The following is a segment of the template strand of human...

The following is a segment of the template strand of human BRCA1 gene: $$ 3^{\prime} \text { TGG AAT TAT CTG CTC TTC GCG } 5^{\prime} $$ a. Write the corresponding mRNA segment. b. Write the three-letter and one-letter abbreviations for the corresponding peptide segment. c. If there is a point mutation in the fourth nucleotide triplet and A replaces $\mathbf{G}$, what is the change, if any, in the amino acid sequence?

The following is a segment of the template strand of human BRCA1 gene:
$$
3^{\prime} \text { TGG AAT TAT CTG CTC TTC GCG } 5^{\prime}
$$
a. Write the corresponding mRNA segment.
b. Write the three-letter and one-letter abbreviations for the corresponding peptide segment.
c. If there is a point mutation in the fourth nucleotide triplet and A replaces $\mathbf{G}$, what is the change, if any, in the amino acid sequence?

Key Concepts

Transcription

Transcription is the process by which the DNA template strand is used to synthesize a complementary messenger RNA (mRNA) molecule. In this process, RNA polymerase reads the DNA sequence in a 3? to 5? direction, synthesizing the mRNA in the 5? to 3? direction, replacing thymine (T) with uracil (U). This step is fundamental as it converts the genetic information stored in the DNA into a form that can be read during protein synthesis.

Translation

Translation is the process in which the nucleotide sequence of mRNA is decoded to produce a polypeptide chain, ultimately folding into a functional protein. The mRNA is read in codons—groups of three nucleotides—each of which corresponds to a specific amino acid. The translation occurs in the ribosome, where transfer RNAs (tRNAs) bring the corresponding amino acids based on the mRNA codon sequence, building the chain as per the genetic instructions.

Genetic Code

The genetic code is the set of rules that define the mapping from mRNA codons to amino acids during translation. This code is nearly universal and redundant, meaning that multiple codons can encode the same amino acid. Additionally, amino acids are often represented both by three-letter abbreviations and one-letter abbreviations, which provide a shorthand method for depicting protein sequences.

Point Mutation

A point mutation is a change in a single nucleotide within the DNA sequence. This type of mutation can result in a change in the mRNA codon during transcription, which may subsequently alter the amino acid sequence during translation. Depending on the specific substitution, the point mutation might result in a silent mutation (no change in the amino acid), a missense mutation (change to a different amino acid), or even a nonsense mutation (introduction of a stop codon), each of which can have different effects on protein function.

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