BCHEM LE6 (2025) Flashcards by

Conversion of purines to uric acid in humans are mediated by the following enzymes except?
A. Deaminase
B. Uricase

C. Phosphorylase
D. Oxidase

B. Uricase

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Failure of this transporter is a major factor in human hyperuricemia?
A. URAT1
B. GLUT9
C. ABCG2
D. SLC22

C. ABCG2

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Urate transport disorders can cause hyperuricemia in the majority of gout patients by which mechanism?
A. Increase renal urate secretion

B. Increase renal urate reabsorption

C. Reduced renal excretion
D. Reduced renal reabsorption

C. Reduced renal excretion

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Deficiency in enzymes involved in the Salvage pathway of purines lead to accumulation of?
(0/1 Point)

A. HGPRT
B. PRPP
C. Hypoxanthine
D. Adenine

C. Hypoxanthine

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Most relevant pathway which also offers significant perspectives for pharmacologic approach of hyperuricemia?

A. ADA
B. mdN
C. XDH
D. XOR

D. XOR

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Key enzymes in the synthesis of pyrimidines?

A. CPSI

B. DHODH
C. IMPDH
D. ADSS

B. DHODH

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Increase in purine nucleotide levels is sufficient to induce expression of this cell surface glycoprotein in cancer cells?
A. MICA
B. NKG2D

C. M-CSF

D. TLR

A. MICA

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Downregulation of nucleotide metabolic pathways as true anticancer mechanism are brought about by?
A. Mutant P53

B. Mitogen-activated protein kinase

C. Ribonucleotide reductase regulatory subunit

D. Oncogen induced senescence

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Oncogenes and tumor suppressor genes are key regulatory molecules in?
A. Salvage pathway nucleotide synthesis

B. De novo nucleotide synthesis
C. Both
D. None

B. De novo nucleotide synthesis

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Expression of this nucleotide inhibits antitumor immune response?
A. Guanosine
B. Thymine
C. Adenosine
D. Cytosine

D. Cytosine

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Which of the following has an

adenine-containing nucleotide in its structure?

A. PRPP

B. Coenzyme A

C. Carbamoyl phosphate

D. SAM

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Delivery of cholesterol to liver and other tissues by plasma lipoproteins leads to a reduction in de novo cholesterol synthesis and decrease in the synthesis of:
a. LDL receptors
b. HDL receptors
c. VLDL receptors

d. triacylglycerol receptors

a. LDL receptors

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Which of the following is true?

a. Spherical lipoprotein particles have a hydrophilic core of triacylglycerols
b. Lipoproteins have cholesteryl esters surrounded by a phospholipid layer associated with cholesterol and lipids.
c. As the lipid-to-protein ratio decreases, particles becomes larger

d. As the lipid-to-protein ratio decreases, particles becomes more dense

d. As the lipid-to-protein ratio decreases, particles becomes more dense
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This nucleotide activates protein kinases during glycogen breakdown:
A. ATP
B. GTP
C. Cyclic GMP

D. Cyclic AMP

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Chylomicrons transports dietary triacylglycerol to muscles and dietary cholesterol to liver.
They are formed and secreted by :
a.liver
b.intestinal mucosa
c. kidneys
d,pancreas

b.intestinal mucosa

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It is activated by high-density lipoproteins to form cholesteryl esters:
a. LCAT
b. apo-C
c. apo-E
d.HMGCO-A

a. LCAT

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Major structural protein for HDL1:

a. apo-A-1

b. apo-B-48

c. apo-E

d. apo-B-100

e. apo-A-1

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The only structural protein in LDL that contains another apoprotein domain plus the LDL receptor recognition domain permitting binding to LDL receptors:
a. apo-A-1
b. apo- B-48
c. apo-E
d. apo-B-100

d. apo-B-100
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Which of the following is not true of free cholesterol in the cytosol?
a. Activates ACAT

b.Suppresses HMG CoA reductase; decreases de novo synthesis of cholesterol
c. Suppresses further LDL receptor synthesis; decreases further uptake of LDL

d. Mediates esterification of receptors removed from peripheral tissues by HDL.

