Chapter 7: Gene mutations

Question 1

can be defined as an alteration in DNA sequence

Answer 1

mutation

Question 2

What are the three possible forms that mutations may take regarding changes to DNA sequence?

Answer 2

-Single base-pair substitution,
-deletion or insertion of one or more base pairs, -major alteration in chromosome structure

Question 3

Where can mutations occur within a gene, and provide examples of these locations?

Answer 3

Within regions coding for protein or within noncoding regions such as introns and regulatory sequences

Question 4

describes the potential outcomes of a mutation with respect to its impact on observable traits?

Answer 4

Phenotype changes

Question 5

What determines the extent to which a mutation alters the characteristics of an organism?

Answer 5

Type of cell affected and the degree of alteration in gene function

Question 6

Differentiate between mutations in somatic cells and germ cells in terms of heritability.

Answer 6

Germ cell mutations are heritable, contributing to genetic diversity and diseases, while somatic cell mutations are not passed to the next generation but may affect cellular function or lead to tumors.

Question 7

“Microlesion or base substitution” usually refers to a small or microscopic injury or damage, often in the context of tissues or organs.

types of gene mutation

• a change of one base pair to another in a DNA

Answer 7

Point mutation, or base substitution

Question 8

a change of one base pair to another in a DNA which results in the
creation of a new triplet that codes for a different amino acid in the protein product

Answer 8

Missense mutation

Question 9

the outcome is that the triplet will be changed into a stop codon,
resulting in the termination of translation of the protein

Answer 9

Nonsense mutation-

Question 10

if the point mutation alters a codon but does not result in a change in the
amino acid at that position in the protein (due to degeneracy of the genetic code)

Answer 10

Silent mutation

Question 11

base substitution involving a pyrimidine replaces a pyrimidine or a purine
replaces a purine

Answer 11

Transition

Question 12

• if a purine replaces a pyrimidine, or vice versa

Answer 12

Transversion

Question 13

used to describe the type of mutation involving the insertion or deletion of one or more nucleotides within a gene?

Answer 13

Frameshift mutation

Question 14

What consequence does the loss or addition of a single nucleotide have on the three-letter codons during translation in a gene?

Answer 14

It causes all subsequent three-letter codons to be changed.

Question 15

What specific aspect of the triplet reading during translation is altered in frameshift mutations?

Answer 15

The frame of triplet reading

Question 16

How would you characterize the potential severity of the results of frameshift mutations, especially when they occur early in the coding sequence?

Answer 16

The results can be very severe.

Question 17

Explain the significance of frameshift mutations in terms of their impact on the coding sequence during translation.

Answer 17

Frameshift mutations alter the frame of triplet reading during translation, leading to significant consequences, particularly if they occur early in the coding sequence.

Question 18

type of mutations:

Changes a single DNA nucleotide

Answer 18

Base substitution

Question 19

Base substitution in which a purine replaces a purine or a pyrimidine replaces a pyrimidine

Answer 19

Transition

Question 20

Base substitution in which a purine replaces a pyrimidine or a pyrimidine replaces a purine

Answer 20

Transversion

Question 21

Addition of one or more nucleotides

Answer 21

Insertion

Question 22

Deletion of one or more nucleotides

Answer 22

Deletion

Question 23

Insertion or deletion that alters the reading frame of a gene

Answer 23

Frameshift mutation

Question 24

Deletion or insertion of a multiple of three nucleotides that does not alter the reading frame

Answer 24

In-frame deletion or insertion

Question 25

Increases the number of copies of a set of nucleotides

Answer 25

Expanding nucleotide repeats

Question 26

Changes the wild-type phenotype to a mutant phenotype

Answer 26

Forward mutation

Question 27

Changes a mutant phenotype back to the wild-type phenotype

Answer 27

Reverse mutation

Question 28

Changes a sense codon into a different sense codon, resulting in the incorporation of a different amino acid in the protein

Answer 28

Missense mutation

Question 29

Changes a sense codon into a nonsense (stop) codon, causing premature termination of translation

Answer 29

Nonsense mutation

Question 30

Changes a sense codon into a synonymous codon, leaving the amino acid sequence of the protein unchanged

Answer 30

Silent mutation

Question 31

Changes the amino acid sequence of a protein without altering its ability to function

Answer 31

Neutral mutation

Question 32

Causes a complete or partial loss of function

Answer 32

Loss-of-function mutation

Question 33

Causes the appearance of a new trait or function or causes the appearance of a trait in inappropriate tissue or at an inappropriate time

Answer 33

Gain-of-function mutation

Question 34

Causes premature death

Answer 34

Lethal mutation

Question 35

Suppresses the effect of an earlier mutation at a different site

Answer 35

Suppressor mutation

Question 36

Suppresses the effect of an earlier mutation within the same gene

Answer 36

Intragenic suppressor mutation

Question 37

Suppresses the effect of an earlier mutation in another gene

Answer 37

Intergenic suppressor mutation

Question 38

4 Phenotypic Effects of Mutations

Answer 38

-Loss-of- function mutation -Null mutation -Recessive mutation -Dominant mutation

Question 39

one that reduces or eliminates the function of the gene product

Answer 39

Loss-of- function mutation

Question 40

a mutation that results in the complete loss of function?

