BIOCHEM 423- UNIT 4 EXAM REVIEW
QUESTIONS AND ANSWERS 100% PASS
DNA is more resistant to hydrolysis than RNA. What feature of DNA is responsible for this
characteristic? - ANS the absence of a 2′-hydroxyl group in deoxyribose
The difference between a nucleoside and a nucleotide is that: - ANS nucleotides contain one
or more phosphate groups, whereas nucleosides have none.
The major interaction stabilizing the double helical structure of DNA is: - ANS hydrogen bonds
between bases on opposite strands.
An important key to understanding the structure and function of DNA was the observation that
the amount of A equaled the amount of T and the amount of G equaled the amount of C. This
important observation was made by: - ANS Erwin Chargaff.
Which compound is found in DNA but not in RNA? - ANS thymine
Write the complementary sequence for TCGAAC. Write the new sequence in the standard 5′→3′
notation - ANS 5'- GTTCGA-3'
Using Chargaff's rule, determine the percentages of all of the bases in DNA that is 26% thymine.
- ANS A: 26%
C: 24%
G: 24%
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, How many hydrogen bonds exist between this DNA strand and its complementary strand?
5′-CCGAGGC-3′ - ANS C/G = 3 H bonds (6 total)
A/T= 2 H bonds (1 total)
(6x3) + (2x1) = 20 Hydrogen bonds
The composition, in mole-fraction units, of one of the strands of a double helical DNA molecule
is [A]=0.30 and [G]=0.24. This strand is the reference strand.
- What is the total [T] and [C] for the reference strand?
-What is the total [A] and [G] for the complementary strand?
- What is the total [T] for the complementary strand?
- What is the total [C] for the complementary strand? - ANS -[A] + [G] = 0.54 so the remaining
[T] + [C] = 0.46
-Complementary strand [A] + [G] = 0.46
- [T] = 0.3
- [C] = 0.24
How is circular DNA compacted within the nucleoid of a cell? - ANS supercoiling
What is the term for two circular DNA molecules that differ only in the number of helical turns,
also called linking number? - ANS topoisomers
Label each level of DNA packaging in the eukaryotic chromosome with the appropriate term
(least to greatest) - ANS 1. dna double helix
2. histone protein
@COPYRIGHT ALL RIGHTS RESERVED PAGE 2 OF 14
QUESTIONS AND ANSWERS 100% PASS
DNA is more resistant to hydrolysis than RNA. What feature of DNA is responsible for this
characteristic? - ANS the absence of a 2′-hydroxyl group in deoxyribose
The difference between a nucleoside and a nucleotide is that: - ANS nucleotides contain one
or more phosphate groups, whereas nucleosides have none.
The major interaction stabilizing the double helical structure of DNA is: - ANS hydrogen bonds
between bases on opposite strands.
An important key to understanding the structure and function of DNA was the observation that
the amount of A equaled the amount of T and the amount of G equaled the amount of C. This
important observation was made by: - ANS Erwin Chargaff.
Which compound is found in DNA but not in RNA? - ANS thymine
Write the complementary sequence for TCGAAC. Write the new sequence in the standard 5′→3′
notation - ANS 5'- GTTCGA-3'
Using Chargaff's rule, determine the percentages of all of the bases in DNA that is 26% thymine.
- ANS A: 26%
C: 24%
G: 24%
@COPYRIGHT ALL RIGHTS RESERVED PAGE 1 OF 14
, How many hydrogen bonds exist between this DNA strand and its complementary strand?
5′-CCGAGGC-3′ - ANS C/G = 3 H bonds (6 total)
A/T= 2 H bonds (1 total)
(6x3) + (2x1) = 20 Hydrogen bonds
The composition, in mole-fraction units, of one of the strands of a double helical DNA molecule
is [A]=0.30 and [G]=0.24. This strand is the reference strand.
- What is the total [T] and [C] for the reference strand?
-What is the total [A] and [G] for the complementary strand?
- What is the total [T] for the complementary strand?
- What is the total [C] for the complementary strand? - ANS -[A] + [G] = 0.54 so the remaining
[T] + [C] = 0.46
-Complementary strand [A] + [G] = 0.46
- [T] = 0.3
- [C] = 0.24
How is circular DNA compacted within the nucleoid of a cell? - ANS supercoiling
What is the term for two circular DNA molecules that differ only in the number of helical turns,
also called linking number? - ANS topoisomers
Label each level of DNA packaging in the eukaryotic chromosome with the appropriate term
(least to greatest) - ANS 1. dna double helix
2. histone protein
@COPYRIGHT ALL RIGHTS RESERVED PAGE 2 OF 14
