Biology 12

THINKING LAB

Interpreting Micrographs

Background

Transcription and translation have been understood largely
through experimental analysis and deduction. However,
micrographs (photographs taken through electron
microscopes) can sometimes be used to confirm, clarify, or
expand on hypotheses about such molecular events. In this
lab, you will interpret and describe the events taking place
in the micrographs shown.

You Try It

1.For each micrograph, write a title that briefly states

what is taking place.

2.Write a short caption for each micrograph that identifies

the visible structures and explains how the events

shown should be interpreted.

3.In a few paragraphs of text, describe the events

captured in each micrograph, the events that preceded

those captured, and the events that will likely follow.

Include information about structures or molecules that

are involved but not pictured.

4.Draw and label diagrams of each micrograph that show

in greater detail the events taking place.

5.Exchange your material with a partner. In what ways did

your two interpretations differ? How would you change

your interpretation as a result?

Chapter 8 Protein Synthesis • MHR 279

DNA

RNA polymerase

transcription

factors

transcription

factors

transcription

rate increases

initiation

complex

promoter

sequence

operator gene

sequence

TATA

box

Figure 8.34In a eukaryotic cell, a particular sequence of events (such as the
one shown in this model) is needed to turn on gene expression. Most of the
cell’s genome remains unexpressed most of the time.

The operator sequence is located some distance

from the promoter sequence that pertains to the

gene to be transcribed. One group of transcription

factors binds to this operator sequence.

A

The interaction between the transcription factors

and the operator sequence causes the DNA

molecule to bend, bringing the transcription factors

into contact with the promoter sequence. At the

same time, their interaction causes other

transcription factors to collect near the promoter

sequence.

B

The transcription factors bind with one another and

with the promoter sequence to produce an initiation

complex. This complex increases the affinity of

RNA polymerase for the promoter, thereby

increasing the rate of transcription.

C

A B