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K1-MBOD Block 5 > Amino Acid Nitrogen > Flashcards

Amino Acid Nitrogen Flashcards

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1
Q

What is a zymogen?

A

larger, inactive form of a protease that is cleaved to make its active form.

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2
Q

Where is pepsin most likely to be active?

A

Stomach

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3
Q

Where would trypsin, chymotrypsin, elastase, and carboxypeptidase most likely be active?

A

small instestine

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4
Q

Which digestive enzyme plays a key role in activating other protein-digesting enzymes?

A

trypsin

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5
Q

Where is pepsinogen secreted?

A

chief cells of stomach

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6
Q

Where is HCl in the stomach produced?

A

Gastric parietal cells

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7
Q

Which of these proteins are likely be denatured in low pH environments?

pepsin, trypsin, chymotrypsin, elastase, carboxypeptidase

A

All except pepsin, which is a stomach enzyme that remains active in acidic pH’s.

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8
Q

What mechanism raises the pH of the small intestine to ensure pancreatic digestive enzymes remain active?

A

bicarbonates are released into small intestine to raise pH.

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9
Q

Which enzyme cleaves pepsinogen to produce its active form, pepsin?

A

Pepsinogen is autocatalytic. HCl in the stomach changes its structural conformation and allows it to cleave and activate itself.

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10
Q

Where is bicarbonate secreted from?

A

exocrine pancreas

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11
Q

What cleaves trypsinogen to form active trypsin which then activates the other pancreatic proteases?

A

enteropeptidase (also called enterokinase)

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12
Q

Which of these enzymes is the most specific?

tyrpsin, chymotrypsin, elastase

A

trypsin is most specific, cleaving peptide bonds from lysine and arginine

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13
Q

What type of residues does chymotrypsin prefer?

A

Residues that contain hydrophobic or acidic AA’s

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14
Q

Which protease would likely cleave alanine, glycine, or serine (AAs with small side chains)?

A

Elastase. Also cleaves elastin

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15
Q

Which protease is commonly found in neutrophils?

A

Elastase

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16
Q

Define endopeptidase.

A

digestive proteases that hydrolyze peptide bonds within chains. Pepsin, trypsin, chymotrypsin, and elastase are all endopeptidases.

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17
Q

Define exopeptidase.

A

protease that removes either the amino acid at the N-terminus or C-terminus

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18
Q

What is an exopeptidase that works on the N-terminus called?

A

aminopeptidase

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19
Q

What is an exopeptidase that works on the C-terminus called?

A

carboxypeptidase

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20
Q

What might happen if the inhibitor for trypsinogen activation were defective?

A

Trypsin could activate the other pancreatic proteases while still in the pancreas, causing digestion of intracellular pancreatic proteins, leading to pancreatitis.

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21
Q

Which exopeptidase preferentially releases hydrophobic amino acids form the carboxy ends of peptide chains?

A

Carboxypeptidase A.

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22
Q

Where are exopeptidases produced?

A

intestinal epithelial cells

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23
Q

Where are exopeptidases most active?

A

In the brush border

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24
Q

What two transport methods allow absorption of AAs from intestinal lumen?

A

Secondary active Na+ depedent transport

Facilitated diffusion.

