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Amino Acid Metabolism Flashcards

(59 cards)

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1
Q

how many grams of protein do our bodies turn over a day?

A

300g

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2
Q

intake vs excretion

A

protein 100g/day

carbon dioxide, urea and ammonia 100g/day

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3
Q

what is the source of the amino acid pool?

A

diet and some body proteins if required

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4
Q

classifications of amino acid dependent on availability

A

essential, non-essential and semi-essential

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5
Q

essential amino acids

A

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

amino acids that cannot be synthesised de novo

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6
Q

conditionally essential

A

arginine, cysteine, glutamine, glycine, proline, serine, tyrosine

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7
Q

non essential

A

alanine, asparagine, aspartate and glutamate

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8
Q

enzymes involved in dietary absorption of amino acids

A

pepsin- non specific, maximally active at low stomach pH

proteolytic enzymes of the pancreas in the intestinal lumen

trypsin and chymotrypsin act in the duodenum

amino peptidases, digest proteins from the amino terminal end

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9
Q

what do trypsin and chymotrypsin prefer cleaving?

A

chymotrypsin- peptides where the amino acid N terminal bond is bound to trypsin, tyrosine, phenylalanine or leucine

trypsin- cleaves peptide chains normally at the carboxyl end bound to arginine or lysine

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10
Q

how are di and tripeptides taken up into the intestinal cells?

A

transported in a hydrogen ion symporter called PepT1

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11
Q

another important transporter

A

active sodium linked transport, along with the sodium-potassium ATPase maintaining the sodium concentration gradient

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12
Q

why does protein turnover occur?

A

damaged/incorrectly produced/folded proteins need to be removed

signalling proteins need to be removed and produced as needed

enzymes are often up/down regulated as a part of regulatory mechanisms

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13
Q

how do we know which proteins to break down?

A

proteins are tagged with ubiquitin using ubiquitin ligase

the tased protein is then directed into the proteasome for degradation

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14
Q

ubiquitin ligase structure + function of different subunits

A

ligases are made from three components E1, E2, E3

E1 & E2 are responsible for activating the ubiquitin

E3 recognises the protein to be ubiquinated

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15
Q

How does E3 work?

A

able to recognise damaged/misfolded proteins

it can also recognise certain n-terminal residues which signal the half life of a protein

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16
Q

syndrome related to ubiquitination

A

Angelman’s syndrome

  • a genetic disease with features of severe motor and intellectual disability
  • caused by mutations in ubiquitin ligase
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17
Q

overall regulation of protein synthesis/breakdown

A

insulin

  • net anabolic effect by stimulating chain initiation; effects on transcription are protein specific
  • inhibition of protein breakdown

thyroid hormones, cortisol
- net catabolic effect

anabolic steroids- net anabolic effect, such as testosterone

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18
Q

how else can amino acids be classified?

A

unionised or zwitterions

side chain

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19
Q

first two divisions of side chain

A

hydrophobic, non polar and hydrophilic, polar

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20
Q

further divisions of hydrophobic + amino acids

A

aromatic

  • glycine
  • alanine
  • valine
  • leucine
  • isoleucine
  • methionine
  • proline

alkyl

  • tryptophan
  • phenylalanine
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21
Q

further divisions of hydrophilic + amino acids

A

neutral

  • tyrosine
  • serine
  • threonine
  • cysteine
  • glutamine
  • asparagine

acidic

  • glutamic acid
  • aspartic acid

basic

  • lysine
  • histidine
  • argenine
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22
Q

explain the concept of positive and negative nitrogen balance

A

positive nitrogen balance is associated with periods or growth and repair, when the mass intake of nitrogen is greater than the loss from the body, greater protein pool

negative nitrogen balance is associated with burns, fevers and periods of fasting, where the mass intake is lower than the loss from the body, decrease in protein pool

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23
Q

what stops catabolism for going forward with some amino acids?

A

presence of an alpha amino group prevents oxidative breakdown

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24
Q

how is this overcome?

