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Describe Membrane Proetins

2% of the molecules in plasma membrane
50% of its weight


Describe Transmembrane proteins

-Pass through membrane
-Have hydrophilic regions in contact with cytoplasm and extracellular fluid
-Have hydrophobic regions that pass back and forth through the lipid of the membrane
-Most are Glycoproteins
-can drift about freely in phospholipid film
-Some anchored to cytoskeleton


What are Peripheral Proteins?

-Adhere to one face of the membrane
-usually tethered to cytoskeleton


How to membrane receptors work?

The facilitate Cell communication via chemical signals

-Receptors - Surface proteins on plasma membrane of target cell.
-Bind these chemicals (hormones, neurotransmitters)
- Receptor usually specific for one substrate


Describe the Second Messenger System*

Chemical first messenger (epinephrine) binds to a surface receptor.
- triggers changes within the cell that produces a second messenger in the cytoplasm.

-Receptor activates G protein (an intracellular peripheral protein)
-Guanosine triphosphate (GTP) an ATP like compound

-G protein relays signal to adenylate cyclase which converts ATP to cAMP (2nd messenger)

-cAMP activates a kinase in the cytosol

-Kinases add phosphate groups to other cellular enzymes.
-Activates some enzymes, and inactivates others triggering a wide variety of physiological changes in cells.

-Up to 60% of modern drugs work by altering activity of G proteins