BCH 3025
BCH 3025 Revised Exam Correct
Verified Answers 2025
The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine
is:
A) a deoxyribonucleoside.
B) a purine nucleotide.
C) a pyrimidine nucleotide.
D) adenosine monophosphate.
E) adenosine. - Correct Ans-E
A major component of RNA but not of DNA is:
A) adenine.
B) cytosine.
C) guanine.
D) thymine.
E) uracil. - Correct Ans-E
The difference between a ribonucleotide and a deoxyribonucleotide is:
A) a deoxyribonucleotide has an —H instead of an —OH at C-2.
B) a deoxyribonucleotide has configuration; ribonucleotide has the configuration at C-1.
C) a ribonucleotide has an extra —OH at C-4.
D) a ribonucleotide has more structural flexibility than deoxyribonucleotide.
E) a ribonucleotide is a pyranose, deoxyribonucleotide is a furanose. - Correct Ans-A
Which one of the following is true of the pentoses found in nucleic acids?
A) C-5 and C-1 of the pentose are joined to phosphate groups.
B) C-5 of the pentose is joined to a nitrogenous base, and C-1 to a phosphate group.
C) The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond.
D) The pentoses are always in the -furanose forms.
E) The straight-chain and ring forms undergo constant interconversion. - Correct Ans-D
The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA:
A) always link A with T and G with C.
B) are susceptible to alkaline hydrolysis.
C) are uncharged at neutral pH.
D) form between the planar rings of adjacent bases.
E) join the 3' hydroxyl of one nucleotide to the 5' hydroxyl of the next. - Correct Ans-E
BCH 3025
,BCH 3025
The phosphodiester bond that joins adjacent nucleotides in DNA:
A) associates ionically with metal ions, polyamines, and proteins.
B) is positively charged.
C) is susceptible to alkaline hydrolysis.
D) Links C-2 of one base to C-3 of the next.
E) links C-3 of deoxyribose to N-1 of thymine or cytosine. - Correct Ans-A
The alkaline hydrolysis of RNA does not produce:
A) 2'- AMP.
B) 2',3'-cGMP.
C) 2'-CMP.
D) 3',5'-cAMP.
E) 3'-UMP. - Correct Ans-D
The DNA oligonucleotide abbreviated pATCGAC:
A) has 7 phosphate groups.
B) has a hydroxyl at its 3' end.
C) has a phosphate on its 3' end.
D) has an A at its 3' end.
E) violates Chargaff's rules. - Correct Ans-B
For the oligoribonucleotide pACGUAC:
A) the nucleotide at the 3' end has a phosphate at its 3' hydroxyl.
B) the nucleotide at the 3' end is a purine.
C) the nucleotide at the 5' end has a 5' hydroxyl.
D) the nucleotide at the 5' end has a phosphate on its 5' hydroxyl.
E) the nucleotide at the 5' end is a pyrimidine. - Correct Ans-D
The nucleic acid bases:
A) absorb ultraviolet light maximally at 280 nm.
B) are all about the same size.
C) are relatively hydrophilic.
D) are roughly planar.
E) can all stably base-pair with one another. - Correct Ans-D
Which of the following statements concerning the tautomeric forms of bases such as
uracil is correct?
A) The all-lactim form contains a ketone group.
B) The lactam form contains an alcohol group.
BCH 3025
,BCH 3025
C) The lactam form predominates at neutral pH.
D) They are geometric isomers.
E) They are stereoisomers. - Correct Ans-C
In a double-stranded nucleic acid, cytosine typically base-pairs with:
A) adenosine.
B) guanine.
C) inosine.
D) thymine.
E) uracil. - Correct Ans-B
In the Watson-Crick model for the DNA double helix (B form) the A-T and G-C base
pairs share which one of the following properties?
A) The distance between the two glycosidic (base-sugar) bonds is the same in both
base pairs, within a few tenths of an angstrom.
B) The molecular weights of the two base pairs are identical.
C) The number of hydrogen bonds formed between the two bases of the base pair is
the same.
D) The plane of neither base pair is perpendicular to the axis of the helix.
E) The proton-binding groups in both base pairs are in their charged or ionized form. -
Correct Ans-A
The experiment of Avery, MacLeod, and McCarty in which nonvirulent bacteria were
made virulent by transformation was significant because it showed that:
A) bacteria can undergo transformation.
B) genes are composed of DNA only.
C) mice are more susceptible to pneumonia than are humans.
D) pneumonia can be cured by transformation.
E) virulence is determine genetically. - Correct Ans-B
Chargaff's rules state that in typical DNA:
A) A = G.
