plasma membrane

Question 1

what are the roles of the cell surface membrane ?

Answer 1

-partially permeable acts as a barrier between cytoplasm and the external environment
- site of cell signalling

Question 2

what is the role of membrane within the cells ?

Answer 2

-compartmentalisation .e.g forms organelles such as mitochondria
allows different reactions to be isolated in a different parts of the cell and creates specific env.

• site of attachment for ribosomes (RER) and enzymes .
  -partially permeable barrier between the cytoplasm and inside of the organelle -regulates movement of molecules in and out of the organelle

Question 3

why was the model of membrane structure termed as fluid mosaic model ?

Answer 3

fluid : phospholipid are free to move in the layer relative to each other - giving membrane flexibility
- mosaic - the proteins embedded in the membrane , vary in shape ,size ,
model - simple easy way of explaining

Question 4

what are the functions of phospholipid ?

Answer 4

-forms a barrier
- allows small ,uncharged /non polar , fat soluble molecules through diffusion
- partially permeable -regulates mov of molecules across a membrane by size and charge .

Question 5

what are function of glycolipid?

Answer 5

acts as a cell marker antigen
- used by immune system to recognise cells as self or non self
-

Question 6

what are functions of intrinsic protein ?

Answer 6

makes membrane selectively permeable
- acts as transport proteins
-channel proteins - aq/hydrophilic channel
- allows mov of charged and polar molecules by faciliated by diffusion
- carrier proteins - moves molecules by diffusion and active transport -has to change shape to allow

Question 7

what are function of extrinisic protein ?

Answer 7

transport of molecules across the membrane

Question 8

outline functions of glycoproteins ?

Answer 8

-cell signalling -glycoprotein is a receptor for a chemical messenger
- binding site for transport proteins
- cell adhesion - holds cells of a tissue together
- carbs chain binds to water - stabilises the structure of the cell surface membrane

Question 9

why is cholesterol important in membrane ?

Answer 9

regulates fluidity of the membrane
- interacts with the fatty acid tails of neighbouring phosopholipid -stops them from moving away from each other and becoimg too fluid
- increases packing in membrane

Question 10

list components of cell surface membrane

Answer 10

cholesterol
extrinsic proteins
glycoproteins
intrinsic proteins

Question 11

explain what is meant by the term cell signalling

Answer 11

:cells communicate with each other to control processes inside the cells
: uses messenger molecules e.g hormones
: molecules travel in the body - blood
messenger molecule detected by the cell -binds to a receptor on its cell membrane

Question 12

what are factors that affects membrane structure ?

Answer 12

temperature
solvent

Question 13

describe how membrane structure is affected at below 0 degree

Answer 13

• phospholipid have less kinetic energy so don’t move
  -cold denature the carrier and channel protein -leaving gaps between phospholipid -increases permeability
• ## ice crystals pierce through the mebrane increasing permeability

Question 14

describe the affect of temperature from 0-45degree

Answer 14

• temperature increases -phospholipids have more kinetic energy - move more increasing the permeability
  -more movement more gaps between phospholipids

Question 15

describe how increasing temperature above 45 degree affects the membrane structure ?

Answer 15

• the phospholipids bilayer starts to melts -disrupting structure thus increasing permeability
  -channels and carrier proteins denature leaving GAPS between the phospholipid bilayer by increasing the permeability .

Question 16

what are factors affect the membrane structure ?

Answer 16

• temperature
• solven - alcohol,

Question 17

define diffusion ?

Answer 17

the overall movement of particles from a region of high conc to lower conc