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Chapter 21: Problem 109

The base sequences in mRNA that code for certain amino acids are Glu: GAA, GAG Val: \(\quad\) GUU, GUC, GUA, GUG Met: AUG Trp: UGG Phe: UUU, UUC Asp: GAU, GAC These sequences are complementary to the sequences in DNA. a. Give the corresponding sequences in DNA for the amino acids listed above. b. Give a DNA sequence that would code for the peptide trp-glu-phe-met. c. How many different DNA sequences can code for the tetrapeptide in part b? d. What is the peptide that is produced from the DNA sequence T-A-C-C-T-G-A- A-G? e. What other DNA sequences would yield the same tripeptide as in part d?

Short Answer

Expert verified
a. Glu: CTT, CTC; Val: CAA, CAG, CAT, CAC; Met: TAC; Trp: ACC; Phe: AAA, AAG; Asp: CTA, CTG. b. ACC-CTT-AAA-TAC. c. 4 different DNA sequences. d. met-asp-phe. e. TAC-CTA-AAA, TAC-CTA-AAG, TAC-CTG-AAA, TAC-CTG-AAG.

Step by step solution

01

Complementary base-pairing rules dictate that Adenine (A) always pairs with Thymine (T) and Cytosine (C) always pairs with Guanine (G) in DNA. In mRNA, Uracil (U) replaces Thymine (T). Thus, A in DNA pairs with U in mRNA, and T in DNA pairs with A in mRNA. a. #Step 2: Finding complementary DNA sequences#

Use the complementary base-pairing rules to find the corresponding DNA sequences for the given amino acids: Glu: CTT, CTC Val: CAA, CAG, CAT, CAC Met: TAC Trp: ACC Phe: AAA, AAG Asp: CTA, CTG b. #Step 3: Constructing a DNA sequence for a given peptide#
02

To code for the peptide trp-glu-phe-met, use the corresponding DNA sequences for each amino acid: Trp: ACC Glu: CTT or CTC (choose any one) Phe: AAA or AAG (choose any one) Met: TAC One possible DNA sequence is ACC-CTT-AAA-TAC. c. #Step 4: Calculating possible DNA sequences for a given peptide#

For the peptide trp-glu-phe-met, calculate the possible DNA sequences based on the number of options for each amino acid: Trp: 1 option Glu: 2 options Phe: 2 options Met: 1 option Multiply the number of options for each amino acid: 1 × 2 × 2 × 1 = 4 So, there are 4 different DNA sequences that can code for the tetrapeptide in part b. d. #Step 5: Translating a DNA sequence into a peptide#
03

Given the DNA sequence T-A-C-C-T-G-A-A-G, the corresponding mRNA sequence is: A-U-G-G-A-C-U-U-C (remembering to switch T with A and vice versa) Now, reading the mRNA sequence in groups of three, find the corresponding amino acids using the initial sequences: AUG: Met GAC: Asp UUC: Phe The peptide produced is met-asp-phe. e. #Step 6: Finding alternative DNA sequences producing the same peptide#

The peptide sequence from part d is met-asp-phe, so we can find the alternative DNA sequences by determining all possible combinations that code for these amino acids: Met: TAC Asp: CTA or CTG (choose any one) Phe: AAA or AAG (choose any one) The following combinations can yield the same tripeptide met-asp-phe: 1. TAC-CTA-AAA 2. TAC-CTA-AAG 3. TAC-CTG-AAA 4. TAC-CTG-AAG These are 4 alternative DNA sequences that produce the same tripeptide as the DNA sequence T-A-C-C-T-G-A-A-G.

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