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MEH > Session 1- protein and aa metabolism > Flashcards

Session 1- protein and aa metabolism Flashcards

1
Q

What effect do these hormones have on protein synthesis?

  • Insulin
  • Growth hormone
  • Cortisol

How does cortisol exert its effect?

A

Insulin and growth hormone promote uptake of amino acids and protein synthesis

Cortisol promotes proteolysis in muscle by activating aminotransferases in the liver

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2
Q

Is excess protein stored?

A

No, the amino acids are converted to metabolites or excreted

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3
Q

What is the first step in amino acid breakdown?

A

Removal of the amino group by transamination/ deamination

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4
Q

Amino acid catabolism; What happens to the amino group?

What is the remaining structure called?

A

If not transferred to another aa, it is converted to urea and excreted via the urine
Urea; (CO(NH2)2)

C-skeleton of the amino acid

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5
Q

What are ketogenic and glucogenic amino acids?

A

The C-skeletons of ketogenic amino acids produce acetyl CoA which can make ketone bodies

C-skeletons of glucogenic amino acids produce intermediates in gluconeogenesis. E.g. pyruvate

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6
Q

Name two ketogenic amino acids

Name amino acids which are both ketogenic and glucogenic

A

Lysine & leucine

Tryptophan 
Tyrosine
Isoleucine
Phenylalanine 
Threonine
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7
Q

Metabolism of glucose, fatty acids, amino acids and ketone bodies all produce which molecule?

A

Acetyl CoA

enters the TCA cycle

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8
Q

How many kg of nitrogen is there in the body?

Most of the nitrogen in the body is found where?

A

Approx. 2kg

Mostly proteins (90%) then DNA & RNA

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9
Q

Average half life of a protein?

Total protein turnover per day in an adult?

A

80 days

300-400 g per day

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10
Q

What is a positive nitrogen balance?

When does it occur?

A

Taking in more protein than you excrete

Periods of active growth, pregnancy and tissue repair

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11
Q

What is a negative nitrogen balance?

When does it occur?

A

Taking in less nitrogen than you excrete

Starvation, malnutrition, trauma

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12
Q

How does nitrogen enter and leave the body?

A

Enters mostly in protein

Leaves via 
- urea (85%)
- creatinine 
- ammonia
- uric acid 
some direct loss of protein via hair, skin, nails
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13
Q

How to remember the 10 essential amino acids?

A

PVT TIM HALL

Phenylalanine
valine
threonine
tryptophan 
isoleucine
methionine
histidine 
arginine (conditional)
leucine
lysine
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14
Q

Name three amino acids which are conditionally essential

Explain when they become essential

A

Tyrosine - only if phenylalanine is low (its precursor)

Arginine - only during periods of active growth bc the body can produce small amounts

Cysteine - only if methionine (its precursor) is low

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15
Q

Which amino acid is the precursor for Tyrosine?

A

Phenylalanine

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16
Q

Which amino acid is the precursor for Cysteine?

A

Methionine

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17
Q

Normal fasting concentration of amino acids in the blood?

A

3mmol/L

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18
Q

Which 4 non-essential amino acids make up 50% of the free pool?

A

glutatmine, alanine, proline, glycine

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19
Q

Why do you need to keep taking in amino acids if most are recycled?

A

To replace those which are lost

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20
Q

Where do the carbon and nitrogen atoms come from to make new amino acids?

A
  • carbon from intermediates of glycolysis, the pentose phosphate pathway and the Krebs Cycle
  • amino group from transamination or ammonia
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21
Q

What happens to excess amino acids?

A

Converted to intermediates of carbohydrate and lipid metabolism OR
oxidised for energy

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22
Q

Which two signalling molecules are made from amino acids?

A

nitric oxide (from L-arginine)

Hydrogen sulphide (from L-cysteine)

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23
Q

These amino acids are used to make what nitrogenous compounds?

  • Trytophan
  • Histidine
  • Tyrosine
  • Glycine
A
  • seratonin, 5-HT
  • histamine
  • thyroid hormones, melanin, catecholamines
  • purines, porphyrins, creatine, glutathione
24
Q

Where does most amino acid catabolism occur?

How does use of acetyl CoA change in starvation?

A

liver

Usually oxidised to CO2 and water but in starvation/ diabetes, it’s converted to ketone bodies and glucose

25
Q

Which 2 aminotransferases do we test for liver function?

What does the amino acid react with?
What is it converted to?

A

Alanine aminotransferase

Aspartate aminotransferase?

(keto acid)
alpha ketoglutarate
> glutamate

26
Q

aminotransferases convert these amino acids to what?

  • Alanine
  • Aspartate

Aspartate is an important intermediate in synthesis of ____ .

A
  • Alanine becomes Pyruvate
  • Aspartate becomes Oxaloacetate
  • Urea
27
Q

Where do D amino acids come from and how do we use them?

A

They come from plants and bacteria so enter the body through the diet
We do NOT use them in protein synthesis, instead they are converted to keto acids and NH3, ammonia

28
Q

Why do we convert D-amino acids to keto acids?

A

Keto acids are not optically active

29
Q

What does glutaminase do?

A

Glutamine to glutamate + ammonia (NH3)

30
Q

What does glutamaTe dehydrogenase do?

