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Biology 1090 > DNA Mutations (Lecture 9) > Flashcards

DNA Mutations (Lecture 9) Flashcards

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1
Q

18.1 Mutations are inherited alterations in the DNA sequence

The importance of mutations

Why are mutations necessary?

A

they are necessary for creating diversity, but can also be responsible for disease

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2
Q

What are the types of gene mutations (based on their molecular nature)?

A
  • Base Substitutions
    • Transition
    • Transversion
  • Insertions and deletions
    • Frameshift mutations
    • In-frame insertions and deletions
  • Expanding nucleotide repeats
    • Increase in the number of copies of a set of nucleotides
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3
Q

Base Substitutions

What are Transitions?

A

Purine → Purine

Possible base changes

A → G

G → A

Pyrimidine → Pyrimidine

T → C

C → T

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4
Q

Base Substitutions

What are Transversions?

A

Purine → Pyrimidine

Possible base changes

A → C

A → T

G → C

G → T

Pyrimidine → Purine

C → A

C → G

T → A

T → G

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5
Q

Original DNA sequence

GGG AGT GTA GAT CGT

Give an example of

a) Base substitution
b) Base insertion
c) Base deletion

A

A base substitution alters a single codon

An insertion or a deletion alters the reading frame and may change many codons

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6
Q

Examples of human genetic diseases caused by expanding nucleotide repeats.

A
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7
Q

3?

  1. This DNA molecule has 8 copies of a CAG repeat

What happens next in #2?

A
  1. The two strands separate…
  2. …and the strands replicate
  3. In the course of replication, a hairpin forms on the newly synthesized strand…
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8
Q
  1. In the course of replication, a hairpin forms on the newly synthesized strand….

What happens in #5?

A
  1. …. causing part of the template strand to be replicated twice and increasing the number of repeats on the newly synthesized strand
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9
Q

7?

  1. …. causing part of the template strand to be replicated twice and increasing the number of repeats on the newly synthesized strand

What happens in #6?

A
  1. The two strands of the new DNA molecule separate…
  2. … and the strand with extra CAG copies serves as a template for replication
  3. The resulting DNA molecules contains 5 additional copies of the CAG repeat
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10
Q

Phenotypic Effects of Mutations

What is forward mutation?

A

wild type → mutant type

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11
Q

Phenotypic Effects of Mutations

What is a reverse mutation?

A

mutant type → wild type

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12
Q

Phenotypic Effects of Mutations

What is a missense mutation?

A

amino acid → different amino acid

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13
Q

Phenotypic Effects of Mutations

What is a nonsense mutation?

A

sense codon → nonsense codon

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14
Q

Phenotypic Effects of Mutations

What is a silent mutation?

A

codon → synonymous codon

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15
Q

Phenotypic Effects of Mutations

What is a neutral mutation?

A

change in amino acid but no change in function

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16
Q
A
17
Q

Phenotypic Effects of Mutations

No mutation?

A
18
Q

Suppressor Mutations

  1. A forward mutation changes the wild type into…
  2. A _______ mutation restores the wild type gene and the phenotypes
  3. A suppressor mutation occurs…
  4. and produces an individual that has both the….
  5. but has the _______ phenotype
A
  1. A forward mutation changes the wild type into a mutant phenotype
  2. A reverse mutation restores the wild type gene and the phenotypes
  3. A suppressor mutation occurs at a site different from that of the original mutation…
  4. …and produces an individual that has both the original mutation and the suppressor mutation…
  5. … but has the wild-type phenotype
19
Q

Suppressor Mutations

  1. Harlequin Maple trees are a result of what?
  2. Occasionally, you will see all green leaves in a Harlequin Maple. These are known as what?
  3. A secondary mutation that masks or suppresses the effects of the first mutation results in what?
A
  1. Harlequin Maple trees are a result of a mutation in chlorophyll production. They are partly albino.
  2. Occasionally, you will see all green leaves in a Harlequin Maple. These are known as revertants.
  3. A secondary mutation that masks or suppresses the effects of the first mutation results in a wild-type phenotype.
20
Q

The effects of single-base mutations vary enormously

Given AGA = Arginine

What is a silent mutation? (no effect)

Nonsense mutation? (results in truncation)

Missense mutation? ( changes one amino acid)

A

Given AGA = Arginine

Silent: AGG = Arginine

Nonsense: TGA = “stop”

Missense: AAA = Lysine Conserved

Missense: AGT = Serine non-conserved

21
Q

A mutation that affects _______________________ to DNA can have some serious effects.

