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Metabolism > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

How many stages of carbohydrate metabolism are there?

A

4

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2
Q

What happens in stage 1?

A

Breakdown to building block molecules

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3
Q

Where does stage 1 occur?

A

GI tract

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4
Q

What happens in stage 2?

A

Breakdown to metabolic intermediates (glycolysis)

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5
Q

Where does stage 2 occur?

A

Cytoplasm + mitochondria

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6
Q

What happens in stage 3?

A

Kreb’s cycle

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7
Q

Where does stage 3 occur?

A

Mitochondria

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8
Q

What happens in stage 4?

A

Oxidative phosphorylation

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9
Q

Where does stage 4 occur?

A

Mitochondria

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10
Q

Which stages are oxidative?

A

Stage 2

Stage 3

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11
Q

What does oxidative mean?

A

Releases ‘reducing power’ (NADH, FADH2)

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12
Q

Which enzymes are involved in stage 1?

A

Amylase
Lactase
Sucrase
Isomaltase

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13
Q

What are the types of lactose intolerance?

A

Primary lactase deficiency
Secondary lactase deficiency
Congenital lactase deficiency

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14
Q

What is primary lactase deficiency?

A

Absence of lactase persistence allele - occurs in adults

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15
Q

What is secondary lactase deficiency?

A

Caused by injury to small intestine

  • gastroenteritis
  • coeliac disease
  • crohn’s disease
  • UC
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16
Q

What is congenital lactase deficiency?

A

Rare autosomal recessive defect in lactase gene

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17
Q

What are the symptoms of lactose intolerance?

A

Bloating/cramps
Flatulence
Diarrhoea
Vomiting

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18
Q

How are monosaccharides absorbed?

A

Active transport by SGLT1 into intestinal epithelial cells
Passive transport via GLUT2 into blood
Uptake by target cells - facilitated diffusion - GLUT 1-5

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19
Q

Where are GLUT1 found?

A

Fetal tissues
Adult erythrocytes
BBB

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20
Q

Where are GLUT2 found?

A

Kidney
Liver
Pancreatic B cells
Small intestine

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21
Q

Where are GLUT3 found?

A

Neurons

Placenta

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22
Q

Where are GLUT4 found?

A

Adipose tissue

Striated muscle

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23
Q

Where are GLUT5 found?

A

Spermatazoa

Intestine

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24
Q

What is stage 2 also known as?

A

Glycolysis

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25
Q

What is the function of glycolysis?

A

Oxidation of glucose
NADH production (2 per glucose)
Syntheiss of ATP from ADP (2 per glucose)
Produces C3 + C6 intermediates

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26
Q

What is produced by glycolysis?

A

2 pyruvate
2 NADH
2 ATP

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27
Q

What are the key enzymes of glycolysis?

A

Hexokinase
Phophofructokinase-1
Pyruvate kinase

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28
Q

What does hexokinase do?

A

Converts glucose to glucose-6-P using ATP

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29
Q

What is hexokinase replaced by in the liver?

A

Glucokinase

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30
Q

What does phosphofurctokinase-1 do?

A

Convert fructose-6-P to fructose 1,6-bis-P using ATP

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31
Q

What does pyruvate kinase do?

A

Converts phosphoenplpyruvate to pyruvate producing ATP

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32
Q

How many reactions make up glycolysis?

A

10

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33
Q

How many stages is glycolysis divided into?

A

2

34
Q

What happens in stage 1 of glycolysis?

A

Phosphorylation of glucose to G-6-P
- makes glucose negatively charge (cant pass back out)

Uses 2 ATP

Commiting step = reaction 3

35
Q

Which reactions are in stage 1 of glycolysis?

A

1 -3

36
Q

Which reactions are in stage 2 of glycolysis?

A

4 - 10

37
Q

What happens in stage 2 of glycolysis?

A

Reaction 4 = cleavage of C6 into 2 C3

Reaction 6 = NADH produced

Reaction 7 + 10 = ATP produced

Reaction 10 = irreversible production of pyruvate

38
Q

What is the net gain of ATP in glycolysis?

A

2 ATP

39
Q

What are the important intermediates in glycolysis?

A

Glycerol phosphate

2,3-bisphosphoglycerate

40
Q

Why is glycerol phosphate important?

A

Important to triglyceride and phospholipid biosynthesis

41
Q

Where is glycerol phosphate produced?

A

Adipose tissue

Liver

42
Q

Where is 2,3 BPG produced?

A

RBCs

43
Q

Why is 2,3 BPG important?

A

Regulates O2 affinity in haemogloin

44
Q

What is the key regulator of glycolysis?

A

Phosphofructokinase

45
Q

How is phosphofructokinase regulated?

A

Allosteric regualtion

  • inhibited by ATP
  • stimulated by AMP

Hormonal regulation

  • stimulated by insulin
  • inhibited by glucagon
46
Q

What else regulates glycolysis?