A

Glutamate to alpha ketoglutarate

+ NH4+ and NADH

31
Q

When can amino acids be toxic?

What can this cause?

A

If they’re not broken down correctly;
Accumulate/ toxic byproducts of improper breakdown

Mental retardation and developmental abnormalities

32
Q

What does PKU stand for?

What process is defective in PKU?

A

Phenylketonuria (PKU)

Conversion of phenylalanine to tyrosine

33
Q

Which enzyme is usually defective in phenylketonuria?

Normal range of phenylalanine in the blood?
Conc. in PKU?

A

phenylalanine hydroxylase

Usually lower than 0.1, can rise to 1mmol/ L in PKU

34
Q

If undiagnosed what are the consequences of PKU and why?

What precaution does the UK take to diagnose early?

A
  • inhibition of brain development

phenylpyruvate (metabolite of secondary pathways) - inhibits pyruvate uptake into mitochondria
- interferes with energy metabolism in the brain

Screened for in the heel prick test performed on new born babies

35
Q

In homocystinuria, which amino acid can’t be broken down?

What is the deficient enzyme?

A

Methionine
(Cysteine is formed from methionine)

CBS enzyme
(Cystathionine beta synthase)

36
Q

How is homocystinuria inherited?

Why is the concentration of plasma methionine high?

What is present in the urine?

A

autosomal recessive

  • Homocysteine can’t be converted to cysteine
  • It accumulates and some is converted to methionine
  • homocystINE (oxidised homocysteine)
37
Q

How does untreated homocystinuria present?

Which other condition can it be mistaken for in children?

A

disorders of connective tissue, muscle, CNS and the cardiovascular system

Marfan’s Syndrome

38
Q

Which protein is not expressed in Marfan’s Syndrome?

What happens to this protein in homocystinuria?

A

Fibrillin 1

the structure is disrupted

39
Q

Where does ammonia in the body come from?

How does it mostly exist in the body?

A

produced by tissues and absorbed from gut

As the ammonium ion, NH4+

40
Q

Why are levels of plasma ammonia very low?

Symptoms of high ammonia?

A
  • Toxic to cells
  • CNS is extremely sensitive to ammonia

slurred speech, blurred vision, tremors, coma, death

41
Q

How does hyperammonia cause its neurological symptoms?

A

Two theories

  • Reacts with alpha ketoglutatrate;
  • removing it from the TCA cycle (slows)
  • disrupts energy supply to brain

Change intracellular pH thus affecting NT release

42
Q

Why is hyperammonia seen in liver disease?

A

Liver is site of NH3 detoxification

43
Q

Two ways ammonia is detoxified in the liver?

A
  • Converted to urea

- used in synthesis of nitrogenous compounds

44
Q

Which amino acid is highest in the blood?

When do its levels rise further?

A

Glutamine

After a protein rich meal

45
Q

Where does aspartate come from?

A

Transamination of oxaloacetate

46
Q

The nitrogen atoms in Urea come from ___ &____?

A

Aspartate and ammonium, NH4+

47
Q

Why does re-feeding syndrome occur?

A

Enzymes of the urea cycle are induced to work; if the diet is low in protein, the enzymes deregulate

When given a high protein meal, the body cannot detoxify the ammonia (by conversion to urea) and the patient suffers hyperammonaemia

48
Q

What underlying condition creates the neurological symptoms of refeeding syndrome?

Which enzymes are not functioning?

A

Hyperammonaemia

(bc they can’t detoxify the ammonia from protein metabolsim)

Inducible enzymes of the urea cycle

49
Q

Where in the body does bacteria break urea into ammonia which is absorbed?

A

The small intestine (urea can diffuse in)

50
Q

The C skeletons of Ketogenic amino acids produce _____.

What do glucogenic C skeletons produce?

What are the glucogenic products used in?

A

Acetyl CoA

glutamic acid
aspartic acid
serine
- gluconeogenesis

51
Q

What size are amino acids which are both ketogenic and glucogenic?

A 
Large amino acids;
phenylalanine 
tyrosine
tryptophan 
isoleucine
threonine
52
Q

Which reaction does all these enzymes perform?

  • D amino acid oxidase
  • Glutaminase
  • Glutamate dehydrogenase

Which toxic by-product do they produce?

A

Deamination (removal of amino group)

Ammonia, NH3

53
Q

Why is glutamate dehydrogenase enzyme in aa metabolism?

Where is the enzyme?

A

Reversible reaction; catalyses amino acid synthesis and breakdown

glutamate <> alpha- ketoglutarate

54
Q

Which processes produce Ammonia?

A

Deamination by

  • glutaminase and
  • glutamate dehydrogenase
  • D amino acid oxidase
  • Produced by bacteria in the gut from urea
55
Q

Glutaminase reaction

A

Deamination

- glutamine to glutamate (acid) and NH3

56
Q

Glutamate dehydrogenase

A

Deamination
- glutamate to alpha- ketoglutarate

Glutamate, NAD+ and water&raquo_space;
a- Ketoglutarate, NH4+, NADH and H+

57
Q

How does ammonium become ammonia?

A

NH4+ and OH-
>
NH3 + H2O

MEH (9 decks)

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