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Most common hyperlipoproteinemia where there is Increased triacylglycerol beginning at puberty with increased incidence of coronary artery disease and peripheral vascular disease:
a. Type I
b. Type II
c.Type III
d. Type IV

d. Type IV
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Most commonly a familial hypertriglyceridemia with exacerbating factors particularly common in alcoholics and individuals with diabetic ketoacidosis:
a. Type I
b. Type III
c.Type V
d. Type VI

c.Type V

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Which of the following is true about plasma lipoproteins?
a. They are held together by covalent bonds.
b. They are composed of a neutral lipid core surrounded by esterified cholesterol.
c. They have varied protein to lipid ratio.
d. The principal lipid carried by lipoprotein particles are chylomicrons.

c. They have varied protein to lipid ratio.

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Which of the following proteins are the major carriers of triacylglycerols?
a. VLDL and LDL

b. chylomicrons and VLDL
c. chylomicrons and LDL
d. VLDL and HDL

b. chylomicrons and VLDL

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Transporter of lipid that is lowest in density but largest in size. It contains the highest percentage of lipid and the smallest of protein:
a. Chylomicron

b. VLDL
c. LDL
d. HDL

a. Chylomicron
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25. As the lipid-to-protein ratio decreases, particles become smaller and more dense in the following order: a. chylomicron > HDL> VLDL > LDL b chylomicron > VLDL > LDL > HDL. c. HDL>LDL>VLDL > chylomicron d. HDL>LDL>VLDL > chylomicron

b chylomicron > VLDL > LDL > HDL.

26. This apolipoprotein antagonizes ApoE & is known to inhibit lipoprotein lipase. (0/1 Point) A, apoB B. apoB C. apo C-IIl D. apo C-II

D. apo C-II

27. Site of action of hormone sensitive lipase that degrades stored triacylglycerols activated by cAMP-dependent protein kinase: A. stomach B. pancreas C. adipocytes D. liver

C. adipocytes

28. Nascent triglyceride-rich very low density lipoproteins are secreted from the : A. intestinal mucosal cells B. liver C. stomach D. pancreas

B. liver

29. The initiating step in the modification of apoB involves which process? A. Peroxidation of polyunsaturated fatty acids in the LDL lipids. B. Regulation of modified LDL taken up by macrophages C. Acetylation of apolipoprotein B D. Oxidation of circulating macrophages with low levels of scavenger receptor activity.

A. Peroxidation of polyunsaturated fatty acids in the LDL lipids.

30. After addition of carbohydrate residues in the Golgi apparatus, chylomicrons are released into the cells through: a. exocytosis b. reverse pinocytosis c. reverse endocytosis d. pinocytosis

d. pinocytosis

31. This transfers cholesterol from HDL to VLDL and triacylglycerols from VLDL to HDL a. Lipoprotein lipase (LPL) b. Cholesteryl Ester Transfer Protein(CETP) c. Hepatic Lipase (HPL) d. CURL

b. Cholesteryl Ester Transfer Protein(CETP)

32. Familial hypercholesterolemia is usually secondary to a deficiency in: a. apoCII b. apoB48 c. apoB100 d. apoCIII

a. apoCII

33. Which of the following best describes the role of the cholesterol ester transfer protein? a.It converts cholesterol from LDL to cholesterol esters b.It exchanges cholesterol esters from HDL to other lipoproteins c.It acts as a ligand for hepatic receptors of LDL d.It is the major protein of VLDL

b.It exchanges cholesterol esters from HDL to other lipoproteins

34. Which of the following comprises Metabolic Syndrome? A. elevated HDL, hypertension, elevated blood sugar, obesity B. elevated LDL, hypertension, elevated blood sugar, obesity C. elevated HDL, hypertension, elevated triglycerides, obesity D. elevated LDL, hypotension, elevated blood sugar, obesity

B. elevated LDL, hypertension, elevated blood sugar, obesity

35. Which makes up 15% of the white matter of the brain? A. sulfogalactocerebrosides B. sulfoglucocerebrosides C. triacylglycerols D. ganglioside GM1

