Chapter 3.1

Question 1

Describe Membrane Proetins

Answer 1

2% of the molecules in plasma membrane

50% of its weight

Question 2

Describe Transmembrane proteins

Answer 2

• 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

Question 3

What are Peripheral Proteins?

Answer 3

• Adhere to one face of the membrane

- usually tethered to cytoskeleton

Question 4

How to membrane receptors work?

Answer 4

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

Question 5

Describe the Second Messenger System*

Answer 5

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