Biology Now, 2e

180 ■ CHAPTER 10 How Genes Work

GENETICS

G U G A G U C

CC

A

GG

UAC

Methionine

Methionine

Ribosome

Covalent

bond

Start codon

Start codon

Glycine

Glycine

mRNA

mRNA

Stop codon

Stop codon

A tRNA molecule

carrying glycine

binds to the

second codon.

tRNA

Later

The ribosome links

the first amino acid

(methionine) to the

second (glycine) to

begin the amino acid

chain of a protein.

Start codon

mRNA

Stop codon

The first tRNA, now

unloaded, is released.

Tobacco cell

A tRNA molecule

carrying the amino

acid methionine

binds to the start

codon.

As the ribosome

moves one codon

at a time, tRNA

molecules bind to

mRNA, allowing the

ribosome to link

the amino acids in

the correct order.

Translation begins

when mRNA binds

to a ribosome.

When the ribosome

reaches a stop

codon, the mRNA

and the completed

amino acid chain

both separate from

the ribosome.

Completed

amino acid chain

Start codon

mRNA

Stop codon

Serine

U AC

A UGG GGU C C AGCUG AGUG AGUC

U

AC C

ACGG

C CC

C CC

U

UU

C CC

U AC

1

2

3

Specifies the order of

amino acids in a protein

using a series of

three-base codons,

where different amino

acids are specified by

particular codons.

As a major component

of ribosomes, assists in

making the covalent

bonds that link amino

acids together to make a

protein.

Transports the correct

amino acid to the

ribosome, using the

information encoded in

the mRNA; contains a

three-base anticodon

that pairs with a

complementary codon

revealed in the mRNA.

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

G UGA GUC Transfer RNA (tRNA)

G UGA GUC A UGG GGU C C AGCUG AGUG AGUC

G UGA GUC A UGG GGU C C AGCUG AGUG AGUC

G UGA GUC A UGG GGU C C AGCUG AGUG AGUC

Figure 10.8

Plants making proteins, II: Translation

In translation, the hemagglutinin mRNA directs the

synthesis of the hemagglutinin protein. M

(You will need to finish reading the section on

translation to answer the following three questions.)

Q1: Which amino acid always begins

an amino acid chain? Which codon and

anticodon are associated with that amino

acid?

Q2: Each of the codons for stopping

translation binds to a tRNA molecule that

does not carry an amino acid. How would

the binding of a stop codon cause the

completed amino acid chain to be released?

Q3: Given the partial mRNA sequence that

you specified in Figure 10.6’s question 3 as

being transcribed from the DNA template

strand, what is the amino acid sequence

that would be translated?