phosphate in the liver and pancreatic B-islet cells, works with GLUT2 as a glucose sensor

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11
Q

What induces Glucokinase?

A

insulin in the liver

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12
Q

What is the function of Phosphofrutokinase-1?

A

phosphorylates fructose 6-phosphate to fructose 1,6, biphosphate using ATP

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13
Q

What is the function of Phosphofrutokinase-2?

A

produces F2,6-BP that activates PFK-1

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14
Q

What inhibits and activates Phosphofrutokinase-2?

A

it is activated by insulin and inhibited by glucagon

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15
Q

What is the function of Glycaldhyde-3-phosphate dehydrogenase?

A

produced NADH to feed into the mitochondrial ETC when oxygen is present.
also phosphorylates Glyceraldehyde-3-phosphate to 1,3,-bisphosphoglycerate

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16
Q

What is the function of 3-phosphoglycerate kinase?

A

substrate-level phosphorylation transferring phosphate from 1,3, bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate

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17
Q

What is the function of pyruvate kinase?

A

substrate-level phosphorylation transferring from Phosphoenolpyruvate to ADP forming ATP and pyruvate

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18
Q

What are the irreversible enzymes in glycolysis?

A

glucokinase or hexokinase, PFK-1, and pyruvate kinase

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19
Q

What inhibits and activates Phosphofrutokinase-1?

A

it is inhibited by ATP, citrate, and activated by AMP, F26BP

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20
Q

What activates and inhibits pyruvate kinase?

A

Fructose 1-6-Bisphosphatase activates, and acetyl-CoA inhibits pyruvate

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21
Q

How is NADH oxidized when oxygen or mitochondria are absent?

A

by cytoplasmic lactate dehydrogenase

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22
Q

Describe glycolysis in erythrocytes

A

1,3, BPG is converted to 2,3, BPG via BPG Mutase that the RBC can use to

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23
Q

What are the rate-limiting enzymes of carbohydrate metabolism?

A

Glycolysis: phosphofructokinase-1
Fermentation: lactase dehydrogenase
Glycogeneiss: glycogen synthase
Glycogenolysis: glycogen synthase phosphorylase
Gluconeogenesis: Fructose-1,6, biphosphatase
Pentose Phosphate Pathway: Glucose 6-phosphate dehydrogenase

24
Q

What are the steps of glycolysis?

A

Glucose → Glucose 6-Phpspahte (G6P) via Hexokinase. Step is irreversible
G6P → Fructose 6-Pphopsate (F6P) via Isomerase
F6P → Fructose-1-6-Biphosphatase (F16BP) via phosphofructokinase 1 (PFK-1)
F-1-6-BP → DHA and GA3P via Aldose
GA-3P → 1-3-BPG via GA-3-PDH, facilitated with the reduction of NADH to NAD+ which can be used in the ETC or in Fermentation
1-3-BPG → 3PG via 3-PGK. The lost phosphate from 1-3 BPG is used to construct ATP
3-PG → 2-PG via Mutase
2PG → PEP via Enolase
PEP → Pyruvate via Pyruvate Kinase. Step is irreversible

25
Q

What is the role of galactokinase?

A

to store of galactose in the cell

26
Q

How is galactose converted to glucose-1-phosphate?

A

galactose is converted to glocose-1-phophate via galatcose-1-phosphate uridyltransferase and epimerase

27
Q

What are the 3 fates of pyruvate made from glycolysis?

A
  1. converted to acetyl-CoA by pyruvate dehydrogenase to enter into the Citric Acid Cycle if ATP is needed
  2. FA synthesis i B-oxidation if sufficient ATP is present.
  3. converted to oxaloacetate by pyruvate carboxylate and enters into gluconeogenesis
28
Q

What physiological changes promote a right shift of the oxygen disassociation curve (Bohr Effect)?

A

high 2,3-BPG, low pH, high [H+] protons, high CO2, all of which occur during exercise

29
Q

What is the role of mutases?

A

they move functional groups from one place in a molecular to another

30
Q

What are the effects of 2,3-BPG on hemoglobin?

A

it binds allosterically to the B-chains of HbA and decreases its affinity for oxygen

31
Q

What is glycogenesis?

A

the synthesis of glycogen using glycogen synthase and branching enzymes

32
Q

What is the function of glycogen synthase?

