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Biochemistry Leyland > Leyland 5 Catabolism stage 2 > Flashcards

Leyland 5 Catabolism stage 2 Flashcards

1
Q

Glycolysis

A
  • Central pathway of sugar metabolism
  • Present in all cell types
  • Takes place in the cytoplasm
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2
Q

Glycolysis

Overall reaction:

A

glucose + 2 Pi + 2 ADP + 2 NAD+ → 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

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3
Q

Stage 1

A
  • Input of some energy

* ATP used to phosphorylate intermediates

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4
Q

Stage 2

A
  • C6 converted to 2 x C3
  • ATP produced
  • NADH produced
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5
Q

Aldolase

A

4
• doubly phosphorylated C6 sugar is converted into 2 x monophosphorylated sugars

Fructose 1,6 bisphosphate -> glyceraldeyde 3-phosphate + dihydroxyacetone phosphate

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6
Q

net yield

A

2x ATP per molecule of glucose converted to pyruvate.

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7
Q

Glyceraldehyde 3-phosphate dehydrogenase

A

• Generation of NADH

glyceraldyhde 3-phosphate + Pi -> 1,3, Bisphosphoglycerate

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8
Q

Phosphoglycerate kinase

A
  • Generation of ATP
  • Substrate-level phosphorylation

1,3, Bisphosphoglycerate -> 3-phosphoglycerate

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9
Q

Substrate level phosphorylation

A

Direct formation of ATP by transfer of phosphate group from 1,3 BPG to ADP

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10
Q

Summary of glycolysis

A 
•	Glucose oxidised to pyruvate
•	  C6 and C3 cmpds only;  no loss of CO2
•	  Generates :
    2 ATP (net)
    2 NADH
•	  Overall exergonic (-ve DG)
•	  Irreversible pathway 
glucose  +  2 Pi  +  2  ADP  +  2 NAD+  →  2 pyruvate  +  2 ATP  +  2 NADH  +  2 H+
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11
Q

Glycolysis under aerobic conditions

A
  • Pyruvate further oxidised in citric acid cycle
  • NADH used to form ATP on oxidative phosphorylation
  • NAD+ regenerated to allow glycolysis to continue
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12
Q

Stage III under aerobic conditions

A
  • Stage III of catabolism does not occur
  • NADH would not be oxidised
  • Glycolysis stops due to lack of NAD+
  • No ATP produced
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13
Q

yeast and some microorganisms:

A

Conversion of pyruvate to ethanol allows the oxidation of NADH to NAD

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14
Q

In mammals:

• when the supply of oxygen is inadequate

A

Pyruvate + lactate dehydrogenase -> Lactate
(eg skeletal muscle during rigorous exercise)
• in cells without mitochondria (eg red blood cells)

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15
Q

Regulation of Metabolism

A

Flux through metabolic pathways needs to be regulated in response to the demands of the cell.

In metabolic pathways, enzymes catalyzing essentially irreversible steps are potential sites of control.

Some enzymes can be regulated by :
• allostery (activator/inhibitor binds at ‘other’ site)
• covalent modification (phosphorylation/dephosphorylation)

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16
Q

Glycolysis: Key enzymes:

A

Hexokinase

  1. Phosphofructokinase
  2. Pyruvate kinase
17
Q

Hexokinase (HK)

A
  • phosphorylates glucose
  • ATP consumed
  • traps glucose inside the cell

Glucose -> glucose -6-phosphate

18
Q

Phosphofructokinase (PFK)

A
  • phosphorylates fructose 6-phosphate
  • ATP consumed

phosphorylates fructose 6-phosphate -> fructose 1,6-bisphosphate

19
Q

Pyruvate kinase

A

• Generation of ATP
• Substrate-level phosphorylation
phosphoenolpyruate -> pyruvate

20
Q

Catabolism of other monosaccharides

A

All require activation: addition of phosphate, addition of UDP
2. Most sugar metabolism occurs in the liver

21
Q

Fructose metabolism

A

Fructose (+ fructokinase)
-> fructose 1-phosphate ( + fructose 1-phosphate aldolase) -> glyceraldehyde + didroxyacetone phosphate (+triose kinase) -> glyceraldehyde 3-phosphate

22
Q

fructosuria

A

Genetic deficiency of fructokinase causes fructosuria

Hereditary fructose intolerance is a severe condtion caused by lack of aldolase B

23
Q

Galactose metabolism

A

galactose + atp -> glucose 1 - phosphate + ADP + H+

24
Q

galactosaemia

A

Non-classical :Cataract formation

Classical: Abnormal mental development

25
Q

The pentose phosphate pathway (PPP)

A

Catabolism of sugars – 5C sugar - phosphates

Cytosolic
Important in liver, RBC, adipose tissue

26
Q

The pentose phosphate pathway (PPP)

Phase I Oxidative

A
  • Irreversible

* Produces NADPH, CO2 and 5-C sugars

27
Q

The pentose phosphate pathway (PPP)

Phase II Non-oxidative

A
  • Reversible

* Produces 3-carbon sugars

28
Q

Importance of The pentose phosphate pathway (PPP)

A
  1. NADPH production
    - reductive biosynthesis (e.g. FA biosynthesis)
    - removal of hydrogen peroxide (free radicals)
    - reduction of abnormally formed disulphide bonds
    - cytochrome P450 enzyme function
    - phagocytosis by white blood cell
    - synthesis of nitric oxide

Biochemistry Leyland (11 decks)

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