Plasma Membranes

Question 1

What are the roles of the membrane?

Answer 1

-Separates internal and external environments
-intercellular membranes form compartments(nucleus, mitochondria and RER) and vacuoles.
-Material exchange control(Partially permeable)
done by diffusion, facilitated diffusion, osmosis and active transport
-Partially permeable barriers
-Cell signalling/ communication

Question 2

When was the fluid mosaic model outlined?

Answer 2

1972

Question 3

Why is the model fluid?

Answer 3

-Phospholipids move around via diffusion
-phospholipids move sideways in their layers
-Different types of proteins inside the bilayer that move around

Question 4

Why is the model mosaic?

Answer 4

Scattered patterns due to proteins within the bilayer

Question 5

What are the main components of the bilayer

Answer 5

-Phospholipids
-Cholesterol
-Glycolipids, glycoproteins
-Transport proteins

Question 6

Function and structure of phospholipids

Answer 6

Tails form hydrophobic core, act as a barrier to most water soluble substances, non polar fatty acid tails stop polar molecules from passing across the membrane.
- can be chemically modified to act as signalling molecules
(move in the bilayer to activate other molecules)

Question 7

Function and structure of Cholesterol

Answer 7

Increases the fluidity of the membrane by stopping it from becoming too fluid when the temperature is too low, stops phospholipids from
packing too closely together
At higher temperatures interactions between cholesterol and phospholipid tails
Cholesterol increases the mechanical strength and stability of membranes

Question 8

what are the two types of proteins in membranes

Answer 8

intrinsic and extrinsic membranes

Question 9

what are intrinsic proteins

Answer 9

transmembrane proteins that are embedded through both layers of the membrane. There amino acids have hydrophobic R groups on their external surface which interacts with the hydrophobic core of the membrane and keeps it in place

Question 10

Channel proteins

Answer 10

provides hydrophilic(polar channel) for passive movement of polar molecules/ions down the concentration gradient through membranes
held in place by hydrophobic interactions

Question 11

carrier proteins

Answer 11

passive transport and active transport into cells, protein changes shape

Question 12

glycoproteins

Answer 12

embedded in the cell-surface membrane attached to a carbohydrate chain varying lengths/ shapes. Used in cell adhesion(joining of cells to make tissues) and cell signalling(receptors)

Question 13

how does cell signalling work

Answer 13

chemical binds to receptor and elicits response from the cell. can cause a direct response or many events in the cell

Question 14

glycolipids

Answer 14

lipids with attached carbohydrate chain, cell markers/ antigens recognised by the cells immune system as self or non self

Question 15

extrinsic proteins

Answer 15

present in one side of the bilayer hydrophilic interactions hold it up, can be present in either layer or move between them

Question 16

cholesterol

Answer 16

lipid with hydrophilic end and hydrophobic end maintains fluidity of the membrane

Question 17

how does cholesterol act

Answer 17

between phospholipids with hydrophilic end interacting with the head and hydrophobic acting on the tail pulling them closer together
adds stability without making them too rigid
stops them being solid by stopping them from grouping too much together

Question 18

how does temperature affect the bilayer

Answer 18

more Ke so phospholipids move faster, makes bilayer more fluid and loses its structure, the higher the temperature the more it breaks down
increases permeability of the membrane proteins in the membrane denature and permeability also increases

Question 19

how do solvents affect the membrane

Answer 19

organic solvents dissolves the membrane disrupting the cells
strong alcohols are toxic and destroy bodily cells less concentrated solutions dissolve the membranes and non polar molecules enter the membrane and their presence disrupts the membrane

Question 20

what is diffusion

Answer 20

net movement of particles from an area of high concentration from a high concentration down the concentration gradient
occurs passively until there is an equilibrium in concentration between the two areas

Question 21

diffusion speeds reason

Answer 21

particles are constantly colliding slowing down overall next movement so movement of particles over a long distance is slower that’s why cells are similar so they can have faster rates of diffusion

Question 22

what are the factors that affect diffusion

Answer 22

temperature- more Ke so molecules will move faster(faster diffusion)
concentration difference- higher the difference faster the rate of diffusion because overall movement from high to low con is higher

Question 23

diffusion across membranes

Answer 23

only molecules that are non polar and
charged molecules/ions cant pass through easily as they are repelled by hydrophobic interior
polar molecules can pass through (H20 partially positive but at slow rate)
smaller polar molecules can pass through more easily

Question 24

factors that affect the rate of diffusion across membranes

Answer 24

surface area- larger Surface area higher the rate of diffusion
thickness of membrane- thinner exchange surface, higher thee rate of diffusion

Question 25

Facilitated diffusion

Answer 25

way for polar molecules/ ions to pass
most protein molecules are specific to one molecule/ ion
facilitated diffusion involves carrier proteins which change shape when a specific molecule binds onto it

Question 26

active transport definition

Answer 26

active movement of moleculels/ ions in or out of a cell from a area of low concentration to an high concentration which requires energy(and carrier proteins)
supplied by ATP

Question 27

Na+ K+ pump

Answer 27

-molecule that needs to be transporrted binds to receptors in channel protein on the outside of the cell
-on inside of cell ATP binds onto the carrier protein and is hydrolysed into ADP and Phosphate
-binding of phosphate molecule causes the protein to change shape opening up to inside the cell
-molecule released into the cell
-phosphate molecule released from carrier protein and combines with ADP to form ADP
-carrier protein returns to normal

Question 28

Bulk transport

Answer 28

for molecules that are too big to fit through channel/carrier proteins

Question 29

endocytosis

Answer 29

phago/pinocytosis cell surface membrane bends inwards when comes in contact with the material, membrane enfolds the material and eventually membrane fuses and forms a vesicle which pinches off into the cytoplasm for further processing

Question 30

exocytosis

Answer 30

reverse of exocytosis vesicle from the Golgi apparatus fuses with the cell membrane which bends and released the contents
ATP required for both processes

Question 31

what is water potential

Answer 31

pressure exerted by water molecules with a membrane/ container measured in Pa or Kpa

Question 32

Osmosis

Answer 32

net movement of water molecules from an area oh high water potential to an area of low water potential through a partially permeable membrane

Question 33

increase of pressure in water

Answer 33

if solution is in a closed system and water diffuses in there is an increase in hydrostatic pressure

Question 34

cytolysis (hypotonic)

Answer 34

higher water potential outside the cell than inside so water moves in the cell cant handle the increase in water so it bursts

Question 35

crenation(hypertonic)

Answer 35

Lower water potential outside than inside so water in cytoplasm moves out and the cell shrinks

Question 36

how do animals combat this

Answer 36

they are able to regulate the water potential of liquids in the blood so there is equal water potential

Question 37

how do plant cells differ

Answer 37

they cannot control the water potential of things in their immediate environment (roots surrounded by almost pure water)
they have a strong cell wall that so hydrostatic pressure only causes turgor

Question 38

plasmolysis

Answer 38

placed in a lower Water potential solution, cytoplasm reduces in volume which pulls the membrane away from the cell wall (plasmolysed)