CHAPTER 5 Flashcards
(203 cards)
1
Q
Its primary function is to store and transfer genetic information.
A
deoxyribonucleic acid (DNA)
2
Q
It functions primarily in the synthesis of proteins, the molecules that carry out
essential cellular functions.
A
ribonucleic acid (RNA)
3
Q
The components of these include a
A
(a) five-carbon (pentose) sugar, (b)
phosphate, and (c) four heterocyclic amines called nitrogenous bases.
4
Q
is an unbranched
Polymer-containing monomer units
called nucleotides.
A
nucleic acid
5
Q
is a three-subunit
molecule in which a pentose sugar is
bonded to both a phosphate group and
a nitrogen-containing heterocyclic
base.
A
nucleotide
6
Q
Where is DNA primarily located in a cell?
A. Cytoplasm
B. Mitochondria
C. Nucleus
D. Ribosomes
A
Answer: C. Nucleus
Explanation: DNA is found in the nucleus, where it stores and transfers genetic information.
7
Q
What is the main function of RNA?
A. Storing genetic information
B. Catalyzing chemical reactions
C. Synthesizing proteins
D. Transporting energy
A
Answer: C. Synthesizing proteins
Explanation: RNA plays a key role in protein synthesis by acting as a messenger and facilitating translation.
8
Q
Which sugar is found in RNA?
A. Glucose
B. Ribose
C. Deoxyribose
D. Fructose
A
Answer: B. Ribose
Explanation: RNA contains ribose, a pentose sugar, while DNA contains deoxyribose.
9
Q
What distinguishes deoxyribose from ribose?
A. Deoxyribose contains one more oxygen atom than ribose.
B. Deoxyribose lacks an -OH group on the 2′ carbon.
C. Deoxyribose contains two phosphate groups.
D. Deoxyribose contains uracil instead of thymine.
A
Answer: B. Deoxyribose lacks an -OH group on the 2′ carbon.
Explanation: The absence of the hydroxyl group (-OH) on the 2′ carbon of deoxyribose distinguishes it from ribose.
10
Q
Which nitrogenous base is found in RNA but not DNA?
A. Adenine
B. Thymine
C. Uracil
D. Cytosine
A
Answer: C. Uracil
Explanation: RNA contains uracil (U) instead of thymine (T), which is found in DNA.
11
Q
What is the building block of nucleic acids?
A. Amino acids
B. Nucleotides
C. Fatty acids
D. Monosaccharides
A
Answer: B. Nucleotides
Explanation: Nucleotides, composed of a sugar, phosphate, and nitrogenous base, are the monomers of nucleic acids.
12
Q
What are nucleosides composed of?
A. Sugar and phosphate
B. Sugar and nitrogenous base
C. Nitrogenous base and phosphate
D. Sugar, phosphate, and nitrogenous base
A
Answer: B. Sugar and nitrogenous base
Explanation: Nucleosides consist of a sugar bonded to a nitrogenous base.
13
Q
Which bond connects the sugar and nitrogenous base in a nucleoside?
A. β-N-glycosidic bond
B. Phosphodiester bond
C. Hydrogen bond
D. Ionic bond
A
Answer: A. β-N-glycosidic bond
Explanation: The sugar and nitrogenous base in a nucleoside are linked by a β-N-glycosidic bond.
14
Q
What is added to a nucleoside to form a nucleotide?
A. Another sugar molecule
B. A nitrogenous base
C. A phosphate group
D. A protein chain
A
Answer: C. A phosphate group
Explanation: A nucleotide is formed when a phosphate group is added to a nucleoside.
15
Q
Where does the phosphate group attach in a nucleotide?
A. C1′ of the sugar
B. C2′ of the sugar
C. C3′ of the sugar
D. C5′ of the sugar
A
Answer: D. C5′ of the sugar
Explanation: The phosphate group binds to the 5′ carbon of the sugar in a nucleotide.
16
Q
What defines the primary structure of nucleic acids?
A. The 3D helical arrangement of the strands
B. The alternating sugar-phosphate backbone
C. The sequence of nitrogenous bases
D. The hydrogen bonds between strands
A
Answer: C. The sequence of nitrogenous bases
Explanation: The primary structure of nucleic acids is defined by the linear sequence of bases.
17
Q
Which type of bond links nucleotides in the backbone of nucleic acids?
A. Hydrogen bond
B. Glycosidic bond
C. 3′,5′-phosphodiester bond
D. Peptide bond
A
Answer: C. 3′,5′-phosphodiester bond
Explanation: Nucleotides in nucleic acids are linked by 3′,5′-phosphodiester bonds between their sugar and phosphate groups.
18
Q
What is the charge of a nucleic acid molecule, and why?
A. Neutral, due to balanced components.
B. Positive, due to the sugar backbone.
C. Negative, due to phosphate groups.
D. Variable, depending on the nitrogenous bases.
A
Answer: C. Negative, due to phosphate groups.
Explanation: The phosphate groups in the backbone contribute a negative charge to nucleic acids.
19
Q
What is found at the 5′ end of a nucleic acid strand?
A. Free hydroxyl group
B. Free phosphate group
C. Free nitrogenous base
D. Free ribose sugar
A
Answer: B. Free phosphate group
Explanation: The 5′ end of a nucleic acid strand typically has a free phosphate group.
20
Q
Which property contributes to the acidic nature of nucleic acids?
A. The presence of ribose sugar
B. The presence of nitrogenous bases
C. The free hydroxyl groups on the phosphate backbone
D. The non-terminal phosphate groups in the backbone
A
Answer: D. The non-terminal phosphate groups in the backbone
Explanation: Non-terminal phosphate groups exhibit acidic behavior, contributing to the nucleic acid’s acidic nature.
21
Q
are produced by the
combination of a sugar, either ribose
(in RNA) or 2′-deoxyribose (in DNA),
with a purine or a pyrimidine base.
A
Nucleosides
22
Q
The sugar unit of a nucleotide is either the pentose _____ or the pentose __________.
