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Biochemistry II > Exam 3: Sample Questions > Flashcards

Exam 3: Sample Questions Flashcards

1
Q
  1. What role does biotin play in acetyl CoA synthesis?
A
  • Prosthetic group on active site that gives pyruvate carboxylase its functionality
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2
Q
  1. List 3 arachidonic acid products along with one of their affects
A
  1. Prostaglandins
    • Effect the transit of RBCs through capillaries
      -Decrease the production of gastric acid
  2. Thromboxane
    -Involved in blood clotting
  3. Prostacyclin
    -Basodialators
    -Decrease platelet aggregation
  4. Leukotrienes
    -Involved in allergic reactions
    -Promotes inflammation
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3
Q
  1. What is the source of all carbons found in cholesterol?
A

acetyl CoAs

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4
Q
  1. Identify the 5 stages of cholesterol synthesis
A
  1. Mevalonate production
    -From 3 AcCoAs
  2. Isoprenoids
  3. Squalene
    -From 6 isoprenoids
  4. Cyclize squalene to lanosterol
  5. Cholesterol is formed
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5
Q
  1. What stage of cholesterol synthesis explains cholesterol not showing up on the fossil record until the earth became aerobic?
A
  • The cyclization during lanosterol formation
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6
Q
  1. What regulates the transcription and translation of HMGCoA reductase?
A

Transcription
-Steroid response element that is associated with DNA enzyme
Translation
-Nonsterol mevalonate metabolites

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7
Q
  1. What enzyme plays a major role in regulating cholesterol synthesis in the body?
A
  • HMGCoA Reductase
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8
Q
  1. What is the 3C carrier used in fatty acid synthesis?
A
  • Acyl carrier protein (ACL)
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9
Q
  1. What role does thioesterase play in determining the fatty acid that a particular cell produces?
A
  • Dictates whether the molecule is palmitate or something else during the cleavage stage of fatty acid synthesis
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10
Q
  1. Write the overall reaction for the synthesis of palmitate.
A

8AcCoA + 7ATP + 14NADPH ————–> palmitate + 14NADP+ + 6H2O + 7ADP + 7Pi + 8CoA

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11
Q
  1. Name the 2 enzymes that metabolize/modify arachidonic acid and one of the molecule types that each of the enzymes can form.
A
  1. Cyclooxygenase
    • Forms: prostaglandins, prostacyclin, thromboxane
  2. Lipoxygenase
    • Forms: leukotrienes
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12
Q
  1. Describe all the ways that HMGCoA Reductase can be regulated.
A

HMG CoA synthase

HMG CoA lyase

Feedback inhibition
-cholesterol inhibits

covalent modification
-phosphorylation inhibits

transcriptionally
-decrease cholesterol -> increase gene transcription

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13
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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14
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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15
Q
  1. What is the role of CETP in HDL?
A
  • Antiport
  • Transfers CE (cholesterol ester) from HDL to another lipoprotein
  • Transfers triglycerides to HDL
  • Allows LCAT to esterify more cholesterol
  • Low CETP promotes HDL formation
  • Moves CE and triglycerides from VLDL.LDL.HDL
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16
Q
  1. List the 3 ways that the level of cholesterol in cells is regulated.
A
  1. Dietary
  2. HMGCoA Reductase
  3. ACAT activity
  4. Target HMGCoA reductase
  5. ACAT
    • Esterifies cholesterol
  6. LDL receptors
    • Downgrade w/ excess cholesterol
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17
Q
  1. List 3 steroid products of cholesterol metabolism, excluding calcitriol.
A
  1. Aldosterone
  2. Estradiol
  3. Progesterone
  4. Cortisol
  5. Corticosterone
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18
Q
  1. 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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19
Q
  1. Identify the 3 ways that glutamate can be made.
A
  1. Glutamate Dehydrogenase
  2. Glutamate Synthase
  3. BCAA Transaminase
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20
Q
  1. Identify 2 conditionally essential amino acids. Why are they conditionally essential?
A
  1. Arginine
  2. Glutamine
    • b/c they are only required under certain physiological conditions such as septic shock & burn victims
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21
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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22
Q
  1. Identify the precursor molecule that is used in both pyrimidine and purine synthesis.
A

PRPP

23
Q
  1. What nucleotide base is thymine made from? What is the primary difference between the two?
A
  • pyrimidine base
  • Made from: methylated uracil
  • Difference: thymine has an extra methyl group on its structure
24
Q
  1. List the 3 enzymes that are important to purine catabolism.
A

Nucleotidase
- Converts nucleotides to nucleosides
Nucleotide phosphorylase
- Degrades nucleosides to a free base & R-1-P
Phosphoribomutase
- Converts R-1-P to R-5-P

25
Q
  1. How is allopurinol used to treat gout?
A
  • b/c it is a purine analog that inhibits xanthine oxidase therefore reducing the amount of uric acid in the tissues
26
Q
  1. List 3 methods of regulating purine synthesis.
A
  1. PRPP synthesis
    • Inhibition by purine nucleotides
    • Allows substrate channeling
  2. Phosphoribosyl amine synthesis
    • Inhibition by purine nucleotides
    • Example of cumulative feedback inhibition
  3. IMP
    • GMP inhibits xanthylate formation
    • AMP inhibits adenylsosunccinate formation
  4. Substrate Balancing
    • ATP used to make GMP
    • GTP used to make AMP
27
Q
  1. What enzyme plays a role in regulating cholesterol synthesis in the body?
A

