Consider the following segment of DNA:
    5'-...ATGCCAGTCACTGACTTG...-3'
    3'-...TACGGTCAGTGACTGAAC...-5'
If the lower strand of DNA serves as the template transcribed into mRNA, how many peptide bonds are present in the polypeptide fragment into which the mRNA is translated?

Verified step by step guidance

1. Identify the template strand of DNA, which is the lower strand in this case (3'-...TACGGTCAGTGACTGAAC...-5'). This strand will be used to synthesize the complementary mRNA sequence.
2. Determine the mRNA sequence by transcribing the template strand. Replace each base with its complementary RNA base: A pairs with U, T pairs with A, G pairs with C, and C pairs with G. The resulting mRNA sequence will be 5'-...AUGCCAGUCACUGACUUG...-3'.
3. Locate the start codon (AUG) in the mRNA sequence. This codon signals the beginning of translation and the synthesis of the polypeptide chain.
4. Divide the mRNA sequence into codons (groups of three nucleotides) starting from the AUG codon. Each codon corresponds to a specific amino acid, except for stop codons, which terminate translation.
5. Count the number of codons that encode amino acids (excluding the stop codon). The number of peptide bonds in the polypeptide will be one less than the number of amino acids, as each bond links two amino acids together.

Key Concepts

Transcription

Transcription is the process by which the genetic information encoded in DNA is copied into messenger RNA (mRNA). During transcription, RNA polymerase binds to the DNA template strand and synthesizes a complementary RNA strand. The mRNA then carries the genetic code from the nucleus to the ribosome, where it will be translated into a protein.

Translation

Translation is the process by which the sequence of nucleotides in mRNA is decoded to produce a specific polypeptide or protein. This occurs in the ribosome, where transfer RNA (tRNA) molecules bring amino acids to the mRNA template according to the codon sequence. Each codon, a sequence of three nucleotides, corresponds to a specific amino acid, and the polypeptide chain is formed through peptide bonds between these amino acids.

Peptide Bonds

Peptide bonds are the chemical bonds that link amino acids together in a polypeptide chain. They form during the translation process when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water. The number of peptide bonds in a polypeptide is always one less than the number of amino acids, as the first amino acid does not form a bond with a preceding one.