Biochemistry > Week 14 > Flashcards

Week 14 Flashcards

(52 cards)

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1
Q

What is the amino acid pool?

A

Free amino acids in cells, blood, and extracellular fluid

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2
Q

Are amino acids stored in the body?

A

No, excess amino acids are degraded

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3
Q

Sources of amino acids in the pool?

A

Dietary protein, endogenous protein degradation, amino acid synthesis

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4
Q

What is protein turnover?

A

Continuous synthesis and degradation of body proteins

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5
Q

Main systems for endogenous protein degradation?

A

Ubiquitin–proteasome system (cytosol) and lysosomal system

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6
Q

Enzyme that begins protein digestion in stomach?

A

Pepsin

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7
Q

What activates pepsinogen?

A

HCl and autocatalysis

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8
Q

Major pancreatic proteases?

A

Trypsin, chymotrypsin, elastase, carboxypeptidases

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9
Q

What activates trypsinogen?

A

Enteropeptidase (enterokinase)

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10
Q

Final products absorbed by intestine?

A

Free amino acids, dipeptides, tripeptides

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11
Q

First step in amino acid catabolism?

A

Removal of amino group (transamination)

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12
Q

What happens to the carbon skeleton of amino acids?

A

Converted to metabolic intermediates (glucose, ketone bodies, CO₂)

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13
Q

What is transamination?

A

Transfer of amino group from amino acid to α-ketoglutarate

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14
Q

Enzymes that catalyze transamination?

A

Aminotransferases (AST, ALT)

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15
Q

Required coenzyme for transamination?

A

Pyridoxal phosphate (vitamin B6)

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16
Q

Major amino acid formed by transamination?

A

Glutamate

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17
Q

What is oxidative deamination?

A

Removal of amino group from glutamate as free ammonia

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18
Q

Enzyme responsible?

A

Glutamate dehydrogenase

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19
Q

Where does oxidative deamination occur?

A

Liver and kidney mitochondria

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20
Q

What is produced from oxidative deamination?

A

Ammonia and α-ketoglutarate

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21
Q

Why must ammonia be transported safely?

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A

Ammonia is toxic to the brain

22
Q

Main nitrogen transport molecules?

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A

Glutamine and alanine

23
Q

Why is glutamine important for nitrogen transport?

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A

Carries two nitrogen atoms safely in blood

24
Q

Enzyme that forms glutamine?

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A

Glutamine synthetase

25
Organs that use glutamine for ammonia production?
Liver, kidney, intestine
26
Kidney role of glutamine?
Produces NH₄⁺ for acid–base regulation
27
What is the alanine-glucose cycle?
Transport of nitrogen from muscle to liver as alanine
28
In muscle: pyruvate + amino group → ?
Alanine
29
In liver: alanine → ?
Pyruvate + ammonia
30
Purpose of alanine-glucose cycle?
Removes nitrogen from muscle and provides glucose
31
What is nitrogen balance?
Nitrogen intake − nitrogen loss
32
Positive nitrogen balance means?
Intake > loss (growth, pregnancy, recovery)
33
Negative nitrogen balance means?
Loss > intake (starvation, illness, trauma)
34
Nitrogen balance in healthy adults?
Zero (equilibrium)
35
Why is ammonia toxic to the brain?
Depletes α-ketoglutarate → impairs TCA cycle
36
Effect of ammonia on neurotransmitters?
Alters glutamate and GABA levels
37
Purpose of urea cycle?
Convert toxic ammonia into urea for excretion
38
Where does urea cycle occur?
Liver
39
Cellular locations of urea cycle steps?
First 2 in mitochondria, remaining in cytosol
40
Rate-limiting enzyme of urea cycle?
Carbamoyl phosphate synthetase I (CPS I)
41
What is NAG?
Allosteric activator of CPS I
42
How is NAG synthesized?
From acetyl-CoA and glutamate
43
What increases NAG production?
Arginine and high-protein diet
44
Two nitrogen atoms in urea come from where?
Free ammonia and aspartate
45
Both nitrogen atoms originate from which amino acid?
Glutamate
46
ATP required per urea molecule?
3 ATP (4 high-energy bonds)
47
What is hyperammonemia?
Elevated blood ammonia
48
Causes of hyperammonemia?
Urea cycle defects, liver failure
49
Symptoms of hyperammonemia?
Vomiting, tremors, cerebral edema, coma
50
Why is hyperammonemia life-threatening?
Brain toxicity and ATP depletion
51
Why do urea cycle defects cause neurologic symptoms?
Ammonia impairs neuronal energy metabolism
52
Why is the liver essential for nitrogen disposal?
It contains all urea cycle enzymes
Biochemistry
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