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MEH- Aboli > Carbohydrate metabolism > Flashcards

Carbohydrate metabolism Flashcards

1
Q

Blood glucose level

A

~5mM

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2
Q

Tissues that have absolute glucose requirement (4 things)

A
  • Erythrocytes (no mitochondria)
  • Neutrophils (low O2)
  • Innermost cells of renal medulla (low O2)
  • Lens of eye (no mitochondria)
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3
Q

What is starch broken down into by salivary amylase?

A

Oligosaccharides

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4
Q

Disaccharidases attached to brush border membrane of small intestine (5 things)

A
  • Lactase
  • Pancreatic amylase
  • Isomaltase
  • Glycoamylase
  • Sucrase
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5
Q

Why isn’t cellulose digested?

A

Beta 1,4 linkages can’t be digested as bacteria producing those enzymes not present in human GI tract

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6
Q

Primary lactase deficiency (3 things)

A
  • Lack of lactase persistence allele
  • Highest prevalence in northwest europe
  • Only occurs in adults
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7
Q

Secondary lactase deficiency (3 things)

A
  • Caused by injury to small intestine: gastroenteritis, coeliac, Crohn’s, ulcerative colitis
  • In both adults and infants
  • Generally reversible
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8
Q

Congenital lactase deficiency (3 things)

A
  • Autosomal recessive defect in lactase gene
  • Very rare
  • Can’t digest breast milk
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9
Q

Absorption of monosaccharides (4 things)

A
  • SGLT1: active transport into intestinal epithelial cells
  • GLUT2: passive transport into blood supply
  • GLUT1-GLUT5: facilitated diffusion into target cells
  • GLUTS have different tissue distribution and affinities
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10
Q

GLUT1 (3 things)

A
  • Foetal tissues
  • Adult RBC
  • Blood-brain barrier
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11
Q

GLUT2 (4 things)

A
  • Kidney
  • Liver
  • Pancreatic beta cells
  • Small intestine
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12
Q

GLUT3 (2 things)

A
  • Neurones
  • Placenta
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13
Q

GLUT4 (2 things)

A
  • Adipose tissue
  • Striated muscle
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14
Q

GLUT5 (2 things)

A
  • Spermatozoa
  • Intestine
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15
Q

Why are there so many steps in glycolysis (4 things)?

A
  • Chemistry easier in small stages
  • Efficient energy conversion
  • Gives versatility
  • Can be controlled
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16
Q

Phase 1 of glycolysis (3 things)

A
  • Phosphorylation makes glucose -ve so can’t go back across plasma membrane
  • Irreversible step due to large -ve free energy change
  • Commiting step of metabolism of glucose via glycolysis
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17
Q

Glycerol phosphate- important intermediate (5 things)

A
  • Important to triglyceride and phospholipid biosynthesis
  • Produced in adipose and liver tissue
  • Lipid synthesis in adipose tissue requires glycolysis
  • Liver can also phosphorylate glycerol directly
  • Enzyme: glycerol 3 phosphate dehydrogenase
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18
Q

1,3- bisphosphoglycerate- important intermediate (3 things)

A
  • Produced in RBC
  • Regulator of Hb-O2 affinity (promotes release)
  • Enzyme: bisphosphoglycerate mutase
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19
Q

Glycolysis- clinical application (3 things)

A
  • Rate of glycolysis up to 200x greater in cancer
  • Measure uptake of FDG (radioactive modified hexokinase substrate)
  • Imaging with positron emission tomography (PET)
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20
Q

Allosteric regulation of phosphofructokinase in muscle (4 things)

A
  • Inhibited by high ATP (ratio of AMP:ATP)
  • Inhibited by high citrate
  • Stimulated by high AMP
  • Stimulated by F-1,6-BP
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21
Q

Hormonal regulation of phosphofructokinase in liver (3 things)

A
  • Inhibited by glucagon
  • Stimulated by insulin
  • Done by covalent modification (phosphorylation)
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22
Q

Hexokinase regulation

A

Product inhibition by G-6-P

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23
Q

Pyruvate kinase regulation (2 things)

A
  • Hormonal activation
  • Stimulated by high insulin:glucagon ratio
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24
Q

Why do some cells convert pyruvate to lactate (2 things)?

A
  • Some cells have no stage 3 or 4 of metabolism (e.g. RBC, lens of eye)
  • Supply of O2 is sometimes inefficient
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25
Q

Lactate production without major exercise- which tissues? (5 things)

A
  • RBC
  • Skin
  • Skeletal muscle
  • Brain
  • GI tract
26
Q

Lactate production under strenuous exercise (2 things)

A
  • Plasma levels increase 10 fold in 2-5 mins
  • Back to normal by 90 mins
27
Q

Lactate production under pathological situations- 2 examples

A
  • SHOCK
  • Congestive heart disease
28
Q

Lactate dehydrogenase in tissue- which tissues and what happens (2 things)

A
  • RBC, skeletal muscle, skin, brain, GI tract
  • In low O2, pyruvate converted to lactate
29
Q

Lactate dehydrogenase in liver and kidney (4 things)

A
  • Impaired in liver disease
  • Sensitive to thiamine deficiency
  • Alcohol reduces NAD+ available
  • Enzyme deficiencies can result in LDH to be deficient
30
Q

What are relative rates of plasma lactate concentration determined by (3 things)?

