Study Guide for Exam 4
Dairon Rodriguez
Chapter 14: Mutation, DNA Repair, and Cancer
14.1 Mutation
List the different ways that mutations can alter the amino acid sequence of
a polypeptide.
Mutations are a change in the nucleotide sequence on the genetic material. Essential to the
continuity of life because they are a source of variation for natural selection. New mutations are
more likely to be harmful than beneficial, they can be neutral or positive.
DNA repair systems reverse DNA damage
Cancer is a disease caused by gene mutations
Point mutation examples:
Base substitution
a. 5’ – GGCGCTAGATC – 3’ 5’ – GGCGCTAGATC – 3’
b. 3’ – CCGCGATCTAG – 5’ 3’ – CCGCGATCTAG – 5’
Add or delete a single base pair
a. 5’ – GGCGCTAGATC – 3’ 5’ – GGCAGCTAGATC – 3’
b. 3’ – CCGCGATCTAG – 5’ 3’ – CCGTCGATCTAG – 5’
Gene mutations may affect amino acid sequences:
a. Silent mutation (Base Substitution): Does not alter the amino acid sequence. Due to
degeneracy of genetic code
b. Missense mutation (Base Substitution): Changes a single amino acid in a polypeptide.
May or may not alter function if substituted amino acid is similar in chemistry to original.
Ex: Sickle-cell disease (an example of an altered function)
c. Nonsense mutation (Base Substitution): Change from a normal codon to a stop codon,
that causes translation to be terminated earlier than expected, producing a truncated
polypeptide.
d. Frameshift mutation (Addition of deletion of a single base): Addition or deletion of
nucleotides (excluding multiples of 3). Completely different amino acid sequence
, downstream from mutation. Such a large change in polypeptide structure is likely to
inhibit protein function.
(side note): Changes in protein function may affect the ability of an organism to survive and to
reproduce, except for silent mutations, new mutations are more likely to produce polypeptides
that have reduced rather than enhanced function. However, mutations can occasionally produce a
polypeptide that has an enhanced function. Such mutations may change in frequency in a
population over the course of many generations due to natural selection.
(side note):
Enhance: Mejorar
Inhibit: Quitar la function
Offspring: Descendencia
Distinguish between mutations in somatic cells and in germ-line cells.
The time and location of a mutation determines its severity and the heritability
Germ-line cells give rise to gametes. Mutation can occur in sperm or egg cell, or in gamete
progenitor cells. Likewise, when such an individual produces gamete, the mutation may be
transmitted to future generations of offspring. Because humans carry two copies of most genes, a
new mutation in a single gene has a 50% chance of being transmitted from parent to offspring
Somatic cells are all other body cell. Mutations within somatic cells can occur early or late in
development. What are the consequences of a mutation that happens during the embryonic stage?
Ex: a mutation occurred within a single embryonic cell. This single somatic cell was the
precursor for many cells of the adult. Therefore, in the adult, a patch of tissue contains cells that
carry the mutation. The size of any patch depends on the timing of a new mutation. In general,
the earlier a mutation occurs during development, the larger the patch. An individual with
somatic regions that are genetically different from each other is called a mosaic.
(side note): Although a change in hair color is not a harmful consequence, mutations during
early stages of life can be quite harmful, especially if they disrupt essential developmental
processes. Even though it is sensible to avoid environmental agents that cause mutations at any
stage of life, the possibility of somatic mutations is a compelling reason to avoid such agents
during the early stages of life such as embryonic and fetal development, infancy, and early
childhood.
Discuss the difference between spontaneous and induced mutations.
, Spontaneous mutations result from abnormalities in biological processes: Ex. DNA replication
DNA polymerase can make mistakes during DNA replication by putting the wrong base in a
newly synthesized daughter strand. Though such errors are rare due to the proofreading function
of DNA polymerase, they do occur. The rates of spontaneous mutations vary from species to
species and from gene to gene. Larger genes are usually more likely to incur a mutation than are
smaller ones. A common rate of spontaneous mutation among various species is approximately 1
mutation for every 1 million genes per cell division. This is the expected rate of spontaneous
mutation, which creates the variation that is the raw material of evolution.
Induced mutations are caused by environmental agents that enter the cell and alter the structure
of DNA. They cause the mutation rate to be higher than the spontaneous mutation rate. Agents
that cause mutation are called mutagens. Mutagenic agents can be categorized as chemical or
physical mutagens.
Induced mutations: deamination (caused by different chemicals) and pyrimidine dimer
(caused by UV)
*Mutagens: Chemical or physical agents that alter DNA. They disrupt DNA Replication, and
sometimes insert between the bases to distort the helix structure.
*To test for mutagens, the Ames test is used.
Induced mutations: deamination (caused by different chemicals) and pyrimidine dimer (caused
by UV)
Deamination causes mispairing and mutations. Deamination is caused by nitrous acid, which
deaminates bases, changing C to U so that it pairs with the wrong nucleotide.
Pyrimidine Dimers are formed by UV light, causing gaps or incorporation of incorrect bases. The
UV light provides energy for covalent bonding between two thymine bases. Thymine Dimers
prevent DNA Polymerase from proceeding normally.
14.2 DNA Repair
All living organisms require the ability to repair damage to DNA in order to minimize
mutation
Two components:
Detection of damage
Repair of damage
Nucleotide Excision Repair (NER)
Most common DNA repair system. The region encompassing several nucleotides in the
damaged strand is removed from the DNA. The intact undamaged strand is used as a
template for resynthesis of a normal complementary strand. This system is found in all
eukaryotes and prokaryotes.
Explain the connection between defects in DNA repair systems and the
inherited human disease Xeroderma pigmentosum.
