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Endocrine
System
Protein vs
Lipid
Hormones
AP Biology
2007-2008
How do hormones act on target cells
 Lipid-based hormones

hydrophobic & lipid-soluble
 diffuse across cell membrane & enter cells
 bind to receptor proteins in cytoplasm & nucleus
 bind to DNA as transcription factors
 turn on genes
 enter the nucleus of the target cell &

influence the expression of the cell’s gene
and synthesis of new proteins
http://highered.mcgrawhill.com/olc/dl/120109/bio46.swf
AP Biology
Action of lipid (steroid) hormones
steroid hormone
target cell
S
S
cytoplasm
1
blood
S
protein
carrier
cross cell membrane
2
binds to receptor protein
becomes
transcription factor
5
S
3
mRNA read by ribosome
plasma membrane
DNA
4
mRNA
nucleus
6
protein
7
protein secreted
AP Biology
ex: secreted protein = growth factor (hair, bone, muscle, gametes)
How do hormones act on target cells
 Protein-based hormones

AP Biology
hydrophilic & not lipid soluble
 can’t diffuse across cell membrane
 bind to receptor proteins in cell
membrane
 trigger secondary messenger
pathway
 activate internal cellular response
enzyme action, uptake or secretion
of molecules…
How do hormones act on target cells
 unable to cross the plasma membrane of
the target cells, bind with proteins
(receptors) embedded in the plasma
membrane, this sparks a 2nd messenger
(eg. cyclic AMP) to the receptor site. Most
hormones in the brain are peptide
hormones
 Eg. epinephrine binds to the plasma
membrane, ATP → cyclic AMP (messenger)
activates glycogen hydrolysis
AP Biology
signal-transduction pathway
Action of protein hormones
1
protein
hormone
P
signal
plasma membrane
binds to receptor protein
activates
G-protein
activates enzyme
cAMP
receptor
protein
activates
cytoplasmic
signal
GTP
cytoplasm
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target
cell
acts as 2° messenger
transduction
ATP
ATP
activates
enzyme
2
secondary
messenger
system
activates
enzyme
produces an action
3
response
How do hormones act on target cells
 transduction: the action or process of
converting something and especially
energy or a message into another form
 http://highered.mcgrawhill.com/sites/0072437316/student_view0/c
hapter47/animations.html# (adrenaline
video)
AP Biology
Ex: Action of epinephrine (adrenaline)
adrenal gland
signal
1
epinephrine
activates
G protein
receptor
protein
in cell
membrane
activates GTP
3
activates
adenylyl cyclase
cAMP
GDP
transduction
4
GTP
2
ATP
activates
protein kinase-A
5
activates
phosphorylase kinase
cytoplasm
liver cell
AP Biology
released
to blood
activates
glycogen phosphorylase
glycogen
6
glucose
7
response
Animation of hormone action
 http://www.wisconline.com/objects/ViewObject.aspx?ID
=AP13704 tutorial-try on own time!
AP Biology