Mechanisms Of Hormonal Activity
I). Steroid Hormones
A). Direct Gene Activation
B). Step-by-step
1). Diffuse through the membrane
2). Binds & activates intracellular receptor.
3). Steroid-Receptor complex binds to DNA receptor protein
4). Activates a gene.
5). Gene transcribed into messenger RNA.
6). mRNA goes to the ribosomes
7). Translate mRNA into protein.
II). Amino Acid Hormones
A). General Steps:
1. Hormone Receptor Protein
2. Effector Enzyme
3. Second Messenger
4. Metabolic Responses Triggered
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B). Second Messenger: Cyclic-AMP (cAMP)
1). Hormone Receptor (first messenger)
- Hormone binds to the plasma membrane at a specific site.
- Receptor protein changes shape and activates the G protein
2). Effector Enzyme
G protein complex activates adenylate cyclase.
Adenylate cyclase breaks GTP to GDP.
Generates second messenger cyclic-AMP from ATP
3). Second Messenger
moves around the cell triggering chemical reactions with protein kinases.
- cyclic-AMP
C). Second Messenger: PIP-Calcium
Functions to increase Ca++ transport
1). Hormone Receptor (first messenger)
Hormone binds to the plasma membrane
Receptor protein changes shape and can bind with G protein
G protein binds with GTP replacing GDP.
2). Effector Enzyme
G protein-GTP complex activates Phospholipase
Phospholipase breaks GTP to GDP.
PIP2 (phosphatyidyl inositol byphospate) into diacylglycerol and IP3 (inositol triphosphate)
3). Second Messenger
Diacylglycerol activates protein kinase
IP3 releases Ca++ 4). Third messenger
- Ca+ activates enzymes
Comparison between cAMP and PIP2:
Both combine on a cell membrane
G-protein
Differences between cAMP and PIP2:
III). Prostaglandins
Lipid substances that are present in very small amounts