Structurally, the only difference between these two sugars occurs at carbon 2′
A
ribose,2′-deoxyribose
23
Q
is a derivative of purine
A
Caffeine
24
Q
is a derivative of pyrimidine
A
Thiamine (vit B)
25
Identify the nucleotide component derived from phosphoric acid (H₃PO₄) that loses two hydrogen atoms under cellular pH to form a hydrogen phosphate ion (HPO₄²⁻).
Answer:
Phosphate group
Explanation:
The phosphate group, derived from phosphoric acid, forms HPO₄²⁻ under cellular pH conditions and is an essential component of nucleotides.
26
what the suffix used to name nucleosides derived from purines and pyrimidines.
-osine for purines
-idine for pyrimidines
27
First, the ________and __________react to form a two-subunit
entity called a _______(not nucleotide, s versus t).
pentose sugar, nitrogen-containing base, nucleoside
28
The nucleoside reacts with a ________ to form the three-subunit entity called
a nucleotide
phosphate group
29
Nucleoside =?
sugar + base
29
The base is always attached to C1′ of the sugar,
which is always in a β-configuration. (T/F)
T
30
Nucleotide = ?
nucleoside + phosphate
31
. For purine bases, attachment is through _____; for
pyrimidine bases, _____ is involved.
N9,N1
32
The bond connecting the sugar and base is a _______
β-N-glycosidic
linkage
33
A molecule of water is formed as the two
molecules bond together; a ___________occurs.
condensation reaction
34
. For pyrimidine bases, the suffix ______is used
-idine
34
are named as derivatives of the base that they contain; the base’s
name is modified using a suffix.
Nucleosides
35
The prefix _________- is used to indicate that the sugar present is
deoxyribose.
deoxy
36
Nucleotides are nucleosides that have a ____________present.
phosphate group bonded to the pentose
sugar
37
The phosphate group is attached to the sugar at the ____′ position through a
___________.
C5,phosphoester linkage
38
As with nucleoside formation, a molecule of water is produced in nucleotide
formation. Thus, overall, ____________are produced in combining a
sugar, base, and phosphate into a nucleotide.
two molecules of water
39
Because the sugar–phosphate
backbone of a given nucleic acid
does not vary, the primary
structure of the nucleic acid
depends only on the sequence of
bases present
5′ T–G–C–A 3′
40
Each nonterminal phosphate
group of the sugarphosphate backbone is
bonded to two sugar
molecules through a 3′,5′-
__________.
phosphodiester linkage
41
Two strands of DNA form a
right-handed double helix.
42
The bases in opposite strands _______according to
the AT/GC rule.
hydrogen bond
42
are pieces of DNA that
carry the genetic instructions, or genes, of
an organism
Chromosomes
43
44
Organisms such as the
_________ (no true nucleus surrounded
by a nuclear membrane and there are no
true membrane-bound organelles) have
only a ________
prokaryotes, single chromosome
45
. Others, the
_________ (have cells containing a true
nucleus enclosed by a nuclear membrane),_______
, each of which
has many different levels of structure.
eukaryotes, have many chromosomes
46
The
complete set of genetic information in all
the chromosomes of an organism is called
the _______.
genome
47
The first level of structure is the ________,
which consists of a strand of DNA wrapped
around a small disk made up of _________.
nucleosome, histone proteins
48
This
complex of DNA and protein is termed
________ and makes up the eukaryotic
chromosomes
chromatin
49
The nucleosomes then coil into a larger
structure called the ________
condensed fiber
50
is an individual’s complete set of chromosomes
karyotype
51
an extra copy of chromosome 21
Some traits: varying degrees of mental challenges, a flattened face, and short stature
Down syndrome
52
An extra copy of chromosome 18
Some traits: extreme mental and physical defects and early death
Edward syndrome
53
An extra copy of chromosome 13
Some traits: extreme mental and physical defects and early death
Patau syndrome
54
Males with two X chromosomes and one Y
Some traits: show sexual immaturity and breast development
Klinefelter syndrome
55
Males with an extra Y chromosome
Some traits: unusually tall
XYY syndrome
55
Females with an extra X chromosome
Some traits: unusually tall, have problems with spoken language and processing spoken
words, coordination problems, and weaker muscles
Triple X syndrome
56
Females with only a single X chromosome
Some traits: short stature, a webbed neck, and sexual immaturity
Turner syndrome
57
It is thought that 50% of all miscarriages are the result of abnormal chromosome numbers.(T/F)
T
58
is the biochemical process by which DNA molecules produce
exact duplicates of themselves.
DNA replication
59
: ATP-dependent chromatin remodeling
complexes facilitate the sliding or removal of nucleosomes from DNA ahead of
the replication fork (
Chromatin disassembly (eukaryotes)
59
. The point at which the ______
is unwinding,
DNA double helix
59
binds and breaks and the hydrogen
bonds between complementary bases
DNA helicase
60
which is constantly changing (moving), is called the ________.
replication fork
61
: the enzyme ________generates short strands of RNA that bind to
the single-stranded DNA to initiate DNA synthesis (one primer in the leading
strand and multiple primers in the lagging strand)
primase
61
binds to the strand at the site of the primer and begins
adding new base pairs complementary to the strand by forming new
phosphodiester linkages
Polymerase
61
: continuous 5’ to 3’ direction (towards helicase)
leading strand
62
Once both the continuous and discontinuous strands are formed, an enzyme
called ________removes all RNA primers from the original strands, which
are replaced with appropriate bases.
exonuclease
62
in short Okazaki fragments (elongation is away from the
helicase)
lagging strand
63
Another exonuclease “______” the newly formed DNA to check, remove
and replace any errors.
proofreads
64
_______ joins Okazaki fragments together forming a single unified strand.
DNA ligase
65
A special type of DNA polymerase enzyme called __________ catalyzes the
synthesis of telomere sequences (repeated DNA sequences that act as
protective caps) at the ends of the DNA.
telomerase
66
Once completed, the _______ and its _________
into the familiar double helix shape.
parent strand, complementary DNA strand coils
67
breaks the hydrogen
bonds between the DNA strands.