A

Hexokinase
- inhibited by G-6-P

High levels of NADH causes inhibition

47
Q

How can NAD+ be produced with no oxygen?

A

Lactate dehydrogenase reaction

48
Q

How is lactate produced?

A

NADH + H+ + pyruvate - NAD+ + lactate

Uses enzyme lactate dehydrogenase

49
Q

How is fructose metabolised?

A

Fructose -(fructokinase)> Fructose-1P -(aldolase)> 2 Glyceradehyde-3-P

50
Q

How many ATP are used in fructose metabolism?

A

2

51
Q

What is essential fructosuria?

A

Fructokinase missing

- fructose in urine

52
Q

What is fructose intolerance?

A

Aldolase missing
- Fructose-1-P accumulates in liver

Remove fructose from diet

53
Q

How are galactose metabolised?

A

Galactose converted to galactose-1-P (galactokinase)

Galactose-1-P converted to glucose-1-P (galactose-1-P uridyl transferase) via circuit of UDP-galactose -> UDP-glucose (UDP-galactose 4-epimerase)

54
Q

What is galactosaemia?

A

Inability to utilise galactose

55
Q

What are the types of galactosaemia?

A

Galactokiase deficiency (RARE) - galactose accumulates

Transferase deficiency (COMMON) - galactose + galactose-1-P accumulate

56
Q

What is the problem with galactosaemia?

A

Galactose enters another pathway with aldose reductase which depletes NADPH

Depletion of NADPH causes lens problems

57
Q

How is galactosaemia managed?

A

Lactose free diet

58
Q

What is the pentose phosphate pathway?

A

Parallel pathway to glycolysis that produces pentose sugars and NADPH

59
Q

How many steps to the pentose phosphate pathway are there?

A

2

60
Q

Where does the pentose phosphate pathway occur?

A

Cytoplasm

61
Q

What happens in the first stage of the pentose phosphate pathway?

A

Oxidative decarboxylation

Glucose-6-P -(G6P dehydrogenase)-> C5 sugar + CO2

Converts NADP+ to NADPH

62
Q

What happens in the second stage of the pentose phosphate pathway?

A

Rearrangement to glycolytic intermediates

3 C5-sugars -> 2Fructose-6-P + Glyceraldehyde-3-P

63
Q

What are the functions of the pentose phosphate pathway?

A

Produce NADPH in cytoplasm

  • biosynthetic reducing power
  • maintain free -SH groups on proteins

Produce C5 sugar for nucleotides

64
Q

What happens in G6PDH deficiency?

A

Pentose phosphate pathway has a key role in providing NADPH to maintain SH group of proteins

G6PDH deficiency can cause structural defects in proteins

  • RBCs
  • lens of eye
65
Q

What happens to pyruvate at the end of glycolysis?

A

Pyruvate dehydrogenase

  • transports pyruvate across mitochondrial membrane
  • combines pyruvate with CoA
  • converts NAD+ to NADH
66
Q

What provides the cofactor for pyruvate dehydrogenase?

A

Vitamin B1

67
Q

What activates pyruvate dehydrogenase?

A 
Pyruvate
CoASH 
NAD+ 
ADP 
Insulin
68
Q

What inhibits pyruvate dehydrogenase?

A

Acetyl-CoA
NADH
ATP
Citrate

69
Q

What is stage 3 of carbohydrate metabolism?

A

Tricarboxylic acid (TCA) cycle

70
Q

What is the TCA cycle also known as?

A

Krebs cycle

71
Q

What are the principles of the TCA cycle?

A

Acetyl-CoA uses 3NAD+, FAD and 2H20

Produces 2CO2, 3NADH and FADH

72
Q

Which enzymes regulate TCA cycle?

A

Isocitrate dehydrogenase

α-ketoglutarate dehydrogenase

73
Q

What happens in stage 4 of carbohydrate metabolism?

A

Electron transport
ATP synthesis
NADH + FADH2 re-oxidised

74
Q

What processes are used to create energy?

A

Electron transport

  • NADH + FADH2 transferred through carrier molecules
  • releases energy in steps

Oxidative phosphorylation
- free energy used to drive ATP synthesis

75
Q

What drives the flow of electrons?

A

Proton pumps

76
Q

What produces ATP?

A

ATP synthase
- from ADP + Pi + 2H+

Flow of protons maintains proton gradient for pumps

77
Q

What is required in oxidative phosphorylation?

A

O2

78
Q

What inhibits oxidative phosphorylation?

A

Cyanide - blocks electron transport

Uncouplers - reduce proton gradient = no drive for ATP synthesis

79
Q

What is brown adipose tissue?

A

Adipose tissue containing thermogenin - a naturally-occurring uncoupling protein

80
Q

What happens to brown adipose tissue in the cold?

A

NA activates thermogenin which means electron transport is uncoupled from ATP synthesis

Extra energy from proton gradient is released as heat

Metabolism (10 decks)

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