Final answer:
In double-stranded DNA, there are six reading frames, three for each strand, determined by the presence of a start codon. Protein synthesis typically uses only one of the strands, known as the sense strand, to serve as a template for mRNA. Both strands can code for proteins, ensuring genetic diversity and complexity.
Step-by-step explanation:
There are six reading frames in a double-stranded DNA, three on each strand. Each strand has a 5' to 3' direction, with three possible reading frames that can be read in sets of three nucleotides, known as codons. The decision on which frame to use is typically determined by the presence of a start codon, which in most cases is AUG and signifies where the protein-coding sequence begins.
During the process of protein synthesis, only one of the strands, termed the sense strand, is used as a template for mRNA synthesis. The complementary strand is known as the antisense strand. The sense strand has the same sequence as the mRNA except that thymine (T) is replaced by uracil (U). However, both DNA strands can potentially code for different proteins, depending on the cell's requirements and specific gene regulation mechanisms. This flexibility allows for a more complex and diverse set of proteins to be produced from a limited amount of genetic material.
The AP Biology Curriculum Framework emphasizes that the double-stranded structure of DNA ensures high fidelity in the replication process, which is necessary for the transmission of genetic information to the next generation.