B) A = C.
C) A = U.
D) A + T = G + C.
E) A + G = T + C. - Correct Ans-E
Based on Chargaff's rules, which of the following are possible base compositions for
double-stranded DNA?
%A %G %C %T %U
A) 5 45 45 5 0
BCH 3025
, BCH 3025
B) 20 20 20 20 20
C) 35 15 35 15 0
D) all of the above
E) none of the above - Correct Ans-A
In the Watson-Crick structure of DNA, the:
A) absence of 2'-hydroxyl groups allows bases to lie perpendicular to the helical axis.
B) adenine content of one strand must equal the thymine content of the same strand.
C) nucleotides are arranged in the A-form.
D) purine content (fraction of bases that are purines) must be the same in both strands.
E) two strands are parallel. - Correct Ans-A
In the Watson-Crick model of DNA structure:
A) both strands run in the same direction, 3' 5'; they are parallel.
B) phosphate groups project toward the middle of the helix, where they are protected
from interaction with water.
C) T can form three hydrogen bonds with either G or C in the opposite strand.
D) the distance between the sugar backbone of the two strands is just large enough to
accommodate either two purines or two pyrimidines.
E) the distance between two adjacent bases in one strand is about 3.4 Å. - Correct Ans-
E
Which of the following is not true of all naturally occurring DNA?
A) Deoxyribose units are connected by 3',5'-phosphodiester bonds.
B) The amount of A always equals the amount of T.
C) The ratio A+T/G+C is constant for all natural DNAs.
D) The two complementary strands are antiparallel.
E) Two hydrogen bonds form between A and T. - Correct Ans-C
In the Watson-Crick model of DNA structure (now called B-form DNA):
A) a purine in one strand always hydrogen bonds with a purine in the other strand.
B) A-T pairs share three hydrogen bonds.
C) G-C pairs share two hydrogen bonds.
D) the 5' ends of both strands are at one end of the helix.
E) the bases occupy the interior of the helix. - Correct Ans-E
The double helix of DNA in the B-form is stabilized by:
A) covalent bonds between the 3' end of one strand and the 5' end of the other.
B) hydrogen bonding between the phosphate groups of two side-by-side strands.
C) hydrogen bonds between the riboses of each strand.
BCH 3025
BCH 3025 Revised Exam Correct
Verified Answers 2025
The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine
is:
A) a deoxyribonucleoside.
B) a purine nucleotide.
C) a pyrimidine nucleotide.
D) adenosine monophosphate.
E) adenosine. - Correct Ans-E
A major component of RNA but not of DNA is:
A) adenine.
B) cytosine.
C) guanine.
D) thymine.
E) uracil. - Correct Ans-E
The difference between a ribonucleotide and a deoxyribonucleotide is:
A) a deoxyribonucleotide has an —H instead of an —OH at C-2.
B) a deoxyribonucleotide has configuration; ribonucleotide has the configuration at C-1.
C) a ribonucleotide has an extra —OH at C-4.
D) a ribonucleotide has more structural flexibility than deoxyribonucleotide.
E) a ribonucleotide is a pyranose, deoxyribonucleotide is a furanose. - Correct Ans-A
Which one of the following is true of the pentoses found in nucleic acids?
A) C-5 and C-1 of the pentose are joined to phosphate groups.
B) C-5 of the pentose is joined to a nitrogenous base, and C-1 to a phosphate group.
C) The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond.
D) The pentoses are always in the -furanose forms.
E) The straight-chain and ring forms undergo constant interconversion. - Correct Ans-D
The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA:
A) always link A with T and G with C.
B) are susceptible to alkaline hydrolysis.
C) are uncharged at neutral pH.
D) form between the planar rings of adjacent bases.
E) join the 3' hydroxyl of one nucleotide to the 5' hydroxyl of the next. - Correct Ans-E
BCH 3025
,BCH 3025
The phosphodiester bond that joins adjacent nucleotides in DNA:
A) associates ionically with metal ions, polyamines, and proteins.
B) is positively charged.
C) is susceptible to alkaline hydrolysis.
D) Links C-2 of one base to C-3 of the next.
E) links C-3 of deoxyribose to N-1 of thymine or cytosine. - Correct Ans-A
The alkaline hydrolysis of RNA does not produce:
A) 2'- AMP.
B) 2',3'-cGMP.
C) 2'-CMP.
D) 3',5'-cAMP.
E) 3'-UMP. - Correct Ans-D
The DNA oligonucleotide abbreviated pATCGAC:
A) has 7 phosphate groups.