This, in turn, causes supercoiling
of the molecule
DNA helicase
68
alleviates
positive supercoiling ahead of
the replication fork.
Topoisomerase
69
_________keep the _________.
They also protect the strands from
degradation and prevent
secondary structure formation.
Single-strand binding proteins, parental strands apart
70
______________ “reads” each
parental strand (or template) and
catalyzes the polymerization of a
complementary ________.
DNA polymerase III, daughter strand
71
molecules are the precursors
for DNA replication.
Deoxyribonucleotide triphosphate
(dNTP)
72
. In this reaction, a
___________ is released as a
phosphoester bond is formed
between the 5′-phosphoryl group of
the nucleotide being added to the
chain and the 3′-OH of the
nucleotide on the daughter strand.
pyrophosphate group
73
The ___________
dismantles after the
convergence of the two
replication forks (not
shown)
replisome complex
74
, ________ catalyzes the
synthesis of a small piece of RNA (10-
12 nucleotides) called an ________
that serves to “prime” the process of
DNA replication.
primase,RNA primer
75
The ends of the linear chromosomes have specialized DNA “caps” known as
_________
telomeres: : repetitive sequences that code for no particular gene
76
DNA replication begins at a unique sequence known as the ___________.
Replication occurs ________ at the rate of about 500 new nucleotides every
second!
replication origin, bidirectionally
77
In humans, a six base pair sequence, ________, is repeated 100 to 1000 times
TTAGGG
78
The point at which the new deoxyribonucleotide is added to the growing daughter
strand is called the ________
replication fork
79
The __________ of
molecular biology states
that in cells the flow of
genetic information
contained in DNA is a one-way street that leads from
DNA to RNA to protein
central dogma
80
An _______ is any part of a gene that
will form a part of the final
mature RNA produced by that
gene after ______ have been
removed by RNA splicing.
exon, introns
81
In RNA splicing, introns are
removed and exons are covalently
joined to one another as part of
generating the________.
mature RNA
82
is the process by which DNA directs the synthesis of hnRNA/mRNA
molecules that carry the coded information needed for protein synthesis
Transcription
83
83
is a process by which several different proteins that are variations of a
basic structural motif can be produced from a single gene
Alternative splicing
83
A given triplet in mRNA
contains a base sequence, transcribed from DNA, that translates
to a specific amino acid. This triplet is called a
codon
84
during which a complementary copy of DNA, called mRNA, is created
by RNA polymerase.
Transcription
84
Question 1: Directionality of Nucleotide Chains
What is the significance of the 5′ and 3′ ends in a nucleotide chain?
A. The 5′ end is always attached to a nitrogenous base, while the 3′ end is attached to a sugar.
B. The 5′ end normally carries a free hydroxyl group, while the 3′ end carries a free phosphate group.
C. The 5′ end carries a free phosphate group, while the 3′ end carries a free hydroxyl group.
D. Both the 5′ and 3′ ends are indistinguishable in function.
C. The 5′ end carries a free phosphate group, while the 3′ end carries a free hydroxyl group.
84
How is the sequence of bases in a nucleic acid strand conventionally read?
A. From the 3′ end to the 5′ end.
B. From the 5′ end to the 3′ end.
C. Randomly, as directionality does not affect reading.
D. Both directions simultaneously.
B. From the 5′ end to the 3′ end.
85
What contributes to the negative charge of the nucleic acid backbone?
A. Free nitrogenous bases.
B. The free –OH group of each phosphate.
C. The 1– charge on each nonterminal phosphate group.
D. The 3′ hydroxyl group of the sugar.
C. The 1– charge on each nonterminal phosphate group.
86
Why does each nonterminal phosphate group in the nucleic acid backbone exhibit acidic behavior?
A. It releases an H+ ion due to a free –OH group.
B. It is bound to the nitrogenous base.
C. It forms hydrogen bonds with adjacent bases.
D. It stabilizes the sugar-phosphate backbone.
A. It releases an H+ ion due to a free –OH group.
87
A. It releases an H+ ion due to a free –OH group.
B. Proteins and nucleic acids share backbones that are invariant in structure.
88
What distinguishes one DNA or RNA molecule from another?
A. The structure of the sugar-phosphate backbone.
B. The sequence of nitrogen bases attached to the backbone.
C. The presence of a 3′ or 5′ end.
D. The overall charge of the molecule.
B. The sequence of nitrogen bases attached to the backbone.
89
Which of the following is a shared characteristic of the primary structure of nucleic acids and proteins?
A. Both are composed of identical repeating units.
B. Both have invariant backbones and sequence-specific attachments.
C. Both have bases attached to their backbones that vary in polarity.
D. Both use only phosphodiester linkages in their backbones.
B. Both have invariant backbones and sequence-specific attachments.
90
What role do phosphodiester bonds play in the structure of nucleic acids?
A. They link nitrogenous bases to the sugar-phosphate backbone.
B. They join the sugar molecules of one nucleotide to the phosphate group of the next.
C. They provide hydrogen bonding between bases.
D. They are responsible for the helical shape of DNA.
B. They join the sugar molecules of one nucleotide to the phosphate group of the next.
91
Which of the following parallels can be drawn between nucleic acid and protein structures?
A. Both exhibit variation in their backbone structures.
B. Both are read from the 3′ end to the 5′ end.
C. Both have a sequence of attachments that define their specificity.
D. Both have nitrogenous bases as their primary structural unit.
C. Both have a sequence of attachments that define their specificity.
92
Why is the directionality of the 5′ and 3′ ends critical in nucleic acids?
A. It allows for the antiparallel arrangement of DNA strands.
B. It determines the overall charge of the molecule.
C. It ensures that only purines are paired with pyrimidines.
D. It stabilizes the sugar-phosphate backbone.
A. It allows for the antiparallel arrangement of DNA strands.
93
What repeat distance in the DNA double helix corresponds to a single complete 360° turn?
