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Physiology > Metabolism II > Flashcards

Metabolism II Flashcards

1
Q

3 sources of free AAs?

A

1- injested protein
2- endogenous protein
3- biosynthesis

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2
Q

T/F biosynthesis of AAs is sufficient to allow net synthesis of protein

A

FALSE-

ingest 55 g + biosynthesize 300g = stored as protein 300 g + excrete AAs 55 g

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3
Q

use of free amino acids

A

1- to make protein
2- incorporated into urea & excreted
3- carbon skeleton used for energy
4- used to make puridine/pyrimidine/heme

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4
Q

describe nitrogen balance

A

nitrogen ingested (protein) - nitrogen excreted (urea) = 0

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5
Q

things that would cause positive nitrogen balance

A

child growth, pregnancy, body building

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6
Q

things that would cause negative nitrogen balance

A

starvation, vegetarianism, trauma, infection, cancer, burn, sepsis, surgery

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7
Q

what is transamination?

A

the transfer of amino group to alpha keto gluterate to form glutamate

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8
Q

what cofactor is required for transamination?

A

pyridoxal phosphate, derivative of B6

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9
Q

what is glutamate broken down into to form urea?

A

aspartate & ammonia

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10
Q

how is glutamate broken down into aspartate? what is the key enzyme?

A

glutamate + oxaloacete = akg + aspartate

aspartate transaminase

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11
Q

how is glutamate broken down into ammonia? what is the key enzyme?

A

glutamate + NDP+ + H20= NH4+ + akg + NADPH

glutamate dehydrogenase

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12
Q

where does urea biosynthesis primarily occur?

A

liver

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13
Q

what are the major components of the urea cycle?

A
  • ornithine + cabamoyl phosphate - citrulline- argino-succinate- arginine- urea
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14
Q

what is the 1* regulated enzyme in the urea cycle?

A

caramoyl phosphate synthase I, regulated by N-acetyl glutamate (produced from glutamate)

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15
Q

what enzyme converts arginine to urea?

A

arginase

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16
Q

2 things that go into urea cycle

A

cabamoyl phosphate, aspartate

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17
Q

two things spit out of urea cycle

A

urea, fumerate

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18
Q

which two AAs carry nitrogen to liver when AA metabolism occurs in other tissues?

A

alanine & glutamine

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19
Q

difference between glucogenogenic & ketogenic carbon skeletons?

A

glucogenogenic- yields CAC intermediates, or pyruvate

ketogenic- yields acetyl coa, acetoacetyl coa, acetoacetate

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20
Q

what two factors causes AA storage after a meal?

A

stimulation of protein synthesis by AAs & insulin; inhibition of degradation by insulin

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21
Q

what happens to circulating AAs overnight?

A

decrease, lack of insulin allows for protein degradation & release of AAs for liver to use in glucogenogenesis

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22
Q

what is THF and what does it do?

A
  • reduced form of folic acid
  • involved in transfer of one-carbon units, on C-10 or C-5, in multiple metabolic pathways, including the biosynthesis of purines & thymidine (1 pyrimidine)
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23
Q

what disorder can a dietary deficiency of folate lead to?

A
  • reduced rate of DNA synthesis, erythrocyte precursors cells grow large but do not divide= megaloblastic anemia
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24
Q

what does the active form of THF required?

A

methylcobalamin (a derivative of B12)

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25
Q

purines?

A

adenine & guanine

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26
Q

pyrimidines?

A

cytosine & uracil & thymine

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27
Q

what can be build from purines & pyrimidines?

A
  • nucleoside- base + sugar (adenosine, guanosine)

- nucleotide- nucleoside + phosphate group (adenosine monophosphate)

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28
Q

difference between ribose and deoxyribose?

A

deoxyribose has no hydroxyl group on 2’ carbon

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29
Q

5 molecules that provide atoms in purine ring

A

aspartate glycine, glutamine, Co2, FH4 derivative (tetrahydrofolate)

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30
Q

step in purine synthesis that creates the activated form of ribose 5 phosphate?

A

r5p—– ribosephosphate pyrophosephate kinase — PRPP

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31
Q

step in purine synthesis which is the committed step, is highly regulated

A

PRPP—— glutamine PRPP amidotransferase —- 5-phosphoribosylamine

32
Q

branch point in purine synthesis

A

IMP can become AMP or GMP

33
Q

things that regulated the committed step in purine synthesis

A

AMP, GMP (negative)

PRPP (positive)

34
Q

how to target tumors using purine synthesis pathways

A

6-mercaptopurine- looks like adenine- tumor cells divide a lot, don’t recycle purines as much, drug inhibits enzymes in purine synthesis pathway

35
Q

3 things pyrimidines are synthesized from

A

aspartate, glutamine, CO2

36
Q

regulated step in pyrimidine synthesis

A

glutamine + CO2 + 2ATP —— carbamoyl phosphate synthetase II ——— carbamoyl phosphate

37
Q

T/F Pyrimidine ring is synthesized first and then attached to ribose 5 phosphate

A

TRUE

38
Q

precursor for synthesis of other pyrimidine nucleotides

A

UMP

39
Q

what turns ribonucleoside 5’ diphosphates to deoxyribonucleoside 5’ diphosphates?