A. sulfogalactocerebrosides

36. Which of the sphingolopids has no glycerol backbone? A. cardiolipin B. plasmalogen C. lecithin D. sphingomyelin

D. sphingomyelin

37. Which phospholipid serves as the precursor for the generation of IP3 and 1,2 DAG? A. phosphatidyl choline B. phosphatidyl inositol C. phosphatidyl serine D. phosphatidyl ethanolamine

B. phosphatidyl inositol

38. Which ganglioside serves as the receptor for cholera toxin in the intestinal cells? A. GM2 B. GM1 C. GM3 D. GM4

B. GM1

39. Which intermediate is shared both for the synthesis of phospholipids and triacylglycerols? A. 1,2 diacyglycerol B. cholesterol C. HMGCoA D. glycerol 3 PO4

A. 1,2 diacyglycerol

40. A 3 year old child was brought to the medical center and found to have hepatosplenomegaly, with ataxia, dysarthria, dysphagia, dystonia sometime going into gelastic cataplexy with laughing, supranuclear gaze, dementia and sometimes seizures. What is the nature of the disease? A. Guacher’s B. Niemann Pick’s C. Krabbe’s D. Tay Sach’s

B. Niemann Pick’s

41. Among the following special lipids, which is a glycerophospholipid? A. cardiolipin B. galactosyl ceramide C. GM2 D. sphingomyelin

A. cardiolipin

42. The enzyme that is deficient in Niemann Pick’s disease? A. glucocerebrosidase B. hexosaminidase A C. sphingomyelinase D. β-galactocerebrosidase

C. sphingomyelinase

43. Among the following special lipids, which utilizes sphingosine for it synthesis? A. cardiolipin B. plasmalogen C. lecithin D. sphingomyelin

sphingomyelin

44. Which of the following phospholipids acts as a lipotropic agent? A. phosphatidyl choline B. phosphatidyl inositol C. phosphatidyl serine D. cardiolipin

A. phosphatidyl choline

45. Degradation of a galactocerebroside generates which components? A. sphingosine + fatty acid + galactose B. glycerol + fatty acids + phosphoric acid + galactose C. glycerol + fatty acids + phosphoric acid + nitrogenous base + galactose D. sphingosine + fatty acid + phosphoric acid + galactose

A. sphingosine + fatty acid + galactose

46. What is the major component of the lung surfactant? A. dipalmitoyllecithin B. dipalmitoylphosphatidyl serine C. dipalmtoylcephalin D. dipalmitoylphosphatidyl inositol

A. dipalmitoyllecithin

47. Ethanolamine is the nitrogenous base of which phospholipid? A. cardiolipin B. phosphatidyl inositol C. lecithin D. cephalin

D. cephalin

48. What is the significance of L:S ratio determination of amniotic fluid in a pregnant female? A. fetal heart rate B. fetal lung maturity C. fetal head size D. expected date of delivery

B. fetal lung maturity

49. What are the degradative components of ceramide? A. sphingosine + fatty acid B. glycerol + fatty acid + phosphoric acid C. glycerol + fatty acid + phosphoric acid + nitrogenous base D. sphingosine + fatty acids + phosphoric acid

A. sphingosine + fatty acid

50. Sphingosine is not a structural component of this special lipid? A. cerebrosides B. gangiolisides C. sphingomyelin D. plasmalogen

D. plasmalogen

51. How many sugar moieties are present in GM2? A. one B. three C. four D. two

B. three

52. What is the letter M in GM2 represent? A. sialic acid residues B. N-acetyl galactose residues C. glucose residues D. N-acetyl glucosamine residues

A. sialic acid residues

53. In eukaryotes, cardiolipin is synthesized from the condensation of : A. serine + CDP- DAG B. phosphatidyl glycerol + CDP-DAG C. removal of carbon dioxide D. head group exchange

B. phosphatidyl glycerol + CDP-DAG

54. What is the precursor of the second messenger utilized in the regulation of the cytidyl transferase enzyme used in the synthesis of phospholipids? A. GTP B. PIP2 C. Ca2+ D. ATP