A. 0.34 nm
B. 2 nm
C. 3.4 nm
D. 10 nm
C. 3.4 nm
94
What does it mean for the two strands of DNA to be antiparallel?
A. Both strands run in the 5′-to-3′ direction.
B. One strand runs 5′-to-3′, and the other runs 3′-to-5′.
C. The nitrogenous bases are not aligned correctly.
D. Both strands are identical in their directionality.
B. One strand runs 5′-to-3′, and the other runs 3′-to-5′.
95
Why can only A-T and C-G base pairings occur within the DNA double helix?
A. The helix interior can only accommodate two pyrimidines.
B. Only purine-purine pairs fit properly within the helix.
C. Hydrogen bonding possibilities are most favorable for A-T and C-G pairings.
D. Base-stacking interactions prevent other pairings.
C. Hydrogen bonding possibilities are most favorable for A-T and C-G pairings.
96
Which of the following contributes to the stabilization of the DNA double helix?
A. Ionic bonding between the phosphate groups.
B. Covalent bonding between adjacent bases.
C. Hydrogen bonding and base-stacking interactions.
D. Disulfide bridges between purines and pyrimidines.
C. Hydrogen bonding and base-stacking interactions.
97
What is the primary contribution of base-stacking interactions in DNA?
A. They prevent denaturation of the helix under high temperatures.
B. They ensure that the DNA strands remain antiparallel.
C. They stabilize the double helix through hydrophobic interactions.
D. They facilitate hydrogen bonding between nitrogenous bases.
C. They stabilize the double helix through hydrophobic interactions.
98
What is the diameter of the DNA double helix, as determined by X-ray diffraction studies?
A. 0.34 nm
B. 1 nm
C. 2 nm
D. 3.4 nm
C. 2 nm
99
Which feature allows purines and pyrimidines to pair specifically within the DNA double helix?
A. Hydrophobic interactions between similar bases.
B. Hydrogen bonds form only between purines and pyrimidines.
C. Size constraints in the helix allow only purine-pyrimidine pairs.
D. Phosphate backbones restrict purine-purine interactions.
C. Size constraints in the helix allow only purine-pyrimidine pairs.
100
Why are hydrogen bonds crucial in the DNA double helix?
A. They covalently link the sugar-phosphate backbones of both strands.
B. They provide strong, permanent stability to the helix.
C. They stabilize the structure collectively despite being weak individually.
D. They create hydrophobic interactions between bases.
C. They stabilize the structure collectively despite being weak individually.
101
How did X-ray diffraction studies contribute to the understanding of DNA structure?
A. By identifying the base-pairing rules.
B. By revealing distances and dimensions of the helix.
C. By explaining the antiparallel nature of DNA strands.
D. By demonstrating the role of base-stacking interactions.
B. By revealing distances and dimensions of the helix.
102
What forms the "steps" of the DNA double helix, often compared to a spiral staircase?
A. The sugar-phosphate backbones.
B. Hydrogen bonds between the phosphate groups.
C. Nitrogenous base pairs.
D. Base-stacking interactions.
C. Nitrogenous base pairs.
103
What does the 0.34 nm repeat distance in DNA correspond to?
A. The spacing between each turn of the helix.
B. The diameter of the DNA double helix.
C. The spacing between stacked nitrogenous bases.
D. The length of the sugar-phosphate backbone.
C. The spacing between stacked nitrogenous bases.
104
What is true regarding the number of chromosomes in eukaryotic organisms?
A. All eukaryotic organisms have the same number of chromosomes.
B. Chromosome number varies across species, but the structure is consistent.
C. The number and structure of chromosomes vary widely among species.
D. Humans have the highest number of chromosomes among eukaryotes.
B. Chromosome number varies across species, but the structure is consistent.
105
What is the primary role of histone proteins in eukaryotic cells?
A. To encode genetic information.
B. To provide structural support and compact DNA within the nucleus.
C. To replicate DNA during cell division.
D. To catalyze the transcription of genes.
B. To provide structural support and compact DNA within the nucleus.
106
What is a karyotype, and what is its purpose?
A. A sequence of DNA used for genetic engineering.
B. A laboratory image of chromosomes used to detect abnormalities.
C. A method for coiling DNA into chromosomes.
D. A structure formed by histone proteins and DNA.
B. A laboratory image of chromosomes used to detect abnormalities.
107
108
109
110
111
112
113
Why is it essential for DNA replication to be highly accurate?
A. Errors in DNA replication slow down cell division.
B. Inaccurate replication may cause lethal mutations in critical genes.
C. Chromosomes would lose their compact structure without accuracy.
D. Histone proteins cannot support defective chromosomes.
B. Inaccurate replication may cause lethal mutations in critical genes.
114
What mechanism allows long DNA molecules to fit inside the eukaryotic nucleus?
A. Folding of DNA into a triple helix.
B. Binding of DNA to RNA molecules for structural support.
C. Wrapping of DNA around histone protein complexes.
D. Breaking DNA into smaller fragments.
C. Wrapping of DNA around histone protein complexes.
115
What happens to a cell that lacks a critical gene?
A. It becomes cancerous.
B. It dies because essential functions cannot be performed.
C. It mutates to compensate for the missing gene.
D. It survives but cannot divide.
B. It dies because essential functions cannot be performed.
116
Which of the following can a karyotype detect?
A. The presence of histone proteins in chromosomes.
B. Abnormalities in chromosome number or structure.
C. Mutations in the DNA sequence of a gene.
D. Levels of gene expression in a cell.
B. Abnormalities in chromosome number or structure.
117
What feature of histone proteins contributes to chromosome compaction?
A. Their ability to form covalent bonds with DNA.
B. Their role in unwinding the DNA double helix.
C. Their positive charge, which interacts with negatively charged DNA.
D. Their enzymatic activity, which coils the DNA.
C. Their positive charge, which interacts with negatively charged DNA.
118
Why are mutations in critical genes often lethal?