B) has a hydroxyl at its 3' end.
C) has a phosphate on its 3' end.
D) has an A at its 3' end.
E) violates Chargaff's rules. - Correct Ans-B
For the oligoribonucleotide pACGUAC:
A) the nucleotide at the 3' end has a phosphate at its 3' hydroxyl.
B) the nucleotide at the 3' end is a purine.
C) the nucleotide at the 5' end has a 5' hydroxyl.
D) the nucleotide at the 5' end has a phosphate on its 5' hydroxyl.
E) the nucleotide at the 5' end is a pyrimidine. - Correct Ans-D
The nucleic acid bases:
A) absorb ultraviolet light maximally at 280 nm.
B) are all about the same size.
C) are relatively hydrophilic.
D) are roughly planar.
E) can all stably base-pair with one another. - Correct Ans-D
Which of the following statements concerning the tautomeric forms of bases such as
uracil is correct?
A) The all-lactim form contains a ketone group.
B) The lactam form contains an alcohol group.
BCH 3025
,BCH 3025
C) The lactam form predominates at neutral pH.
D) They are geometric isomers.
E) They are stereoisomers. - Correct Ans-C
In a double-stranded nucleic acid, cytosine typically base-pairs with:
A) adenosine.
B) guanine.
C) inosine.
D) thymine.
E) uracil. - Correct Ans-B
In the Watson-Crick model for the DNA double helix (B form) the A-T and G-C base
pairs share which one of the following properties?
A) The distance between the two glycosidic (base-sugar) bonds is the same in both
base pairs, within a few tenths of an angstrom.
B) The molecular weights of the two base pairs are identical.
C) The number of hydrogen bonds formed between the two bases of the base pair is
the same.
D) The plane of neither base pair is perpendicular to the axis of the helix.
E) The proton-binding groups in both base pairs are in their charged or ionized form. -
Correct Ans-A
The experiment of Avery, MacLeod, and McCarty in which nonvirulent bacteria were
made virulent by transformation was significant because it showed that:
A) bacteria can undergo transformation.
B) genes are composed of DNA only.
C) mice are more susceptible to pneumonia than are humans.
D) pneumonia can be cured by transformation.
E) virulence is determine genetically. - Correct Ans-B
Chargaff's rules state that in typical DNA:
A) A = G.
B) A = C.
C) A = U.
D) A + T = G + C.
E) A + G = T + C. - Correct Ans-E
Based on Chargaff's rules, which of the following are possible base compositions for
double-stranded DNA?
%A %G %C %T %U
A) 5 45 45 5 0
BCH 3025
, BCH 3025
B) 20 20 20 20 20
C) 35 15 35 15 0
D) all of the above
E) none of the above - Correct Ans-A
In the Watson-Crick structure of DNA, the:
A) absence of 2'-hydroxyl groups allows bases to lie perpendicular to the helical axis.
B) adenine content of one strand must equal the thymine content of the same strand.
C) nucleotides are arranged in the A-form.
D) purine content (fraction of bases that are purines) must be the same in both strands.
E) two strands are parallel. - Correct Ans-A
In the Watson-Crick model of DNA structure:
A) both strands run in the same direction, 3' 5'; they are parallel.
B) phosphate groups project toward the middle of the helix, where they are protected
from interaction with water.
C) T can form three hydrogen bonds with either G or C in the opposite strand.
D) the distance between the sugar backbone of the two strands is just large enough to
accommodate either two purines or two pyrimidines.
E) the distance between two adjacent bases in one strand is about 3.4 Å. - Correct Ans-
E
Which of the following is not true of all naturally occurring DNA?
A) Deoxyribose units are connected by 3',5'-phosphodiester bonds.
B) The amount of A always equals the amount of T.
C) The ratio A+T/G+C is constant for all natural DNAs.
D) The two complementary strands are antiparallel.
E) Two hydrogen bonds form between A and T. - Correct Ans-C
In the Watson-Crick model of DNA structure (now called B-form DNA):
A) a purine in one strand always hydrogen bonds with a purine in the other strand.
B) A-T pairs share three hydrogen bonds.
C) G-C pairs share two hydrogen bonds.
D) the 5' ends of both strands are at one end of the helix.
E) the bases occupy the interior of the helix. - Correct Ans-E
The double helix of DNA in the B-form is stabilized by:
A) covalent bonds between the 3' end of one strand and the 5' end of the other.
B) hydrogen bonding between the phosphate groups of two side-by-side strands.
C) hydrogen bonds between the riboses of each strand.
BCH 3025
