Cell membranes

Question 1

Function of membranes in cells

Answer 1

1. serve as barriers to keep things in the cell and to keep things out of the cell (a mode of protection)
2. Serve as areas for localization of proteins
3. Receive information via localized areas of communication
4. Import & export of small molecules via protein mediated means
5. Movement and expansion
   - interaction w/ neighbors requires: adhesion, movement to new place or movement to stay in the same place

Question 2

In animal cells, is composed of 40% lipid, 50% protein, and 10% carbohydrate.
-Contains hydrophobic and hydrophilic regions

Answer 2

Lipid bilayer structure

Question 3

Very common lipid, most common is phophotil choline

• Contains a polar (hydrophilic) head and a fatty acid tail.
• is fluid due to unsaturation

Answer 3

Phospholipids

Question 4

Double bonds; liquid at room temp.

Answer 4

unsaturation

Question 5

Single bonds; solid at room temp.

Answer 5

saturation

Question 6

Bilayer formation

Answer 6

-is most energetically favorable because of H2O interactions (H2O makes a “cage” around the hydrophobic molecule)

Question 7

Formation of sealed compartments: lipid bilayer

Answer 7

• Energetically favorable: Sealed compartment formed by phospholipid bilayer (will self seal if penetrated)
• Energetically unfavorable: planar phophokipid bilayer with edges exposed to H2O

Question 8

Fluidity of the membrane

Answer 8

• lateral diffusion
• flexion (bending)
• rotation
• Flip-flop only occurs with the aide of enzymes (hydrophobic vs. hydrophilic)

Question 9

Fluidity of the membrane depends on composition

Answer 9

• If fatty acids are shorter, the membrane will move more fluidly
• If fatty acids are longer, the membrane will be more viscous
  1. bonds
  2. length of fatty acids
  3. amount of cholesterol

Question 10

• Acts as a “buffer” to balance membrane fluidity
• Makes less fluid in unsaturated regions and more fluid in saturated regions
• Can fit within the membrane because of its small size

Answer 10

Cholesterol

Question 11

• Specific region(s) on a membrane that keep signaling molecules together.
• Has different properties than the membrane surrounding it.
• one way to make membrane asym. (membrane is usually asym)

Answer 11

Lipid raft(s)

Question 12

Synthesis of membranes

Answer 12

• ER synthesizes and adds phospholipids to the cytosolic half of ER bilayer
• Scramblase catalyzes transfer of random phospholipids from one monolayer to another (moves from one leaflet to another)
• symmetric growth of both halves of bilayer

Question 13

Membrane asymmetry

Answer 13

• Cell exterior: asym. lipid bilayer of plasma membrane
• Cytosol:
  
  • delivery of new membrane from ER to golgi membrane
  • flippase catalyzes transfer of specific phospholipids to cytosolic monolayer of golgi
  • golgi moves membrane to plasma membrane

Question 14

Organelle responsible for packing and shipping material; also adding carbohydrates

Answer 14

Golgi

SEE NOTES FOR DIAGRAM OF PHOSPHOLIPIDS

Question 15

Functions of membrane proteins

Answer 15

1. Transporters and Channels: Include ions (K+, Na+, glucose, amino acids, and metabolites)
2. Anchors provide movement and adhesion for overall cell or specific lipids (actin, matrix)
3. Receptors bind to hormones, neurotransmitters; act as cell surface markers.