How Cells Make Protein: Translation - Biology Worksheet Page 3

ADVERTISEMENT

Name: _____________________
Period: _____ Date: _________________
Understanding Protein Synthesis
1. Protein Synthesis: The details
The first phase of protein synthesis is called initiation. Initiation begins as a strand of mRNA leaves the nucleus.
The small subunit of a ribosome attaches to the leading end of the mRNA. A tRNA carrying the amino acid methionine binds
with the start codon AUG. Initiation ends as the large subunit of the ribosome binds with the small subunit, completing the
ribosome.
Elongation involves synthesis of an increasingly long chain of amino acids, or polypeptide. A second tRNA, carrying a
second amino acid, comes to the ribosome, and sits on the codon immediately adjacent to the start codon. The ribosome
catalyzes a peptide bond between the first amino acid that had been brought to the ribosome, and this new amino acid,
forming a dipeptide (a mini-protein with two amino acids). Next, the ribosome moves over to the next mRNA codon. As
another tRNA bearing a third amino acid comes to the ribosome, the first tRNA gets discharged into the cytoplasm. The
ribosome then catalyzes another peptide bond, forming a tri-peptide (a chain of three amino acids). This process of
ribosomal movement from one codon to the next, arrival of new tRNAs with new amino acids, and formation of new peptide
bonds results in an increasingly long polypeptide.
The process ends only when the ribosome reaches a stop codon. This codon, instead of coding for an amino acid,
codes for a protein called a release factor to enter the ribosome. The release factor causes the polypeptide to disconnect
from the last tRNA, and for the entire initiation complex (ribosome, tRNA, and mRNA) to fall apart. The polypeptide folds
up into its three dimensional shape, completing the protein synthesis process.
2. A storyboard for protein synthesis. Write a brief description of what’s happening in each step.
1.
2.
3.
4.
5.
6.
7.
8.
Page 3 of 8

ADVERTISEMENT

00 votes

Related Articles

Related forms

Related Categories

Parent category: Education
Go
Page of 8