A portion of a DNA template strand has the base sequence 5′-...ACGCGATGCGTGATGTATAGAGCT...-3′

Assume the mRNA is written in the correct reading frame. Determine the amino acid sequence encoded by this fragment. Identify the N- and C-terminal directions of the polypeptide.

Verified step by step guidance

1. Identify the direction of the DNA template strand. The given sequence is 5′ to 3′, but the template strand is typically read 3′ to 5′ for transcription.
2. Transcribe the DNA template strand to mRNA. Remember that RNA polymerase synthesizes mRNA in the 5′ to 3′ direction, using the DNA template strand.
3. Convert the DNA template sequence to its complementary mRNA sequence. Replace each DNA base with its RNA complement: A with U, T with A, C with G, and G with C.
4. Determine the mRNA sequence in the 5′ to 3′ direction. This is the sequence that will be translated into a polypeptide.
5. Translate the mRNA sequence into an amino acid sequence using the genetic code. Identify the start codon (AUG) to begin translation and continue until a stop codon is reached. The N-terminal is the start of the polypeptide, and the C-terminal is the end.

Key Concepts

Transcription

Transcription is the process by which the genetic information in DNA is copied into messenger RNA (mRNA). During this process, RNA polymerase binds to the DNA template strand and synthesizes a complementary RNA strand, replacing thymine (T) with uracil (U). Understanding transcription is essential for determining how the DNA sequence translates into an mRNA sequence, which is the first step in protein synthesis.

Translation

Translation is the process by which the mRNA sequence is decoded to synthesize a polypeptide chain, which will fold into a functional protein. This occurs in the ribosome, where transfer RNA (tRNA) molecules bring specific amino acids to the growing polypeptide chain based on the codon sequence of the mRNA. Knowing how to read the mRNA codons is crucial for determining the corresponding amino acid sequence.

Amino Acid Structure and Polypeptide Directionality

Amino acids are the building blocks of proteins, each with a specific side chain that determines its properties. Polypeptides have directionality, with an N-terminal (amino end) and a C-terminal (carboxyl end). Understanding this directionality is important for correctly identifying the sequence of amino acids and their orientation in the final protein structure, which affects its function.