Question

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

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

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#

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#

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.

Key concepts

mRNA Codon

In the realm of genetics, understanding the concept of mRNA codons is essential. Codons are sequences of three nucleotides found on the messenger RNA (mRNA) molecule. Each codon corresponds to a specific amino acid or a stop signal during protein synthesis. The mRNA sequence is transcribed from a DNA template, where complementary base pairing ensures that the correct sequence is created. In mRNA, you will find adenine (A) pairing with uracil (U) and cytosine (C) pairing with guanine (G). This differs from DNA where adenine pairs with thymine (T).

When ribosomes read the mRNA, they decode the codons to string together amino acids into a polypeptide chain, forming proteins. For instance, the codon AUG not only codes for the amino acid methionine but also serves as a start signal for protein synthesis. Understanding codons is crucial for unraveling how genetic information is expressed in living organisms.

Amino Acids

Amino acids are the building blocks of proteins, which are vital for countless functions in living organisms. There are 20 standard amino acids, each having a unique side chain that determines its properties and role in proteins. These amino acids are linked together by peptide bonds to form proteins based on the sequence dictated by mRNA codons.

During the process of translation, tRNA molecules bring the corresponding amino acids to the ribosome, as dictated by the mRNA codons. Each tRNA has an anticodon that is complementary to a specific mRNA codon, ensuring that the correct amino acid is added to the growing peptide chain. For example, the mRNA codon UUU codes for the amino acid phenylalanine. This systematic and precise matching ensures that proteins are built correctly according to the genetic instructions. Amino acids not only form proteins but can also have roles in metabolism and other cellular processes.

Complementary Base Pairing

Complementary base pairing is a fundamental concept in molecular biology. It explains how the nucleotides of DNA and RNA interact specifically with one another through hydrogen bonds. In DNA, adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). However, in RNA, uracil (U) replaces thymine, so adenine pairs with uracil instead.

This pairing is crucial for the replication of DNA and the transcription of DNA into RNA. During transcription, the RNA polymerase enzyme reads the DNA strand and synthesizes a complementary RNA strand. This new RNA strand will have base pairs that are complementary to the DNA template, ensuring accurate genetic information transfer. For example, if the DNA sequence is ATCG, the corresponding mRNA sequence will be UAGC. Complementary base pairing also plays an essential role in the matching of tRNA anticodons with mRNA codons during translation, ensuring accurate protein synthesis. Understanding this concept is vital for comprehending how genetic information is conserved and expressed in cells.