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Questions and Answers
Gene mutations can only be caused by inserting additional nucleotides.
Gene mutations can only be caused by inserting additional nucleotides.
False (B)
Chromosomal mutations generally affect more than one gene.
Chromosomal mutations generally affect more than one gene.
True (A)
Point mutations occur at multiple points in the DNA sequence.
Point mutations occur at multiple points in the DNA sequence.
False (B)
All mutations are harmless to organisms.
All mutations are harmless to organisms.
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Mutations can be heritable if they alter the DNA in a germ cell.
Mutations can be heritable if they alter the DNA in a germ cell.
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A chromosomal mutation involving deletion results in the loss of part of a chromosome and can affect gene expression.
A chromosomal mutation involving deletion results in the loss of part of a chromosome and can affect gene expression.
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The term 'position effect' refers to a situation where a gene is permanently inactivated during cell division.
The term 'position effect' refers to a situation where a gene is permanently inactivated during cell division.
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Germ-line cells are responsible for giving rise to somatic cells such as muscle and skin cells.
Germ-line cells are responsible for giving rise to somatic cells such as muscle and skin cells.
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Induced mutations are caused solely by spontaneous errors during DNA replication.
Induced mutations are caused solely by spontaneous errors during DNA replication.
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Chromosomal rearrangements have no effect on the genes they contain.
Chromosomal rearrangements have no effect on the genes they contain.
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The temperature range for E. coli with a ts mutation is 33-38°C.
The temperature range for E. coli with a ts mutation is 33-38°C.
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Spontaneous mutations can occur due to errors in DNA replication.
Spontaneous mutations can occur due to errors in DNA replication.
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Heterochromatic regions are often associated with increased gene expression.
Heterochromatic regions are often associated with increased gene expression.
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A point mutation involves the substitution of only a single base pair.
A point mutation involves the substitution of only a single base pair.
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Transversions are changes of a purine to a pyrimidine or a pyrimidine to a purine.
Transversions are changes of a purine to a pyrimidine or a pyrimidine to a purine.
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Silent mutations alter the amino acid sequence of a polypeptide.
Silent mutations alter the amino acid sequence of a polypeptide.
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Mutations that involve the addition or deletion of three nucleotides do not cause a frameshift.
Mutations that involve the addition or deletion of three nucleotides do not cause a frameshift.
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A beneficial mutation reduces an organism's chance of survival and reproduction.
A beneficial mutation reduces an organism's chance of survival and reproduction.
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Down promoter mutations decrease the rate of transcription.
Down promoter mutations decrease the rate of transcription.
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A neutral mutation typically lowers the chance of an organism's survival.
A neutral mutation typically lowers the chance of an organism's survival.
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Conditional mutations express their effects only under specific environmental conditions.
Conditional mutations express their effects only under specific environmental conditions.
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Nonsense mutations result in a polypeptide that is complete and functional.
Nonsense mutations result in a polypeptide that is complete and functional.
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Frameshift mutations involve addition or deletion of nucleotides in multiples of one or two.
Frameshift mutations involve addition or deletion of nucleotides in multiples of one or two.
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Ionizing radiation includes X-rays and gamma rays and has short wavelength.
Ionizing radiation includes X-rays and gamma rays and has short wavelength.
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Nonionizing radiation can penetrate deeply into biological materials.
Nonionizing radiation can penetrate deeply into biological materials.
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Thymine dimers caused by nonionizing radiation may lead to mutations during DNA replication.
Thymine dimers caused by nonionizing radiation may lead to mutations during DNA replication.
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The first step in DNA repair is the synthesis of normal DNA.
The first step in DNA repair is the synthesis of normal DNA.
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Mismatch repair involves correcting a base pair mismatch in DNA.
Mismatch repair involves correcting a base pair mismatch in DNA.
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Direct repair involves the removal of both the abnormal DNA and the normal DNA segment.
Direct repair involves the removal of both the abnormal DNA and the normal DNA segment.
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Homologous recombination repair is used at single-strand breaks in DNA.
Homologous recombination repair is used at single-strand breaks in DNA.
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Base excision repair removes an abnormal base or nucleotide from DNA.
Base excision repair removes an abnormal base or nucleotide from DNA.
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Deamination of cytosine produces uracil.
Deamination of cytosine produces uracil.
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5-methylcytosine deamination results in the formation of uracil.
5-methylcytosine deamination results in the formation of uracil.
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Tautomeric shifts can lead to AC and GT base pairs.
Tautomeric shifts can lead to AC and GT base pairs.
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X-rays are a type of physical mutagen that can cause base deletions.
X-rays are a type of physical mutagen that can cause base deletions.
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Alkylating agents add methyl or ethyl groups to bases and disrupt nucleotide pairing.
Alkylating agents add methyl or ethyl groups to bases and disrupt nucleotide pairing.
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Intercalating agents distort the helical structure of DNA.
Intercalating agents distort the helical structure of DNA.
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Base analogs such as 5-bromouracil can be incorporated into DNA during replication.
Base analogs such as 5-bromouracil can be incorporated into DNA during replication.
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Adenine and cytosine predominantly exist in their enol forms.
Adenine and cytosine predominantly exist in their enol forms.
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Chemical mutagens are classified only as physical mutagens.
Chemical mutagens are classified only as physical mutagens.
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Deamination leads to mutation only if repair enzymes fail to correct the problem.
Deamination leads to mutation only if repair enzymes fail to correct the problem.
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Proteins associated with DNA repair include UvrA, UvrB, UvrC, and UvrE.
Proteins associated with DNA repair include UvrA, UvrB, UvrC, and UvrE.
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Mismatch repair systems are found in all species.
Mismatch repair systems are found in all species.
