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MEH A > Session 3 Lecture 2 > Flashcards

Session 3 Lecture 2 Flashcards

1
Q

Give some examples of major nitrogen containing compounds?

A

Amino acids, proteins, purine + pyrimidines (DNA/RNA)

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2
Q

What are the 9 essential amino acids?

A

Isoleucine, lysine, threonine, histidine, leucine, methionine, phenylalanine, tryptophan and valine

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3
Q

Where do the carbon atoms for non-essential amino acid synthesis come from?

A

Intermediates of glycolysis, pentose phosphate pathway and Krebs cycle

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4
Q

What is stage 1 catabolism of protein?

A

Occurs in the GI tract where proteases and peptidases hydrolyse peptide bonds to release free amino acids.

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5
Q

The amino acids absorbed into the circulation are used by tissues for?

A

Protein synthesis, synthesis of various nitrogen containing compounds eg creating, purine and haem

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6
Q

What stimulates the uptake of amino acids into tissues?

A

Insulting and growth hormone stimulate uptake into skeletal muscle, adipose tissue and liver

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7
Q

What effect does cortisol have on the uptake of amino acids?

A

Cortisol has the opposite effect therefore promoting the breakdown of muscle proteins and release of amino acids.

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8
Q

What happens if you have an excess of amino acids?

A

Not stored in the body but are broken down in stage 2 of catabolism

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9
Q

What is stage 2 of catabolism of amino acids?

A

Each amino acid found in protein has its own pathway. All of these pathways end up converting the amino acid to group of molecules used as organic precursor molecules

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10
Q

What products are made by the end of stage of catabolism of sugars, fatty acids, glycerol and amino acids?

A

Acetyl coA

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11
Q

What happens after stage 2 of protein amino acid catabolism?

A

The products can enter stage 3 catabolism which is the TCA cycle

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12
Q

What is nitrogen balance?

A

In healthy adults, the amount of nitrogen taken into the body equals the amount of N lost from the body

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13
Q

What is a positive nitrogen balance?

A

Intake>output

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14
Q

When does positing nitrogen balance occur?

A

During period of active growth and pregnancy

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15
Q

What is negative nitrogen balance?

A

Intake

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16
Q

What causes a negative nitrogen balance?

A

Starvation, malnutrition and trauma

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17
Q

What is the amino acid pool?

A

This is the total amount of free amino acids in the body (intracellular and extracellular)

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18
Q

What is amino acid re-utilisation?

A

Approx 75% of the amino acids released during protein breakdown are reutilised for protein synthesis

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19
Q

What is the function of amino acids?

A

Main function are protein synthesis and other N-compounds

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20
Q

What happens if too much amino acid is supplied than what is needed?

A

Not stored but are converted to intermediates of carbohydrate and lipid metabolism or oxidised to provide energy.

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21
Q

Name some important signalling molecules that are synthesised from amino acids L-arginine and L-cysteine respectively.

A

Nitric oxide and hydrogen sulphide

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22
Q

What is the main site of breakdown of most amino acids?

A

Liver

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23
Q

What is the common pathway of the breakdown of amino acids?

A
  • The C-atoms are converted to intermediates of carbohydrate and lipid metabolism
  • Start with the removal of NH2- group (tranamination or deamination)
  • The N atoms are usually converted to urea
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24
Q

What are all of the carbon atoms converted to?

A

Converted to one or more of the following; pyruvate, oxaloacetate fumerate etc

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25
Q

What is meant by glucagenic?

A

They can be used to synthesises glucose or glycogen

26
Q

Give some examples of glucogenic substances

A

Pyruvate, oxaloacetate, fumarate, alpha ketoglutarate and succinyl coA

27
Q

What is meant by ketogenic?

A

They can be used to synthesise fatty acids or ketone bodies.

28
Q

Give some examples of ketogenic substances

A

Acetyl coA acetoacetyl coA

29
Q

Name some substances that are both glucogenic and ketogenic

A

Isoleucine, tyrosine, phenylalanine and tryptophan

30
Q

Why do you need to remove the nitrogen from the amino acids?

