PSL201Y1 Study Guide - Final Guide: Protein Kinase A

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8 Mar 2011
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LECTURE FOUR: RECEPTORS AND SIGNALLING
Q: how do sex steroids interact with their receptors to give male or female characteristics?
4KRZGRHVHSLQHSKULQHVLJQDO³ILJKW-or-IOLJKW´UHVSRQVHXVLQJ*-proteins?
Q: how can insulin activating its tyrosine kinase receptor still result in diabetes?
\ÆA: disease affects the cascade
LQVXOLQFDQVWLOOELQGWRWKHUHFHSWRULW¶VWKHFDVFDGHWKDWLVDIIHFWHG^WKHFDVFDGHWKDWUHVXOWVIURPWKHELQGLQJRILQVulin})
HORMONAL SIGNALLING
Mechanism
Effects
Other Considerations
- hormone binds to complementary site on
receptor in nucleus or cytoplasm
- XSRQELQGLQJWRUHFHSWRUWKHUHFHSWRU¶V
conformation and activity change
- LQWUDFHOOXODUVLJQDOOLQJSDWK¶VDFWLYLW\FKDQJHV
target cell responds
o will not affect receptors that are not of
interest
o target cells are cells that express the
appropriate receptors for the hormones
of interest
lipophilic hormones
Ætestosterone (an androgen) Æestradiaol (an estrogen)
\Æmales and females Æonly in females {ovaries}
((why does a hormone bind its own receptor?))
Æhigh affinity
ÆVDWXUDEOH UHDFKDSODWHDXWKHPRUHKRUPRQH\RXDGGZRQ¶WDIIHFWWKHELQGLQJUDWHRQFHWKHSODWHDXKDVEHHQUHDFKHGRQO\Vo many receptors)
Æspecific = because of the complimentary sequences oIOLJDQGVDQGUHFHSWRUVQHHGVWREHVSHFLILFRUHOVHWKHKRUPRQHZRQ¶WNQRZZKHUHWRDFW
Æreversible = binding of hormone to a receptor is not permanent, there are multiple ways of regulating binding
Q: if you add more hormone, will more hormone bind its receptor?
A: Æyes, it will ± increases in a linear fashion, until it reaches a plateau where all the receptors have been bound by hormones = saturated
::X-axis = total labelled testosterone (nM) ::Y-axis = bound labelled testosterone (fmoles/mg protein)
Q: can you remove hormone from its receptor?
A: Æassign an arbitrary number for the amount of bound labelled hormones ± assume 100%
Æadd non-labelled hormone and the more non-labelled hormone added, the more the amount of bound labelled hormones declines
\Æthis is because the new non-labelled hormone added is competing with the labelled hormones for binding sites on the receptor
::X-axis = non-labelled steroid concentration (M) ::Y-axis = labelled steroid bound
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((what characteristics do receptors share?))
Ælarge proteins
Æfamilies (receptors are organized into families based on their
functional properties)
Æmultiple receptors for one ligand (can have opposing functions ±
depends on the target tissue) *note: possible because it is the receptor
that determines the function of the hormone
Ævariable number in target receptors/cells
Æactivated and inhibited
Ælocated in cell membrane, cytoplasm, nucleus
(depends on types of hormones that bind to it)
SPOTLIGHT ON:ESTROGEN
Composition
Mechanism
Effects
Other Considerations
- formed from testosterone
- formed in the ovaries
because the ovaries contain
aromatase ± a converting
enzyme
enters the cell and bind to its receptor in the
cytoplasm
estrogen response element in DNA ± sequence that
can interact with estrogen and estrogen-formed
complexes
estrogen response element allows binding of
estrogen+its receptor to DNA
estrogen complex moves into the nucleus and with
co-activator, binds to DNA
DNA-hormone-co-activator complex binds to the
particular DNA fragment that is responsible for
synthesis of female proteins
o only turns on a
particular fragment of
DNA/certain genes ±
genes that give female
characteristics
¾ having a receptor inside
the cell and having
subsequent movement into
the nucleus can have direct
effects on gene expression
¾ the binding of estrogen to
DNA is the rate-
limiting/control step
¾ co-activator is a very
important mediator
4KRZGRSHSWLGHDQGDPLGHKRUPRQHVZKLFKFDWGLIIXVHWKURXJKWhe lipid membrane change intracellular activity?
Æhormone binds onto receptors outside of the cell
*receptors are (I) receptor-enzymes = linked to kinases, or (II)-protein-coupled receptors = epinephrine or glucagon
Æinside the cell there is a second messenger system that is activated by extracellular hormone binding
Æthis results in the phosphorylation of proteins
Æleads to cellular response
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