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Biochem Exam 3 > 31 - Amino Acid Catabolism > Flashcards

31 - Amino Acid Catabolism Flashcards

1
Q

In mammals, amino acids derived from the degradation of dietary proteins or the turnover of cellular proteins are deaminated, and the ________ is used for biosynthetic pathways or excreted as urea. The remaining _______ skeletons are metabolized by energy conversion pathways to generate ATP, glucose, fatty acids, or ketone bodies.

A

Nitrogen

Carbon

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2
Q

The _______ has low pH that denatures (unfolds) proteins and activates pepsin (pepsin likes low pH).

A

Stomach

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3
Q

In the small intestines, enteropeptidase (cleaves in middle) in the duodenum cleaves trypsinogen, activating ________ (hydrolyzes peptide bonds).

A

Trypsin

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4
Q

In the small intestines, __________ are exopeptidases, which cleave or “chew” from the N-term (ends).

A

Aminopeptidases

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5
Q

In the small intestines, _________ break apart dipeptides.

A

Dipeptidases

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6
Q

After being broken down, amino acids, dipeptides, and tripeptides are able to be transported into the ______.

A

Cells

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7
Q

Cells have 2 primary structures that degrade proteins, which are…

A

Proteasome

Lysosome

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8
Q

The degrades proteins into bite-size chunks, not individual amino acids.

A

Proteasomes

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9
Q

______ Rule states that the ________ amino acid identity determines the rate of ubiquitination.

A

N-end

N-terminal

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10
Q

Proteins with these type of N-terminal residues last a long time (>20 hours).

A

Small and nonpolar

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11
Q

Proteins with these type of N-terminal residues last from 2-30 minutes (intrinsically destabilizing residues).

A

Large

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12
Q

Proteins with these type of N-terminal residues last from 3-30 minutes (destabilizing residues after chemical modification).

A

Polar/Charged

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13
Q

This is a protein that binds to the proteasome.

A

Ubiquitin

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14
Q

Ubiquitinated proteins are fragmented in the ________. Degradation is a form of regulation.

A

Proteasome

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15
Q

T/F. Ubiquitin is reusable.

A

True

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16
Q

The proteasome costs _______ to remove ubiquitin and degrade proteins.

A

ATP

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17
Q

The proteasome is an _______, and has a ______ piece that is the catalytic/proteolytic domain and ______ piece that is the regulatory domain.

A

ATPase
20S
19S

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18
Q

S stands for Svedberg or ________ units. S units are NOT proportional to size.

A

Sedimentation

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19
Q

20S + 19S = ______ proteasome

20S + 19S + 19S = ______ proteasome

A

26S

30S

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20
Q

Cytosolic ________ further degrade the peptide fragments produced in the proteasome. Eventually, we are left with a pool of individual amino acids.

A

Proteases

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21
Q

What are the 3 things we can do with individual amino acids?

A

Reduce - Dispose of nitrogen through the urea cycle
Reuse - Make new proteins
Recycle - Repurpose the carbon skeletons

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22
Q

What is the first thing we have to do before we can reduce or recycle amino acids?

A

Deaminate the amino acids (leaves behind carbon skeleton)

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23
Q

Most amino acids follow a 2-enzyme mechanism for deamination (normal pathway), which is…

A

Aminotransferase + Glutamate dehydrogenase

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24
Q

Serine and Threonine are deaminated by the action of a single enzyme (special pathway) called…

A

Dehydratase

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25
Q

For deamination (normal pathway), aminotransferases and dehydratases are unique per amino acid but the coenzyme is always…

A

Pyridoxal phosphate

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26
Q

In direct deamination (serine and threonine only), water is removed through ________ then water is added back to remove the NH4+ in ________.

A

Dehydration

Deamination

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27
Q

Serine is deaminated to form…

A

Pyruvate

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28
Q

Threonine is deaminated to form…

A

Alpha-keotbutyrate (intermediate)

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29
Q

In the normal pathway of deamination, step 1 involves aminotransferases making _______.

A

Glutamate

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30
Q

T/F. The normal pathway of deamination is not reversible.

A

False. The pathway is very reversible.

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31
Q

There are two special aminotransferases, this is the name for the Aspartate Aminotransferase (AST).

A

Serum Glutamate-Oxaloacetate Transaminase (SGOT)

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32
Q

SGOT catalyzes the interconversion of _______ and _______.

A

Aspartate

Oxaloacetate

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33
Q

Alpha-amino acid + ___________ = ___________ + Glutamate (*Enzyme is aminotransferase)

A

Alpha-ketoglutarate

Alpha-keto acid

34
Q

There are two special aminotransferases, this is the name for the Alanine Aminotransferase (ALT).

A

Serum Glutamate-Pyruvate Transaminase (SGPT)

***Not reversible

35
Q

SGPT catalyzes the interconversions of ________ and ________.

A

Alanine

Pyruvate

36
Q

In the normal pathway of deamination step 2, ________ _______ releases an ammonium (NH4+) ion.

A

Glutamate dehydrogenase

37
Q

What is put into the reaction for step 2, and what is released?

A

NAD+; H2O

NADH; NH4+

38
Q

What is formed at the end of the normal deamination pathway?

A

Alpha-ketoglutarate

39
Q

What is the intermediate in step 2 of the normal deamination pathway?

A

Schiff-base intermediate (after NAD+, before H2O)

40
Q

This is a toxic byproduct of amino acid catabolism.

A

NH4+

41
Q

NH4+ can be converted to ______ in the liver, which is then transported to the kidneys to be excreted from the body.

