Session 3 Lecture 2

Question 1

Give some examples of major nitrogen containing compounds?

Answer 1

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

Question 2

What are the 9 essential amino acids?

Answer 2

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

Question 3

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

Answer 3

Intermediates of glycolysis, pentose phosphate pathway and Krebs cycle

Question 4

What is stage 1 catabolism of protein?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What stimulates the uptake of amino acids into tissues?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What happens if you have an excess of amino acids?

Answer 8

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

Question 9

What is stage 2 of catabolism of amino acids?

Answer 9

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

Question 10

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

Answer 10

Acetyl coA

Question 11

What happens after stage 2 of protein amino acid catabolism?

Answer 11

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

Question 12

What is nitrogen balance?

Answer 12

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

Question 13

What is a positive nitrogen balance?

Answer 13

Intake>output

Question 14

When does positing nitrogen balance occur?

Answer 14

During period of active growth and pregnancy

Question 15

What is negative nitrogen balance?

Answer 15

Intake

Question 16

What causes a negative nitrogen balance?

Answer 16

Starvation, malnutrition and trauma

Question 17

What is the amino acid pool?

Answer 17

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

Question 18

What is amino acid re-utilisation?

Answer 18

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

Question 19

What is the function of amino acids?

Answer 19

Main function are protein synthesis and other N-compounds

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Nitric oxide and hydrogen sulphide

Question 22

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

Answer 22

Liver

Question 23

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

Answer 23

• 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

Question 24

What are all of the carbon atoms converted to?

Answer 24

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

Question 25

What is meant by glucagenic?

Answer 25

They can be used to synthesises glucose or glycogen

Question 26

Give some examples of glucogenic substances

Answer 26

Pyruvate, oxaloacetate, fumarate, alpha ketoglutarate and succinyl coA

Question 27

What is meant by ketogenic?

Answer 27

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

Question 28

Give some examples of ketogenic substances

Answer 28

Acetyl coA acetoacetyl coA

Question 29

Name some substances that are both glucogenic and ketogenic

Answer 29

Isoleucine, tyrosine, phenylalanine and tryptophan

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

Transamination and deamination

Question 33

What is transamination?

Answer 33

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

Question 34

What enzymes are involved in transamination?

Answer 34

Aminotransferases that are specific for each amino acid.

Question 35

What is the reaction of transamination?

Answer 35

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

Question 36

What do most aminotranferase enzymes use as ketoacid 2?

Answer 36

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

Question 37

What do all aminotransferases require?

Answer 37

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

Question 38

Name two transaminases that are clinically important?

Answer 38

ALT and AST

Question 39

What is ALT?

Answer 39

Alanine aminotransferases | Converts alanine to glutamate

Question 40

What is AST?

Answer 40

Aspartame aminotransferase | Converts glutamate to aspartate

Question 41

What are plasma ALT and AST levels a measure of?

Answer 41

Part of the liver function test

Question 42

What is deamination?

Answer 42

Liberates amino group as free ammonia

Question 43

What enzymes are responsible for deamination?

Answer 43

Amino acid oxidises Glutaminase Glutamate dehydrogenase

Question 44

Where does deamination occur?

Answer 44

Mainly occurs in liver and kidney

Question 45

What are dietary D- amino acids?

Answer 45

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

Question 46

Why and how must ammonia be removed?

Answer 46

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

Question 47

Describe some features of urea

Answer 47

Extremely water soluble High nitrogen content Non-toxic Chemically inert

Question 48

How is most urea excreted?

Answer 48

In the urine via the kidneys

Question 49

How is urea synthesised?

Answer 49

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

Question 50

What happens in the urea cycle?

Answer 50

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

Question 51

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

Answer 51

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.

Question 52

Where does the aspartate in the urea cycle come from?

Answer 52

Aspartate is formed from oxaloacetate by transamination

Question 53

How many enzymes are involved in the urea cycle?

Answer 53

5

Question 54

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

Answer 54

Related to the need to dispose of ammonia

Question 55

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

Answer 55

Induced high enzyme levels

Question 56

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

Answer 56

Suppresses the levels

Question 57

What is refeeding syndrome?

Answer 57

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

Question 58

When does refeeding syndrome occur?

Answer 58

When you give nutritional support to severely malnourished patients

Question 59

Why can defect occur in the urea cycle?

Answer 59

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

Question 60

What do genetic defects in the urea cycle lead to?

Answer 60

Hyperammonaemia | Accumulation/excretion of urea cycle intermediates

Question 61

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

Answer 61

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

Question 62

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

Answer 62

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