Biology 12

Chapter 8 Protein Synthesis • MHR 263

8.3 From RNA to Protein: Translation

If you play a musical instrument, you know that it
is possible to create a nearly infinite variety of tunes
by experimenting with different combinations of
notes. If you want to play a particular song
accurately, however, you must read the symbols on
a musical score and use these instructions to play a
series of notes in precise sequence (as in Figure 8.14).
Like any act of translation, turning the notes on a
page into music requires a translator — in this case,
someone who knows how to read music and how
to play the instrument. The musical instrument is
also an important component, since the correct
sounds could not be made without this complex
piece of equipment.

Figure 8.14To play a particular song, a musician translates
symbols on a page with the aid of a musical instrument. In an
analogous way, a cell creates proteins by translating mRNA
codons with the aid of its protein synthesis “equipment.”

In an analogous way, it is possible to generate
any number of polypeptides using the amino acids
available in a cell. For a cell to create the particular
proteins it needs, however, it must translate mRNA
codons into amino acid sequences. This process
requires both a chemical “translator” and a set of
cellular protein synthesis “equipment.” Once

mRNA reaches the cytoplasm, these elements work

together to assemble the protein products. In the

text that follows, you will learn about the key

components of a cell’s protein synthesis equipment.

Transfer RNA (tRNA)

Different transfer RNAor tRNAmolecules link

each codon on the mRNA with its specific amino

acid. Like mRNA, tRNA molecules are transcribed

from genes on the DNA template. Unlike mRNA,

however, tRNA molecules do not remain as a

linear strand. Instead, base pairing between

complementary nucleotides on different regions

of each tRNA molecule causes the molecule to fold

into the characteristic three-lobed shape you see

in Figure 8.15.

Figure 8.15Each tRNA molecule is about 80 nucleotides

long. By convention, the anticodon sequence is written in

the 3 ′to 5 ′direction, opposite to the convention for DNA

and mRNA. This practice makes it easier to match

anticodons to their complementary codon sequence.

anticodon

loop

iso OH

amino acid attaches here

anticodon

codon

mRNA

GAU

AUC

5 ′

5 ′

3 ′

3 ′

5 ′ 3 ′

5 ′ 3 ′

EXPECTATIONS

Explain the steps involved in translation.

Describe the structure and function of the main nucleic acids and enzymes

involved in translation.

Investigate, through simulation, the cell structures and molecules involved

in transcription and translation.