16. Structure and function of the cell membrane proteins

Question 1

Proteins embedded in membranes? ( all 3 categories)

Answer 1

PERIPHERAL MEMBRANE PROTEINS

• On membrane surface - mainly on systolic side
• They interact w/ cytoskeletal elements - to influence shape/motility
• Not amphipathic
• Bound to polar regions of integral proteins

INTEGRAL MEMBRANE PROTEINS

• They span the entire width of membrane
• Therefore crosses through both polar/non polar regions
• Proteins cant be removed from membrane w/out disrupting lipid BL

LIPID BOUND PROTEINS

• Entirely enclosed w/in the membrane

Question 2

What are membrane functions dependent on?

Answer 2

• Chemical comp
• If there are asymmetries in comp b/w the 2 surfaces
• The spec proteins attached/associated w/ membrane

Question 3

Protein in-depth functions?

Answer 3

•Pumps
Serve to transport certain ions (e.g. Na+) actively across membranes.
They also transport macromolecules (AA/sugars) across the membrane.
•Channels
Allow the passage of small ions, molecules and water across the plasma membrane in either direction.
•Receptor Proteins
Recognition and binding of ligands in processes such as hormonal stimulation, coated vesicle endocytosis, and antibody reactions.
•Linker proteins
Anchor the intracellular cytoskeleton to the extracellular matrix.
•Enzymes
- Adenosion Triphosphatases have specific roles in ion pumping:
- ATP synthase is the major protein of the inner mitochondrial membrane
- Digestive enzymes such as dissacharidases
+ dipeptidases are integral membrane proteins.
•Structural proteins
– Visualized by the freeze fracture method
- Certain proteins/ lipids are concentrated in regions of the plasma membrane –> specific functions.