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Metabolism II > Session 4 > Flashcards

Session 4 Flashcards

1
Q

What is Glycogen synthesis called?

A

Glycogenesis

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2
Q

What enzyme catalyses the first step in Glycogenesis?

A

Hexokinase

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3
Q

What enzyme catalyses the second step in Glycogenesis?

A

Phosphoglucomutase

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4
Q

What enzyme catalyses the fourth step in Glycogenesis?

A

Glycogen synthase & Branching enzyme

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5
Q

What enzyme catalyses the first step in Glycogen breakdown?

A

Glycogen phosphorylase attacks the alpha 1,4 bonds & Debranching enzyme attacks alpha 1,6

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6
Q

What enzyme catalyses the second step in Glycogen breakdown?

A

Phosphoglucomutase

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7
Q

What enzyme catalyses the third step in Glycogen breakdown?

A

Glucose 6-phosphatase

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8
Q

Contrast the Glycogen stores in Muscles and the Liver

A

Muscle - G6P, muscle only

Liver - Glucose for all tissues of the body

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9
Q

Explain the clinical consequences of Glycogen storage disease

A 
Abnormality in enzymes of Glycogen metabolism;
Tissue damage if excessive storage
Fasting hypoglycaemia
Poor exercise tolerance
Glycogen structure may be abnormal
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10
Q

Define Gluconeogenesis

A

The process where Glucose is produced when there are no Carbohydrates.
Liver is the main site
Reversible steps of glycolysis used in gluconeogenesis, irreversible bypassed.

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11
Q

Name some of the substrates for Gluconeogenesis

A 
Pyruvate
Lactate
Glucerol
AA
NOT Acetyl CoA
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12
Q

WHat 3 steps of Glycolysis are bypassed in Gluconeogenesis?

A

1, 3 & 10

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13
Q

How are steps 1 & 3 of Glycolysis bypassed in Gluconeogenesis?

A

Thermodynamically spontaneous reactions catalysed by glucose 6-phosphatase and fructose 1,6-bisphophatase

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14
Q

How is step 10 of Glycolgysis bypassed in Gluconeogenesis?

A

2 reactions catalysed by pyruvate carboxylase and PEPCK (Use ATP)

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15
Q

Which reaction provides a ‘link’ between the Krebs cycle and Gluconeogenesis?

A

Step 10 reaction enables products of AA catabolism (intermediates of TCA cycle) to synthesise glucose.

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16
Q

How is Gluconeogenesis regulated?

A

Hormonal control on PEPCK and Fructose 1,6-bisphosphonate

Increased by Glucagon, decreased by Insulin

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17
Q

What controls Triacylglycerol storage?

A

Promoted by Insulin

Depleted by anti insulin hormones (Glucagon, Adrenaline, Cortisol, Thyroxine, GH)

18
Q

How are Fatty acids degraded?

A

Beta oxidation. 2C removed at a time (As Acetyl CoA) until only 2 left.
Needs NAD+, FAD & O2

19
Q

How are fatty acids synthesised?

A

Lipogenesis - Synthesised from Acetyl CoA using ATP and NADPH
Fatty acid synthase complex adds 2Cs at a time by adding 3Cs and having CO2 lost

20
Q

How is Lipogenesis controlled?

A

Acetyl~CoA carboxylase enzyme (Converts Acetyl CoA to 3C compound)
Allosteric regulation - citrate activates and AMP inhibits
Regulation by covalent modification - Insulin activates by promoting dephosphorylation. Glucagon & Adrenaline inhibit the enzyme by promoting phosphorylation

21
Q

How are Amino acids catabolised?

A

Each has its own pathway;
Amino group removed –> Urea (Deamination/Transamination)
Remaining C skeleton reused

22
Q

What are Ketogenic Amino acids?

A

Ones that can produce Acetyl CoA as it goes on to make Ketone bodies

23
Q

What are Glucogenic Amino acids?

A

Ones that produce molecules which can be used for Glucose synthesis in Gluconeogenesis

24
Q

What enzymes are used in Transamination?

A

Aminotransferases

25
Q

What enzymes are used in Deamination?

A

L & D-amino acid oxidases (Convert AA to Keto acids)

D amino acids must NOT be used in protein synthesis as proteins would be structurally abnormal & non functional

26
Q

Define Phenylketonuria (PKU)

A

Inherited disorder

Urine contains large amounts of phenylketones produced from phenylalanine

27
Q

Which enzyme is usually defective in PKU?

A

Phenylalanine hydroxylase. (Oxidises Phenylalanine to Tyrosine)
Results in high levels of Phenylalanine - metabolised by other pathways to produce various products including phenylpyruvate - excreted in the urine.

28
Q

How is PKU diagnosed?

A

Detection of phenylketones in the urine or high phenylalanine blood concn (normal is <0.1mM).

29
Q

How is PKU treated?

A

A diet low in Phenylalanine

Left untreated can inhibit brain development due to inhibition of pyruvate uptake by phenylpyruvate

30
Q

Define Homocystinuria

A

Autosomal recessive defect in methionine metabolism

Type 1 - deficiency in CBS enzyme

31
Q

How is Homocystinuria detected?

A

Elevated levels of homocysteine and methionine in plasma (and homocystine – the oxidised form of homocysteine in the urine)

32
Q

What are the consequences of Homocystinuria?

A

Chronic elevated plasma levels of homocysteine cause disorders of connective tissue, muscle, CNS and the cardiovascular system - Easily confused with Marfan’s syndrome in children

33
Q

Why do you measure blood and urine Creatinine?

A

Breakdown product of Creatine.
Produced at constant rate by spontaneous muscle atrophy
Amount of excretion in 24hrs is proportional to the muscle mass of the individual. - measure of muscle mass.

34
Q

Why is Ammonia metabolised by the body?

A

Toxic - rapidly detoxified & removed. Peripheral blood concentration is normally kept very low (25-40microM)

35
Q

Why is Ammonia toxic?

A

CNS very sensitive.
Involves reaction with alpha-ketoglutarate to form glutamate in mitochondria via glutamate dehydrogenase removing alpha¬-ketoglutarate from the TCA cycle- disrupting energy to brain cells.
Affects pH in cells of CNS & interferes with neurotransmitter synthesis/release.

36
Q

What are the signs of Hyperammonaemia?

A

Blurred vision, tremors, coma & death

Seen in Liver disease

37
Q

How can Ammonia be detoxified?

A

Synthesis of N-compounds such as glutamine (Requires ATP and glutamine synthetase) or by conversion to urea
Glutamine is transported to Kidneys - hydrolysed by glutaminase releasing ammonia - disposed of in the urine

38
Q

Why is Urea beneficial?

A

Very soluble in water
It is non-toxic, metabolically inert and has a high nitrogen-content (47%)
Good way of disposing of nitrogen

39
Q

How is Urea synthesis regulated?

A

NOT feedback inhibition because the function of the cycle is to dispose.
Enzymes are inducible by a high-protein diet, and repressed by low-protein/starvation.

40
Q

What is important to remember when treating people who have suffered starvation?

A

Gradual re-introduction of protein to prevent hyperammonaemia as the enzymes can slowly be reactivated

41
Q

What do diseases of the Urea cycle cause?

A

Hyperammonaemia
High concentration/excretion of the urea cycle intermediates.
Usually mental retardation
Can cause death

42
Q

How do you treat diseases of the Urea cycle?

A

Low protein diet and replacing essential AA with keto acids that use NH4+ when converted to amino acids, so lowers NH4+ concentration

Metabolism II (16 decks)

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