Chapter 3: cell/plasma membrane

Question 1

Chemical composition of membranes

Answer 1

1. Phospholipid bilayer
2. proteins:
   - some span the membrane and others attached to one surface of bilayer.
   - performs many functions such as transduction signal, enzyme activity and transport.

Question 2

membrane proteins based on location on plasma membrane

Answer 2

One that looks like a bone: transmembrane protein

one looks like a stone: integral membrane protein

one that looks like pancreas: peripheral membrane protein

Question 3

Fluid Mosaic Model of membrane structure

Answer 3

1. Mosaic: how cell membrane looks and functions like.

mixed composition of many macromolecules such as
- integral proteins,
- peripheral proteins,
- phospholipids,
- glycolipids

2. Fluid: Allow lipids and membrane proteins to move laterally and sideways.

Question 4

Classification of membrane proteins based on functions

Answer 4

1. Transport proteins
2. enzymes
3. receptors
4. structural proteins
5. cell adhesion proteins
6. cell surface markers

first three are transmembrane proteins

Question 5

membrane proteins

Answer 5

1. Transport proteins:
   - passive transport, dont require ATP energy, move from high concentration to low concentration.
   -eg. co2, 02

• active transport, need ATP energy, move from low concetration to high concentration
  -eg. sodium, potassium

2. enzymes:
   -attached to interior surface of membrane to help catalyse chemical reactions
3. Receptors:
   -chemical messages from other cells
   -binding of a messenger to a receptor may trigger signal transduction.
4. Structural proteins:
   -support shape of membrane
   -eg. biconcave shape of RBC
5. Cell adhesion:
   -special proteins that glue cells to one another
6. cell surface markers: glycolipids ( protein/carb chain shape), glycoproteins (lipid/carb chain shape)

Question 6

How does substances move across the membrane

Answer 6

1. keeps essential substances inside the cell
2. regulate passage of materials
3. bilayer as layer
4. protein as selective gates, selectively permeable membrane

Question 7

Mechanism

Answer 7

1. passive process
   -diffusion
   -faciliatated diffusion
   -osmosis
2. active process
   -active transport
   -endocytosis (in)
   -exocytosis(out)

Question 8

Passive diffusion

Answer 8

-Gases pass through membranes without work by cells
-Area of high concentration to low concentration
-Transport of oxygen and co2 in lungs

Question 9

Facilitated diffusion

Answer 9

-polar molecules cannot easily access
-a form of passive transport, hence dont need energy
-from high concentration to low concentration
-channel or transport proteins

Question 10

osmosis

Answer 10

-transport of water
-water travel from low solute to high solute concentration, high water to low water.
solute: salt
solvent: water
solution: saltwater

Question 11

tonicity and osmosis

Answer 11

1. hypotonic: too muchh water and low solute cause swelling
2. hypertonic: too little water and high solute, shrinkage
3. isotonic: same solute and solvent concentration

Question 12

active transport

Answer 12

• Need energy
  -change structure to move substances

Question 13

What are the two solutes used for active transport across the membrane (MCQ)

Answer 13

• Sodium-potassium pump
• nerve cell

Question 14

exocytosis

Answer 14

-move large molecules or particles out of cells through plasma membrane.
-vesicle containg molecules or particles and expel contents
-eg. removal waste from cells

Question 15

endocytosis

Answer 15

-uptake of materials too large to penetrate membrane
-membrane fold inward, like a flower closing with hand, trap material