A

To allow carbon skeleton of amino acids to be utilised in oxidative metabolism.

31
Q

What happens once the nitrogen has been removed from amino acids?

A

Nitrogen can be incorporates into other compounds or excreted from the body as urea.

32
Q

What two main pathways facilitate removal of nitrogen from amino acids?

A

Transamination and deamination

33
Q

What is transamination?

A

This is when the amino groups of amino acids are initially transferred to other molecules

34
Q

What enzymes are involved in transamination?

A

Aminotransferases that are specific for each amino acid.

35
Q

What is the reaction of transamination?

A

Amino acid 1 + keto acid 2 => amino acid 2 + keto acid 1

36
Q

What do most aminotranferase enzymes use as ketoacid 2?

A

They use alpha ketoglutarate and this is converted to glutamate
When oxaloacetate is used, it is converted to aspartate which is an important intermediate in synthesis of urea

37
Q

What do all aminotransferases require?

A

Require the co-enzyme pyridoxal phosphate which is a derivative of vitamin B6

38
Q

Name two transaminases that are clinically important?

A

ALT and AST

39
Q

What is ALT?

A

Alanine aminotransferases

Converts alanine to glutamate

40
Q

What is AST?

A

Aspartame aminotransferase

Converts glutamate to aspartate

41
Q

What are plasma ALT and AST levels a measure of?

A

Part of the liver function test

42
Q

What is deamination?

A

Liberates amino group as free ammonia

43
Q

What enzymes are responsible for deamination?

A

Amino acid oxidises
Glutaminase
Glutamate dehydrogenase

44
Q

Where does deamination occur?

A

Mainly occurs in liver and kidney

45
Q

What are dietary D- amino acids?

A

Found in pleasant and bacterial cell and therefore enter body via diet. Enzymes convert these into ketoacids which are not optically active.

46
Q

Why and how must ammonia be removed?

A

Ammonia is very toxic and must be removed. Ultimately converted to urea or excreted directly in urine.

47
Q

Describe some features of urea

A

Extremely water soluble
High nitrogen content
Non-toxic
Chemically inert

48
Q

How is most urea excreted?

A

In the urine via the kidneys

49
Q

How is urea synthesised?

A

Urea is synthesised in the liver by the urea cycle and transported via the blood to the kidneys

50
Q

What happens in the urea cycle?

A

The NH2 groups of urea come from NH4+ and aspartate.

51
Q

Where does the NH4+ in the urea cycle come from?

A

Comes from the actions of enzymes in the liver that deaminate amino acids released NH3 and from NH3 produced by gut bacteria that enters the liver via the portal circulation.

52
Q

Where does the aspartate in the urea cycle come from?

A

Aspartate is formed from oxaloacetate by transamination

53
Q

How many enzymes are involved in the urea cycle?

A

5

54
Q

What is the amount of urea cycle enzymes normally related to?

A

Related to the need to dispose of ammonia

55
Q

What effect will a high protein diet have on the urea cycle enzymes?

A

Induced high enzyme levels

56
Q

What affect will low protein diet or starvation have on the urea cycle?

A

Suppresses the levels

57
Q

What is refeeding syndrome?

A

This is when the urea cycle is down regulated and you get ammonia toxicity

58
Q

When does refeeding syndrome occur?

A

When you give nutritional support to severely malnourished patients

59
Q

Why can defect occur in the urea cycle?

A

Autosomal recessive genetic disorders caused by deficiency of one of enzymes in the urea cycle.

60
Q

What do genetic defects in the urea cycle lead to?

A

Hyperammonaemia

Accumulation/excretion of urea cycle intermediates

61
Q

How will someone present if they have defects in the urea cycle?

A

Mental retardation. Sever cases the child will die 1 day after birth. Seizes, coma, death.

62
Q

What treatments do you give people who have defects in the urea cycle?

A

Low protein diets and diets in which keto acids of the essential amino acids are used to replace the amino acids themselves.

MEH A (19 decks)

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