KEY TERMS:
- Transcription describes synthesis of RNA on a DNA template.
- Translation is synthesis of protein on the mRNA template.
- A coding region is a part of the gene that represents a protein sequence.
- The antisense strand (Template strand) of DNA is complementary to the sense strand, and is the one that acts as the template for synthesis of mRNA.
- The coding strand (Sense strand) of DNA has the same sequence as the mRNA and is related by the genetic code to the protein sequence that it represents.
- Only one of the two strands of DNA is transcribed into RNA.
Gene expression occurs by a two-stage process.
- Transcription generates a single-stranded RNA identical in sequence with one of the strands of the duplex DNA.
- Translation converts the nucleotide sequence of mRNA into the sequence of amino acids comprising a protein. The entire length of an mRNA is not translated, but each mRNA contains at least one coding region that is related to a protein sequence by the genetic code: each nucleotide triplet (codon) of the coding region represents one amino acid.
Only one strand of a DNA duplex is transcribed into a
messenger RNA. We distinguish the two strands of DNA as depicted in Figure 5.2:
- The strand of DNA that directs synthesis of the mRNA via complementary base pairing is called the template strand or antisense strand. (Antisense is used as a general term to describe a sequence of DNA or RNA that is complementary to mRNA.)
- The other DNA strand bears the same sequence as the mRNA (except for possessing T instead of U), and is called the coding strand or sense strand.
In this chapter we discuss mRNA and its use as a template
for protein synthesis. In 6 Protein
synthesis we discuss the process by which a protein is synthesized. In 7 Using the genetic code we discuss the
way the genetic code is used to interpret the meaning of a sequence of mRNA. And
in 8 Protein localization we turn to
the question of how a protein finds its proper location in the cell when or
after it is synthesized.