Study These Flashcards
A

alpha amino groups must be removed before catabolism can proceed, the nitrogen can be incorporated into other compounds or excreted

the process if called deamination and produced an alpha-veto acid and ammonia

25
3 different types of deamination
oxidative non-oxidative hydrolytic
26
explain oxidative deamination + which amino acids
amino acid becomes oxidised by NADP+ to form an alpha keto acid alpha ketoglutarate and NADPH + H+ and an ammonium ion catalysed by glutamate dehydrogenase glutamate
27
profile on glutamate dehydrogenase
mostly used in the liver and kidney NAD+ used as coenzyme in oxidative deamination NADP+ in reductive amination direction of reaction depends on substrate availability
28
regulation of glutamate dehydrogenase
deamination allosterically modulated by high ADP and GDP amination allosterically modulated by high ATP and GDP
29
what is a process that happens to amino acids other than glutamate?
transamination
30
explain transamination
amino acids are funnelled into glutamate to enable breakdown amino transferase catalyses the conversion of one amino acid into an alpha keto acid and then another keto acid into an amino acid
31
specific amino transferase examples
alanine transaminase ala + alpha ketoglutarate to pyruvate and glutamate aspartate transaminase asp + alpha ketoglutarate to oxaloacetate and glutamate
32
what do all transamination reactions require?
the cofactor pyridoxal phosphate, derived from pyridoxine vit B6
33
how does pyridoxal phosphate work?
forms a Schiff base with a lys residue in the active site of the transaminase
34
which amino acids under transamination + what do they produce and their relevance ?
alanine- pyruvate keto acid, can be added into glycolysis aspartate- oxaloacetate- added to TCA cycle leucine- 2-oxo-3-methyl valerate- oxidised in muscle isoleucine- 2-oxo-4-methyl valerate- oxidised in muscle valine- 2-oxo-3-methyl butyrate oxidised in muscle
35
what ketoacid does the deamination of glutamate produce + function?
alpha ketoglutarate, which is a substrate in the TCA cycle
36
2 examples of non oxidative deamination
serine to pyruvate and ammonium, catalysed by serine dehydratase threonine to alpha ketobutyrate and ammonium, catalysed by threonine dehydratase
37
why are the enzymes called dehydratases?
because the dehydration precedes deamination
38
why are serine and threonine directly deaminated?
they have an OH group
39
explain hydrolytic deamination + where this occurs
glutamine to glutamate, with water to ammonium catalysed by glutaminase intestinal cells and renal cortex
40
why is amino acid release from muscle important?
muscle has the largest store of protein in the body, typically 5-7kg during starvation, glucose continues to be oxidised, so it must come from non-glucose sources
41
what percentage of total free amino acids does skeletal muscle store?
50%
42
stages of the Cahill cycle in muscle
1. glucose to pyruvate in glycolysis | 2. pyruvate to alanine and an alpha ketoacid in transamination
43
stages of Cahill cycle in liver
1. alanine transamination to pyruvate and release of ammonia | 2. pyruvate to glucose via gluconeogenesis
44
what is glutaminase + functions ?
mitochondrial tissue specific isozyme that converts glutamine to glutamate helps generate urea expressed in kidneys to generate ammonium ions to help in acid-base balance expressed I neurones to assist neurotransmission
45
reaction that form glutamine + where it occurs
glutamate to glutamine catalysed by glutamate synthetase ammonium ion used ATP to ADP and Pi muscle
46
what is waste nitrogen excreted as in humans?
90% urea, the rest 10% ammonia
47
why is ammonia released in small amounts?
toxic so limited, however some still needed to maintain acid-base balance
48
why is urea excreted instead?
safe, non toxic means to excrete nitrogen
49
what is urea produced from?
ammonium ions
50
urea cycle stages
1. HCO3- + NH4+ to form carboxyl phosphate, catalysed by carboxyl phosphate synthesise-I along with 2ATP to form 2ADP and Pi. occurs in mitochondria 2. carbomoyl phosphate to citrulline 3. citrulline to argininosuccinate 4. argininosuccinate to arginine 5. arginine to urea and ornithine 6. ornithine combined with carbamoyl phosphate to produce citrulline
51
what is the urea cycle linked to + how?
TCA cycle through argininosuccinate
52
regulation of urea cycle
enzymes are coordinately up regulated by glucagon and glucocorticoids carboxyl phosphate synthesise is the controlling step
53
how else can amino acids be classified
based on possible metabolic fates, such as glycogenic if enter TCA cycle or ketogenic via acetyl CoA or mixed
54
glucogenic amino acids
``` ala gly arg his met asn asp cys glu gln pro ser thr val ```
55
ketogenic
leu | lys
56
both
ile phe trp tyr
57
how is ammonia transported to the liver?
in the form of glutamine glutamate + ammonia forms glutamine
58
three branched chain amino acids
leucine, isoleucine and valine
59
explain stages of branched chain metabolism
1. branched chain amino acids undergo transamination to form keto acids 2. branched chain amino acid dehydrogenase complex converts the keto acids into acetyl CoA derivatives 3. can then be converted into acetyl CoA or succinyl CoA to join the TCA cycle

Metabolism (13 decks)

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