Membrane Structure

Question 1

what is the plasma membrane? what does it control? what is responsible for this control?

Answer 1

-it is the boundary that separates a living cell from its
surroundings
-Controls movement of molecules into and out of cell
-its structure

Question 2

what is “selectively permeable”?

Answer 2

allows some substances to cross more easily than others

Question 3

what are the marcomolecule components of a cell membrane? which kind specifically are the most abundant?

Answer 3

• lipids and proteins

- phospholipids

Question 4

what are the components of a phospholipid? how do their parts interact with water?

Answer 4

1. 1 glycerol
2. 2 fatty acids
3. 1 phosphate group
   Hydrocarbon tails of fatty acids –> hydrophobic
   Phosphate head –> hydrophilic

Question 5

How are phospholipids arranged in cell membranes?

Answer 5

• they from a bilayer (2 layers)
• Hydrophilic heads interact with water –> form outside layers of membrane
• hydrophobic tails hide away from water –> in the middle of membrane

Question 6

what must membranes have in order to function? why?

Answer 6

• fluidity

- fluidity allows for movement of atoms/molecules in and out of cell

Question 7

which direction can lipids/other protections move in the membrane? can they move the other direction?

Answer 7

laterally

- can switch with lipids from other side of bilayer, but it is very rare

Question 8

what happens to a membrane when temperature decreases? what can a membrane do to adjust to temperature changes?

Answer 8

• membranes go from fluid state to solid state

- can change it’s lipid composition

Question 9

Membranes rich in … fatty acids are more fluid than those rich in … fatty acids

Answer 9

• in unsaturated fatty acids

- in saturated fatty acids

Question 10

what is cholesterol; where is it found?

Answer 10

• it is a rigid steroid lipid

- found wedged between phospholipids in cell membrane

Question 11

what is the effect that cholesterol has on membrane fluidity at a high temp, how? low temp, how?
what is the overall effect cholesterol has on membrane fluidity?

Answer 11

high temp –> cholesterol reduces membrane fluidity, by decreasing phospholipid movement
low temp –> cholesterol increases membrane fluidity, by blocking phospholipids from packing tightly together

-reduces changes in membrane fluidity

Question 12

how can proteins be arranged in cell membranes? what are these called?

Answer 12

1. transmembrane proteins –> integral proteins –> inserted and span the membrane (hydrophilic regions on the outside, hydrophobic regions in the inside)
2. peripheral proteins –> bound to surface of membrane on one side

Question 13

what kind of proteins are transport proteins?

Answer 13

transmembrane

Question 14

what do proteins in the membrane determine?

Answer 14

most of the membrane specific functions

Question 15

what are the 6 major functions of membrane proteins?

Answer 15

1. Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to cytoskeleton and extracellular matrix

Question 16

what is a carbohydrate covalently linked to a protein called? linked to a lipid?

Answer 16

glycoprotein

glycolipid

Question 17

how can cells recognize one another?

Answer 17

by the types of membrane carbohydrates - species, individuals, and cell types in an individual

Question 18

what is distinct about the lipid bilayers in a membrane? what is distinct about proteins in the membrane?

Answer 18

• have 2 distinct faces –> inside face, outside face
• the two lipid layers may differ in lipid composition
• Each protein has directional orientation in the membrane

Question 19

what are the steps in the synthesis of membranes?

Answer 19

1. Membrane proteins and lipids are synthesized in ER and carbohydrates are added to transmembrane proteins (makes glycoproteins)
2. move in vesicle to golgi apparatus
3. Inside Golgi –> carbohydrates on glycoproteins are modified and carbohydrates are added to lipids
4. Glycoproteins and glycolipids and secretory proteins are transported in vesicles to plasma membrane
5. Outside face of vesicle becomes continuous with cytoplasmic face, with carbohydrates of glycoproteins and glycolipids positioned on extracellular face of membrane