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SFM Exam 1 > Carb Metabolism > Flashcards

Carb Metabolism Flashcards

1
Q

Anaerobic glycolysis

A

Occurs in cells that lack mitochondria (RBCs)
Critical source of ATP for RBCs
Important in overworked muscles that lack O2
Glucose is converted to pyruvate then metabolized to lactate

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2
Q

True or false: All cells carry out glycolysis

A

True

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3
Q

Why is glucose important in mammals?

A

It is the only fuel that RBCs can use and the only fuel that the brain can use under non-starvation conditions

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4
Q

GLUT 1

A

Ubiquitous but high expression in RBCs and the brain

High affinity

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5
Q

GLUT 2

A

Main transporter in the liver

Low affinity

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6
Q

GLUT 3

A

Main transporter in neurons

High affinity

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7
Q

GLUT 4

A

Present in skeletal muscle, heart and adipose tissue
Insulin dependent
Sequestered in vesicles in cells
Insulin signaling causes fusion of vesicles with plasma membrane and placement/insertion of GLUT 4 in the membrane
-increases GLUT 4 induced glucose uptake
-initiated when exercising

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8
Q

Which of the 4 GLUTs are regulated?

A

Only GLUT 4 is regulated (by insulin) and the rest are unregulated (depend on a concentration gradient)

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9
Q

What is the net yield of glycolysis?

A

2 ATP, 2 NADH and 2 pyruvate

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10
Q

What is the RLS of glycolysis?

A

Phosphorylation of F6P to F16BP catalyzed by PFK-1

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11
Q

List the substrates of glycolysis in order

A 
Glucose 
G6P 
F6P 
F16BP —> DHAP and G3P 
13BPG 
3PG 
2PG 
PEP 
Pyruvate
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12
Q

List the enzymes of glycolysis in order

A 
Hexokinase/glucokinase 
Phosphoglucose isomerase 
PFK-1 
Triose phosphate isomerase/aldolase 
G3P dehydrogenase 
Phosphoglycerate kinase 
Phosphoglycerate mutase 
Enolase
Pyruvate kinase
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13
Q

Which enzymes of glycolysis use ATP?

A

Hexokinase/glucokinase and PFK-1

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14
Q

What inhibits hexokinase?

A

G6P (its product)

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15
Q

What is PFK-1 activated by?

A

AMP and F26BP

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16
Q

What inhibits PFK-1?

A

ATP and citrate

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17
Q

How does high insulin/low glucagon affect PFK-1?

A

It activates protein phosphatases, dephosphorylates PFK-2/FBPase-2 (triggers kinase activity) producing F26BP which activates PFK-1

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18
Q

How does high glucagon/low insulin affect PFK-1?

A

It induces high cAMP concentration, activates PKA, phosphorylates PFK-2/FBPase-2 (triggering phosphorylation activity) and reducing PFK-1 activity

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19
Q

Tarui disease

A

Deficiency in PFK-1
Exercise induced muscle cramps and weakness
Hemolytic anemia
High bilirubin and jaundice

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20
Q

What activates pyruvate kinase?

A

F16BP and insulin

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21
Q

What is pyruvate kinase inhibited by?

A

ATP, alanine and glucagon

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22
Q

How does a high insulin concentration influence pyruvate kinase?

A

Stimulates phosphorylase, dephosphorylation of PK (active form)

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23
Q

How does high glucagon concentration influence pyruvate kinase?

A

cAMP activates PKA, phosphorylates PK (inhibited form)

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24
Q

What is G6P a precursor for?

A

PPP

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25
Q

G6P is converted to glucose 1 phosphate which is used in what?

A

Galactose metabolism, glycogen synthesis, uronic acid synthesis

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26
Q

Fancon-Bickel syndrome is caused by what?

A

Mutation in GLUT 2 transporter

Pts are unable to take up glucose, fructose and galactose

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27
Q

Why is maintaining levels of glucose important?

A

Because the brain depends on glucose as its primary fuel and RBCs use glucose as their only fuel

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28
Q

How many grams of glucose is needed by the whole body?