A. They destabilize the DNA molecule entirely.
B. They lead to the loss of structural proteins like histones.
C. They disrupt essential biological functions required for survival.
D. They increase chromosome number, leading to cell death.
C. They disrupt essential biological functions required for survival.
118
Which situation would most likely require a karyotype analysis?
A. Determining gene expression levels in a cancer cell.
B. Identifying the presence of a single-nucleotide mutation.
C. Diagnosing Down syndrome or other chromosomal abnormalities.
D. Assessing the presence of histone protein defects.
C. Diagnosing Down syndrome or other chromosomal abnormalities.
119
Why does DNA polymerase III require an RNA primer during DNA replication?
A. It can only initiate DNA synthesis on a single strand of DNA.
B. It can only elongate DNA strands from a free 3′-OH group provided by an RNA primer.
C. It catalyzes the formation of RNA primers before DNA synthesis begins.
D. It requires an RNA template to synthesize DNA strands.
B. It can only elongate DNA strands from a free 3′-OH group provided by an RNA primer.
120
What did Watson and Crick propose about DNA replication?
A. DNA replicates by breaking apart completely and forming two entirely new strands.
B. DNA replication involves an enzyme reading one strand and synthesizing a complementary strand, resulting in semiconservative replication.
C. DNA forms identical copies by self-folding into two double helices.
D. DNA replication occurs without the need for enzymatic activity.
B. DNA replication involves an enzyme reading one strand and synthesizing a complementary strand, resulting in semiconservative replication.
120
What is the main challenge posed by the antiparallel orientation of DNA strands during replication?
A. Both strands must be synthesized in the 3′ to 5′ direction.
B. DNA polymerase can only synthesize one strand continuously in the 5′ to 3′ direction, requiring lagging strand synthesis for the other.
C. DNA polymerase cannot recognize antiparallel strands.
D. Both strands are synthesized at the same rate, leading to replication errors.
B. DNA polymerase can only synthesize one strand continuously in the 5′ to 3′ direction, requiring lagging strand synthesis for the other.
121
Why was
15
N
15
N used in the Meselson and Stahl experiment?
A. It is a radioactive isotope that tracks DNA synthesis.
B. It replaces the nitrogen in DNA bases, allowing density differentiation.
C. It serves as a template for DNA synthesis.
D. It inhibits the synthesis of DNA, ensuring replication stops after one cycle.
B. It replaces the nitrogen in DNA bases, allowing density differentiation.
121
How is the lagging strand of DNA synthesized?
A. Continuously in the 5′ to 3′ direction.
B. In small fragments called Okazaki fragments that are later joined together.
C. In the 3′ to 5′ direction, opposite to the leading strand.
D. Without the need for primers.
B. In small fragments called Okazaki fragments that are later joined together.
121
After one cycle of replication in the Meselson and Stahl experiment, what was observed?
A. Two separate bands of heavy and light DNA.
B. A single intermediate-density band, representing hybrid DNA.
C. Only light DNA, indicating full replacement of heavy DNA.
D. No distinct bands due to incomplete replication.
B. A single intermediate-density band, representing hybrid DNA.
122
What constraint does DNA polymerase III face during DNA replication?
A. It can only elongate DNA strands in the 3′ to 5′ direction.
B. It can only synthesize in the 5′ to 3′ direction.
C. It requires DNA strands to be parallel for replication.
D. It synthesizes RNA strands before DNA strands.
B. It can only synthesize in the 5′ to 3′ direction.
123
What ensures accurate base pairing during DNA replication?
A. The equal size of purines and pyrimidines.
B. The hydrogen-bonding specificity between complementary bases.
C. DNA polymerase’s ability to synthesize both strands simultaneously.
D. The incorporation of RNA primers into the DNA strand.
B. The hydrogen-bonding specificity between complementary bases.
123
Why do only A-T and G-C base pairings occur?
A. Purines can only pair with purines, and pyrimidines with pyrimidines.
B. Purines pair with pyrimidines, fitting within the DNA helix and allowing optimal hydrogen bonding.
C. Hydrogen bonding is only possible between identical bases.
D. Base pairings are random but stabilized by the DNA backbone.
B. Purines pair with pyrimidines, fitting within the DNA helix and allowing optimal hydrogen bonding.
124
How is the leading strand synthesized during DNA replication?
A. By synthesizing short fragments that are later joined together.
B. Continuously in the 5′ to 3′ direction using a single RNA primer.
C. In the 3′ to 5′ direction using multiple RNA primers.
D. Through random nucleotide addition without primers.
B. Continuously in the 5′ to 3′ direction using a single RNA primer.
125
Why does the lagging strand require multiple RNA primers during DNA replication?
A. Because DNA synthesis occurs in the same direction as the replication fork.
B. Because it is synthesized discontinuously in short fragments called Okazaki fragments.
C. To facilitate continuous synthesis by DNA polymerase III.
D. To enable RNA polymerase to synthesize the strand.
B. Because it is synthesized discontinuously in short fragments called Okazaki fragments.
126
What enzyme is responsible for removing RNA primers during lagging strand synthesis in prokaryotes?
A. DNA ligase
B. DNA polymerase III
C. DNA polymerase I
D. Ribonuclease H
C. DNA polymerase I
127
Which enzyme is responsible for sealing the gaps between Okazaki fragments on the lagging strand?
A. DNA polymerase I
B. DNA polymerase III
C. Primase
D. DNA ligase
D. DNA ligase
128
What role does DNA polymerase III play in ensuring the fidelity of DNA replication?
A. It removes RNA primers from the lagging strand.
B. It synthesizes primers to initiate DNA replication.
C. It proofreads and corrects errors in the newly synthesized strand.
D. It seals Okazaki fragments into a continuous strand.
C. It proofreads and corrects errors in the newly synthesized strand.
129
In eukaryotic cells, what enzyme removes RNA primers from Okazaki fragments?
A. DNA polymerase I
B. DNA ligase
C. Ribonuclease H
D. DNA polymerase III
In eukaryotic cells, what enzyme removes RNA primers from Okazaki fragments?
