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Biochemistry II > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

describe 3 methods of regulating HMG CoA reductase activity.

A
  1. transcription: steroid response element w/ DNA enzyme
  2. translation: non-sterol mevolonate metabolites
  3. degradation: mem. portion senses mevolate/cholesterol
  4. phosphorylation: glucagon & insulin - energy: AMP dependent kinase
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2
Q

Describe the mechanism of ribonucleotide reductase.

A
  • Transfers a free radical from enzyme to substate
  1. Movement of unpaired electron from tyrosine on R2 to substrate
  2. Hydrogen removed from C3
  3. OH refection from C2 as H2O
  4. C2 reduction by sulfhydryls on R1
  5. Return hydrogen to C3
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3
Q

Identify the 3 organs that are important to calcitriol synthesis.

A
  1. Skin
    • Splits 7-dehydrocholesterol w/ light
  2. Liver
    • Hydroxylated a C25
    • D-binding protein
    • Transports D3 to kidneys
  3. Kidneys
    • Form calcitriol
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4
Q
  1. What ultimately makes an amino acid essential?
A
  • If α-keto acid is not able to be made then it is considered an essential amino acid
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5
Q

which compound plays a significant role in the formation of purines as well as the de novo pathway of nucleotide synthesis? what is the enzyme responsible for the formation of this compound?

A
  • PRPP
  • PRPP synthetase
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6
Q
  1. Describe the mechanism to replace a carbonyl group with an amino group.
A

Carbonyl tautomerizes

  1. React tautomer w/ phosphoryl donor
  2. Nitrogen atom attacks
    • Nucleophilic attack on tetrahedral intermediate
  3. Removal of phosphate group

enamine formation: N replaces O from carbonyl group

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7
Q
  1. Compare and contrast chylomicrons and VLDL.
A

Both aid in transport triglycerides through the blood

Chylomicrons
- Dietary lipids
- Seen in the GI tract
VLDL
- Endogenous
- Seen in the liver

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8
Q
  1. Briefly describe the role of HDL and LDL in regards to cholesterol transport.
A
  • HDL: transports cholesterol to the liver
  • LDL: transports cholesterol to tissues
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9
Q

how is pyrimidine synthesis similar to amino acid catabolism?

A

carbonyl phosphate & aspartate

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10
Q

describe the stages of the nitrogen cycle

A
  1. nitrogen fixation: N2 -> NH4+
  2. nitrification: NH4+ -> NO2- -> NO3-
  3. reduction: NO3- -> NH4+
  4. denitrification: NO3- -> N2
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11
Q

what specific steps of atherosclerosis might be prevented by taking antioxidants?

A
  • damage to endothelial cells lining capillaries
  • formation of foam cells
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12
Q

what portion of cholesterol is removed in order to make steroids?

A

the aliphatic side chain

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13
Q

what is the steroid ‘grandparent’?

A

pregnenolone

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14
Q

Identify the methods to regulate purine synthesis

A
  1. PRPP
  2. phosphoribosyl amine synthesis
  3. IMP
  4. substrate balancing
  5. purine repressor protein in bacteria
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15
Q
  1. Provide the roles of SAM in amino acid synthesis.
A
  • Preferred methyl donor
  • induces fruit ripening
  • Met synthesis
  • Polyamines
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16
Q
  1. Provide the roles of THF in amino acid synthesis.
A
  • Carrier of
    Methyl
    Methylene
    Formyl
    Methenyl
    Formimino
  • Formed from folic acid
    Amino acid synthesis
    Neural tube defect prevention
17
Q

provide 3 families of amino acids in regard to their synthesis

A
  1. oxaloacetate
  2. pyruvate
  3. a-ketoglutarate
  4. 3-phosphoglycerate
  5. R-5-P
18
Q

provide functions of nucleotides other than DNA/RNA synthesis

A
  • energy
  • glycogen metabolism
  • coenzymes
  • regulation
  • group transfers
19
Q

how is allopurinol used to treat gout?

A

allopurinol is a purine analog that inhibits xenthalate oxidase which will reduce the amount of citric acid in tissues

20
Q

what are the 2 pathways that purine nucletodes can be made?

A
  1. de novo

by recycling the elements already found within the body

21
Q
  1. Explain what is meant by the intestinal-renal axis in regards to arginine synthesis.
A
  • Small intestine: Gln -> Cit
    • Kidney: Cit -> Arg
22
Q
  1. Identify the 3 ways that glutamate can be made.
A
  1. Glutamate Dehydrogenase
  2. Glutamate Synthase
  3. BCAA Transaminase
23
Q

describe the major steps associated with atherosclerosis

A
  1. damage to endothelial cell lining
  2. migration of LDL and platelets
  3. recruitemnt of smooth muscle cells & macrophages
  4. activation of macrophages
  5. formation of foam cells
  6. formation of atheroma
24
Q

provide reaction types/processes involved in making NEAA

A
  1. transamination
  2. glycine related
  3. non amino acid amino group transfers
25
Q

what amino acid is used to make pyrimidines & purines? which one uses more of the amino acids atoms in synthesis?

A
  • aspartate
  • pyrimidines
26
Q

provide a major difference between purine and pyrimidine synthesis

A

pyrimidines are built as the base alone and do not have R-5-P attached to it. in the synthesis pathway R-5-P is added

27
Q
  1. Other than nucleotides, provide 2 compounds or types of compounds that amino acids can serve as the precursor of.
A
  • histamine
  • sphingosine
  • NAD+
  • nitric oxide
  • thyroxine
  • epinephrine

Biochemistry II (6 decks)

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