Hormones as Control Agents

• Some hormones bind to membrane receptors on cell surfaces.
• Others enter cells to bind with regulatory proteins to initiate transcription, often with the aid of enhancer sequences.

Chromosome puffs are portions of the polytene chromosome in which the DNA has loosened up in response to ecdysone to allow transcription. Translation of transcripts from puffed regions produces protein components of saliva.

In vertebrates, some hormones such as somatotropin which is a growth hormore have widespread effects because most of the body's cells have receptors for it. Whereas, others such as prolactin that stimulates milk production affects only the mammary glands because only they have the receptors.

REVIEW: Hormones may ______ gene transcription in target cells.
a. promote
b. inhibit
c. participate in
d. both a and b

Answer d