A. DNA polymerase I
B. DNA ligase
C. Ribonuclease H
D. DNA polymerase III
130
Why do eukaryotic chromosomes become shorter with each round of replication?
A. DNA polymerase synthesizes new strands faster than the parental strands degrade.
B. DNA polymerase cannot completely replicate the ends of linear chromosomes.
C. DNA ligase fails to join Okazaki fragments at the ends of chromosomes.
D. Ribonuclease H removes DNA nucleotides instead of RNA primers.
B. DNA polymerase cannot completely replicate the ends of linear chromosomes.
131
Which of the following is a direct consequence of the limitations of DNA polymerase in eukaryotes?
A. The entire genome is replicated multiple times.
B. Both leading and lagging strands become progressively shorter after replication cycles.
C. RNA primers remain intact after DNA synthesis is complete.
D. DNA polymerase synthesizes in the 3′ to 5′ direction.
B. Both leading and lagging strands become progressively shorter after replication cycles.
132
Which of the following describes Okazaki fragments?
A. Short fragments synthesized continuously on the leading strand.
B. RNA primers synthesized by DNA polymerase I.
C. Discontinuous DNA fragments synthesized on the lagging strand.
D. Fragments that are only synthesized during eukaryotic DNA replication.
C. Discontinuous DNA fragments synthesized on the lagging strand.
133
Why do telomeres need protection from the cell's DNA repair systems?
A. Because they have a double-stranded DNA structure resembling damaged DNA.
B. Because they have single-stranded overhangs that resemble damaged DNA.
C. Because they lack a stable DNA sequence at the ends.
D. Because they do not contain histone proteins.
B. Because they have single-stranded overhangs that resemble damaged DNA.
134
What is the role of the single-stranded overhangs in protecting telomeres in humans?
A. They allow the binding of histones to stabilize the telomeres.
B. They bind to complementary repeats in double-stranded DNA to form protective loops.
C. They activate telomerase to repair the telomeres continuously.
D. They recruit enzymes for DNA synthesis at the ends.
B. They bind to complementary repeats in double-stranded DNA to form protective loops.
135
What is the primary function of the Shelterin complex?
A. To repair damaged telomeres by activating DNA repair mechanisms.
B. To protect telomeres from DNA repair mechanisms and regulate telomerase activity.
C. To enhance histone binding to telomeres for structural stability.
D. To prevent the synthesis of telomeres by DNA polymerase.
B. To protect telomeres from DNA repair mechanisms and regulate telomerase activity.
136
Which statement correctly describes the composition of a typical eukaryotic chromosome?
A. It is made of 85% DNA and 15% protein.
B. It is made of 15% DNA and 85% protein.
C. It consists only of DNA with no associated proteins.
D. It contains equal amounts of DNA and protein.
B. It is made of 15% DNA and 85% protein.
137
What is the primary function of histones in chromosomes?
A. To protect telomeres from degradation.
B. To form structural units for stable arrangement of long DNA molecules.
C. To catalyze the replication of DNA during the S phase.
D. To regulate the activity of telomerase in the cell.
B. To form structural units for stable arrangement of long DNA molecules.
138
Which of the following best describes homologous chromosomes?
A. Identical DNA sequences that code for the same traits.
B. Similar but not identical DNA sequences that code for the same traits in different forms.
C. Unrelated chromosomes with identical telomere sequences.
D. Chromosomes that interact with telomeres for DNA repair.
B. Similar but not identical DNA sequences that code for the same traits in different forms.
139
What is an example of a trait coded by homologous chromosomes?
A. Blue eyes and brown eyes.
B. Histone composition in chromatin.
C. Complementary DNA and RNA strands.
D. Protective loops in telomeres.
A. Blue eyes and brown eyes.
140
What happens to DNA after it is replicated in the cell?
A. It forms a protective loop at the ends of chromosomes.
B. It binds to histones to form structural units called chromosomes.
C. It activates the Shelterin complex for structural stabilization.
D. It undergoes degradation at telomeric regions.
B. It binds to histones to form structural units called chromosomes.
141
What might happen if telomeres were not protected from DNA repair systems?
A. The entire chromosome would degrade after replication.
B. DNA repair enzymes might incorrectly treat telomeres as damaged DNA.
C. The histones would fail to bind to the telomeres, destabilizing the chromosome.
D. Telomerase would become hyperactive, leading to excessive DNA synthesis.
B. DNA repair enzymes might incorrectly treat telomeres as damaged DNA.
142
What provides the most stable arrangement for long DNA molecules in eukaryotic cells?
A. Protective loops at the telomeres.
B. Interaction with histones to form chromosome structures.
C. Activation of telomerase at the replication fork.
D. Binding to Shelterin complexes for stabilization.
B. Interaction with histones to form chromosome structures.
143
Why is DNA replication more complex in eukaryotes than in prokaryotes?
A. Eukaryotes have single-stranded DNA, which requires more enzymes for replication.
B. Eukaryotic chromosomes are longer and have multiple replication origins.
C. Prokaryotes do not use bidirectional DNA replication.
D. Eukaryotes replicate their DNA without forming replication bubbles.
B. Eukaryotic chromosomes are longer and have multiple replication origins.
143
What is the role of multiple replication origins in eukaryotic DNA replication?
A. They help replicate DNA in only one direction along the chromosome.
B. They create "bubbles" of newly synthesized DNA that facilitate faster replication.
C. They reduce the need for helicase enzymes.
D. They allow RNA to be directly incorporated into the DNA sequence.
B. They create "bubbles" of newly synthesized DNA that facilitate faster replication
144
Which statement correctly describes bidirectional DNA replication in eukaryotes?
A. DNA synthesis occurs in one direction from each replication origin.
B. Replication proceeds in opposite directions from each replication origin.
C. Replication starts at the ends of the chromosome and proceeds inward.
D. Each replication bubble forms in only one direction along the chromosome.
B. Replication proceeds in opposite directions from each replication origin.
144
How do antimetabolites inhibit DNA replication?