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25
Which AA's does carboxypeptidase B preferentially release form peptide chains?
Arginine and lysine (because they are basic AA's) when they are on the C-terminus.
26
What is the primary method of AA absorption in the intestinal lumen?
Na+ dependent transport proteins in luminal membrane of intestinal cell brush border
27
Do intestinal epithelium cells have high or low cellular Na+?
Low. Na-K-ATPase pump forces them out of the cell continually, generating a gradient.
28
Which transport mechanism moves AAs from intestinal epithelium cells to the interstitial fluid? Is this transport uni or bidirectional?
Facilitated transporters in the serosal membrane. During fasting states, AAs are moved from the interstitial fluid back into the cells across the serosal membrane to provide energy to the cell (bidirectional)
29
Why do patients with cystinuria and Hartnup disease have hyperaminoaciduria but not hyperaminoacidemia?
Patients with Hartnup disease and cystinuria have defective transport proteins in both intestine and kidney. Patients do not absorb AAs at normal rate and also do not reabsorb AAs from the glomural filtrate back into blood at normal rate, causing low blood AA. Because the glomural filtrate AAs are not reabsorbed, the urine has high AA concentration (hyperaminoaciduria)
30
What is the primary method of transport for AA's into body cells (not renal or intestinal)?
Na+-dependent cotransporters. This allows cells from other tissues to concentrate AAs from blood.
31
Where is the N system for glutamine uptake present in the body?
the liver. not present in other tissues
32
Describe autophagy.
Intracellular components are surrounded by membranes that then fuse with lysosomes for degredation. This is triggered by cell starvation, and recycles old proteins to generate AAs for synthesis of new AAs and temporary fasting survival.
33
Which AA does ubiquitin bind to on peptide chains
Lysine
34
What happens to a protein that has been bound by ubiquitin?
Ubiquitin marks a protein for proteosome degradation.
35
A region of a protein rich in what AAs would cause it to have a short half-life? What system is it likely to be degraded by?
PEST - proline, glutamate (E), serine, and threonine These sequences make an AA likely to be degraded by the ubiquitin-proteosome system rather rapidly, causing short half-lives.
36
Would you expect decreased plasma AA levels in a patient who had a defect in the intestinal and renal transporter for cystine and other basic AAs?
No, even though there will be decreased digestive absorption and increased excretion, these are non-essential AAs and will be synthesized from other sources to maintain plasma levels.
37
Describe Hartnup disease.
Defect to intestinal and renal AA transport that involves neutral, essential AAs (isoleucine, leucine, phenylalanine, threonine, tryptophan and valine) as well as nonessential alanine, serine and tyrosine. Usually patients develop photosesnsitive rash and pellagra (lack of Vitamin B3/Niacin) as well as hyperaminoacidurea. Treatment by administering megadoses of niacin and other vitamins.
38
What cycle is necessary for the production of glutathione? What does glutathione do?
gamma-glutamyl cycle. | Protects cells from oxidative damage
39
What enzyme reacts with an extracellular AA to transport it across the membrane and form a gamma-glutamyl amino acid?
gamma-glutamyl transpeptidase
40
What AA is the gamma-glutamyl cycle involved in salvaging?
cysteine. The cycle uses this to form Glutathione
41
What AAs are used to form Glutathione?
glutamate, cysteine and glycine
42
Describe Kwashiorkor.
Wasting disease. Deficiency of protein in diet that is adequate in calories causes muscle wasting and decreased plasma proteins (especially albumin). This causes edema, distended abdomens. Digestive enzymes can no longer be formed due to lack of essential AAs, leading to further nutritional problems.
43
List the essential AAs.
PVT TIM HALL. | Phenylalanine-Valine-Tryptophan, Threonine-Isoleucine-Methionine, Histidine-Arginine-Lysine-Leucine
44
List the ketogenic AAs.
LL - leucine and lysine
45
List the AAs that are both ketogenic and glucogenic.
PITTT (Pitt with three T's) - Pheynylalanine, Isoleucine, Threonine, Tyrosine, Tryptophan
46
What happens to excess digested protein?
Protein is broken down to AAs. If these AAs are not used for protein synthesis, they will be converted to glucose or triacylglycerols
47
Where is amino acid nitrogen converted to urea?
Liver
48
Where do the two nitrogens in urea come from?
NH4+ and nitrogen of aspartate
49
What two major AA's are formed from muscle breakdown during fasting? Where is each of these processed for energy production?
