Protein and AA metabolism Flashcards
(81 cards)
1
Q
what is N equilibrium
A
intake = output
normal state adults
no change in body proteins
2
Q
what is positive N balance
A
intake > output
- increase body protein
- pregnancy, growth ,recovery from malnutrition
3
Q
what is negative N balance
A
intake < output
- loss of body protein
- trauma, infection, malnutrition
4
Q
what is the average dietary protein intake for 70 Kg male
A
16g N
5
Q
what is the average amount of body proteins for 70 Kg male
A
2Kg N
6
Q
what is the average weight of amino acid pool for 70 Kg male
A
16g N
7
Q
what is the average weight of nitrogen containing compounds for 70 Kg male
A
60g N
8
Q
what is the average weight of loss skin, hair, nails for 70 Kg male
A
2g N
9
Q
what is the average weight of n waste products for 70 Kg male
A
14g N
10
Q
what is protein turnover
A
proteins undergoing continuous breakdown and resynthesis
11
Q
what is the half life of a protein
A
80g
12
Q
when are protein reserves metabolised and how is this controlled
A
occurs during extreme stress (starvation)
hormonal control
13
Q
describe how insulin and growth hormone affet protein synthesis and protein degradation
A
- increases synthesis
- decreases degradation
14
Q
describe how gluocorticoids (cortisol ) affects protein synthesis and degradation
A
- decreases synthesis
- increases degdradation
15
Q
what is cushing’s syndrome
A
excessive breakdown of protein from excess cortisol
weakens skin structure leading to striae
16
Q
what type of amino acids can the body synthesise
A
non- essential
17
Q
where do the carbon atoms come from for AA synthesis
A
- intermediates of glycolysis
- PPP
- krebs
18
Q
where does the amino group come from for amino acid synthesis
A
- provided by other AAs (transamination)
- ammonia
19
Q
what does tyrosine produce
A
- catecholamines
- melanin
- thyroid hormone
20
Q
what does cysteine produce
A
- hydrogen sulphide
- glutathione
21
Q
what does tryptophan produce
A
- nicotinamide
- serotonin
- melatonin
22
Q
what does histidine produce
A
- histamine
23
Q
what does glutamate produce
A
- GABA
24
Q
what does arginine produce
A
nitric oxide
25
what does serine produce
sphingosine
26
what does glycine produce
- purines
- glutathione
- haem
- creatine
27
why must excess AAs be broken down
they cannot be stored or excreted so broken down into small molecules
28
where is the major breakdown site of AAs
liver
29
what do all pathways of breakdown of AAs have in common
- C atoms converted to intermediates of carb and lipid metabolism
- removal of NH2 group
- N atoms usually converted
30
why is the removal of the amino group necessary in breakdown of AAs
so carbon skeleton can be used for metabolism and N can be incorporated into other compound or excreted as urea
31
what are the two methods of removing amino groups from AAs
- transamination
- deamination
32
describe the process of transamination
transferring one amino group from one AA to another using and forming keto acids usually a-ketoglutarate
AA1 + keto acid 2 --> AA2 + keto acid 1
33
what are the enzymes involved in transamination
- alanine aminotransferase (ALT)
- aspartate aminotransferase (AST)
34
what does the ALT enzyme do
converts alanine and a-ketoglutarate to pyruvate and glutamate
35
what does the AST enzyme do
aspartate and a-ketoglutarate --> oxalacetate and glutamate
36
why are ALT and AST levels measured in blood and when would they be high
check liver function
levels high in necrosis :
- viral hepatitis
- autoimmune liver disease
- toxic injury
37
what co-enzyme do ALT and AST need
pyridoxal phosphate which is a B6 derivative
38
what is deamination
the process of liberating the amino group to free ammonia
39
where does deamination occur
in liver and kidney
40
what enzymes are involved in deamination
- L and D amino acid oxidases
- glutaminase
- glutamate dehydrogenase
41
why do humans have high activity of D amino acid oxidase
D amino acids are found in plant and bacteria cells so enter through diet and must not be used for protein synth as will form abnormal proteins as human proteins are in L form so change them into keto acids
42
what does glutaminase do
- high specificity
- converts glutamine to glutamate and ammonia
43
what does glutamate dehydrogenase do
- high specificity
- converts glutamate + NAD + H2O --> a-ketoglutarate + NH4 + NADH + H+