D. ATP

55. What is the predominating hormone in the cells when cytidyl transferase enzyme binds to the endoplasmic reticulum membrane? A. insulin B. glucagon C.adrenaline D. Thyroxine

A. insulin

56. What ganglioside accumulates in Tay Sach’s disease? A. GM1 B. GM2 C. GT3 D. GD2

E. GM2

57. What is the enzyme deficient in generalized gangliosidosis? A. beta-galactosidase B. hexoseaminidase A C. arylsulfatase A D. beta-glucosidase

A. beta-galactosidase

58. In Fabry’s disease, this globoside accumulation can lead to end-stage renal disease A. ceramide trihexoside B. lactosyl ceramide C. galactosyl ceramide D. glycosyl ceramide

A. ceramide trihexoside

59. This is a glucosylceramide lipidoses that results from a deficiency of beta-glucosidase: A. Faber’s disease B. Fabry’s disease C. Gaucher’s disease D. Niemann Pick disease

C. Gaucher’s disease

60. A 45-year-old male patient presents with intense redness, heat, and pain over his left metatarsophalangeal joint of the big toe. Fluid from this joint shows negatively birefringent crystals. This disease is caused by a genetic defect in glucose-6-phosphatase. Which of the following nucleoticde bases lead to the increased synthesis of the crystals? A. Adenine B. Cytosine C. Uracil D. Thymine

A. Adenine

61. A researcher wants to develop a method of labeling purines with 15N for use in future spectroscopic studies. Purine synthesis will be done in a test tube using only the enzymes necessary to synthesize purines via the de novo pathway. Which starting material should be labeled with the heavy nitrogen in order to maximize 15N incorporation into purines? A. Aspartate B. Acetyl-CoA C. Orotic acid D. Ribose-5-phosphate

A. Aspartate

62. A patient has been recently diagnosed with colorectal cancer. The physician treats the patient with a combination of chemotherapeutic drugs, one of which is Methotrexate. The synthesis of this base is expected to decrease: A. Dihydrofolate B. Thymine C. Tetrahydrofolate D. Adenine

B. Thymine

63. A patient exhibits fasting hypoglycemia and lactic acidosis under fasting conditions. Hepatomegaly is also evident. A glucagon challenge only releases about 10% of the expected level of glucose from the liver. The patient has also developed gout due to an increase in the levels of which of the following metabolites? A. Ribose-5-phosphate B. Glutamine C. ATP D. NADH

A. Ribose-5-phosphate

64. Individuals with gout are given allopurinol for long-term management of the disease. In such individuals, which of the following bases would be expected? A. Decreased PRPP synthesis B. Increased orotic acid excretion C. Folic acid deficiency D. Elevated levels of xanthine

D. Elevated levels of xanthine

65. A penicillin-allergic child was given a Co-trimoxazole, a sulfonamide-containing antibiotic, for otitis media. Which process is affected ? A. DNA polymerase activity B. Bacterial folate absorption C. PABA conversion to Folate D. Conversion of ribonucleotides to deoxyribonucleotides

C. PABA conversion to Folate

66. What is the biochemical mechanism that leads to Severe Combined Immunodeficiency? A. Uric acid accumulation B. Phosphate Trapping C. Xanthine oxidase inhibition D. Glucose-6-phosphatase deficiency

B. Phosphate Trapping

67. Pyrimidines differ from purines in both structure and metabolite solubility. Which of the following is a pyrimidine base? A. thymine B. guanine C. inosine D. adenine

A. thymine

68. Phosphates attached to nucleotides provide energy for chemical reactions. The phosphates in GTP are attached to what entity of the nucleotide? A. pentose sugar B. guanine base C. hexose sugar D. the ether oxygen of the glycosidic bond

A. pentose sugar

69. In biochemistry, it is important to identify the charge of molecules to determine their chemical behaviour when present in solution. Which of the following is negatively charged at physiologic pH? A. nucleotide B. nucleoside C. purine base D. pyrimidine base

A. nucleotide

70. Watson and Crick, in their ground-breaking paper, found that the nucleotides in RNA and DNA: A. are attached to an inorganic phosphate by van der Vaals bonds B. Are linked by phosphodiester bonds C. Are arranged in a triple helix D. Contain at least 3 hydrogen bonds in all base pairs