Glutamine and Alanine. Glutamine is converted to alanine in the kidney. Alanine is processed in the liver to form glucose, ketone bodies, and urea. Note, there are other AAs formed and they enter bloodstream to be processed by liver.
50
What happens to the triacylglycerides formed from excess protein digestion?
They are packed and secreted from the liver as VLDLs.
51
What is transamination concerning AA's?
removal of nitrogen from AA's
52
What happens to the nitrogen lost from an AA in transamination?
N is transfered to alpha-ketoglutarate to form glutamate
53
What does an AA become after it loses a Nitrogen in transamination?
the corresponding alpha-keto-acid. | for aspartate this is OAA
54
Which AAs undergo transamination?
all except threonine and lysine
55
Which is the dominant form at physiological pH: NH3 or NH4+?
equilibrium favors NH4+ by a factor of 100 at physiological pH (Note, NH3 is present in the body though because it is able to pass through membranes)
56
What is pyridoxal phosphate (PLP)?
A cofactor in transamination reaction
57
What enzyme is used to form NH4+ from glutamate? What is used as a cofactor? Where does the reaction occur?
glutamate dehydrogenase. Either NAD+ or NADP+ is used as a cofactor. Reaction occurs in mitochondria of most cells.
58
What enzyme catalyzes the deamination of serine and threonine?
serine dehydratase
59
What AAs have R group amides that can be released as NH4+?
Glutamine and Asparagine-
60
What enzyme catalyzes the deamination of Asn? What is formed?
asparaginase. Yields aspartate and NH4+
61
What reaction does glutaminase catalyze and what are the products?
Deamination of glutamine to form glutamate and NH4+
62
How is glutamine synthesized?
Glutamane synthetase fixes ammonia to glutamate using ATP. This occurs in the cytoplasm of cells.
63
What two AAs carry the NH4+ before they it is used to form urea?
Glutamate and Aspartate
64
What are the two major carriers of NH4+ in blood?
Glutamine and Alanine
65
Where is glutamine synthatase located?
In the cytoplasm of most cells
66
If ammonia levels are high and start to leave the liver before they can be converted to urea, what happens to keep ammonia levels from becoming toxic?
Excess ammonia is converted to glutamine by glutamine synthatase to prevent free ammonia buildup in circulation
67
What do NH4+, bicarbonate, and 2 ATP react together to form? What enzyme is involved in catalyzing the reaction and where is it found?
carbomoyl phosphate. | carbamoyl phosphate synthatase I (CPS1) found in the mitochondria of liver and intestine
68
What does carbamoyl phosphate react with in the urea cycle and what does it form?
carbamoyl phosphate reacts with ornithine to form citrulline. This occurs in the mitochondria
69
How does citrulline get across the mitochondrial membrane?
It is exchanged for cytoplasmic ornithine.
70
What does citrulline react with in the cytoplasm and what does it form?
Citrulline reacts with aspartate to produce arginosuccinate. Catalyzed by argininosuccinate synthetase and powerd by ATP--> AMP
71
What does argininosuccinate lyase do?
Argininosuccinate lyase cleaves argininosuccinate to form fumarate and arginine
72
In the urea cycle, what happens to the fumarate after arginosuccinate is cleaved to form arginine and fumarate?
Fumarate is converted to malate using fumarase. The malate is then put into the TCA cycle to form OAA, which can be transaminated to aspartate (recycled)
73
What happens to the arginine formed by the cleavage of argininosuccinate?
Arginine is cleaved by arginase to produce urea and regenerate ornithine
74
What type of regulation does the urea cycle have (what is it called)?
Feedfoward regulation (as more substrate ammonia appears, more urea is formed)
75
What does NAG do?
it allosterically activates CPSI to upregulate the urea cycle by producing more carbomoyl phosphate
76
What two reactions would high levels of arginine in the liver stimulate?
Synthesis of NAG | Produces more onithine
77
Why is ammonia toxic to the brain?
It depletes TCA cycle intermediates and ATP in the CNS by binding with ketoglutarates to form glutamate and glutamine. GABA levels increase
78

| Why is ammonia toxic to the brain?

It depletes TCA cycle intermediates and ATP in the CNS by binding with ketoglutarates to form glutamate, which is rapidly consumed to form glutamine. This leads to low ATP, low glutamate, and high glutamine.

In addition, high ammonia levels increase GABA (a neuro inhibitor) ligand binding properties and concentration in brain.

79

| What treatment would be given to a patient with a urea cycle enzyme defect?

massive arginine supplementation to counteract the inability to regenerate urea cycle intermediates and form argininosuccinate

K1-MBOD Block 5 (2 decks)

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