
Concept explainers
A.
To determine: Whether the statement, “a bacterial replication fork is asymmetrical because it contains two DNA polymerase molecules that are structurally distinct” is correct.
Introduction: DNA is the blueprint of life and contains genetic information.
A.

Answer to Problem 7Q
Explanation of Solution
During DNA replication, one strand that runs in the direction of bacterial replication fork (5′-3′) is continuous and is referred as the leading strand. The other strand is made in fragments known as Okazaki fragments and is known as the lagging strand. On these strands, DNA polymerase enzyme molecules catalyze the synthesis of DNA. All the DNA polymerase molecules are structurally identical and thus, the given statement is incorrect. The replication fork is asymmetrical, as the lagging strand is synthesized in fragments and then they are ligate together by DNA ligase.
B.
To determine: Whether the statement, “Okazaki fragments are removed by a nuclease that degrades RNA” is correct.
Introduction: DNA is the blueprint of life and contains genetic information. Replication of DNA is semiconservative. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA can undergo spontaneous damage from water every day. DNA damage may be caused due to environment insults, and DNA replication errors. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
B.

Answer to Problem 7Q
Explanation of Solution
When new DNA strands are formed, RNA primers are removed by nuclease enzyme and gaps are filled with DNA by DNA polymerase enzyme. The gaps between Okazaki fragments of DNA are connected by DNA ligase enzyme. Thus, the statement is incorrect as only RNA primers are removed by nuclease (RNase).
C.
To determine: Whether the statement, “the error rate of DNA replication is reduced both by proofreading by DNA polymerase and by DNA mismatch repair” is correct.
Introduction: DNA is the blueprint of life and contains genetic information. Replication of DNA is semiconservative. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA can undergo spontaneous damage from water every day. DNA damage may be caused due to environment insults, and DNA replication errors. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
C.

Answer to Problem 7Q
Explanation of Solution
When new DNA strands are formed, RNA primers are removed and gaps are filled with DNA by DNA polymerase enzyme. DNA polymerase enzyme adds DNA nucleotides to an existing strand with high fidelity. It proofreads the DNA strand to check for any errors or mismatch with an error rate of 107
D.
To determine: Whether the statement, “in the absence of DNA repair, genes are unstable” is correct.
Introduction: DNA is the blueprint of life and contains genetic information. Replication of DNA is semiconservative. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA can undergo spontaneous damage from water every day. DNA damage may be caused due to environment insults, and DNA replication errors. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
D.

Answer to Problem 7Q
Explanation of Solution
DNA is the blueprint of life and contains genetic information. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA damage may be caused due to environment insults, and DNA replication occurs. However, cells have DNA repair mechanisms that detect damage and repair it. The cells undergo programmed cell death, that is, apoptosis. If DNA repair systems are absent, then the damage would accumulate due to some mutations, it would cause diseases such as cancer. Many genes would become inactive, thus the statement is correct.
E.
To determine: Whether the statement, “none of the aberrant bases formed by deamination occur naturally in DNA” is correct.
Introduction: DNA is the blueprint of life and contains genetic information. Replication of DNA is semiconservative. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA can undergo spontaneous damage from water every day. DNA damage may be caused due to environment insults, and DNA replication errors. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
E.

Answer to Problem 7Q
Explanation of Solution
DNA damage occurs continuously in cells every day. Deamination is the spontaneous hydrolysis of
F.
To determine: Whether the statement, “cancer can result from the accumulation of mutations in somatic cells” is correct.
Introduction: DNA is the blueprint of life and contains genetic information. Replication of DNA is semiconservative. The integrity of DNA is essential for life, and if there is any damage to it, it will lead to mutation and disease. DNA can undergo spontaneous damage from water every day. DNA damage may be caused due to environment insults, and DNA replication errors. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
F.

Answer to Problem 7Q
Explanation of Solution
DNA damage occurs continuously in cells every day. It may be caused due to environment insults, and DNA replication occurs. However, cells have DNA repair mechanisms that detect damage and repair it. The cells that are not repaired undergo programmed cell death. If the damage accumulates due to some mutations, it would cause diseases such as cancer.
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Chapter 6 Solutions
Essential Cell Biology (fifth Edition)
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