A

160g per day

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29
Q

Daily glucose requirement of the brain?

A

120g

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30
Q

Glucose present in body fluids?

A

20g

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31
Q

Glucose readily available from glycogen?

A

190g

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32
Q

Direct glucose reserves are sufficient to meet glucose needs for how long?

A

About a day

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33
Q

When does gluconeogenesis occur?

A

When glucose and glycogen stores are depleted (ex. Starvation, exercise and ketogenic diet (low carb))

34
Q

Gluconeogenesis bypasses the 3 irreversible steps of glycolysis catalyzed by hexokinase/glucokinase, PFK-1 and PK, and replaces them with what?

A

Pyruvate carboxylase, PEP carboxykinase, F16BPase and G6Pase

35
Q

List the precursors for gluconeogenesis

A

Fructose, galactose, glycogen, glycerol, propionate, lactate, alanine and amino acids (except leucine and lysine)

36
Q

What is the RLE of gluconeogenesis?

A

F16BPase which breaks down F16BP to F6P

37
Q

What is pyruvate carboxylase (gluconeogenesis) activated by?

A

Acetyl CoA and cortisol

38
Q

What is PEP carboxykinase (gluconeogenesis) activated by?

A

Cortisol, glucagon and thyroxine

39
Q

What is F16BPase (gluconeogenesis) activated by?

A

Cortisol and citrate

40
Q

What inhibits F16BPase (gluconeogenesis)?

A

AMP and F16BP

41
Q

What is glucose 6 phosphatase (gluconeogenesis) activated by?

A

Cortisol

42
Q

Explain the Cori cycle

A

Links lactate produced from anaerobic glycolysis in RBCs and exercising muscle to gluconeogenesis in the liver then the glucose produced in the liver is transported back to RBCs and muscle

43
Q

What is the purpose of the Cori cycle?

A

Prevents lactate accumulation and re-generates glucose

44
Q

F16BP deficiency

A

Similar to Tarui disease in glycolysis
Presents in infancy or early childhood
Hypoglycemia, lactic acidosis and ketosis

45
Q

Von Gierke disease (GSD 1a)

A

Deficiency in G6Pase

Inefficient release of free glucose into the blood stream by the liver in gluconeogenesis and glycogenolysis

46
Q

When sucrose is cleaved by sucrase what are the products?

A

Glucose and fructose

47
Q

When lactose is cleaved by lactase what are the products?

A

Galactose and glucose

48
Q

What is the RLE in the PPP?

A

G6P dehydrogenase which reduces NADP to NADPH and oxidizes G6P to G-phosphoglucono-delta-lactose

49
Q

Which phase of PPP is favored if cells (like rapidly dividing cells) have a high demand for ribulose 5 P?

A

Oxidative phase is favored to produce ribulose 5P

50
Q

Which phase of the PPP is favored if cells have a high demand for NADPH?

A

Non oxidative products are channeled into gluconeogenesis for re-entry into the PPP to produce NADPH

51
Q

Glucose molecules within a glycogen chain are linked together via what?

A

Alpha 1,4 glycosidic bonds

52
Q

Branch points within a glycogen molecule are formed via what?

A

Alpha 1,6 glycosidic bonds

53
Q

Non-reducing ends of glycogen contain a

A

Terminal glucose with a free OH group at C4

54
Q

Reducing ends of glycogen consist of

A

Glucose monomer connected to a protein called glycogenin

55
Q

Glycogenin creates a

A

Short glycogen polymer on itself and serves as a primer of glycogen synthesis

56
Q

How is glycogen stored?

A

It is stored as granules that contain glycogen and enzymes that are needed for glycogen metabolism
Stored in the liver, muscle and other tissues

57
Q

What is the function of liver glycogen?

A

Regulate blood glucose levels

58
Q

What is the function of muscle glycogen?

A

Provides a reservoir of fuel (glucose) for physical activity

59
Q

What is the RLE of glycogenesis?

