Biology Now, 2e

Tobacco’s New Leaf ■ 179

Two-Step Dance, Translation: RNA to Protein

The microscopic molecular dance inside the

tobacco cells continues with translation. Once

the hemagglutinin gene has been transcribed

into mRNA in the nucleus, it is time to make

mature mRNA (Figure 10.7). This mRNA is

then ready to leave the nucleus.

To review, transcription occurs when RNA

polymerase binds to a promoter, unzips the

DNA helix, and constructs a strand of mRNA

based on the DNA template strand. Transcrip-

tion ends at the terminator sequence, and the

mRNA is then processed, at which time noncod-

ing introns are spliced out of the sequence. Voilà!

mRNA is created from a gene.

Coding sequence

Nucleus

Hemagglutinin gene

Introns

Initial RNA product

mRNA

mRNA

Exons

Introns removed

Coding regions linked

Cytoplasm

Nuclear

envelope

Nuclear

pore

Transcription

Figure 10.7

Processing mRNA for export to the cytoplasm

In eukaryotes, introns must be removed before an mRNA leaves the nucleus.

Q1: In your own words, define RNA splicing. When during gene expression does it occur?

Q2: What do you predict would happen if the introns were not removed from RNA before

translation? Why would it be a problem if the introns were not removed?

Q3: Where is the mRNA destined to go once it has been transported out of the nucleus?