Biology Now, 2e

Tobacco’s New Leaf ■ 177

Outbreak! Samples of the

flu virus are taken from

sick people and sent to

medical labs to be

sequenced.

Healthy people are

injected with the flu

vaccine and develop

immunity to the flu virus

(see Figure 2.1 for details).

The virus is sequenced,

and the genetic sequence

is sent to Medicago (and

other vaccine producers).

Medicago identifies a

portion of the DNA to

synthesize—in this

case, the gene for

hemagglutinin, a protein

from the virus’s surface.

The hemagglutinin

proteins are purified to

produce a vaccine.

The tobacco is harvested,

and the hemagglutinin

proteins are extracted.

The synthesized hemagglutinin

gene is inserted into the

Agrobacterium genome, and

the bacteria replicate.

The tobacco expresses the

hemagglutinin gene, producing

the hemagglutinin protein that

the gene encodes.

The tobacco is infected

with Agrobacterium,

which transfers the

synthesized

hemagglutinin gene to

the tobacco genome.

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9

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8 7

4

6

5

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Figure 10.5

From outbreak to vaccine

During flu season or any other viral outbreak, a large network of medical professionals and scientists is

activated to create a vaccine quickly and effectively. M

Q1: In which of the step(s) illustrated here does DNA replication occur? In which step(s) does

gene expression occur?

Q2: Why do vaccine producers not simply replicate the entire viral genome, instead isolating the

gene for one protein and replicating only that gene?

Q3: What role do the bacteria play in this process? Why are they needed?

RNA polymerase binds to a segment of DNA

near the beginning of the gene that is called

a promoter. The promoter contains a specific

sequence of DNA bases that the RNA poly-

merase recognizes and binds. At Medicago,

scientists attach specific promoters to the

hemagglutinin gene so that the plant cell’s

RNA polymerase can identify the gene and

actively transcribe it, maximizing the rate of

transcription, says Vézina.