A

it attached glucose molecules from UDP-glucose to the growing glycogen chain, forming a-1,4 glycosidic links b/w glucose molecules

33
Q

What is the function of branching enzymes?

A

moves a block of oligoglucose from one branch and adds it to the growing glycogens in a new branch using a-1,6 glycosidic links

34
Q

What stimulates and inhibits Glycogen synthase?

A

Insulin and ATP stimulate glycogen synthase, and Epinephrine, glucagon, and AMP inhibit it

35
Q

What is gluconeogensis?

A

done in the cytoplasm and mitochondria of liver cells

36
Q

What is glycogenolysis?

A

the breakdown of glycogen to glucose-1-phosphate using glycogen phosphorylase and debranching enzyme

37
Q

What is the role of the debranching enzyme?

A

moves a block of oligosaccharides from one branch and connects it to the chain using a-1,4 glycosidic links. it also removes branching points connected via a-1,6 glycosidic links, freeing up glucose molecules

38
Q

What is the function of Glycogen phosphorylase?

A

serves as the rate-limiting step in glycogenolysis. It removes glucose molecules from glycogen using phosphorylation, breaking the alpha-1-4 glycosidic linkages, and releasing glucose monomers but stops at branch points.

39
Q

What inhibits and activates Glycogen phosphorylase?

A

Insulin and ATP inhibit glycogen phosphorylase
Epinephrine, glucagon, and AMP stimulate it (opposite of glycogen synthase)

40
Q

Where do Glycolysis, the TCA, PPP/HMP shunt, and Oxidative phosphorylation occur?

A

Glycolysis occurs in the cytoplasm.
The citric acid cycle occurs in the mitochondrial matrix (Except succinate dehydrogenase, which is located in the inner membrane)
pentose phosphate pathway/hexone monophosphate shunt occurs in the cytoplasm
Oxidative phosphorylation occurs in the inner membrane.

41
Q

What is the function of glucosidase?

A

it hydrolyzes the leftover alpha-1-6 linkages the debranching enzyme may not catch, releasing individual glucose molecules

42
Q

What is the purpose of the pentose phosphate pathway/hexone monophosphate shunt?

A

ribose 5-phosphate and NADPH

43
Q

What is the rate-limiting step of the Pentose Phosphate pathway/Hexone Monophosphate shunt?

A

glucose-6-phosphate dehydrogenase

44
Q

What activates and inhibits Glucose-6-phosphate Dehydrogenase?

A

activated by NADP+ and insulin and inhibited by NADPH

45
Q

What is the function of Pyruvate Carboxylate?

A

converts pyruvate into oxaloacetate in gluconeogenesis

46
Q

What activates Pyruvate Carboxylate?

A

aCoA form B-oxidation

47
Q

What is the function of Phosphoenolpyruvate Carboxykinase (PEPCK)?

A

converts Oxaloacetate to Phosphoenolpyruvate in gluconeogenesis

48
Q

What activates Phosphoenolpyruvate Carboxykinase (PEPCK)?

A

glucagon and cortisol

49
Q

What is the function of Fructose-1,6,-biphosphate?

A

Converts 1,6-biphosphate to fructose 6-phosphate bypassing phosphofructokinase-1

50
Q

What activates and inhibites Fructose-1,6,-biphosphate?

A

ATP directly and glucagon indirectly (by decreasing levels of F-2,6-BP) activate, and AMP directly and insulin indirectly (bia increase levels of F-2,6-BP)

51
Q

What is generated during fermentation?

A

coenzymes needed in glycolysis - no energy is generated

52
Q

What is the function of fructokinase?

A

fructose is phosphorylated by fructokinase, trapping it in the cells

53
Q

What does aldolase B produce?

A

dihydroxyacetone phosphate (DHAP) and glyceraldehyde (which can be phosphorylated to form glyceraldehyde 3-phosphate)

54
Q

What are the reactants and products of the PDH complex?

A

Pyruvate, NAD+, and CoA are the reactants, and aCoA, NADH, and CO2 are the products.

55
Q

What inhibits the PDH complex?

A

a build-up of the product, aCoA from either TCA or fatty acid b-oxidation signals the cell is energetically satisfied and the production of aCoA should be stopped

56
Q

What is the function of NADPH?

A

antimicrobial resistance via bacterial destruction by bleach within lysosomes, and functional carriage of energy across organelle membranes for use within the mitochondria

Kaplan MCAT (52 decks)

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