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Carbohydrate Metabolism Flashcards

(80 cards)

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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
What is the function of glycolysis?
Oxidation of glucose NADH production (2 per glucose) Syntheiss of ATP from ADP (2 per glucose) Produces C3 + C6 intermediates
26
What is produced by glycolysis?
2 pyruvate 2 NADH 2 ATP
27
What are the key enzymes of glycolysis?
Hexokinase Phophofructokinase-1 Pyruvate kinase
28
What does hexokinase do?
Converts glucose to glucose-6-P using ATP
29
What is hexokinase replaced by in the liver?
Glucokinase
30
What does phosphofurctokinase-1 do?
Convert fructose-6-P to fructose 1,6-bis-P using ATP
31
What does pyruvate kinase do?
Converts phosphoenplpyruvate to pyruvate producing ATP
32
How many reactions make up glycolysis?
10
33
How many stages is glycolysis divided into?
2
34
What happens in stage 1 of glycolysis?
Phosphorylation of glucose to G-6-P - makes glucose negatively charge (cant pass back out) Uses 2 ATP Commiting step = reaction 3
35
Which reactions are in stage 1 of glycolysis?
1 -3
36
Which reactions are in stage 2 of glycolysis?
4 - 10
37
What happens in stage 2 of glycolysis?
Reaction 4 = cleavage of C6 into 2 C3 Reaction 6 = NADH produced Reaction 7 + 10 = ATP produced Reaction 10 = irreversible production of pyruvate
38
What is the net gain of ATP in glycolysis?
2 ATP
39
What are the important intermediates in glycolysis?
Glycerol phosphate | 2,3-bisphosphoglycerate
40
Why is glycerol phosphate important?
Important to triglyceride and phospholipid biosynthesis
41
Where is glycerol phosphate produced?
Adipose tissue | Liver
42
Where is 2,3 BPG produced?
RBCs
43
Why is 2,3 BPG important?
Regulates O2 affinity in haemogloin
44
What is the key regulator of glycolysis?
Phosphofructokinase
45
How is phosphofructokinase regulated?
Allosteric regualtion - inhibited by ATP - stimulated by AMP Hormonal regulation - stimulated by insulin - inhibited by glucagon
46
What else regulates glycolysis?
Hexokinase - inhibited by G-6-P High levels of NADH causes inhibition
47
How can NAD+ be produced with no oxygen?
Lactate dehydrogenase reaction
48
How is lactate produced?
NADH + H+ + pyruvate - NAD+ + lactate Uses enzyme lactate dehydrogenase
49
How is fructose metabolised?
Fructose -(fructokinase)> Fructose-1P -(aldolase)> 2 Glyceradehyde-3-P
50
How many ATP are used in fructose metabolism?
2
51
What is essential fructosuria?
Fructokinase missing | - fructose in urine
52
What is fructose intolerance?
Aldolase missing - Fructose-1-P accumulates in liver Remove fructose from diet
53
How are galactose metabolised?
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
What is galactosaemia?
Inability to utilise galactose
55
What are the types of galactosaemia?
Galactokiase deficiency (RARE) - galactose accumulates Transferase deficiency (COMMON) - galactose + galactose-1-P accumulate
56
What is the problem with galactosaemia?
Galactose enters another pathway with aldose reductase which depletes NADPH Depletion of NADPH causes lens problems
57
How is galactosaemia managed?
Lactose free diet
58
What is the pentose phosphate pathway?
Parallel pathway to glycolysis that produces pentose sugars and NADPH
59
How many steps to the pentose phosphate pathway are there?
2
60
Where does the pentose phosphate pathway occur?
Cytoplasm
61
What happens in the first stage of the pentose phosphate pathway?
Oxidative decarboxylation Glucose-6-P -(G6P dehydrogenase)-> C5 sugar + CO2 Converts NADP+ to NADPH
62
What happens in the second stage of the pentose phosphate pathway?
Rearrangement to glycolytic intermediates 3 C5-sugars -> 2Fructose-6-P + Glyceraldehyde-3-P
63
What are the functions of the pentose phosphate pathway?
Produce NADPH in cytoplasm - biosynthetic reducing power - maintain free -SH groups on proteins Produce C5 sugar for nucleotides
64
What happens in G6PDH deficiency?
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
What happens to pyruvate at the end of glycolysis?
Pyruvate dehydrogenase - transports pyruvate across mitochondrial membrane - combines pyruvate with CoA - converts NAD+ to NADH
66
What provides the cofactor for pyruvate dehydrogenase?
Vitamin B1
67
What activates pyruvate dehydrogenase?
``` Pyruvate CoASH NAD+ ADP Insulin ```
68
What inhibits pyruvate dehydrogenase?
Acetyl-CoA NADH ATP Citrate
69
What is stage 3 of carbohydrate metabolism?
Tricarboxylic acid (TCA) cycle
70
What is the TCA cycle also known as?
Krebs cycle
71
What are the principles of the TCA cycle?
Acetyl-CoA uses 3NAD+, FAD and 2H20 Produces 2CO2, 3NADH and FADH
72
Which enzymes regulate TCA cycle?
Isocitrate dehydrogenase α-ketoglutarate dehydrogenase
73
What happens in stage 4 of carbohydrate metabolism?
Electron transport ATP synthesis NADH + FADH2 re-oxidised
74
What processes are used to create energy?
Electron transport - NADH + FADH2 transferred through carrier molecules - releases energy in steps Oxidative phosphorylation - free energy used to drive ATP synthesis
75
What drives the flow of electrons?
Proton pumps
76
What produces ATP?
ATP synthase - from ADP + Pi + 2H+ Flow of protons maintains proton gradient for pumps
77
What is required in oxidative phosphorylation?
O2
78
What inhibits oxidative phosphorylation?
Cyanide - blocks electron transport Uncouplers - reduce proton gradient = no drive for ATP synthesis
79
What is brown adipose tissue?
Adipose tissue containing thermogenin - a naturally-occurring uncoupling protein
80
What happens to brown adipose tissue in the cold?
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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