Biology Now, 2e

174 ■ CHAPTER 10 How Genes Work

GENETICS

T

he greenhouse is vast, the size of half a

football field. A loud, steady thrum rever-

berates in the room as massive metal fans

push air through the hot, humid space. Mike

Wanner, a tall, serious man with gray hair and

piercing brown eyes, walks through rows of leafy

plants, each a foot and a half tall. He stoops to

rub a leaf between his fingers, then raises his

hand to his nose and sniffs. “That’s what tobacco

smells like,” Wanner shouts, straining to be

heard over the noise of the fans.

Wanner is the North Carolina site manager

for operations at Medicago, a Canadian biotech-

nology company growing tobacco at a facility

outside Durham, once home to Lucky Strike

cigarettes (Figure 10.1). But these plants are

not being grown to smoke, chew, or dip. Instead,

they serve a dramatically different purpose: this

tobacco will be used to make flu vaccines.

Influenza vaccines are normally grown in

chicken eggs—a process that takes months. As

an alternative, companies and researchers have

begun experimenting with “biopharming”—

manufacturing vaccine proteins in plants. Since

most genes contain instructions for building

proteins, scientists insert a gene that codes

for the protein that interests them. This produc-

tion of a protein from a gene occurs via gene

expression—the process by which genes are

transcribed into RNA and then translated to

make proteins (Figure 10.2).

Proteins participate in virtually every process

inside and between cells, so gene expression is the

fundamental way by which genes influence the

structure and function of a cell or organism. It is

the process through which an organism’s geno-

type gives rise to its phenotype (see Chapter 7).

All prokaryotes, eukaryotes, and viruses utilize

gene expression.

In addition to being involved in every process

in a cell, proteins are the key components of

some vaccines. Injected pieces of viral proteins

activate the human immune system to defend

against that virus in the future (see Figure 2.1).

To m a k e t h e s e v a c c i n e s , s c i e nt i s t s mu s t pr o du c e

large quantities of viral proteins. The traditional

method is to inject chicken eggs with a virus, let

the virus multiply in the chicken cells, and then

Figure 10.1

Growing tobacco to treat the flu

To b a c c o p l a n t s g r o w i n a M e d i c a g o g r e e n h o u s e i n Q u e b e c Ci t y, C a n a d a.

Cell

Transcription Translation

mRNA

Cytoplasm

Nucleus

DNA

An mRNA

copy of the

gene is

made in the

nucleus.

Ribosome

mRNA

Protein

Amino acids are

linked to one

another at the

ribosome to

create the protein

encoded by the

mRNA.

Figure 10.2

An overview of gene expression

Genetic information flows from DNA to RNA to

protein during gene expression, which occurs in

two steps: first transcription and then translation.

The transcription of a protein-coding gene

produces an mRNA molecule, which is then

transported to the cytoplasm, where translation

occurs and the protein is made with the help of

ribosomes.