A
  • Production
  • Utilisation (liver, heart, muscle)
  • Disposal (kidney)
31
Q

Hyperlactaemia (3 things)

A
  • 2-5 mM
  • Below renal threshold
  • No change in blood pH (buffering system)
32
Q

Lactic acidosis (3 things)

A
  • Above 5 mM
  • Above renal threshold
  • Blood pH lowered
33
Q

Where is fructose metabolised?

A

Liver

34
Q

Essential fructosuria (2 things)

A
  • Fructokinase missing
  • Fructose in urine, no clinical signs
35
Q

Fructose intolerance (4 things)

A
  • Aldolase missing
  • Fructose-1-P accumulates in liver
  • Leads to liver damage and possible death
  • Managed by removing fructose and sucrose from the diet
36
Q

Deficiency in which 3 enzymes could cause galactosaemia?

A
  • Galactokinase
  • Uridyl transferase
  • UDP-galactose epimerase
37
Q

What is galactose used to synthesise (2 things)?

A
  • Glycoproteins
  • Glycolipids
38
Q

Where is galactose mainly metabolised?

A

Liver

39
Q

2 types of galactosaemia

A
  • Galactokinase deficiency (rare)- galactose accumulates
  • Transferase deficiency (common)- galactose & galactose-1-P accumulate
40
Q

Problems from galactosaemia and treatment (4 things)

A
  • Galactose enters other pathways: aldose reductase converts it to galactitol
  • Depletes lens of NADPH, structure damaged, cataracts
  • Accumulation of galactose-1-P affects liver, kidney, brain
  • Treatment: no lactose in diet
41
Q

What is C5-sugar ribose used to synthesise in pentose phosphate pathway (2 things)?

A
  • Nucleotides
  • DNA & RNA
42
Q

What is NADPH used to synthesise in pentose phosphate pathway (3 things)?

A
  • Fatty acids
  • Steroids
  • GSH regeneration
43
Q

What is the rate limiting enzyme for pentose phosphate pathway?

A

Glucose-6-phosphate dehydrogenase

44
Q

GP6DH deficiency (5 things)

A
  • NADPH conc. decreases in RBC
  • Needed to reduce oxidised glutathione
  • Disulphide bonds formed due to oxidative stress
  • Aggregated proteins leading to Heinz body formation
  • Haemolysis (anaemia)
45
Q

Pyruvate dehydrogenase- what is it and key points (4 things)

A
  • Large multi-enzyme complex (link reaction)
  • Requires coenzymes FAD, Thiamine pyrophosphate & lipoic acid
  • Sensitive to vitamin B1 deficiency
  • Reaction it carries out is irreversible
46
Q

What activates pyruvate dehydrogenase (5 things)?

A
  • Pyruvate
  • CoA
  • NAD+
  • ADP
  • Insulin
47
Q

What inhibits pyruvate dehydrogenase (4 things)?

A
  • Acetyl CoA
  • NADH
  • ATP
  • Citrate
48
Q

Products of TCA cycle from one molecule of glucose (4 things)

A
  • 2x FADH2
  • 4x CO2
  • 6x NADH
  • 2x ATP/GTP
49
Q

Regulation of TCA cycle (3 things)

A
  • Isocitrate dehydrogenase
  • alpha-ketoglutarate dehydrogenase
  • ATP:ADP/NADH:NAD+ ratios
50
Q

Intermediates of TCA cycle key points (3 things)

A
  • Fatty acids, AA & haem in liver
  • Neurotransmitters in brain
  • Replacements for intermediates can come from breakdown of AA
51
Q

How is ATP synthesised during oxidative phosphorylation (3 things)?

A
  • Electrochemical gradient
  • Protons return across membrane via the ATP synthase
  • Also known as proton translocating ATPase/complex
52
Q

How much ATP is produced in oxidative phosphorylation (2 things)?

A
  • 5 moles for every 2 NADH
  • 3 moles for every 2 FADH2
53
Q

How is energy produced in oxidative phosphorylation?

A

Energy from the dissipation of the p.m.f is coupled to the synthesis of ATP from ADP

54
Q

How is oxidative phosphorylation regulated?

A

Ratio of ATP:ADP

55
Q

Inhibition of oxidative phosphorylation and example (2 things)

A
  • Inhibitors block electron transport
  • e.g. cyanide
56
Q

Uncoupling of oxidative phosphorylation (3 things)

A
  • Uncouplers make cristae more permeable to protons
  • No drive for ATP synthesis as p.m.f is dissipated
  • Instead energy used to generate heat
57
Q

Ox/Phos diseases (3 things)

A
  • Genetic defects in proteins encoded by mtDNA
  • Some subunits of PTCs and ATP synthase
  • Decrease in electron transport and ATP synthesis
58
Q

Brown adipose tissue in uncoupling (5 things)

A
  • Has thermogenin (UCP1): naturally occurring coupling protein
  • Noradrenaline activates lipase
  • Fatty acid oxidation
  • Fatty acids activate UCP1
  • UCP1 transports H+ back into mitochondria
59
Q

Oxidative phosphorylation key points (4 things)

A
  • Needs membrane complexes
  • Needs O2
  • Energy coupling is indirect through p.m.f
  • Major process for ATP synthesis in cells needing large amounts of energy
60
Q

Substrate level phosphorylation (4 things)

A
  • Needs soluble enzymes
  • Limited extent in absence of O2
  • Energy coupling direct through hydrolysis of bonds
  • Minor process for ATP synthesis in cells needing large amounts of energy
61
Q

Which enzyme catalyses reaction to phosphorylate glycerol?

A

Glycerol kinase

MEH- Aboli (6 decks)

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