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Causes of Gene Mutation

Gene mutations are changes in the DNA sequence that can alter the function of a gene.
These mutations can arise from:
1. Errors in DNA replication or repair.
2. External agents called mutagens.

Example

Adenine (A) is paired with cytosine (C) instead of thymine (T).

1. Errors in DNA Replication

During DNA replication, DNA polymerase occasionally incorporates the wrong nucleotide, resulting in mismatched base pairs.
Most replication errors are corrected by DNA polymerase’s proofreading ability, but a small fraction escape repair, leading to permanent mutations.

Example

Instead of pairing adenine (A) with thymine (T), DNA polymerase might pair adenine with cytosine (C).

2. Errors in DNA Repair

DNA is constantly subjected to damage from metabolic byproducts and environmental factors.
Repair mechanisms like base excision repair and nucleotide excision repair fix most damage, but:
1. If the repair system fails or introduces errors, mutations can occur.

Example

Faulty repair of double-strand breaks can result in deletions, duplications, or chromosomal rearrangements.

Mutagens: External Causes of Mutation

Mutagens are agents that increase the likelihood of mutations.
They can be classified into two main types:
1. Chemical Mutagens
2. Radiation

Chemical Mutagens

Chemical substances that interfere with DNA structure or function.

Base Analogues: Molecules resembling normal DNA bases but pair incorrectly during replication.

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Question 1

Recap question

Cells deficient in mismatch repair are exposed to ionizing radiation. Compared to cells with only mismatch repair deficiency, what combined effect on mutation types would you expect?

How does DNA polymerase contribute to gene mutations?

Note

A gene mutation refers to a permanent alteration in the DNA sequence that makes up a gene. These changes can occur at various levels, from a single nucleotide to larger segments of DNA.

DNA is composed of four nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).
The sequence of these nucleotides determines the genetic information.
Mutations can change this sequence, potentially altering the function of the gene.

ExampleChanging a single letter in a word: "cat" to "bat" - this small change can completely alter the meaning, just like a point mutation can change a protein's function.

DefinitionGene MutationA permanent change in the DNA sequence of a gene, which can affect its function or expression.

AnalogyThink of DNA as a recipe book. A mutation is like a typo in the recipe - sometimes it doesn't matter, but other times it can ruin the dish.

Causes of Gene Mutation

Gene mutations are changes in the DNA sequence that can alter the function of a gene.
These mutations can arise from:
1. Errors in DNA replication or repair.
2. External agents called mutagens.

Example

Adenine (A) is paired with cytosine (C) instead of thymine (T).

1. Errors in DNA Replication

During DNA replication, DNA polymerase occasionally incorporates the wrong nucleotide, resulting in mismatched base pairs.
Most replication errors are corrected by DNA polymerase’s proofreading ability, but a small fraction escape repair, leading to permanent mutations.

Example

Instead of pairing adenine (A) with thymine (T), DNA polymerase might pair adenine with cytosine (C).

2. Errors in DNA Repair

DNA is constantly subjected to damage from metabolic byproducts and environmental factors.
Repair mechanisms like base excision repair and nucleotide excision repair fix most damage, but:
1. If the repair system fails or introduces errors, mutations can occur.

Example

Faulty repair of double-strand breaks can result in deletions, duplications, or chromosomal rearrangements.

Mutagens: External Causes of Mutation

Mutagens are agents that increase the likelihood of mutations.
They can be classified into two main types:
1. Chemical Mutagens
2. Radiation

Chemical Mutagens

Chemical substances that interfere with DNA structure or function.

Base Analogues: Molecules resembling normal DNA bases but pair incorrectly during replication.

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Questions

Recap questions

1 of 5

Question 1

Recap question

Cells deficient in mismatch repair are exposed to ionizing radiation. Compared to cells with only mismatch repair deficiency, what combined effect on mutation types would you expect?

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Note

A gene mutation refers to a permanent alteration in the DNA sequence that makes up a gene. These changes can occur at various levels, from a single nucleotide to larger segments of DNA.

DNA is composed of four nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).
The sequence of these nucleotides determines the genetic information.
Mutations can change this sequence, potentially altering the function of the gene.

ExampleChanging a single letter in a word: "cat" to "bat" - this small change can completely alter the meaning, just like a point mutation can change a protein's function.

DefinitionGene MutationA permanent change in the DNA sequence of a gene, which can affect its function or expression.

AnalogyThink of DNA as a recipe book. A mutation is like a typo in the recipe - sometimes it doesn't matter, but other times it can ruin the dish.

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

D1.3.4 Causes of gene mutation Notes

Causes of Gene Mutation

1. Errors in DNA Replication

2. Errors in DNA Repair

Mutagens: External Causes of Mutation

Chemical Mutagens

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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Causes of Gene Mutation

1. Errors in DNA Replication

2. Errors in DNA Repair

Mutagens: External Causes of Mutation

Chemical Mutagens

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anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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