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MEH > Protein and Amino Acid Metabolism > Flashcards

Protein and Amino Acid Metabolism Flashcards

1
Q

what are the major nitrogen containing components in the body

A
  • amino acids
  • proteins
  • nitrogenous bases
  • creatine
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2
Q

what is creatinine

A

break down product of creatine and creatine phosphate

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3
Q

what is the level of creatinine in the urine proportional to

A

muscle mass

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4
Q

what is creatinine used as an indicator for

A

renal function (raised levels on damage to nephrons)

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5
Q

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

A

during pregnancy or rapid growth

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6
Q

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

A

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

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7
Q

what is the main method for nitrogen output

A

loss of nitrogen through the faeces and urine

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8
Q

what is proteolysis

A

production of amino acids from proteins

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9
Q

what happens to amino acids in the liver

A

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

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10
Q

what are glucogenic amino acids

A

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

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11
Q

what are ketogenic amino acids

A

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

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12
Q

what determines whether an amino acid is glucogenic or ketogenic

A

their side chains

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13
Q

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

A

tyrosine

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14
Q

what effect does insulin have on protein synthesis

A

increases

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15
Q

what affect does glucocorticoids have on protein synthesis

A

decreases it

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16
Q

what is cushing’s syndrome

A

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

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17
Q

what are non essential amino acids synthesised from

A
  • intermediates of glycolysis
  • pentose phosphate pathway
  • krebs cycle
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18
Q

what is transamination

A

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

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19
Q

what does tyrosine produce

A
  • catecholamines
  • melanin
  • thyroid hormones
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20
Q

what does cysteine produce

A
  • glutathione
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21
Q

what does histidine produce

A

histamine

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22
Q

what does arginine produce

A

nitric oxide

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23
Q

what does glycine produce

A
  • haem
  • creatine
  • purines
  • glutathiones
24
Q

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

A
  • transamination

- deamination

25
Q

outline transamination to produce glutamate

A

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

26
Q

outline transamination to produce aspartate

A

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

27
Q

what coenzymes do aminotransferase enzymes use

A

coenzymes requiring vitamin B6

28
Q

what does alanine aminotransferase do

A

converts alanine to glutamate

29
Q

what can levels of aminotransferase enzymes be used to test

A

liver function tests

30
Q

what do high levels of aminotransferase enzymes mean

A

liver cellular necrosis from toxins, viral hepatitis

31
Q

what is deamination

A

the removal of amine group from an amino acid

32
Q

where does deamination occur

A

liver and kidney

33
Q

why must ammonia be removed

A

it is very toxic

34
Q

what enzymes deaminate amino acids

A
  • amino acid oxidases
  • glutaminase
  • glutamate dehydrogenase
35
Q

what happens to ammonia

A

it is converted to urea

36
Q

why is ammonia converted to urea

A

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

37
Q

outline the urea cycle

A

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

38
Q

how many enzymes are involved in the urea cycle

A

5

39
Q

what induces the urea cycle enzyme levels

A

high protein diet

40
Q

what is refeeding syndrome

A

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

41
Q

what do defects in the urea cycle enzymes lead to

A

hyperammonaemia

accumulation of urea cycle intermediates

42
Q

how do you manage having defects in the urea cycle

A
  • low protein diet

- replace amino acids with keto acids in diet

43
Q

what are symptoms of urea cycle defects

A
  • vomiting
  • seizures
  • coma
  • irritability
  • mental retardation
44
Q

how is ammonia toxic

A
  • can alter the BBB and be toxic to the brain
  • interferes protein synthesis
  • affects pH
  • interferes TCA cycle
45
Q

at what levels should blood levels of ammonia be

A

25-40 micro moles

46
Q

how is ammonia disposed (2)

A
  • 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
47
Q

why is the heel prick test carried out

A

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

48
Q

what is PKU

A

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

49
Q

what are the symptoms of PKU

A
  • intellectual disability
  • seizures
  • developmental delay
    hypopigmentation
50
Q

what do phenylalanine hydroxylase catalyse

A

conversion of phenylalanine into tyrosine

51
Q

what is homocystinurias

A

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

52
Q

what are the treatments for PKU

A
  • controlled low phenyalalanine diet
  • avoid artificial sweeteners
  • avoid high protein foods
53
Q

what are the treatments for Homocystinurias

A
  • low methionine diet
  • avoid milk, meat, eggs, cheese
  • cysteine, Vit B6 supplement
54
Q

why should people with homocystinurias take Vit B6 supplemements

A

as cystathionine requires Vit B6 as a co factor

55
Q

what cant be produced in homocystinurias

A

cysteine

56
Q

what does homocystinurias cause

A

cardiovascular disease

- affects CT, muscle, CNS and CVS

MEH (22 decks)

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