B. Are linked by phosphodiester bonds

71. This amino acid precursor contributes 2 carbon atoms and 1 nitrogen atom to the purine ring structure: A. aspartate B. glutamine C. glycine D. alanine

C. glycine

72. Carbamoyl phosphate, a substrate in pyrimidine nucleotide synthesis, is also an intermediate of this pathway: A. pentose phosphate pathway B. urea cycle C. polyol cycle D. β-oxidation

B. urea cycle

73. The rate-limiting enzyme of purine nucleotide synthesis immediately forms this product: A. Phosphoribosyl pyrophosphate B. Ribose-5-phosphate C. Inosine monophosphate D. Carbamoyl phosphate

A. Phosphoribosyl pyrophosphate

74. Which of the following statements is true of the regulation of purine nucleotide synthesis? A. The presence of both AMP and GMP activates glutamyl amidotransferase. B. An increase in the concentration of PRPP decreases purine nucleotide synthesis. C. The synthesis of AMP increases when the concentration of GMP increases D. The rate of purine biosynthesis decreases when glucose-6-phosphatase activity increases

C. The synthesis of AMP increases when the concentration of GMP increases

75. The C2 of the pyrimidine ring is derived from: A. Carbamoyl phosphate B. Glycine C. Tetrahydofolate D. Aspartate

A. Carbamoyl phosphate

76. This amino acid contributes the most atoms to the purine ring: A. Glycine B. Aspartate C. Glutamate D. Carbamoyl phosphate

A. Glycine

77. The end product of pyrimidine catabolism: A. Ammonia B. β-alanine C. Uric acid D. Orotic Acid

B. β-alanine

78. True of the regulation of purine nucleotide synthesis: A. The presence of both AMP and GMP activates glutamyl amidotransferase. B. An increase in the concentration of PRPP decreases C. The synthesis of AMP increases when the concentration of GMP increases D. The rate of purine biosynthesis decreases when glucose-6-phosphatase activity increases

C. The synthesis of AMP increases when the concentration of GMP increases

79. The synthesis of this nucleotide involves the addition of PRPP when the ring structure of the base is already formed A. purine nucleotides B. pyrimidine nucleotides C. both A and B D. neither A nor B

B. pyrimidine nucleotides

80. These nucleotides are derived from IMP: A. AMP and GMP B. CMP and TMP C. AMP and CMP D. GMP and TMP

A. AMP and GMP

81. This is the first stage in expression of genetic information: A. Replication B. DNA synthesis C. Translation D. Transcription

D. Transcription

82. G-C bonds in DNA are: A. Always equal to the number of A-T bonds in a single DNA strand B. Held together by 2 hydrogen bonds C. Linked together by sharing of electrons D. More resistant to denaturation than A-T bonds

D. More resistant to denaturation than A-T bonds

83. Which of the following bases is not normally seen in RNA? A. Adenine B. Uracil C. Thymine D. Guanine

C. Thymine

84. Which of these is referred to as a linker histone? A. H1 B. H2 C. H3 D. H4

A. H1

85. The chemical nature of RNA differs from that of DNA: A. Ribonucleic acid (RNA) is a polymer of purine and pyrimidine ribonucleotides linked together by 3→5'-phosphodiester bonds analogous to those in DNA B. In RNA, the sugar moiety to which the phosphates and purine and pyrimidine bases are attached is the 2'-deoxyribose of DNA rather than ribose C. The pyrimidine components of RNA are similar to those of DNA D. Both DNA and RNA can be hydrolyzed by alkali to 2'→3' cyclic diesters of the mononucleotides

A. Ribonucleic acid (RNA) is a polymer of purine and pyrimidine ribonucleotides linked together by 3→5'-phosphodiester bonds analogous to those in DNA

86. The following statement is TRUE with regards to tRNA structure and function: A. it has an anticodon arm which binds to a specific amino acid B. it needs to be activated by the attachment of a nucleic acid C. it is a single-stranded molecule bound by intrachain bridges D. it bridges the gap between DNA and RNA synthesis

