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Metabolism II > Session 3 > Flashcards

Session 3 Flashcards

1
Q

What is the major function of the Pentose Phosphate pathway?

A

Produce NADPH

Produce C5 ribosomes that are used in Nucleotide synthesis

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2
Q

What happens in Phase I of the Pentose Phosphate pathway?

A

Glucose 6-phosphate is oxidized and decarboxylated by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in a reaction requiring NADP+.

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3
Q

What happens in Phase II of the Pentose Phosphate pathway?

A

Converts any unused C5-sugar phosphates to glycolysis intermediates

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4
Q

Why is the Pentose Phosphate pathway important?

A

Produces NADPH used in lipid synthesis.- Liver & Adipose tissue
RBCs require NADPH to prevent disulphide bridges

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5
Q

Explain Glucose 6-phoshate dehydrogenase deficiency

A

Rate-limiting enzyme in the pentose phosphate pathway
Point mutation, X-linked
Reduced activity of the enzyme- low levels of NADPH.
Can’t prevent the formation of these disulphide bridges in RBCs - form insoluble aggregates called Heinz bodies

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6
Q

Why is Pyruvate Dehydrogenase important in Glycolysis?

A

Pyruvate dehydrogenase (PDH) converts Pyruvate to Acetyl CoA in an irreversible reaction

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7
Q

What mechanisms control Pyruvate Dehydrogenase?

A

Reaction is energy sensitive. ATP/NADH inhibit and ADP promotes allosterically.
Activated when there is plenty of glucose to be catabolised.
Acetyl~CoA allosterically inhibits PDH

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8
Q

Outline the Krebs cycle

A 
Oxidative pathway in Mitochondria
Requires NAD+, FAD and Oxaloacetate
Breaks the C-C bond in Acetate
Needs O2
Defects in it would be lethal
Makes intermediates that can be used to make AA etc.
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9
Q

What regulates the Krebs cycle?

A

ATP/ADP ratio
NADH/NAD+ ratio
One of the irreversible steps allosterically inhibited by high-energy signal and activated by the low-energy signal

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10
Q

Outline Oxidative Phosphorylation

A

NADH and FAD2H contain high energy electrons transferred to oxygen releasing large amounts of energy to drive ATP synthesis.

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11
Q

How does Uncoupling produce heat?

A

Increased permeability of the inner mitochondrial membrane to protons so P.M.F lost as heat

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12
Q

What are the 3 uncoupling proteins?

A

UCP1 - Expressed in Brown adipose tissue, non shivering thermogenesis
UCP2 - Widely distributed- links to diabetes?
UCP3 - skeletal muscle, brown adipose tissue & heart. Involved in modifying fatty acid metabolism & protecting against ROS damage.
Noradrenaline activates UCP1 and increases P.M.F

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13
Q

Contrast oxidative & substrate level phosphorylation.

A

O - Energy coupling occurs indirectly S - Occurs directly
O - Needs Oxygen S - Doesn’t
O - Needs membrane proteins S - Needs soluble proteins

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14
Q

What are the 3 classes of lipids?

A

Fatty acid derivatives eg TAGs
Hydroxy-methyl-glutaric acid derivatives eg Ketone bodies, Cholesterol
Fat soluble vitamins eg A, D, E & K

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15
Q

How are dietary lipids (mainly Triacylglycerol) broken down?

A

Hydrolysed by pancreatic lipase in the small intestine to release glycerol and fatty acids

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16
Q

How is Glycerol metabolised?

A

Enters blood stream from small intestine, travels to Liver where it is broken down.

17
Q

What properties of Fatty acids make them ideal for storage?

A

Hydrophobic

Highly reduced molecules

17
Q

What properties of Fatty acids make them ideal for storage?

A

Hydrophobic

Highly reduced molecules

18
Q

When are Ketone bodies synthesised?

Extra point - What does it require?

A

When glucose concentration is low.
Extra point - Low insulin/glucagon ratio
Fatty acids to be available

19
Q

What can produce Acetyl CoA?

A 
Fatty Acids
Sugars
Alcohol
Certain amino acids
Oxidised via Krebs cycle
Important intermediate of lipid biosynthesis
20
Q

How are Ketone bodies used?

A

Can be converted to Acetyl CoA and enter Krebs cycle

21
Q

How is Ketoacidosis caused?

A

Acetoacetate and Beta-hydroxybutyrate are relatively strong organic acids
Acetone is volatile and may be excreted via the lungs

22
Q

Why is Ketonuria possible?

A

Because Ketones are water soluble. When concentration gets too high they reach the urinary threshold

23
Q

What are the 3 Ketones produced in the body?

A

Acetone
Acetoacetate (Synthesised in Liver from AcA)
Beta Hydroxybutyrate (Synthesised in Liver from AcA)

24
Q

Why are Saturated fats non essential?

A

Unlike some Unsaturated fats, they can be produced from carbohydrates and amino acids

24
Q

When are Ketone bodies synthesised?

Extra point - What does it require?

A

When glucose concentration is low.
Extra point - Low insulin/glucagon ratio
Fatty acids to be available

Metabolism II (16 decks)

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