1. Hormones Biochemical classification Mechanism of action Hierarchy
Feedback loops
Signal transduction

2. Amino acid derivatives
Polypeptides
Oxytocin
thyrotropin
ACTH
Insulin
glucagon
somatotropin
FSH LH
vasopressin
Steroids
Aldosterone
corticosterone
Progesterone
Estrogen
testosterone
cortisol
Amino acid derivatives
Epinephrine
norepinephrine
dopamine
Thyroxine, T3 and T4
Melatonin
Serotonin

3. Rule: All hormones interact with target cells by
first binding to specific receptors located either on
the plasma membrane or as a cytosolic protein
Rule: The receptor for hormones must be linked
to a component that is able to respond to the
binding of hormone with its receptor
Rule: Substances that fool the responder into
thinking a hormone has bound are call agonists
Rule: Substances that prevent the binding of the
natural hormone and do not elicit a response from
the receptor are called antagonists

4. 1 3 4 5 2 Ca2+ 1 5 2 Nitric oxide 3 4 Insulin IP3 Protein substrates
T-cell
Activation
Glucagon
Insulin 1 3 4 5 2 G G G
IP3 G
G protein
Tyrosine
kinase
Protein
substrates
Cyclic AMP
Cyclic GMP
Ca2+
Diacylgycerol
Calmodulin
PK-C
PK-A
PK-G
Protein Ser/Thr
kinases
Protein substrates
Protein substrates
Multifunctional
kinases
End result is
phosphorylation of
one or more proteins
Other
phospholipases
Protein substrates

5. Hypothalamus Anterior pituitary Nervous Releasing hormones
Posterior pituitary
Thyrotropin
Somatotropin
FSH
Vasopressin
Prolactin LH
Oxytocin
ACTH
Adrenal
Cortex
Adrenal
Medulla
Thyroid
Pancreas
Ovary
Testis
Cortisol
aldosterone
Insulin,
glucagon,
somatostatin
Estradiol
Testosterone T3
Epinephrine
Reproductive
organs
Muscles
liver
Liver,
muscles
Mammary
glands
Tissues

6. Feedback Loops Rule: Hormones elicit their own shut off mechanism
Hypothalamus
Anterior
Pituitary
Corticotropin
releasing factor
Adrenal
Cortex +
-Corticotropin +
Cortisol

7. Rule: All peptide hormones are synthesized as
inactive “pre-pro” precursors
Rule: A signal peptide must be cleaved off to
activate the mature form of the hormone

8. Signal Transduction Action
Definition: The series events and components that
take part in transmitting a hormonal signal to a
the interior of the cell
Membrane or cytosolic Receptor
Signal Initiator
Action
Signal mediator
Target molecule

9. Cyclic AMP System Receptor G-protein Adenylate cyclase c-AMP
Stimulate (Gs) and
inhibit (Gi)
Adenylate cyclase
c-AMP
Protein kinases

10. G-Proteins A family of membrane proteins that exist in an inactive
(GDP) and an active (GTP) state
So-named because they bind GTP, displacing GDP
Work with many receptors
Both Stimulate and inhibit hormone signals
GTP is a time-bomb slowly ticking
When GTP is hydrolyzed to GDP, stimulation is stopped

11. Resting Active Inactive Resting GTP AC ATP AC cAMP AC PO4 AC GDP GTP

12. Adenylate cyclase Signaling System Cell response hormone Inhibitor RiRS AC 
GTP 
GDP  
GDP
4 ATP
GTP AT P
Inactive
protein
ADP
Protein
kinase
4 cAMP
Adenylate cyclase
Signaling System
Active
protein
Cell response

13. Tyrosine Kinase Receptors
Ligand N
Cross
phosphorylation C
Tyrosine Kinase Receptors

14. Growth Hormone Receptor
Extracellular
Growth hormone
Extracellular domain
of Growth Hormone Receptor
Binding to receptor forces dimerization of receptor subunits for cross phosphorylation
=O3PO-
-OPO3=
Tyrosines
Cell membrane (lipid bilayer)
Intracellular
Growth Hormone Receptor

15. Take Home Most hormones never penetrate cells
All hormones have receptors
Internal responses are initiated by the receptor
Receptors work with G proteins
G proteins stimulate protein kinases
Protein kinases comprise a cell signaling cascade
G proteins turn off when GTP is hydrolyzed to GDP, canceling the hormone action

16. Take Home (Part 2) Some receptors are protein tyrosine kinases
Kinase activity is initiated by dimerization
Kinase autophosphorylate receptors
Phosphotyrosines bind to SH-2 domains
Activation starts a kinase cascade
Phosphorylated proteins enter nucleus
DNA transcription turns on specific genes