C. it is a single-stranded molecule bound by intrachain bridges

87. In The 3’ → 5’ –Phosphodiester bonds : A. Join the 3’ hydroxyl group of the deoxypentose of one nucleotide to the 5’ hydroxyl group of deoxypentose of an adjacent nucleotide through a methyl group B. The resulting long branched chain has polarity that are not attached to other nucleotides C. The 5’ end of the chain has a free phosphate attached to it D. The bases located along the resulting deoxyribose-phosphate backbone are by convention always written in sequence from 3’ to 5’ end of chain

C. The 5’ end of the chain has a free phosphate attached to it

88. In the DNA Double Helix , A. The two chains are coiled around a common axis called the Helical Axis B. The overall structure resembles a twisted ladder C. The spatial relationship between the two strands in the helix creates a major (wide) groove and a minor (narrow) groove D. All of the above

D. All of the above

89. True of Chargaff Rule, except: A. In any sample of dsDNA molecules, the concentration of deoxyadenosine nucleotides equals that of thymidine nucleotides B. the concentration of deoxyguanosine nucleotides equals that of deoxycytidine nucleotides C. the concentration of deoxyadenosine nucleotides equals that of Uracil nucleotides D. none of the above

C. the concentration of deoxyadenosine nucleotides equals that of Uracil nucleotides

90. The following statement is false: A. The double helix structure is disrupted by alterations in the pH of the DNA solution B. Heat denatures the DNA strands C. Phosphodiester bonds are broken by heat treatment D. None of the above

C. Phosphodiester bonds are broken by heat treatment

91. Which statement is not true? A. The single stranded DNA has a higher relative absorbance at at 260 nm wavelength than does double stranded DNA B. The melting temperature (Tm) is affected by the number of hydrogen bonds between bases C. DNA that contains high concentrations of Adenine and Thymine denatures at a lower temperature than Guanine and Cytosine-rich DNA D. There are three hydrogen bonds between Adenine and Thymine but only two between Guanine and Cytosine

D. There are three hydrogen bonds between Adenine and Thymine but only two between Guanine and Cytosine

93. True of the B form DNA that is usually found under physiologic conditions: (1/1 Point) A. It is a right-handed helix with ten residues per 360° turn of the helix B. The planes of the bases are parallel to the helical axis C. The width of the double helix is measured at 34 Å, and the distance spanned by one complete turn of the double helix is 20 Å D. One turn of B-DNA includes 10 base pairs, so the rise is therefore 34 Å per base pair

A. It is a right-handed helix with ten residues per 360° turn of the helix

94. Which among major types of RNA that participate in the process of protein synthesis make up about 80% of the total RNA in the cell? A. ribosomal RNA (rRNA) B. transfer RNA (tRNA) C. messenger RNA (mRNA) D. noncoding RNA (ncRNA)

A. ribosomal RNA (rRNA)

95. The two strands of the DNA double-stranded helix are held in register by this bond: A. hydrogen bonds B. van der Waals C. hydrophobic interactions D. all of the above

D. all of the above

96. Which of these histones is not a part of the nucleosome core? A. H1 B. H2A C. H3 D. H4

A. H1

97. The sugar moiety to which the phosphates and purine and pyrimidine bases are attached is a ribose: A. DNA B. RNA C. Both DNA and RNA D. Neither

B. RNA

98. Can be hydrolyzed by alkali to 2',3' cyclic diesters of the mononucleotides: A. DNA B. RNA C. Both DNA and RNA D. Neither

B. RNA

99. Capable of folding back on itself like a hairpin and thus acquiring double-stranded characteristics A. DNA B. RNA C. Both DNA and RNA D. Neither

B. RNA

100. This structural form of DNA has a left-handed helix that contains about 12 base pairs per turn: A. A form B. B form C. C form D. Z form

D. Z form

92. Among the major structural forms of DNA, which has the planes of the base pairs tilted 20° away from the perpendicular to the helical axis? A. A form B. B form C. C form D. Z form

A. A form

BCHEM LE6 (2025) Flashcards

(100 cards)