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Biochemistry > Ch 9: Carbohydrate Metabolism 1 > Flashcards

Ch 9: Carbohydrate Metabolism 1 Flashcards

1
Q

GLUT 2

A

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

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2
Q

GLUT 4

A

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

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3
Q

Glycolysis

A

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

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4
Q

Glucokinase

A

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

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5
Q

Hexokinase

A

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

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6
Q

Phosphofructokinase-1 (PFK-1)

A

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

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7
Q

Phosphofructokinase-2 (PFK-2)

A

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

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8
Q

Glyceraldehyde-3-phosphate dehydrogenase

A

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

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9
Q

3-phosphoglycerate kinase & pyruvate kinase perform

A

important glycolysis enzyme that performs substrate-level phosphorylation

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10
Q

substrate-level phosphorylation

A

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

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11
Q

4 enzymes that catalyze irreversible reactions in glycolysis are

A

glucokinase
hexokinase
PFK-1
pyruvate kinase

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12
Q

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

A

oxidized by mitochondrial electron transport chain

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13
Q

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

A

oxidized by cytoplasmic lactate dehydrogenase

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

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14
Q

Galactose

A

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

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15
Q

galactose-1-phosphate uridyltransferase

A

converts galactose to glucose 1-phosphate

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16
Q

Fructose

A

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

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17
Q

Pyruvate dehydrogenase

A

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

18
Q

Glycogenesis (glycogen synthesis)

A

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

19
Q

Glycogen synthase

A

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

20
Q

Branching enzyme

A

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

21
Q

Glycogenolysis

A

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

22
Q

Glycogen phosphorylase

A

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

23
Q

Debranching enzyme

A

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.

24
Q

Gluconeogenesis

A

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

25
Q

Gluconeogenesis is the reverse of

A

glycolysis

26
Q

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

A

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

27
Q

Pyruvate carboxylase

& PEPCK

A

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

28
Q

Fructose-1,6-bisphosphatase

A

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)

29
Q

Glucose-6-phosphatase

A

converts glucose 6-phosphate to free glucose bypassing glucokinase. it is found only in the endoplasmic reticulum of the liver

30
Q

Pentose Phosphate Pathway (PPP)

A

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)

31
Q

Glucose-6-phosphate dehydrogenase

A

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

32
Q

Rate-limiting enzyme of Glycolysis

A

phosphofructokinase-1

33
Q

Rate-limiting enzyme of Fermentation

A

lactate dehydrogenase

34
Q

Rate-limiting enzyme of Glycogenesis

A

glycogen synthase

35
Q

Rate-limiting enzyme of Glycogenolysis

A

glycogen phosphorylase

36
Q

Rate-limiting enzyme of Gluconeogenesis

A

fructose-1,6-bisphosphatase

37
Q

Rate-limiting enzyme of Pentose Phosphate Pathway

A

glucose-6-phosphate dehydrogenase

38
Q

Glycogenesis

A

synthesis of glycogen granules, beginning with core protein called glycogenin

39
Q

NADPH

A

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

40
Q

How Glycolysis Pushes Forward the Process: Kinases

is a mnemonic for

A

Irreversible steps of glycolysis

Hexokinase
Glucokinase
PFK-1
Pyruvate Kinase

Biochemistry (12 decks)

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