44
what is PKU
phenylketonuria
45
what is the defective enzyme in PKU
what is its normal function
phenylalanine hydroxylase
- normal function: converts phenylalanine --> tyrosine
46
what accumulates in PKU and what does this produce
phenylalanine accumulates in blood so metabolised by other pathways to produce phenylketones in urine (musty smell)
47
what are the symptoms of PKU
- severe intellectual disability
- developmental delay
- microcephaly (small head)
- seizures
- hypopigmentation (tyrosine cannot produce melanin)
48
how is PKU tested for
heel prick test at birth
test for conc of phenylalanine
49
how is PKU treated
- diet with low phenylalanine but high tyrosine
50
what is homocystinuria
a defect in the cystathione-β-synthase
- normally converts homocysteine to cystathione which produces cysteine
51
where does homocyteine come from
breakdown of methionine
52
how is homocystinuria detected
elevated levels of homocysteine and methionine in plasma and the presence of homocystine (oxidised homocysteine) in urine
53
what are the symptoms of homocystinuria
damage to connective and muscle tissue and damage to CNS and CVS
54
how is homocystinuria treated
low methionine diet
avoid milk, fish, eggs , cheese, nuts
supplement with cysteine, vitamin B 6 and 12 and folate
55
what is a glucogenic amino acid
used to synthesise glucose
56
give two examples of glucogenic AA
alanine and cysteine
57
what is a ketogenic AA
used to synthesise FA or ketone bodies
58
give two examples of ketogenic AA
lysine and leucine
59
give two examples of AA that are both ketogenic and glucogenic
tyrosine and tryptophan
60
why must ammonia be quickly removed from cells
it is toxic
61
what is ammonia converted to to be removed
urea
62
how does ammonia affect the CNS
- CNS sensitive to high ammonia (hyperammonaemia)
- blurred vision
- slurred speach
- tremors
- coma
63
why is the CNS sensitive to high ammonia
ammonia reacts with a-ketoglutarate which essentially removes it from the TCA cycle so disrupts energy production and CNS dependent on glucose mainly
- ammonia also affects ph
64
what are the toxic affects of ammonia
- interference with AA transport and protein synth
- disruption of cerebral blood flow
- affect pH
- interefere with metabolism of excitatory NTs
- alteration of blood brain barrier
- interference of TCA cycle (a-ketoglutarate)
65
where is ammonia detoxified
liver
66
what are the two mechanisms of transporting ammonia from other tissues to the liver for detoxification
- glutamine synthesis
- alanine synthesis
67
how does glutamine synthesis work for transporting ammonia and using what enzyme
ammonia combined with glutamate --> glutamine
enzyme: glutamine synthase
transported to liver cleaved into glutamate and NH3
enzyme: glutaminase
68
how does alanine synthesis work for transporting ammonia and using what enzyme
amine groups transferred to glutamate by transamination making pyruvate then pyruvate transaminated to alanine which is transported to the liver
- converted back to pyruvate and glutamate
enzyme: alanine aminotransferase
- glutamate fed into urea cycle
pyruvate for glucose
69
why can urea be excreted in urine
water solule
non-toxic
high N content so effective
70
where is urea synthesised and then transported to
liver
kidney
71
what two places does the urea cycle occur in
cytoplasm
mitochondria
72
what enzyme if involved in the urea cycle and what does it do
glutamate dehydrogenase
converts glutamate into aspartate and NH4
73
what are two necessary reactant for urea cycle
2 ATP
CO2
74
how are the enzymes in urea cycle regulated
inducible so on an as needed basis
- high protein diet induces
- low protein not induced
75
what do defects in the urea cycle cause
- hyperammonaemia
- accum of urea intermediates
76
what are the symptoms of an autosomal recessive defect in urea cycle
vomitting
lethargy
irritability
intellectual disability
seizures
coma
77
how are defects in urea cycle managed
low protein diet
replace amino acids with keto acids
78
what is creatinine
the breakdown product of creatine and creatine phosphate
79
what does creatinine give and indication of
muscle mass as produced at constant rate proportional to muscle mass
80
where is the creatinine excreted
urine
81
why is creatinine measured
test of renal function
- if high in plasma and low in urine kidney is damaged