Dairon Rodriguez
Chapter 14: Mutation, DNA Repair, and Cancer
14.1 Mutation
List the different ways that mutations can alter the amino acid sequence of
a polypeptide.
Mutations are a change in the nucleotide sequence on the genetic material. Essential to the
continuity of life because they are a source of variation for natural selection. New mutations are
more likely to be harmful than beneficial, they can be neutral or positive.
DNA repair systems reverse DNA damage
Cancer is a disease caused by gene mutations
Point mutation examples:
Base substitution
a. 5’ – GGCGCTAGATC – 3’ 5’ – GGCGCTAGATC – 3’
b. 3’ – CCGCGATCTAG – 5’ 3’ – CCGCGATCTAG – 5’
Add or delete a single base pair
a. 5’ – GGCGCTAGATC – 3’ 5’ – GGCAGCTAGATC – 3’
b. 3’ – CCGCGATCTAG – 5’ 3’ – CCGTCGATCTAG – 5’
Gene mutations may affect amino acid sequences:
a. Silent mutation (Base Substitution): Does not alter the amino acid sequence. Due to
degeneracy of genetic code
b. Missense mutation (Base Substitution): Changes a single amino acid in a polypeptide.
May or may not alter function if substituted amino acid is similar in chemistry to original.
Ex: Sickle-cell disease (an example of an altered function)
c. Nonsense mutation (Base Substitution): Change from a normal codon to a stop codon,
that causes translation to be terminated earlier than expected, producing a truncated
polypeptide.
d. Frameshift mutation (Addition of deletion of a single base): Addition or deletion of
nucleotides (excluding multiples of 3). Completely different amino acid sequence
, downstream from mutation. Such a large change in polypeptide structure is likely to
inhibit protein function.
(side note): Changes in protein function may affect the ability of an organism to survive and to
reproduce, except for silent mutations, new mutations are more likely to produce polypeptides
that have reduced rather than enhanced function. However, mutations can occasionally produce a
polypeptide that has an enhanced function. Such mutations may change in frequency in a
population over the course of many generations due to natural selection.
(side note):
Enhance: Mejorar
Inhibit: Quitar la function
Offspring: Descendencia
Distinguish between mutations in somatic cells and in germ-line cells.
The time and location of a mutation determines its severity and the heritability
Germ-line cells give rise to gametes. Mutation can occur in sperm or egg cell, or in gamete
progenitor cells. Likewise, when such an individual produces gamete, the mutation may be
transmitted to future generations of offspring. Because humans carry two copies of most genes, a
new mutation in a single gene has a 50% chance of being transmitted from parent to offspring
Somatic cells are all other body cell. Mutations within somatic cells can occur early or late in
development. What are the consequences of a mutation that happens during the embryonic stage?
Ex: a mutation occurred within a single embryonic cell. This single somatic cell was the
precursor for many cells of the adult. Therefore, in the adult, a patch of tissue contains cells that
carry the mutation. The size of any patch depends on the timing of a new mutation. In general,
the earlier a mutation occurs during development, the larger the patch. An individual with
somatic regions that are genetically different from each other is called a mosaic.
(side note): Although a change in hair color is not a harmful consequence, mutations during
early stages of life can be quite harmful, especially if they disrupt essential developmental
processes. Even though it is sensible to avoid environmental agents that cause mutations at any
stage of life, the possibility of somatic mutations is a compelling reason to avoid such agents
during the early stages of life such as embryonic and fetal development, infancy, and early
childhood.
Discuss the difference between spontaneous and induced mutations.
, Spontaneous mutations result from abnormalities in biological processes: Ex. DNA replication
DNA polymerase can make mistakes during DNA replication by putting the wrong base in a
newly synthesized daughter strand. Though such errors are rare due to the proofreading function
of DNA polymerase, they do occur. The rates of spontaneous mutations vary from species to
species and from gene to gene. Larger genes are usually more likely to incur a mutation than are
smaller ones. A common rate of spontaneous mutation among various species is approximately 1
mutation for every 1 million genes per cell division. This is the expected rate of spontaneous
mutation, which creates the variation that is the raw material of evolution.
Induced mutations are caused by environmental agents that enter the cell and alter the structure
of DNA. They cause the mutation rate to be higher than the spontaneous mutation rate. Agents
that cause mutation are called mutagens. Mutagenic agents can be categorized as chemical or
physical mutagens.
Induced mutations: deamination (caused by different chemicals) and pyrimidine dimer
(caused by UV)
*Mutagens: Chemical or physical agents that alter DNA. They disrupt DNA Replication, and
sometimes insert between the bases to distort the helix structure.
*To test for mutagens, the Ames test is used.
Induced mutations: deamination (caused by different chemicals) and pyrimidine dimer (caused
by UV)
Deamination causes mispairing and mutations. Deamination is caused by nitrous acid, which
deaminates bases, changing C to U so that it pairs with the wrong nucleotide.
Pyrimidine Dimers are formed by UV light, causing gaps or incorporation of incorrect bases. The
UV light provides energy for covalent bonding between two thymine bases. Thymine Dimers
prevent DNA Polymerase from proceeding normally.
14.2 DNA Repair
All living organisms require the ability to repair damage to DNA in order to minimize
mutation
Two components:
Detection of damage
Repair of damage
Nucleotide Excision Repair (NER)
Most common DNA repair system. The region encompassing several nucleotides in the
damaged strand is removed from the DNA. The intact undamaged strand is used as a
template for resynthesis of a normal complementary strand. This system is found in all
eukaryotes and prokaryotes.
Explain the connection between defects in DNA repair systems and the
inherited human disease Xeroderma pigmentosum.
