Biology 12

3.Decide on one plan and assign responsibilities to

each member of your group.

4.Assemble the materials you will need and prepare

your presentation.

Checking the Plan

1.Check your plan against your initial list of the

structures, molecules, and processes involved

in protein synthesis. Have you included all the

important steps?

2.Do the materials you are using help to explain the

processes involved at each step?

3.Has your teacher approved your plan?

Data and Observations

Present your simulation of protein synthesis to the class.
Make a note of any comments you receive from other
groups. Identify which parts of your presentation seemed
to be the most effective at simulating protein synthesis.
Do these results match your initial hypothesis?

Analyze

1.Among the different approaches used by the groups

in the class, which do you think was the most

effective? Explain.

2.Now that you have seen how other groups

approached the problem, how would you revise

your own presentation?

Conclude and Apply

3.Identify three ways in which the two-step process of

protein synthesis helps living cells conserve energy

or reduce the risk of damage from mutations.

4.What are the adaptive advantages and disadvantages

of the presence of introns in eukaryotic cells?

Exploring Further

5.Almost all living organisms on Earth use the same

20 amino acids. However, molecular biologists have

been able to develop a number of artificial amino

acids, which can be used to develop synthetic

proteins that have many potential applications. In

response, some research teams are exploring the

possibility of expanding the genetic code to include

new nucleotides that could be used to code for

artificial amino acids. Use your library or the Internet

to find out more about this research. Write a brief

report explaining some of the hurdles that will have

to be overcome as scientists try to expand the

genetic code. What are some of the scientific and

social implications of this research?

Chapter 8 Protein Synthesis • MHR 267

mRNA

5 ′ 3 ′

E

E

E

P

P

A

A

PA

growing polypeptide incoming

aa-tRNA

molecule

new peptide

bond being

transferred

ribosome

ready for

next aa-tRNA

molecule

Figure 8.19The three steps of the elongation cycle. Once initiated, this cycle will
continue until the protein synthesis equipment encounters a stop signal.

The anticodon of an aa-tRNA

molecule binds to the mRNA

codon exposed in the A site.

A

Enzymes and other

molecules in the

ribosome catalyze the

formation of a bond

between the last

amino acid on

the lengthening

polypeptide and

the new amino acid.

B

The ribosome moves down

the mRNA strand, shifting the

binding sites a distance of

three nucleotides. A new A site

is exposed as the tRNA that

was in the P site is moved to

the E site and released.

C