Biology, Eighth Edition (Raven)

Chapter 15: Genes and How They Work

Protein Synthesis

How is protein synthesis similar to the catalysis of a reaction by an enzyme? Protein synthesis is a series of chemical reactions in which molecules are brought into contact with one another and chemical bonds are formed and broken. The key event in protein synthesis is the formation of bonds between adjacent amino acids in the protein and the breaking of bonds between the same amino acids and the tRNA molecules that first bring the amino acids to the ribosomes. The function of the ribosome is to bind the tRNA molecules and then move through the ribosome. As the tRNAs are moved, the ribosome’s configuration brings the amino acids into contact and then severs the bonds between tRNA and amino acid. In a general sense, RNA is acting as an enzyme that catalyzes the reactions that form the amino acid chain.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Which of the following combinations are correctly matched?

		A)	70S – ribosome
		B)	anticodon – mRNA
		C)	codon – tRNA
		D)	A and B
		E)	A, B, and C

2.	Which of the following occurs as the ribosome shifts down the mRNA by a distance of one codon?

		A)	the tRNA that was in the A site picks up another amino acid
		B)	the tRNA that was in the A site releases the growing polypeptide chain
		C)	the tRNA that was in the A site moves into the P site
		D)	the tRNA that was in the P site moves into the A site
		E)	the tRNA that was in the P site picks up another amino acid

3.	A certain polypeptide is 100 amino acids in length. During translation of this polypeptide, how many amino acids entered through the A site of the ribosome?

		A)	1
		B)	9
		C)	50
		D)	99
		E)	100

4.	The large ribosomal subunit joins the translation initiation complex after the small subunit has already joined.

		A)	True
		B)	False

5.	Elongation of the polypeptide chain is terminated when a stop codon enters the P site of the ribosome.

		A)	True
		B)	False