Question

1. even a gene mutation that is a point mutation, meaning it affects one nucleotide base, can still make a major change

consider the below information for normal hemoglobin:

portion of hemoglobin dna | gga ctc ctc
mrna | ccu gag gag
amino acids | proline-glutamic acid-glutamic acid

sickle cell anemia is caused by a point mutation known as a substitution. show what would occur if the first t (\thymine\) dna base in the portion shown above experienced a mutation with a substitution of a (\adenine\).

sickle cell hemoglobin:

portion of mutated hemoglobin dna: _______________
mrna: _______________
amino acids: _______________

Explanation:

Step1: Identify the original DNA sequence

The original hemoglobin DNA sequence is \( \text{GGA CTC CTC} \). We need to substitute the first \( \text{T} \) (in the second codon \( \text{CTC} \)) with \( \text{A} \). So the mutated DNA sequence becomes \( \text{GGA CAC CTC} \) (since the second codon was \( \text{CTC} \), changing the middle base \( \text{T} \) to \( \text{A} \) gives \( \text{CAC} \)? Wait, no, let's correct. Wait, DNA is composed of bases: A, T, C, G. The original DNA sequence: let's parse the codons. The original DNA is \( \text{GGA} \) (first codon), \( \text{CTC} \) (second codon), \( \text{CTC} \) (third codon). The first \( \text{T} \) is in the second codon \( \text{CTC} \) (positions: first base C, second T, third C). So substituting the second base (T) with A: so the second codon becomes \( \text{CAC} \)? Wait, no, DNA base pairing: when transcribing to mRNA, DNA's T pairs with A in mRNA, C pairs with G, G pairs with C, A pairs with U. Wait, the original DNA is \( \text{GGA CTC CTC} \). Let's write each base:

First codon: G, G, A

Second codon: C, T, C

Third codon: C, T, C

We need to substitute the first T (in the second codon, position 2 of the second codon) with A. So the second codon becomes C, A, C? Wait, no, the second codon is CTC: positions 1: C, 2: T, 3: C. Substitute position 2 (T) with A: so the second codon is CAC? Wait, no, C (position 1), A (position 2), C (position 3): CAC. So the mutated DNA sequence is \( \text{GGA CAC CTC} \)? Wait, no, wait the original DNA is GGA (codon 1), CTC (codon 2), CTC (codon 3). The first T is in codon 2, position 2. So changing T (position 2 of codon 2) to A: codon 2 becomes C (position 1), A (position 2), C (position 3) → CAC. So mutated DNA: GGA CAC CTC.

Step2: Transcribe mutated DNA to mRNA

DNA to mRNA: A→U, T→A, C→G, G→C.

First codon: GGA → mRNA: CCU (G→C, G→C, A→U)

Second codon: CAC → mRNA: GUG (C→G, A→U, C→G)

Third codon: CTC → mRNA: GAG (C→G, T→A, C→G)

So mRNA sequence: \( \text{CCU GUG GAG} \)

Step3: Translate mRNA to amino acids

Use the genetic code:

• \( \text{CCU} \): Proline (same as original first codon)
• \( \text{GUG} \): Valine (original second codon was GAG, which is Glutamic Acid; now GUG is Valine)
• \( \text{GAG} \): Glutamic Acid (same as original third codon)

So amino acids: Proline-Valine-Glutamic Acid

Answer:

• Portion of mutated hemoglobin DNA: \( \boldsymbol{\text{GGA CAC CTC}} \)
• mRNA: \( \boldsymbol{\text{CCU GUG GAG}} \)
• Amino Acids: \( \boldsymbol{\text{Proline-Valine-Glutamic Acid}} \)