1. What Three Compounds Make up the Plasma Membrane and in What Quantities?

1.  What three compounds make up the plasma membrane and in what quantities?

Lipids (about 50%), Proteins (about 45%), Carbohydrates (about 5%)

2.  What are the four primary classes of phospholipids present in a plasma membrane? Draw a generic example of one.

Phosphotidyl choline, inositol, serine, and ethanolamine.

Drawing should show three carbons bonded to each other, with a phosphorous on the last carbon attached to either choline, inositol, serine, or ethanolamine. Two fatty acid chains coming from two of the carbons.

3.  A fatty acid has a hydrophilic polar head group that interacts with the aqueous environment, and a hydrophobic nonpolar tail that interacts with the environment inside of the cell. Fatty acids make up the lipid bilayer of the membrane, which is about 4-5 nanometers thick.

4.  What are three ways to regulate the fluidity of a plasma membrane?

Make the fatty acid tails longer or shorter.

Regulate saturation of the fatty acid tails – increase/decrease number of double bonds

Increase/decrease amount of cholesterol in the membrane

Also an option – increase/decrease temperature

5.  Phosphotidyl choline is primarily found on the outer monolayer, while the other three phospholipids are primarily found on the cytoplasmic monolayer. This creates a difference in charge across the membrane – the outside is positively charged and the inside is negatively charged.

6.  What is a glycolipid and where can they be found?

An oligosaccharide (3-20 carbon monosaccharide) attached to the head of a phospholipid; Generally found on the outer monolayer of the plasma membrane

7.  List a few functions of the proteins present in the plasma membrane.

Enzymatic activity

Transport

Structural components

Cell signaling (especially glycoproteins)

Cell-cell recognition

Intracellular joining

Movement in conjunction with cytoskeletal proteins

8.  What is diffusion and what types of molecules can diffuse?

Diffusion is the movement of molecules from high concentration to low concentration. Small, nonpolar molecules readily diffuse across the plasma membrane (gases like oxygen and carbon dioxide)

9.  What are the three types of carrier proteins? Give an example of each.

Uniport – moving one type of molecule in one direction; ex. Movement of amino acids

Symport - moving two types of molecules in one direction; ex. Glucose-sodium transport in gut cells

Antiport – moving two types of molecule in opposite directions; ex. Sodium-potassium ATPase (pump)

10.  Give an example of a cell that will use endocytosis. Give an example of a cell that will use exocytosis.

Endocytosis – Macrophages

Exocytosis - any type of secretory or glandular cell (like pancreatic cells)

11.  Describe the differences between endocytosis and receptor-mediated endocytosis. What is one molecule that needs to enter the cell through receptor-mediated endocytosis? Why is a clathrin coat needed for some vesicles?

Receptor-mediated endocytosis is very specific for the type of material that it will bring into the cell – requires a receptor on the cell membrane specific for a particular ligand

Clathrin coat needed in receptor-mediated endocytosis to protect the vesicle for destruction ® vesicle and contents will go to a very specific location once inside the cell

LDL (cholesterol) is an example of a molecule that needs to enter the cell through receptor-mediated endocytosis.