A

ribonucleotide reductase

40
Q

when do deoxyribonucleotides increase in concentration?

A

during S-phase, when DNA synthesis occurs

41
Q

what does 5-flurouracil do?

A

converts to fDUMP, inhibits thymidylate synthase which now can’t convert dUMP to dTMP

42
Q

what does methotrexate do?

A

inhibits dihydrofolate reductaste, which turns dihydrofolate (TOXIC) into tetrahydrofolate after the dUMP-dTMP reaction

43
Q

what are the four bases DNA & RNA are broken down into?

A

uracil, thymine, guanine, hypoxanthine

44
Q

what is the key enzyme in the salvage pathway? what is the hypoxanthine reaction?

A

HGPRT-ase

hypoanthine + PRPP –> IMP + PPi

45
Q

what syndrome does a deficiency in HGPRT-ase result in?

A

Lesch-Nyhan (compulsive self-mutilation, gout)

46
Q

what happens to the 10% of purines which aren’t salvaged?

A

they’re metabolized to uric acid via xanthine/xanthine oxidase

47
Q

at the pH of urine, which form predominantes?

A

uric acid instead of urate (uric acid is less soluble than urate)

48
Q

the condition excessive production of uric acid can lead to? what drug treats this?

A

gout

allopurinol

49
Q

Tissues whqere heme biosynthesis is highest, what is the major use of heme in these tissues

A

bone marrow- hemoglobin

liver- cytochromes

50
Q

describe the general structure of heme

A

4 pyrrole molecules linked with bridging carbons for form a porphyrin ring with a ferrous ligand in the center

51
Q

2 molecules that contribute all the atoms for the organic portion of heme

A

carbon & nitrogen

52
Q

2 things used in the first step of the heme biosynthesis pathway + enzyme + product

A

succinyl Coa
glycine
ALA synthase
ALA

53
Q

difference between prophyrinogens and porphyrins

A

phorphyrinogens- no double bonds at bridging carbons, colorless

54
Q

T/F Porphyrinogens cannot be non-enzymatically oxidized to porphyrins

A

FALSE- can be oxidized by light

55
Q

how is heme synthesis regulated?

A

heme inhibits its own synthesis

56
Q

define porphyria

A

partial deficiency of an enzyme involved in heme biosynthesis increasing metabolic intermediates

57
Q

which two intermediates of heme biosynthesis are increased in acute intermittent porphyria

A

ALA & phorphobilinogen (PBG)

58
Q

what causes the photosensitivity in variegate porphia?

A

sunlight converts porphyrinogens into porphyrins which accumulate, further degraded by light, generating tissue-destroying singlet oxygen

59
Q

what is heme degraded by?

A

phagocytic cells of the reticuloendolthelial system (MM’s of spleen, bone marrow, liver)

60
Q

what are the constituents of hemoglobin?

A
  • heme- becomes Fe and bilirubin (cleared w/ albumin)

- globin- degraded into free amino acids

61
Q

what is the product of porphyrin degradation by heme oxygenase

A

biliverdin-9-alpha

62
Q

what is the product of biliverding reductase?

A

indirect/unconjugated bilirubin

63
Q

what is hyperbilirubinemia?

A

bilirubin in serum > 1 mg/dL

64
Q

when does hyperbilirubinemia become a clinical concern?

A

when unconjugated bilirubin rises above 25 mg/dL, it can enter the brain and cause toxic encephalopathy

65
Q

for hemolysis, biliary obstruction and hepatitis/cirrhosis, which forms of bilirubin predominate?

A

hemolysis- unconjugated
biliary obstruction- conjugated
hepatitis/cirrhosis- both

66
Q

what is the liver’s role in drug metabolism?

A

drugs & their metabolites are made hydrophilic in two reactions

67
Q

what are phase 1 reactions in the metabolism of drugs?

A

introduction of -OH or -COOH groups through oxidation

68
Q

what is the enzyme required for phase 1 reactions?

A

NADPH- cytochrome P450 reductase

69
Q

what happens phase 2 reactions in the metabolism of drugs?

A

products of phase 1 reactions are conjugated with compounds (e.g. glycine, sulfate) to make them more hydrophilic

70
Q

Which of the following is false?
A- The liver produces most of the circulating plasma proteins
B- The liver breaks down ketone bodies for energy
C- The liver plays an important role in the interconversion of amino acids
D- The liver stores both copper and iron

A

B- liver doesn’t have the enzymes to break down ketone bodies

71
Q

what is another name for vitamin A? what is it transported in?

A

retinol

transported in chylomicrons

72
Q

what role does the liver play in vit A use?

A

when rentinol levels decrease, the liver mobilizes vit A by hydrolyzing retinyl ester, which binds to retinol-binding protein and is secreted into the blood

73
Q

where are the major vitamin D stores found? how is it transferred?

A

adipose tissue and skeletal muscle

74
Q

what is the role of liver in the life of vitamin D?

A

liver activates vitamin D3 and synthesizes vitamin D binding protein

75
Q

where is the major store of vitamin K? why is it needed in the hepatocyte?

A

skeletal muscle

needed for synthesis of prothrombin (clotting)

Physiology (22 decks)

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