HMGCoA Reductase

28
Q
  1. Provide 2 reaction types or processes involved in making non-essential amino acids.
A
  1. Transamination
    • α-keto acid + amino group -> amino acid
  2. carbon transfer
    • tetrahydrofolate is used to pull amino group off glycine
  3. non amino acid amino group transfer
29
Q
  1. List the methods to regulate NEAA’s
A
30
Q
  1. How is de novo biosynthesis distinguished by de novo pyrimidine biosynthesis?
A

De novo
- Metabolic precursors
- Prevalence: ubiquitous
- Made possible by: multi enzyme complex
Pyrimidine biosynthesis uses a multi enzyme complex
- 2 used in eukaryotes

  1. CPS II, Aspartate, transcarbomoylase, dihydroorotase
  2. OPR transferase, orotidylate decarboxylase
31
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
32
Q
  1. Other than nucleotides, provide 2 compounds or types of compounds that amino acids can serve as the precursor of.
A
  • Histamine: when histidine is decarboxylated
  • NAD+ : from tryptophane
  • Nitric oxide: from nitric oxide synthase
  • Cytochromes
  • Heme
  • Hormones
  • Melanin
  • neurotransmitters
33
Q
  1. How is pyrimidine synthesis similar to amino acid catabolism?
A
34
Q
  1. What nucleotide cannot be made if there was a deficiency in THF?
A

DNA —-thymine

35
Q
  1. What specific step(s) of atherosclerosis might be prevented by taking antioxidants?
A
  • Damage to endothelial cell lining
  • Migration of LDL & platelets

Antioxidants:
- Scavenge free radicals
- Reduce low-grade inflammation
- Reduce blood coagulation & clot formation

36
Q
  1. Provide the roles of SAM in amino acid synthesis.
A
  • Preferred methyl donor
    b/c of increased transfer potential compared to THF
  • formed by an adenosyl transfer from ATP
    driven by: PPi hydrolysis
    produces: active methyl group
  • induces fruit ripening
  • Met synthesis
  • Polyamines
  1. Ornithine conversion to putrescine
  2. SAM decarboxylation & reaction w/ /putrescine
  3. Decarboxylated SAM -> putrescine -> spermidine -> spermine
37
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
38
Q
  1. Provide 3 function of nucleotides other than DNA/RNA synthesis.
A
  1. Used to synthesize UDP-glucose
  2. Energy: ATP & GTP
  3. Coenzymes: NAD, FAD, CoA
  4. Regulation: phosphorylation & adenylation
  5. Group transfers: SAM
39
Q
  1. In regards to purine synthesis, what is meant by substrate balancing in regards to IMP metabolism?
A

IMP conversion to GMP and AMP
- GMP inhibits xanthylate formation
- AMP inhibits adenylosuccinate formation
Substate Balancing
- ATP is used to make GMP
- GTP is used to make AMP

40
Q
  1. What causes gout and how is it treated?
A

Cause: Exceeding the solubility of uric acid
Treatment: Allopurinol
- Inhibits xanthine oxidase
- Reduces the amount of uric acid in tissues

41
Q
  1. Explain what is meant by the intestinal-renal axis in regards to arginine synthesis.
A

Interorgan metabolism plays a major role
Intestinal renal axis
- Small intestine: Gln -> Cit
- Kidney: Cit -> Arg

42
Q
  1. How does bacterial regulation of purine synthesis differ from eukaryotes?
A

Bacteria
- Purines repressor protein
- Block transcription when hypoxanthine of guanylate are high

43
Q
  1. 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
44
Q
  1. What part of cholesterol is removed to make steroids?
A
  • Aliphatic side chain
45
Q
  1. List 3 molecules that amino acids can serve as the precursors for.
A
  1. Histidine -> decarboxylase-histamine
  2. NAD+ -> tryptophan
  3. Nitric oxide
  4. Tetrahydrobiopterin
  5. Serotonin
  6. Dopamine
  7. Norepinephrine
46
Q
  1. What steroid is termed the hormone grandparent?
A
  • Pregnenolone (precursor)
47
Q
  1. Identify the major type of modification that distinguishes the steroids from each other.
A
  • Addition, modification, position of functional groups
  • Configuration of steroid nucleus
48
Q
  1. Identify the roles of the reductase and nitrogenase in regards to nitrogen fixation.
A

Reductase
- Role: provides electrons w/ high reducing power
- Function: uses electrons to reduce N2 -> NH4+
Nitrogenase: ATP requirement
Cofactor
- Iron
- Molybidelenum
- Vanadium

49
Q
  1. From an evolutionary perspective, what is the major reason why we choose not to synthesize essential amino acids?
A

A selective advantage

  • Need 10+ enzymes to make an a.a.
  • Evolutionary advantage
    • A period of famine
50
Q
  1. Identify the major differences between aminotransferases and amidotransferases in regard to nonessential amino acid synthesis.
A

Amidotransferases
- Binds glutamine
- Accepts amido group
- Amidoligase
Aminotransferases
- Transaminase
- Transfer amine group between amino acids and keto acid

51
Q
  1. What is the major precursor for proline synthesis in the liver?
A

arginine

52
Q
  1. What 2 amino acids play a role in making purines and pyrimidines?
A

glutamine & aspartate

53
Q

3 sources for NADPH for fatty acid synthesis

A
  1. malic enzyme
  2. PPP
  3. isocitrate DH (ICDH)

Biochemistry II (6 decks)

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