Biology Now, 2e

184 ■ CHAPTER 10 How Genes Work

GENETICS

Gene

Nucleus

Cytoplasm

Broken-down

mRNA

Broken-down

protein

Protein

mRNA

mRNA

Control point 6:

Protein life

span

Control point 5:

Posttranslation

Control point 4:

Translation

Control point 3:

Breakdown of

mRNA

Control point 2:

Transcription

Control point 1:

DNA packing

Figure 10.11

How gene expression is regulated

In eukaryotes, gene expression can be controlled

at several points along the pathway from gene

to protein to phenotype: before transcription,

at transcription, during RNA processing, or at

translation. Gene expression can also be regulated

after translation, by control of the activity or life

span of the protein.

Q1: As illustrated here, at what control point is transcription regulated?

Q2: What is a possible advantage of regulating gene expression before transcription, versus after?

Q3: If you wanted to up-regulate production of the hemagglutinin protein in a tobacco plant carrying

the hemagglutinin gene, at which control point(s) would that be possible? Justify your reasoning.

points during translation (Figure 10.11).

But for all living cells, a few genes are always

expressed at a low level; their transcription is

not regulated, because these genes are needed

at all times.

At Medicago, the company takes advantage

of gene regulation in tobacco cells to produce

as much hemagglutinin protein as possible.

After the agrobacteria are vacuum-sucked

into the leaves and transcription and trans-

lation begin to actively occur in the tobacco

cells, the plants are sent to grow in an incu-

bation room, where technicians can alter the

humidity, temperature, and level of light to

maximize the amount of protein expressed by

the plants.

“We’ve been able to tweak environmental

conditions of the plants to boost gene expres-

sion,” says Vézina. “You name it, we’ve tried

it.” It’s an important step in the process, adds

Wanner. “We determined what the best condi-

tions for protein expression are.”

To the Market

It’s the end of April, and the final steps are

being taken to isolate and purify the hemag-

glutinin protein from the tobacco plants, to

see how much vaccine can be made in a month.

After the plants have incubated for several

days, the leaves are stripped and diced into

green confetti, then digested with enzymes to