BIOL101 Module 4 Practice Exam
Essential Biology I w/Lab | 100
Comprehensive Questions with Detailed
Rationales
PART 1: DNA & RNA STRUCTURE (Questions 1–12)
Question 1
A nitrogenous base plus a deoxyribose sugar is called a ________,
and a base plus deoxyribose plus a phosphate group is called a
_________.
A) Nucleotide; Nucleoside
B) Nucleoside; Nucleotide
C) Chromatin; Chromosome
D) Codon; Anticodon
,Correct Answer: B) Nucleoside; Nucleotide
Rationale: A nucleoside consists of a nitrogenous base
covalently attached to a sugar (either ribose or deoxyribose)
but lacks a phosphate group. When a phosphate group is
added to the nucleoside, it becomes a nucleotide. Nucleotides
are the building blocks of nucleic acids like DNA and RNA. The
phosphate group is what allows nucleotides to link together
through phosphodiester bonds to form the nucleic acid
backbone.
Question 2
Which of the following nitrogenous bases are classified
as purines?
A) Cytosine and Thymine
B) Adenine and Guanine
C) Uracil and Cytosine
D) Thymine and Uracil
Correct Answer: B) Adenine and Guanine
,Rationale: Purines are nitrogenous bases characterized by a
double-ring structure. Adenine (A) and Guanine (G) are the two
purines found in nucleic acids. Pyrimidines, in contrast, have a
single-ring structure and include Cytosine (C), Thymine (T), and
Uracil (U). This structural difference is important for base pairing
and the overall geometry of the DNA double helix.
Question 3
Which nitrogenous bases are classified as pyrimidines?
A) Adenine and Guanine
B) Cytosine, Thymine, and Uracil
C) Adenine and Thymine
D) Guanine and Cytosine
Correct Answer: B) Cytosine, Thymine, and Uracil
Rationale: Pyrimidines are nitrogenous bases with a single-ring
structure. Cytosine (C), Thymine (T), and Uracil (U) are all
pyrimidines. In DNA, the pyrimidines are cytosine and thymine;
in RNA, uracil replaces thymine. The pairing rules (Chargaff's
, rules) state that purines always pair with pyrimidines: A pairs
with T (or U in RNA), and G pairs with C.
Question 4
In DNA, adenine always pairs with:
A) Guanine
B) Cytosine
C) Thymine
D) Uracil
Correct Answer: C) Thymine
Rationale: This is a fundamental principle of DNA structure
known as complementary base pairing. Adenine (A) forms two
hydrogen bonds with Thymine (T). This specific pairing is
essential for the accurate replication of DNA and the
transmission of genetic information. The A-T pair is held
together by two hydrogen bonds, while the G-C pair is held
together by three hydrogen bonds, making G-C pairs slightly
more stable.
Essential Biology I w/Lab | 100
Comprehensive Questions with Detailed
Rationales
PART 1: DNA & RNA STRUCTURE (Questions 1–12)
Question 1
A nitrogenous base plus a deoxyribose sugar is called a ________,
and a base plus deoxyribose plus a phosphate group is called a
_________.
A) Nucleotide; Nucleoside
B) Nucleoside; Nucleotide
C) Chromatin; Chromosome
D) Codon; Anticodon
,Correct Answer: B) Nucleoside; Nucleotide
Rationale: A nucleoside consists of a nitrogenous base
covalently attached to a sugar (either ribose or deoxyribose)
but lacks a phosphate group. When a phosphate group is
added to the nucleoside, it becomes a nucleotide. Nucleotides
are the building blocks of nucleic acids like DNA and RNA. The
phosphate group is what allows nucleotides to link together
through phosphodiester bonds to form the nucleic acid
backbone.
Question 2
Which of the following nitrogenous bases are classified
as purines?
A) Cytosine and Thymine
B) Adenine and Guanine
C) Uracil and Cytosine
D) Thymine and Uracil
Correct Answer: B) Adenine and Guanine
,Rationale: Purines are nitrogenous bases characterized by a
double-ring structure. Adenine (A) and Guanine (G) are the two
purines found in nucleic acids. Pyrimidines, in contrast, have a
single-ring structure and include Cytosine (C), Thymine (T), and
Uracil (U). This structural difference is important for base pairing
and the overall geometry of the DNA double helix.
Question 3
Which nitrogenous bases are classified as pyrimidines?
A) Adenine and Guanine
B) Cytosine, Thymine, and Uracil
C) Adenine and Thymine
D) Guanine and Cytosine
Correct Answer: B) Cytosine, Thymine, and Uracil
Rationale: Pyrimidines are nitrogenous bases with a single-ring
structure. Cytosine (C), Thymine (T), and Uracil (U) are all
pyrimidines. In DNA, the pyrimidines are cytosine and thymine;
in RNA, uracil replaces thymine. The pairing rules (Chargaff's
, rules) state that purines always pair with pyrimidines: A pairs
with T (or U in RNA), and G pairs with C.
Question 4
In DNA, adenine always pairs with:
A) Guanine
B) Cytosine
C) Thymine
D) Uracil
Correct Answer: C) Thymine
Rationale: This is a fundamental principle of DNA structure
known as complementary base pairing. Adenine (A) forms two
hydrogen bonds with Thymine (T). This specific pairing is
essential for the accurate replication of DNA and the
transmission of genetic information. The A-T pair is held
together by two hydrogen bonds, while the G-C pair is held
together by three hydrogen bonds, making G-C pairs slightly
more stable.
