Protein and Amino Acid Metabolism

Question 1

what are the major nitrogen containing components in the body

Answer 1

• amino acids
• proteins
• nitrogenous bases
• creatine

Question 2

what is creatinine

Answer 2

break down product of creatine and creatine phosphate

Question 3

what is the level of creatinine in the urine proportional to

Answer 3

muscle mass

Question 4

what is creatinine used as an indicator for

Answer 4

renal function (raised levels on damage to nephrons)

Question 5

when is it normal to have a large nitrogen intake than output

Answer 5

during pregnancy or rapid growth

Question 6

when is it normal to have a larger nitrogen output than intake

Answer 6

it is never normal - only occurs in trauma, infection and malnutrition

Question 7

what is the main method for nitrogen output

Answer 7

loss of nitrogen through the faeces and urine

Question 8

what is proteolysis

Answer 8

production of amino acids from proteins

Question 9

what happens to amino acids in the liver

Answer 9

they are broken down into an amino group and the carbon skeleton

Question 10

what are glucogenic amino acids

Answer 10

ones that can undergo gluconeogenesis to give energy e.g. glycine

Question 11

what are ketogenic amino acids

Answer 11

ones that produce ketone bodies to give energy e.g. lysine and leucine

Question 12

what determines whether an amino acid is glucogenic or ketogenic

Answer 12

their side chains

Question 13

give an example of an amino acid that is both glucogenic and ketogenic

Answer 13

tyrosine

Question 14

what effect does insulin have on protein synthesis

Answer 14

increases

Question 15

what affect does glucocorticoids have on protein synthesis

Answer 15

decreases it

Question 16

what is cushing’s syndrome

Answer 16

excessive breakdown of protein occurs weakening the skin structure leading to striae formation

Question 17

what are non essential amino acids synthesised from

Answer 17

• intermediates of glycolysis
• pentose phosphate pathway
• krebs cycle

Question 18

what is transamination

Answer 18

the conversion on one amino acid to another by swapping an amine group of an amino acid with an oxygen of a keto acid

Question 19

what does tyrosine produce

Answer 19

• catecholamines
• melanin
• thyroid hormones

Question 20

what does cysteine produce

Answer 20

• glutathione

Question 21

what does histidine produce

Answer 21

histamine

Question 22

what does arginine produce

Answer 22

nitric oxide

Question 23

what does glycine produce

Answer 23

• haem
• creatine
• purines
• glutathiones

Question 24

what are the 2 methods for removal of nitrogen from amino acids

Answer 24

• transamination

- deamination

Question 25

outline transamination to produce glutamate

Answer 25

alpha ketogluatarate is converted into glutamate and an amino acid into a keto acid by an aminotransferase enzyme

Question 26

outline transamination to produce aspartate

Answer 26

a glutamate is converted into a keto acid and oxaloacetate is converted into aspartate by aspartate aminotransferase

Question 27

what coenzymes do aminotransferase enzymes use

Answer 27

coenzymes requiring vitamin B6

Question 28

what does alanine aminotransferase do

Answer 28

converts alanine to glutamate

Question 29

what can levels of aminotransferase enzymes be used to test

Answer 29

liver function tests

Question 30

what do high levels of aminotransferase enzymes mean

Answer 30

liver cellular necrosis from toxins, viral hepatitis

Question 31

what is deamination

Answer 31

the removal of amine group from an amino acid

Question 32

where does deamination occur

Answer 32

liver and kidney

Question 33

why must ammonia be removed

Answer 33

it is very toxic

Question 34

what enzymes deaminate amino acids

Answer 34

- amino acid oxidases - glutaminase - glutamate dehydrogenase

Question 35

what happens to ammonia

Answer 35

it is converted to urea

Question 36

why is ammonia converted to urea

Answer 36

urea is non toxic, water soluble, inert and excreted in the urine

Question 37

outline the urea cycle

Answer 37

ammonia combines with carbon dioxide. the product combines with aspartate or glutamate which then eventually produces urea

Question 38

how many enzymes are involved in the urea cycle

Answer 38

5

Question 39

what induces the urea cycle enzyme levels

Answer 39

high protein diet

Question 40

what is refeeding syndrome

Answer 40

when malnourished patients have a downregulation of enzymes in the urea cycle and so giving them too much protein quickly increases ammonia toxicity

Question 41

what do defects in the urea cycle enzymes lead to

Answer 41

hyperammonaemia | accumulation of urea cycle intermediates

Question 42

how do you manage having defects in the urea cycle

Answer 42

- low protein diet | - replace amino acids with keto acids in diet

Question 43

what are symptoms of urea cycle defects

Answer 43

- vomiting - seizures - coma - irritability - mental retardation

Question 44

how is ammonia toxic

Answer 44

- can alter the BBB and be toxic to the brain - interferes protein synthesis - affects pH - interferes TCA cycle

Question 45

at what levels should blood levels of ammonia be

Answer 45

25-40 micro moles

Question 46

how is ammonia disposed (2)

Answer 46

- combined with glutamate to form glutamine which is transporter to the liver or kidneys where its cleaved by glutaminase to reform glutamate and ammonia, which is fed into the urea cycle - combined with pyruvate to form alanine which is transported to the liver where its converted back into pyruvate by transamination and the amino group if fed into the urea cycle

Question 47

why is the heel prick test carried out

Answer 47

to screen blood for sickle cell, cystic fibrosis and amino acid metabolism defects (e.g. PKU and Homocystinuria)

Question 48

what is PKU

Answer 48

deficiency in phenylalanine hydroxylase causing the accumulation of phenylalanine which produces phenylketones

Question 49

what are the symptoms of PKU

Answer 49

- intellectual disability - seizures - developmental delay hypopigmentation

Question 50

what do phenylalanine hydroxylase catalyse

Answer 50

conversion of phenylalanine into tyrosine

Question 51

what is homocystinurias

Answer 51

problems with breaking down methionine giving excess homocysteine due to defects in cystathionine beta synthase

Question 52

what are the treatments for PKU

Answer 52

- controlled low phenyalalanine diet - avoid artificial sweeteners - avoid high protein foods

Question 53

what are the treatments for Homocystinurias

Answer 53

- low methionine diet - avoid milk, meat, eggs, cheese - cysteine, Vit B6 supplement

Question 54

why should people with homocystinurias take Vit B6 supplemements

Answer 54

as cystathionine requires Vit B6 as a co factor

Question 55

what cant be produced in homocystinurias

Answer 55

cysteine

Question 56

what does homocystinurias cause

Answer 56

cardiovascular disease | - affects CT, muscle, CNS and CVS