A

A mutation that affects the binding of transcription factors to DNA can have some serious effects.

22
Q

Wild Type Sequence

Given the DNA sequence…

What is the mRNA?

A
23
Q

Given the DNA sequence…

What is the new mRNA strand?

A
24
Q

Given the DNA sequence….

What is the mRNA strand?

A
25
Q

Characteristics of different types of mutations

Base substitution?

Transition?

Transversion?

Insertion?

Deletion?

A

Base substitution - Changes the base of a single DNA nucleotide

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

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

Insertion - Addition of one or more nucleotides

Deletion - Deletion of one or more nucleotides

26
Q

Characteristics of different types of mutations

Frameshift mutation?

In-frame deletion or insertion?

Expanding nucleotide repeats?

Forward mutation?

Reverse mutation?

A

Frameshift mutation - Insertion or deletion that alters the reading frame of a gene

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

Expanding nucleotide repeats - Increases the number of copies of a set of nucleotides

Forward mutation - Changes the wild-type phenotype to a mutant phenotype

Reverse mutation - Changes a mutant phenotype back to the wild-type phenotype

27
Q

Characteristics of different types of mutations

Missense mutation?

Nonsense mutation?

Silent mutation?

Neutral mutation?

Loss-of-function mutation?

A

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

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

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

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

Loss-of-function mutation - Causes a complete or partial loss of function

28
Q

Characteristics of different types of mutations

Gain-of-function mutation?

Lethal mutation?

Suppressor mutation?

Intragenic suppressor mutation?

Intergenic suppressor mutation?

A

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

Lethal mutation - Causes premature death

Suppressor mutation - Suppresses the effect of an earlier mutation at a different site

Intragenic suppressor mutation - Suppresses the effect of an earlier mutation within the same gene

Intergenic suppressor mutation - Suppresses the effect of an earlier mutation in another gene

29
Q

18.2 Mutations Are Potentially Caused by a Number of Different Factors

What are 4 factors?

A
  • Spontaneous replication errors
    • Unequal crossing over
  • Chemically induced mutations
    • EMS
  • Radiation
    • Thymidine Dimers
  • Spontaneous chemical changes
    • Deamination
30
Q

Spontaneous Replication Errors: unequal crossing over can cause insertions and deletions

  1. If homologous chromosomes misalign during crossing over…
  2. … one crossing over results in?
  3. … and the other has a?
A
  1. If homologous chromosomes misalign during crossing over…
  2. … one crossing over results in an insertion…
  3. … and the other has a deletion
31
Q

Chemically Induced Mutations

What are 3 chemically induced mutations?

A
  • Alkylating agents: donate alkyl group
    • Ethylmethylsulfonate EMS
    • Mustard gas
  • Deamination: nitrous acid
  • Hydroxylamine: add hydroxyl group
32
Q

Radiation

Radiation greatly ___________ in all organisms

Pyrimidine dimer is…

A

Radiation greatly increases mutation rates in all organisms

Pyrimidine dimer: two thymine bases block replication.

33
Q

Spontaneous Chemical Changes

What is deamination?

Over time a whole genome can lose much of its CG content due to what?

A

Deamination: loss of an amino group from a base

Over time a whole genome can lose much of its CG content due to spontaneous deamination.

34
Q

Parent Diploid Somatic Cell

After DNA Synthesis what happens to the somatic cell?

A

One of the G:C Alleles changes to a G:T Allele

35
Q

Daughter Diploid Somatic Cell

What happens after DNA Synthesis?

A

Daughter Diploid Somatic Cell After S-phase

New Allele A:T

36
Q

Given… What are the grand daughter diploid somatic cells?

A

Grand daughter Diploid Somatic Cells

Two alleles: T/A and G/C

and

One allele: G/C

Biology 1090 (24 decks)

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