How many amino acids are coded in the DNA segment:
CTC–ATA–CGA–TTC–AAG–TTA?
(a) 18
(b) 9
(c) 6
(d) 3

Verified step by step guidance

1. Understand that each amino acid is coded by a sequence of three nucleotides called a codon in the DNA or mRNA sequence.
2. Count the number of nucleotide triplets (codons) in the given DNA segment: CTC–ATA–CGA–TTC–AAG–TTA.
3. Since each codon corresponds to one amino acid, the total number of amino acids coded is equal to the number of codons.
4. Verify that the DNA segment is properly divided into codons of three nucleotides each, ensuring no incomplete codons are present.
5. Conclude that the number of amino acids coded is the total count of these codons.

Key Concepts

DNA Codons and Amino Acid Coding

DNA sequences are read in groups of three nucleotides called codons, each of which corresponds to a specific amino acid during protein synthesis. Understanding that each codon codes for one amino acid is essential to determine how many amino acids a DNA segment encodes.

Reading Frame and Codon Counting

The reading frame refers to how nucleotides are grouped into codons starting from a specific nucleotide. Counting the total number of codons in a DNA segment involves dividing the total number of nucleotides by three, which directly gives the number of amino acids coded.

Transcription and Translation Basics

DNA is first transcribed into mRNA, which is then translated into a chain of amino acids forming a protein. Although the question focuses on DNA, knowing that the DNA codons correspond to mRNA codons helps in understanding the process of amino acid coding.