The base sequence of the gene coding for a short polypeptide is CTACGCTAGGCGATTGACT. What would be the base sequence of the mRNA transcribed from this gene? Using the genetic code, give the amino acid sequence of the polypeptide translated from this mRNA. (Hint: What is the start codon?)

Verified step by step guidance

1. Identify the template strand and the coding strand in the DNA sequence provided. In this case, the given sequence is the coding strand: CTACGCTAGGCGATTGACT.
2. Transcribe the DNA sequence into mRNA by replacing each DNA base with its complementary RNA base. Remember that adenine (A) pairs with uracil (U) in RNA instead of thymine (T), and cytosine (C) pairs with guanine (G).
3. Locate the start codon (AUG) in the mRNA sequence. This codon marks the beginning of the translation process and codes for the amino acid methionine.
4. Translate the mRNA sequence into an amino acid sequence using the genetic code. Each set of three nucleotides (codon) in the mRNA corresponds to one amino acid in the polypeptide.
5. Continue reading the mRNA sequence codon by codon, translating each until you reach a stop codon (UAA, UAG, or UGA), which does not code for an amino acid but signals the end of translation.

Key Concepts

Transcription

Transcription is the process by which the genetic information in DNA is copied into messenger RNA (mRNA). During transcription, RNA polymerase reads the DNA template strand and synthesizes a complementary RNA strand, replacing thymine (T) with uracil (U). This process is crucial for gene expression, as it produces the mRNA that carries the genetic code from the nucleus to the ribosome for translation.

Genetic Code

The genetic code is a set of rules that defines how sequences of nucleotides in mRNA are translated into amino acids, the building blocks of proteins. Each group of three nucleotides, known as a codon, corresponds to a specific amino acid or a stop signal during protein synthesis. Understanding the genetic code is essential for determining the amino acid sequence of a polypeptide from the mRNA sequence.

Start Codon

The start codon is a specific sequence of nucleotides in mRNA that signals the beginning of translation. The most common start codon is AUG, which codes for the amino acid methionine. Identifying the start codon is critical for correctly interpreting the mRNA sequence and ensuring that the polypeptide is synthesized from the correct point, leading to the proper amino acid sequence.