Types of Control Mechanisms

All cells in your body have the same genetic instructions. However, only a relatively small number of genes are active at any given time in any given tissue.

Which genes are expressed depends on the type of cell, its responses to chemical signals, and built-in control systems.

Regulatory proteins can exert control over gene expression through interactions with: DNA, RNA, new polypeptide chains, or final proteins.

Types of control systems used by cells:

In negative control systems, a repressor protein inhibits some activity. A repressor protein binds to the DNA to block transcription. It can be removed by an inducer.

In positive control systems, an activator protein enhances some activity. An activator protein binds to the DNA and promotes initiation of transcription.

Control can also be exerted by chemical modification. Two examples are methylation of DNA (or the attachment of methyl groups to nucleotide bases) which can inactivate genes, and acetylation of histones that allows DNA unpacking and transcription.

REVIEW: Cell differentiation _____ .
a. occurs in all complex multicelled organisms
b. requires different genes in different cells
c. involves selective gene expression
d. both a and c
e. all of the above

REVIEW: Molecules that interact with DNA to alter gene expression are

REVIEW: In negative control systems, which of the following would cause transcription to proceed?

REVIEW: A regulator gene produces which of the following?

REVIEW: The expression of a given gene depends on the _____.
a. type of cell and its functions
b. chemical conditions
c. environmental signals
d. all of the above