Coupon Accepted Successfully!


Translating the Message

The process of translation involves three distinct steps, all of which occur in the cytoplasm (see Figure 6.2). 
  1. Initiation: The mRNA binds to the ribosome, a molecular machine made up of rRNA and proteins. The ribosome binds at the beginning of the message.
  2. Elongation: The ribosome helps tRNA molecules bind to the mRNA. Each tRNA has two different regions. One region, called the anticodon, contains three nucleotides that bind to the codon in the mRNA transcript via complementary base pairing. The other region has a specific amino acid attached to it. Once the correct tRNA binds with the mRNA, the amino acid on the tRNA is linked to the other amino acids in the growing chain by the ribosome. This results in the formation of a peptide bond. Then the tRNA is released and the ribosome moves down the mRNA chain to the next codon. The tRNA is “recharged” with another amino acid by the enzyme peptidyl transferase, so it can be used again and again.
  3. Termination: When the ribosome encounters a stop codon, it detaches from the mRNA chain and the polypeptide is released.
Most proteins are further processed before they can function in the cell. This processing may occur in the endoplasmic reticulum or in the Golgi (see Chapter 10). Proteins are often phosophorylated by specific enzymes in the cytoplasm. In addition, most proteins are cleaved, or cut, at the beginning of the polypeptide, which removes the initial methionine and other amino acids. So, although every mRNA codes for methionine as the first amino acid, few mature proteins retain this feature.

Test Your Skills Now!
Take a Quiz now
Reviewer Name