A

Urea

42
Q

Urea is composed of 4 pieces, which are…

A

2 amines
1 oxygen
1 carbon

43
Q

Carbamoyl Phosphate Synthetase I (CPSI) combines CO2 and NH3 to make ________ ________, using 2 ATP. Creation of this is the committed step of the urea cycle.

A

Carbamoyl Phosphate

44
Q

______ is an allosteric CPSI.

A

NAG

45
Q

Ornithine and Citrulline are __________ amino acids.

A

Nonproteinogenic

46
Q

________ must move into the mitochondria to combine with Carbamoyl Phosphate to form ________, which is then exported to the cytoplasm.

A

Ornithine

Citrulline

47
Q

In the urea cycle, Aspartate donates an NH3 at the cost of 2 ATP-equivalents. The rest of Aspartate is ________, and the amino acid _______ is created (from aspartate and citrulline).

A

Fumarate

Arginine

48
Q

In the urea cycle, Fumarate is converted to _________ which is used in the TCA cycle or it is converted back to Aspartate by the SGOT aminotransferase.

A

Oxaloacetate (OAA)

49
Q

________ is created when urea is removed from Arginine. The addition of _______ when cleaving Arginine adds the final O of urea.

A

Ornithine

Water

50
Q

At the end of the urea cycle, ornithine enters into the _________ and continues the cycle again.

A

Mitochondria

51
Q

Adult humans produce about ______ grams of urea each day, accounting for about ______ percent of ATP consumption in the liver.

A

30

50

52
Q

Aquatic animals can excrete _______ directly, so amphibians only express urea cycle enzymes at metamorphosis.

A

Ammonia

53
Q

Amino acids can be degraded to 7 different molecules, which are…

A 
Pyruvate 
OAA
Alpha-ketoglutarate
Succinyl-CoA
Fumarate
Acetyl-CoA
Acetoacetate
54
Q

Amino acids are ________ if they are degraded into intermediate molecules that can feed through gluconeogenesis to reform Glucose.

A

Glucogenic

55
Q

Amino acids are ________ if they are degraded into intermediate molecules that can be used to create ketone bodies.

A

Ketogenic

56
Q

Many amino acids can be degraded to more than one possible molecule. Sometimes, amino acids can be both ________ and ________.

A

Glucogenic

Ketogenic

57
Q

In Fate 1, amino acid carbon skeletons are converted to _______.

A

Pyruvate

58
Q

What are the amino acids in Fate 1 that are converted to pyruvate?

A 
Serine
Threonine 
Glycine
Alanine
Cysteine

***CATSG

59
Q

Serine is ________ directly to pyruvate.

A

Deaminated

60
Q

Threonine is converted to ________ after deamination, which then converted to Serine and deaminated directly to pyruvate.

A

Glycine

61
Q

Glycine is converted to ________ in a THF-dependent reaction. This is then deaminated directly to pyruvate.

A

Serine

62
Q

Alanine is exchanged with pyruvate by the action of ______.

A

SGPT

63
Q

Cysteine must be ________ and ________ to form pyruvate.

A

Deaminated

Desulfonated

64
Q

In Fate 2, amino acid carbon skeletons are converted to ________.

A

Oxaloacetate (OAA)

65
Q

What are the amino acids in Fate 2 that are converted to OAA?

A

Asparagine
Aspartate

***ND

66
Q

Asparagine is ________ first from the side chain to form _____ and Aspartate. Aspartate is then exchanged with OAA by the action of ______.

A

Deaminated
NH4+
SGOT

67
Q

In Fate 3, amino acid carbon skeletons are converted to…

A

Alpha-ketoglutarate

68
Q

What are the amino acids in Fate 3 that are converted to Alpha-ketoglutarate?

A 
Glutamine 
Proline
Arginine 
Histidine 
Glutamate

***PHREQ

69
Q

Glutamine is deaminated first from the side chain to form ______ and ________. This is then converted to alpha-ketoglutarate by Glutamate Dehydrogenase.

A

NH4+

Glutamate

70
Q

Proline, Arginine, and Histidine can all be converted to ________, which is then converted to alpha-ketoglutarate by Glutamate Dehydrogenase.

A

Glutamate

71
Q

Glutamate is converted to Alpha-ketoglutarate by…

A

Glutamate Dehydrogenase

72
Q

In Fate 4, amino acid carbon skeletons are converted to _________.

A

Succinyl-CoA

73
Q

Which amino acids are converted to Succinyl-CoA in Fate 4?

A

Methionine
Valine
Isoleucine

***MIV

74
Q

Methionine, Valine, and Isoleucine can be converted into ________ in a B12-dependent pathway. Part of Methionine’s conversion is through S-Adenosylmethionine (SAM). Propionyl-CoA is then converted to Succinyl-CoA.

A

Propionyl-CoA

75
Q

Even though the conversion of Propionyl-CoA to Succinyl-CoA is used in the Beta-oxidation of fatty acids with an odd number of carbons, we care more that Succinyl-CoA can be used in the…

A

TCA Cycle

76
Q

In Fate 5, amino acid carbon skeletons are converted to _______.

A

Fumarate

77
Q

In Fate 6, amino acid carbon skeletons are converted to ________.

A

Acetyl-CoA

78
Q

In Fate 7, amino acid carbon skeletons are converted to ________.

A

Acetoacetate

79
Q

The remaining amino acids that follow Fates 5, 6, or 7 are more complex. Oftentimes they are split to multiple fates, such as these two amino acids…

A

Phenylalanine

Tyrosine

80
Q

What are the ketogenic amino acids?

A

Leucine

Lysine

81
Q

What are the BOTH glucogenic and ketogenic amino acids?

A 
Isoleucine 
Phenylalanine 
Threonine 
Tryptophan 
Tyrosine

Biochem Exam 3 (10 decks)

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