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2. Biochemistry > Week 9 (protein metabolism) > Flashcards

Week 9 (protein metabolism) Flashcards

1
Q

Define catabolism

A

Breaking down complex compounds into simpler ones

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2
Q

Define anabolism

A

Building complex compounds from simpler ones.

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3
Q

What is metabolism?

A

Catabolism and anabolism combined

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4
Q

Explain the process of protein turnover

A

Proteins are turned over in the body all the time.
Old ones are broken down and new ones are made.

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5
Q

How many grams of protein turnover happens in a day in healthy individuals?

A

300-500g

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6
Q

What part of an amino acid makes up the ammonia?

A

Amino group

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7
Q

Which parts of an amino acid make up the carbon skeleton?

A

Side chain
Carboxyl group

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8
Q

What is the fate of amino acids?

A

Excess amino groups are excreted into urea.
The whole molecule is a building block for nitrogenous compounds.
The carbon skeleton is converted into metabolic intermediates.

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9
Q

Where are most amino acids metabolised?

A

Liver

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10
Q

What happens to ammonia?

A

Some ammonia generated is recycled and the rest is excreted via urea.

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11
Q

What happens to excess ammonia?

A

Excess ammonia generated in other tissues travels to liver to be metabolised.

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12
Q

Name the four amino acids in NH4+ metabolism

A

Glutamine
Glutamate
Alanine
Aspartate

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13
Q

How do carbon skeletons enter the citric acid cycle?

A

Via different intermediates

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14
Q

Describe glucogenic amino acids

A

Amino acids that can be converted into glucose and include most amino acids.

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15
Q

Describe ketogenic amino acids

A

Amino acids that can only be converted into acetyl-CoA and acetoacetyl-CoA.
Exclusively lysine and leucine

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16
Q

Why must essential amino acids be provided by the diet?

A

Essential amino acids cannot be synthesised by the body.

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17
Q

Can non-essential amino acids be synthesised by the body?

A

Yes - they can be synthesised by the body even under stress.

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18
Q

What is the first step in amino acid metabolism (transamination)?

A

NH4+ from one amino acid is transferred to alpha-ketoglutarate to make glutamate.

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19
Q

What is the effect of transamination?

A

NH4+ from many different amino acids are ‘collected; as glutamate.
Glutamate acts as NH4+ donor for biosynthetic/excretory pathways.

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20
Q

What is transamination catalysed by?

A

Aminotransferase (transaminase) enzymes.
Different aminotransferases for different amino acids.

21
Q

Describe PLP

A

PLP is derived from vitamin B6.
It is a carrier of amino groups at the active site of aminotransferases.
PLP is covalently bound to the enzyme at the active site.

22
Q

Name the two forms of PLP

A

Aldehyde = pyridoxal phosphate
Amine = pyridoxamine phosphate

23
Q

Describe the transamination process

A
  1. amino acid substrate donates its amino group to pyridoxal phosphate at the active site of aminotransferase.
  2. that deaminated amino acid then leaves the active site, which now has pyridoxamine phosphate as a coenzyme.
  3. the second substrate, alpha-ketoglutarate, enters the active site.
  4. the amino group on pyridoxamine phosphate is then donated to alpha-ketoglutarate forming a glutamate, which can then dissociate from the active site.
  5. this leaves behind pyridoxal phosphate and an unoccupied active site ready to catalyse the next reaction.
24
Q

What happens to glutamate in the liver?

A

Glutamate undergoes oxidative deamination in the liver.
In hepatocytes glutamate is transported from the cytosol to the mitochondria where it undergoes oxidative deamination.
Enzyme: glutamate dehydrogenase
Coenzyme: NAD+ or NADP+.

25
Q

What is glutamine?

A

Excess ammonia from other tissues is transported to the liver as glutamate.

26
Q

What aminates glutamate?

A

An enzyme glutamine synthetase in a two-step process.

27
Q

What does glutaminase do?

A

Removes NH4+ from the mitochondria of hepatocytes

28
Q

Are the urea cycle and citric acid cycle dependent or independent?

A

Independent

29
Q

How doe the urea cycle and citric acid cycle communicate?

A

Via intermediates:
- malate and glutamate transported into the mitochondrial matrix.
- aspartate transported into cytosol

30
Q

How many compounds do amino acid converge on during catabolic pathways?

A

6

31
Q

Name the two types of amino acids

A

Glucogenic
Ketogenic

32
Q

What can glucogenic amino acids be used to make?

A

Glucose via gluconeogensis

33
Q

What can ketogenic amino acids be used to make?

A

Acetyl-CoA

34
Q

What does biotin (coenzyme) transfer?

A

Carbon as carbon dioxide (highly oxidised)

35
Q

What does S-adenosylmethionine transfer?

A

Carbon as -CH3 (highly reduced)

36
Q

What does tetrahydrofolate transfer?

A

Carbon in several oxidative states.

37
Q

Name the coenzymes involved in transferring a carbon from amino acid susbtrtaes

A

Biotin
S-adenosylmethionine
Tetrahydrofolate

38
Q

How many amino acids converge on pyruvate during catabolism?

A

6

39
Q

How many amino acids converge on acetyl-CoA during catabolism?

A

7

40
Q

How many amino acids converge on a-ketoglutarate during catabolism?

A

5

41
Q

How many amino acids converge on succinyl-CoA during catabolism?

A

4

42
Q

What are oxidised to oxaloacetate?

A

Asparagine
Aspartate

43
Q

How is asparagine converted to aspartate?

A

Through a deamination reaction catalysed by asparaginase.

44
Q

How is aspartate converted to oxaloacetate?

A

Through transamination with alpha-ketoglutarate being aminated to glutamate at the same time.

45
Q

What is oxaloacetate converted to in mammals?

A

Converted to malate then transported into the mitochondria where it can enter the citric acid cycle.

46
Q

What happens to phenylalanine hydroxylase in PKU patients?

A

The phenylalanine hydroxylase is non-functioning which means catabolism proceeds by an alternative pathway.

47
Q

What happens in PKU patients?

A

Phenylalanine and phenylpyruvate accumulate in blood and tissues, which impairs normal brain development.

48
Q

What happens in patients with maple syrup urine disease?

A

They have defective branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex.
They produce urine with a characteristic odour, due to build up of alpha-keto acids.

49
Q

What happens in patients with methylmalonic acidaemia (MMA)>

A

They lack functioning methyl-malonyl-CoA mutase enzyme, which leads to a build up of a toxic intermediate.

2. Biochemistry (7 decks)

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