A. They destroy DNA polymerase enzymes.
B. They mimic molecules required for DNA synthesis, leading to the production of nonfunctional DNA.
C. They block RNA transcription.
D. They prevent the unwinding of the DNA helix.
B. They mimic molecules required for DNA synthesis, leading to the production of nonfunctional DNA.
145
Why is folic acid critical for DNA synthesis?
A. It directly integrates into the DNA strand during replication.
B. It is reduced by dihydrofolate reductase and used in the synthesis of nucleotides.
C. It activates helicase for unwinding the DNA helix.
D. It is required for the synthesis of RNA molecules from DNA.
B. It is reduced by dihydrofolate reductase and used in the synthesis of nucleotides.
145
Role of 6-MP
What effect does the presence of 6-MP have during DNA replication?
A. It inhibits the reduction of folic acid, halting nucleotide synthesis.
B. It replaces adenine in nucleotides, producing nonfunctional DNA.
C. It accelerates the production of hnRNA for replication.
D. It prevents the formation of replication bubbles in eukaryotes.
B. It replaces adenine in nucleotides, producing nonfunctional DNA.
146
What is hnRNA?
A. A type of RNA directly involved in DNA replication.
B. RNA synthesized during DNA transcription, which undergoes post-transcription processing.
C. Mature RNA ready for protein synthesis.
D. A molecule that inhibits DNA synthesis when incorporated into the sequence.
B. RNA synthesized during DNA transcription, which undergoes post-transcription processing.
147
What happens to hnRNA after transcription?
A. It is immediately translated into proteins.
B. It undergoes processing to become messenger RNA (mRNA).
C. It binds to histones to form chromosomes.
D. It is converted into folic acid for nucleotide synthesis.
B. It undergoes processing to become messenger RNA (mRNA).
148
Which of the following occurs during the processing of hnRNA to mRNA in eukaryotes?
A. Addition of a 5’ cap and a poly-A tail, and removal of introns.
B. Replacement of uracil with thymine for stability.
C. Incorporation of nonfunctional nucleotides to regulate translation.
D. Binding with folic acid to enhance mRNA stability.
A. Addition of a 5’ cap and a poly-A tail, and removal of introns.
148
What is the primary function of messenger RNA (mRNA)?
A. To carry genetic instructions for protein synthesis to the ribosomes.
B. To directly bind with DNA during transcription.
C. To provide the template for DNA replication.
D. To synthesize telomerase for chromosome protection.
A. To carry genetic instructions for protein synthesis to the ribosomes.
149
What determines the length of a messenger RNA (mRNA) molecule?
A. The number of exons present in the gene.
B. The length of the protein it encodes.
C. The size of the ribosome it will bind to.
D. The number of nucleotide bases in the genome.
B. The length of the protein it encodes.
150
Which statement best describes ribosomal RNA (rRNA)?
A. It carries genetic information for protein synthesis.
B. It combines with proteins to form ribosomes, which lack informational function.
C. It is the smallest RNA, with 75–90 nucleotide units.
D. It converts hnRNA to mRNA during transcription.
B. It combines with proteins to form ribosomes, which lack informational function.
150
What is the primary function of small nuclear RNA (snRNA)?
A. Facilitating the transport of mRNA out of the nucleus.
B. Aiding the conversion of hnRNA to mRNA by editing the transcript.
C. Delivering amino acids during protein synthesis.
D. Binding with proteins to form ribosomes.
B. Aiding the conversion of hnRNA to mRNA by editing the transcript.
151
Which RNA type is the smallest in terms of nucleotide units?
A. Messenger RNA (mRNA)
B. Small nuclear RNA (snRNA)
C. Ribosomal RNA (rRNA)
D. Transfer RNA (tRNA)
D. Transfer RNA (tRNA)
152
What is the primary role of transfer RNA (tRNA)?
A. Synthesizing ribosomes for protein synthesis.
B. Delivering amino acids to the ribosomes during protein synthesis.
C. Carrying genetic instructions from DNA to the ribosome.
D. Splicing hnRNA to form mRNA.
B. Delivering amino acids to the ribosomes during protein synthesis.
152
What are the two main steps in the production of mRNA?
A. DNA replication followed by RNA transcription.
B. Transcription of hnRNA followed by its editing to form mRNA.
C. Translation of RNA followed by splicing of exons.
D. Binding of RNA polymerase followed by ribosome assembly.
B. Transcription of hnRNA followed by its editing to form mRNA.
152
What is the function of a promoter sequence in transcription?
A. It signals where DNA replication should begin.
B. It binds RNA polymerase and determines the transcription start site.
C. It prevents RNA polymerase from separating the DNA strands.
D. It codes for the RNA polymerase enzyme.
B. It binds RNA polymerase and determines the transcription start site.
152
What is heterogeneous nuclear RNA (hnRNA)?
A. The RNA that carries amino acids to ribosomes.
B. The initial transcript formed during transcription, later processed into mRNA.
C. The RNA found within ribosomes for structural support.
D. The mature RNA directly used for protein synthesis.
B. The initial transcript formed during transcription, later processed into mRNA.
153
Which of the following statements about transcription is correct?
A. Both DNA strands are transcribed simultaneously.
B. Only one strand of DNA is transcribed to produce an RNA copy.
C. The DNA template strand is read in the 5′ to 3′ direction.
D. Transcription results in the synthesis of double-stranded RNA.
B. Only one strand of DNA is transcribed to produce an RNA copy.
154
During chain elongation in transcription, what happens?
A. RNA polymerase binds to the promoter.
B. RNA polymerase synthesizes the RNA strand by adding nucleotides complementary to the DNA template strand.
C. RNA polymerase releases the RNA molecule from the DNA template.
D. Introns are removed from the RNA transcript.
B. RNA polymerase synthesizes the RNA strand by adding nucleotides complementary to the DNA template strand.
154
Which step of transcription involves the RNA polymerase binding to the DNA and separating its strands?
