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A Handbook of Biology

Water-soluble

hormone

Receptor

cAMP activates

secondary messenger

that inturn activates

protein kinases

G protein

Protein kinases

cAMP

Activated

protein

kinases

Protein –

Second messenger

Adenylate

cyclase converts

ATP to cAMP

Activated protein

kinases

phosphorylate

cellular proteins

Blood capillary

Binding of hormone (e.g., FSH)

to its receptor

Adenylate cyclase

Ovarian

cell membrane

Target cell

P

1

2

3

4

ADP

Protein

ATP

ATP

5

Phosphorylated proteins cause

physiological responses

E.g., Ovarian growth

Membrane-bound receptor (E.g., Peptide hormone)

1

Lipid-soluble (estrogen)

hormone

diffuses into cell

Uterine cell

membrane

Blood capillary

Activated

hormone-receptor

complex changes

gene expression

Nucleus

Receptor

mRNA

2

3 Newly formed

mRNA directs

synthesis of

specific proteins

on ribosomes

DNA

Cytosol

Target cell

New proteins change

cell's activity (tissue growth

and differentiation)

4

Transport

protein

Free hormone

Ribosome

New

protein

Intracellular receptor (E.g., Steroid hormone)