Answer 40

Null mutation

Question 41

In a diploid organism, if a recessive mutation is present with the wild-type allele, what phenotype is observed?

Answer 41

Wild-type phenotype

Question 42

What type of mutation results in a mutant phenotype in a diploid organism, even when the wild-type allele is also present?

Answer 42

Dominant mutation

Question 43

2 Two different types of effects

Answer 43

Haploinsufficiency- Dominant gain-of-function mutation

Question 44

occurs when the single wild-type copy of the gene does not produce enough gene product to bring about a wild-type phenotype (example in humans, Marfan syndrome)

Answer 44

Haploinsufficiency

Question 45

results in a gene product with enhanced, negative, or new functions.

Answer 45

Dominant gain-of-function mutation

Question 46

What are the two potential mechanisms by which dominant gain-of-function mutations can occur?

Answer 46

It can result from a change in the amino acid sequence of the protein, conferring a new activity. Alternatively, it may occur due to a mutation in a regulatory region of the gene, leading to higher expression levels or expression at abnormal times or places.

Question 47

2 Classification based on location of mutation

Answer 47

somatic and germ cells mutations

Question 48

this occur in any cell in the body except germ cells and are not transmitted to future generations.

Answer 48

Somatic mutations

Question 49

are transmitted to offspring as gametes.

Answer 49

Germ cell mutations

Question 51

What is the term for a mutation that changes a single DNA nucleotide?

Answer 51

Base substitution

Question 52

2 Types of mutation according to its cause

Answer 52

1. Spontaneous mutations 2. Induced mutations

Question 53

are changes in the nucleotide sequence of genes that appear to occur naturally

Answer 53

result from the influence of extraneous factors either natural or artificial agents, for example, radiation from cosmic and mineral sources and ultraviolet radiation from the sun

Question 54

arise from errors during DNA replication to changes in DNA base pairing

Answer 54

Spontaneous Replication Errors and Chemical Change

Question 55

What are the sources or causes of mutagenic changes related to DNA replication errors and chemical change?

Answer 55

tautomeric shifts, depurinations, deaminations, and reactive oxidant damage.

Question 56

energy of radiation varies inversely with wavelength.

Answer 56

Ionizing Radiation

Question 57

are more energetic than UV radiation.

Answer 57

X rays, gamma rays, and cosmic rays

Question 58

How is the energy of ionizing radiation related to its ability to penetrate tissues?

Answer 58

The energy of ionizing radiation varies inversely with wavelength, making X rays, gamma rays, and cosmic rays more energetic and capable of penetrating tissues deeply.

Question 59

What happens as ionizing radiation penetrates cells, and what are the consequences for genetic material?

Answer 59

Stable molecules and atoms are transformed into free radicals, which can directly or indirectly affect genetic material by altering purines and pyrimidines in DNA, breaking phosphodiester bonds, disrupting the integrity of chromosomes,

Question 60

What is the term for chemical species containing one or more unpaired electrons formed as a result of ionizing radiation?

Answer 60

Free radicals

Question 61

What types of chromosomal aberrations can result from the impact of ionizing radiation on genetic material?

Answer 61

Deletions, translocations, and chromosomal fragmentation.

Question 62

are agents that have the potential to damage DNA and induce mutations in cells.

Answer 62

Mutagens

Question 63

all cells on Earth are exposed to a plethora of agents called mutagens,

Answer 63

. Chemical Mutagens

Question 64

Provide examples of mutagens

Answer 64

Fungal toxins, some industrial pollutants, medical X-rays, and chemicals within tobacco smoke.

Question 65

What is the positive aspect of mutagens mentioned in the context of geneticists?

Answer 65

Geneticists harness some mutagens for use in analyzing genes and gene functions.

Question 66

compounds that can substitute for purines or pyrimidines during nucleic acid biosynthesis.

Answer 66

Base Analogs ex: 5-bromouracil (5-BU)

Question 67

a derivative of uracil, behaves as a thymine analog but is halogenated at the number 5 position of the pyrimidine ring.

Answer 67

5-bromouracil (5-BU)

Question 68

Explain the role of alkylating agents in causing mutations

Answer 68

Alkylating agents, such as sulfur-containing mustard gases, donate an alkyl group, such as CH3 or CH3CH2, to amino or keto groups in nucleotides, causing alterations in the structure of DNA and inducing mutations.

Question 69

are chemicals that have dimensions and shapes that allow them to wedge between the base pairs , causing distortion and unwinding of DNA strands

Answer 69

Intercalating agents

Question 70

How do intercalating agents affect the functions of transcription, replication, and repair in DNA?

Answer 70

by causing distortion and unwinding of DNA strands.

Question 71

How do alterations in DNA structure caused by intercalating agents contribute to mutations during DNA replication and repair?

