Chapter 9, Problem 8CTQ

a.

Summary Introduction

To show:

A deletion by using the DNA sequence: $3\text{'}$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Introduction:

A change in the genetic code during replication is termed as “mutation”. A mutation can occur during replication or recombination. It is a permanent alteration in the nucleotide sequence in $\text{DNA}$. Cells have evolved many “repair mechanisms” due to the lethal potential of $\text{DNA}$ mutations. Mutations that can mutate damaged DNA are, “substitution”, “deletion” or “insertion” of base pairs.

Explanation of Solution

The deletion of three nucleotides from the gene will result in the non coding of that particular amino acid. This will cause the elimination of one amino acid from the polypeptide sequence. This may or may not alter the protein functioning.

Original sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Mutation: If a single T has removed, from the codon “TCC” that encodes arginine from the given DNA sequence:

Mutation occurs: $3\text{'}$ TAC CAG ATA CAC $\cancel{\text{T}}$ CC CCT GCG ACT $5\text{'}$

Mutated strand: $3\text{'}$ TAC CAG ATA CAC CCC CTG CGA CT $5\text{'}$

The amino acid sequence becomes incorrect and it may lead to a malfunctioning of protein.

b.

Summary Introduction

To explain:

An insertion by using the DNA sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Introduction:

A change in the genetic code during replication is termed as “mutation”. A mutation can occur during replication or recombination. It is a permanent alteration in the nucleotide sequence in $\text{DNA}$. Cells have evolved many “repair mechanisms” due to the lethal potential of $\text{DNA}$ mutations. Mutations that can mutate damaged DNA are, “substitution”, “deletion” or “insertion” of base pairs.

Explanation of Solution

The unit of genetic code, which has three nucleotides that code for amino acids, is called codon. The insertion of single nucleotide will shift the reading frame and thus encoding amino acids will be changed. This will lead to inactivation of protein and thus malfunctioning will occur.

Original sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

If a single A is inserted, in the cotton “ATA” that encodes isoleucine from the given DNA sequence:

$\begin{array}{l}3\text{'} \text{TAC CAG}A\text{AT ACA CTC CCC TGC GAC T}\text{5'}\\ \uparrow \\ \text{(insertion)}\end{array}$

The amino acid sequence becomes incorrect and it may lead to a malfunctioning of protein.

c.

Summary Introduction

To explain:

A substitution by using the DNA sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Introduction:

A change in the genetic code during replication is termed as “mutation”. A mutation can occur during replication or recombination. It is a permanent alteration in the nucleotide sequence in $\text{DNA}$. Cells have evolved many “repair mechanisms” due to the lethal potential of $\text{DNA}$ mutations. Mutations that can mutate damaged DNA are, “substitution”, “deletion” or “insertion” of base pairs.

Explanation of Solution

The type of mutation that involves the change of base pair by another leading to the small change in peptide as encoded amino acid got changed is substitution mutation.

Original sequence: ${\text{3}}^{\prime }\text{TAC CAG ATA CAC TCC CCT GCG ACT}{\text{5}}^{\prime }$

If a single C is substituted with G nucleotide, in the codon “CCT” that encoded glycine, from the given DNA sequence:

$\begin{array}{l} \text{(original)}{3}^{\prime }\text{TAC CAG ATA CAC TCC CCT GCG ACT}{\text{5}}^{\prime }\\ \updownarrow \\ \text{(substituded)}{\text{3}}^{\prime }\text{TAC CAG ATA CAC TCC C}G\text{T GCG ACT}{\text{5}}^{\prime }\end{array}$

The amino acid sequence becomes incorrect and it may lead to a malfunctioning of protein or may be a silent mutation. It may not create any change.

d.

Summary Introduction

To explain:

A nonsense mutation by using the DNA sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Introduction:

A change in the genetic code during replication is termed as “mutation”. A mutation can occur during replication or recombination. It is a permanent alteration in the nucleotide sequence in $\text{DNA}$. Cells have evolved many “repair mechanisms” due to the lethal potential of $\text{DNA}$ mutations. Mutations that can mutate damaged DNA are, “substitution”, “deletion” or “insertion” of base pairs.

Explanation of Solution

The nonsense mutations are the mutations that generate the stop codon. The generated stop codon terminates the translational process and thus the protein structure will not be formed because no more amino acids will be added to the sequence.

$\begin{array}{l}\text{(Orginal)}{\text{3}}^{\prime }\text{TAC CAG ATA CAC TCC CCT GCG ACT}{\text{5}}^{\prime }\\ \downarrow \text{(addition}\text{of}\text{stop}\text{codon)}\\ \text{(Nonsense)}{\text{3}}^{\prime }\text{TAC CAG ATA CAC TCC CCT GCG ACT}UGA{\text{5}}^{\prime }\end{array}$

$5^{\prime }$. Nonsense mutation may lead to forming stop codon. After nonsense mutation DNA sequence will be, $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT UGA

e.

Summary Introduction

To explain:

A frameshift mutation by using the DNA sequence: $3^{\prime }$ TAC CAG ATA CAC TCC CCT GCG ACT $5^{\prime }$.

Introduction:

A change in the genetic code during replication is termed as “mutation”. Mutation can occur during replication or recombination. It is a permanent alteration in the nucleotide sequence in $\text{DNA}$. Cells have evolved many “repair mechanisms” due to the lethal potential of $\text{DNA}$ mutations. Mutations that can mutate damaged DNA are, “substitution”, “deletion” or “insertion” of base pairs.

Explanation of Solution

Mutation that occurs due to any insertion or deletion of bases that shift the bases and change the amino acid sequence is termed as Frameshift mutation. Any insertion, deletion or shifting of base can incorrect the amino acid sequence this will lead malfunctioning of protein.