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Thymine dimers can be repaired by photolyase through a process called photoreactivation.
Thymine dimers can be repaired by photolyase through a process called photoreactivation.
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Xeroderma pigmentosum is caused by defects in genes involved in nucleotide excision repair.
Xeroderma pigmentosum is caused by defects in genes involved in nucleotide excision repair.
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DNA polymerase has a 5’ to 3’ proofreading ability that can correct base mismatches.
DNA polymerase has a 5’ to 3’ proofreading ability that can correct base mismatches.
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Mismatch repair mutations in humans are connected to certain types of cancer.
Mismatch repair mutations in humans are connected to certain types of cancer.
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Nucleotide excision repair can only fix thymine dimers.
Nucleotide excision repair can only fix thymine dimers.
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The molecular mechanism of NER is better understood in eukaryotes than in prokaryotes.
The molecular mechanism of NER is better understood in eukaryotes than in prokaryotes.
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Study Notes
Gene Mutation and DNA Repair
- Mutations are variations in DNA, arising from errors during DNA copying, such as inserting the wrong base or skipping a base.
- Mutations originate from the Latin word mutare, meaning "to change."
- Mutations in DNA can cause heritable changes in genetic information.
- Organisms have developed repair mechanisms to fix damaged DNA.
- Mutations can occur at either the chromosomal or gene level.
- Gene mutations affect single genes.
- Chromosomal mutations affect whole chromosomes.
- Point mutations are changes in one or a few nucleotides, occurring at a specific point in the DNA sequence.
- Point mutations typically arise during DNA replication.
- A point mutation involves a base substitution, resulting in either a transition or a transversion.
- A transition is a change from one pyrimidine to another, or one purine to another.
- A transversion is a change from a pyrimidine to a purine, or vice versa.
- Mutations can also involve additions or deletions of short sequences of DNA.
- Mutations in the coding sequence may lead to different types of mutations.
- Silent mutations do not alter the amino acid sequence due to the degeneracy of the genetic code.
- Missense mutations alter the amino acid sequence, some may not affect function.
- Nonsense mutations change a codon to a stop codon, resulting in a truncated polypeptide.
- Frameshift mutations involve the addition or deletion of nucleotides in multiples of one or two, but not three (the size of a codon), altering the reading frame downstream from the mutation.
- New mutations are more likely to lead to reduced function than enhanced function, except for silent mutations.
- Occasionally, a mutation can lead to an enhanced ability of a polypeptide to function, raising the likelihood of survival and reproduction.
- Mutations can occur in germ-line cells (producing gametes) or somatic cells (all other cells).
- The earlier the mutation, the larger the affected area of the body.
- Mutations can be spontaneous or induced.
- Spontaneous mutations arise due to abnormalities in cellular processes, such as during DNA replication.
- Induced mutations are caused by environmental factors, such as chemical or physical mutagens.
- Types of spontaneous mutations include depurination, deamination, and tautomeric shifts.
- Depurination is the removal of a purine (guanine or adenine) from the DNA.
- Deamination is the removal of an amino group from a cytosine base, changing it to uracil.
- Tautomeric shifts are temporary changes in base structure which can lead to mismatches.
- Chemical mutagens, such as nitrous acid, alkylating agents, intercalating agents, and base analogs, can alter the structure of DNA, contributing to mutations.
- Physical mutagens, such as ionizing radiation (X-rays, gamma rays) and non-ionizing radiation (UV light) can cause DNA damage potentially leading to mutations.
- DNA repair mechanisms, such as direct repair, nucleotide excision repair, and mismatch repair, are essential for fixing various types of DNA damage.
- Several human diseases are associated with defects in genes involved in DNA repair.
- Diseases like xeroderma pigmentosum, and Cockayne syndrome are examples of such diseases arising from defects in DNA repair.
- The correct recognition and removal of abnormal DNA is critical in DNA repair processes.
DNA Repair
- Living cells contain several mechanisms for DNA repair.
- DNA repair is mostly a multi-step process.
- DNA repair starts with detecting an irregularity in DNA structure.
- The abnormal DNA is then removed.
- Normal DNA is synthesized to repair the damage.
- Types of DNA repair mechanisms include direct repair, base excision repair, nucleotide excision repair, mismatch repair, homologous recombination repair, and non-homologous end joining.
- Photolyase repairs thymine dimers, restoring the DNA.
- Nucleotide excision repair fixes a wide range of DNA damages including thymine dimers and chemically modified bases.
Mismatch Repair
- DNA replication can occasionally lead to base pair mismatches.
- DNA polymerases have 3' to 5' proofreading abilities that correct these errors.
- A mismatch repair system is activated if proofreading fails, coming to the rescue, by directing the removal of the error in the DNA strand
- These systems are found in all species.
- In humans, defects can lead to specific types of cancer.
- MutL, MutH, and MutS proteins are involved in mismatch repair in E. coli and recognize/remove the error in the newly synthesized DNA strand.
Recombination Repair
- DNA double-strand breaks are very dangerous and can lead to chromosomal rearrangements and deletions.
- Homologous recombination repair (HRR) and non-homologous end joining (NHEJ) repair these breaks in DNA structure by pairing with a homologous chromosome.
Position Effects
- Chromosome rearrangements may affect the expression of a gene due to the breakpoint in the gene itself or its new location.
- This is called position effect; gene expression can be affected because the gene is moved to a position near regulatory sequences for a different gene or to a heterochromatic region.
- The location of regulatory sequences is often bidirectional.
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Description
Test your understanding of gene mutations and DNA repair mechanisms. This quiz covers the types of mutations, their origins, and the implications they have on genetic information. Dive deep into the intricacies of point mutations, chromosomal changes, and the repair processes organisms have developed over time.