Answer 71

Alterations in DNA structure caused by intercalating agents lead to deletions and insertions during DNA replication and repair, ultimately causing frameshift mutations.

Question 72

waves of shorter length than visible light, being inherently more energetic, have the potential to disrupt organic molecules

Answer 72

Ultraviolet Light

Question 73

At what wavelength do purines and pyrimidines most intensely absorb UV radiation?

Answer 73

at a wavelength of about 260 nm

Question 74

Despite the ozone layer's protection, what is the potential consequence of sufficient UV radiation exposure to cells?

Answer 74

Sufficient UV radiation can induce thousands of DNA lesions per hour in any exposed cell.

Question 75

What is one major effect of UV radiation on DNA?

Answer 75

creation of pyrimidine dimers in DNA.

Question 76

also known as transposons or “jumping genes,” since it can move or transpose within and between chromosomes, inserting themselves into various locations within the genome.

Answer 76

Transposable Elements

Question 77

What is the primary consequence of the insertion of a transposon into the coding region of a gene?

Answer 77

The insertion of a transposon into the coding region of a gene may disrupt the gene's normal translation reading frame or induce premature termination of translation of the mRNA transcribed from the gene.

Question 78

Besides creating mutations, what other impact can transposable elements have on a genome?

Answer 78

Transposable elements can alter gene expression and contribute to evolution by moving within a genome.

Question 79

How do geneticists utilize transposons as research tools?

Answer 79

to create mutations, clone genes, and introduce genes into model organisms.

Question 80

7.3.DNA Repair System to Detect and Correct Mutations How do organisms counteract mutations?

Answer 80

Organisms counteract mutations using various DNA repair systems.

Question 81

What are the main types of DNA repair systems

Answer 81

proofreading, mismatch repair, photoreactivation repair, SOS repair, base excision repair, nucleotide excision repair, and double-strand break repair.

Question 82

What is a common source of mutations during DNA replication?

Answer 82

Mutations often arise when an incorrect nucleotide is inserted by DNA polymerase.

Question 83

How frequently does DNA polymerase III, the major DNA synthesizing enzyme in bacteria, make errors during insertion?

Answer 83

DNA polymerase III makes an error approximately once every 100,000 insertions, resulting in an error rate of 10^-5.

Question 84

What is the efficiency of DNA polymerase proofreading in catching errors during replication?

Answer 84

DNA polymerase proofreads each step, catching 99 percent of errors.

Question 85

What action does DNA polymerase take if an incorrect nucleotide is inserted during polymerization?

Answer 85

If an incorrect nucleotide is inserted, the enzyme recognizes the error and "reverses" its direction.

Question 86

What enzymatic activity does DNA polymerase exhibit when acting as a 3ʹ to 5ʹ exonuclease during proofreading?

Answer 86

DNA polymerase acts as a 3ʹ to 5ʹ exonuclease, cutting out the incorrect nucleotide.

Question 87

How does DNA polymerase improve replication efficiency when proofreading?

Answer 87

By cutting out the incorrect nucleotide and replacing it with the correct one, DNA polymerase improves replication efficiency 100-fold, creating only 1 mismatch in every 10^7 insertions.

Question 88

What is the final error rate after DNA polymerase proofreading during replication?

Answer 88

The final error rate is 10^-7, creating only 1 mismatch in every 10^7 insertions.

Question 89

How does mismatch repair address mismatches in replicated DNA?

Answer 89

the incorrect nucleotide is removed, and the correct nucleotide is inserted in its place.

Question 90

Post replication Repair and the SOS Repair System When does post-replication repair respond,

Answer 90

post-replication repair responds after damaged DNA has escaped repair and failed to be completely replicated.

Question 91

purpose or post-replication repair

Answer 91

carry out repair synthesis as replication proceeds.

Question 92

How does the SOS repair system response to the damaged DNA?

Answer 92

by inducing the expression of specific genes, including lexA, recA, and uvr. This system is activated in the presence of a large number of unrepaired DNA mismatches and gaps.

Question 93

Why is the SOS repair system considered a last resort

Answer 93

to minimize DNA damage

Question 94

what happens during SOS repair that makes it potentially mutagenic?

Answer 94

During SOS repair, DNA synthesis becomes error-prone, inserting random and possibly incorrect nucleotides, making it mutagenic. This allows the cell to survive DNA damage that might otherwise be lethal.

Question 95

What is the dependent factor for the process of photoreactivation repair

Answer 95

photoreactivation enzyme (PRE).

Question 96

this enzyme’s mode of action is to cleave the bonds between thymine dimers, thus directly reversing the effect of UV radiation on DNA.

Answer 96

photoreactivation enzyme (PRE).

Question 97

7.4.Evolutionary Significance of Mutations What role do mutations play in terms of genetic variation and natural selection?

Answer 97

- Mutations serve as a source of genetic variation and provide the raw material for natural selection. - Mutations are also the source of genetic damage that contributes to cell death, genetic diseases, and cancer.