A. Initiation
B. Elongation
C. Termination
D. Splicing
A. Initiation
154
During the elongation phase of transcription, which of the following occurs?
A. RNA polymerase rewinds the DNA double helix.
B. RNA polymerase catalyzes the linkage of ribonucleotides complementary to the DNA template strand.
C. RNA polymerase uses ribose to unwind the DNA strands.
D. DNA polymerase replaces RNA polymerase to synthesize the RNA strand.
B. RNA polymerase catalyzes the linkage of ribonucleotides complementary to the DNA template strand.
154
Which of the following distinguishes RNA synthesis from DNA synthesis?
A. T rather than U pairs with A during base pairing.
B. RNA synthesis uses deoxyribose instead of ribose in the nucleic acid backbone.
C. U rather than T pairs with A during base pairing.
D. RNA synthesis involves the addition of dNTPs rather than rNTPs.
C. U rather than T pairs with A during base pairing.
155
What signals the end of the transcription process in eukaryotes?
A. The addition of a poly(A) tail.
B. RNA polymerase binding to a promoter sequence.
C. RNA polymerase reaching a termination sequence on the DNA.
D. Spliceosomes recognizing splice boundaries.
C. RNA polymerase reaching a termination sequence on the DNA.
155
What are spliceosomes composed of?
A. Ribosomal RNA (rRNA) and proteins.
B. Transfer RNA (tRNA) and small ribonucleoproteins (snRNPs).
C. Small nuclear ribonucleoproteins (snRNPs), each containing small RNA molecules and associated proteins.
D. hnRNA and ribozymes.
Correct Answer: C. Small nuclear ribonucleoproteins (snRNPs), each containing small RNA molecules and associated proteins.
155
What is the primary function of the 5′-methylated cap in eukaryotic mRNA?
A. It serves as a binding site for ribosomes during translation.
B. It prevents the binding of snRNPs during splicing.
C. It protects the RNA molecule from enzymatic degradation in the cytoplasm.
D. It signals the end of transcription.
Correct Answer: A. It serves as a binding site for ribosomes during translation.
155
Which of the following describes the role of the poly(A) tail in mRNA?
A. It facilitates the formation of intron-exon boundaries during splicing.
B. It protects the mRNA's 3′ end from enzymatic degradation.
C. It assists in the assembly of the transcription complex.
D. It catalyzes the splicing reactions during hnRNA processing.
B. It protects the mRNA's 3′ end from enzymatic degradation.
156
Which of the following is true about catalytic RNAs involved in splicing?
A. They are DNA molecules that recognize splice boundaries.
B. They are ribozymes that catalyze the splicing of introns from hnRNA.
C. They function exclusively in the cytoplasm.
D. They are enzymes that degrade hnRNA after splicing.
Correct Answer: B. They are ribozymes that catalyze the splicing of introns from hnRNA.
157
Which codon serves as both a start codon and a codon for methionine?
A. UAA
B. AUG
C. UAG
D. UGA
Correct Answer: B. AUG
157
Which of the following best explains the genome-phenome gap?
A. Bacterial genes lack introns, so splicing is not required.
B. Each gene can produce multiple mRNA molecules through alternative splicing.
C. Eukaryotic mRNA undergoes capping, but bacterial mRNA does not.
D. The presence of stop codons limits protein synthesis.
Correct Answer: B. Each gene can produce multiple mRNA molecules through alternative splicing.
157
Which of the following are stop codons?
A. AUG, UUG, UUA
B. UGA, UAA, UAG
C. UUU, UUG, UAA
D. UGA, AUG, UAG
Correct Answer: B. UGA, UAA, UAG
157
Which of the following statements about eukaryotic ribosomes is correct?
A. The small subunit contains three rRNA molecules and 49 proteins.
B. The large subunit contains three rRNA molecules and about 49 proteins.
C. The small subunit contains one rRNA molecule and 49 proteins.
D. Both subunits contain equal numbers of rRNA molecules.
Correct Answer: B. The large subunit contains three rRNA molecules and about 49 proteins.
158
Which of the following initiates protein synthesis during translation?
A. The binding of a stop codon to the ribosome.
B. The attachment of a tRNA with a glycine molecule to the ribosome.
C. The binding of a tRNA with methionine to the start codon on mRNA.
D. The formation of a dipeptide in the ribosomal large subunit.
Correct Answer: C. The binding of a tRNA with methionine to the start codon on mRNA.
159
Which of the following are functions of transfer RNA (tRNA) in protein synthesis?
1 Covalently binding a specific amino acid.
2 Recognizing the codon on mRNA corresponding to its amino acid.
3 Forming peptide bonds between amino acids.
A. 1 and 2 only.
B. 1 and 3 only.
C. 2 and 3 only.
D. 1, 2, and 3.
Correct Answer: A. 1 and 2 only.
160
During translation, what occurs during the process of translocation?
A. The ribosome moves down one codon on the mRNA, shifting the tRNA with the growing peptide chain to the first position.
B. A new tRNA binds to the stop codon on the mRNA.
C. The ribosome dissociates into its large and small subunits.
D. The mRNA strand shifts position to align the next codon with the ribosome.
A. The ribosome moves down one codon on the mRNA, shifting the tRNA with the growing peptide chain to the first position.
161
162
Which of the following signals the termination of translation?
A. The binding of a tRNA with methionine to a start codon.
B. The interaction of ribosomes with the 5′-methylated cap on mRNA.
C. The binding of a release factor to a stop codon on mRNA.
D. The formation of a peptide bond between the final two amino acids.
C. The binding of a release factor to a stop codon on mRNA.
163
What is the primary role of the ribosome in translation?
A. Covalently binding amino acids to tRNA molecules.
B. Decoding mRNA codons into amino acids and forming peptide bonds.
C. Transcribing DNA into RNA.
D. Recognizing introns and exons in the mRNA sequence.
B. Decoding mRNA codons into amino acids and forming peptide bonds.
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