A

Glycogen synthase which catalyzes the transfer of glucose from UDP glucose to the NRE of the glycogen chain

60
Q

What is the RLE of glycogenolysis?

A

Glycogen phosphorylase which catalyzes the cleavage of glucose residue as glucose 1 phosphate from NRE of glycogen

61
Q

What is the fate of glucose 1 phosphate in the liver?

A

It is converted to glucose 6 phosphate by an epimerase and then glucose by glucose 6 phosphatase. Free glucose is then released into the blood stream

62
Q

What is the fate of glucose 1 phosphate in muscle?

A

Skeletal and cardiac myocytes lack G6Pase and cannot hydrolyze Glu6P so instead they use it to generate energy via glycolysis and the TCA cycle

63
Q

Why is regulation of glycogen metabolism important?

A

To maintain blood sugar and to provide energy to muscle

64
Q

What is the active form of glycogen synthase?

A

Dephosphorylated

65
Q

What is the active form of glycogen phosphorylase?

A

Phosphorylation

66
Q

Type 2 diabetes

A

Also called insulin resistance
Reduced sensitivity to insulin
Mutations in insulin receptor &/or downstream signaling proteins

67
Q

What are some causes for down regulation of insulin receptors seen in type 2 DM?

A

Triggered by elevated insulin
Endocytosis and degradation of the insulin receptor
Defective receptors not replaced by translation

68
Q

Normal blood glucose criteria

A

70-100 fasting

<140 fed

69
Q

Pre-diabetic/at risk blood glucose criteria

A

100-125 fasting

>140 fed

70
Q

DM blood glucose criteria

A

> 126 fasting

>199 fed

71
Q

Disorders that affect glycogen breakdown lead to what?

A

Hepatomegaly and hypoglycemia (inability to maintain blood sugar)

72
Q

Pts that suffer from disorders that affect glycogen synthesis depend on what?

A

Glucose rather than glycogen

73
Q

GSD 0

A

Deficiency in glycogen synthase
Pts cannot synthesize and store glycogen
Rely on glucose in the diet
Vulnerable to hypoglycemia when fasting (ex during sleep)
Have muscle cramps due to lack of glycogen in the muscle and need to eat frequently

74
Q

GSD 1a (Von Gierke disease)

A

Deficiency in glucose 6 phosphate
Inefficient release of free glucose into the blood stream by the liver following gluconeogenesis and glycogenolysis
Pts exhibit marked fasting hypoglycemia, lactic acidosis, hepatomegaly due to glycogen buildup and HLD

75
Q

GSD II (Pompe disease)

A

Deficiency in acid maltase aka acid alpha glucosidase
Impairs lysosomal glycogenolysis resulting in accumulation of glycogen in lysosomes
Disrupts normal fxn of muscle and and hepatocytes
Progressive muscle weakness in body including heart and skeletal

76
Q

GSD III (Cori disease)

A

Deficiency in alpha 1,6 glucosidase (debranching enzyme)
Pts possess glycogen molecules with large numbers of short branches
Light hypoglycemia and hepatomegaly

77
Q

GSD IV (Andersen disease)

A

Deficiency in glucosyl 4:6 transferase (branching enzyme)

Pts have long chain glycogen with few branches

78
Q

GSD V (McArdle disease)

A

Deficiency in muscle glycogen phosphorylase
RLS in glycogen breakdown
Pts unable to supply muscles with enough glucose
Have weakness, fatigue, muscle cramping and breakdown
Exercise intolerance

79
Q

GSD VI (Hers disease)

A

Deficiency in liver glycogen phosphorylase
Prevents glycogen breakdown in liver hence it accumulates in the liver casing hepatomegaly
Low blood glucose levels

80
Q

When does PFK-2/FBPase-2 work as a kinase?

A

When it is dephosphorylated which is favored by insulin

81
Q

When does PFK-2/FBPase-2 works as a phosphatase?

A

When it is phosphorylated which is favored by glucagon

SFM Exam 1 (8 decks)

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