Unit 2b- Transport across cell membranes

What is the cell surface membrane

membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment

What is the plasma membrane

membrane that surrounds organelles and cells

What is the function of the cell-surface membrane

- allows different conditions to be established inside and outside a cell

-controls the movement of substances in and out of cells

-provides a surface for reactions to take place

What can move through the membrane

-lipid soluble material

-small molecules like water and carbon dioxide

-non charged particles

-polar molecules

What are the functions of the phospholipid in the membrane

-allow lipid soluble material through

-prevent water soluble materials from entering and exiting the cell

-make the membrane flexible and self sealing

what are the three types of protein found i the phospholipid bilayer

-extrinsic proteins

-channel proteins

-carrier proteins

what are the two transport proteins

channel proteins and carrier proteins

extrinsic

- one side

intrinsic

both sides

channel proteins

allow charged or large molecules through

what kind of diffusion do both channel and carrier proteins do

facillitated

which type of transport protein does active transport sometimes

carrier protein

what does cholesrtrol do

increases the rigidity of the membrane

what are glycolipids

lipids and carbohydrates

what are glycoproteins

proteins and carbohydrates

functions of glycolipids

receptor

recognition sites

stability

attaching cells to form tissues

glycoproteins functions

receptors

recognition sites

cell adhesion ( form tissues)

what are the functions of membranes

-control entry and exit of materials in and out of organelles

-separate organelles

-provide an internal transport system

-isolate enzymes that might damage the cell

-provide surfaces on which reactions can occur

the cell surface membrane allows

- small

-non polar

-lipid soluble

-non charged

fluid-mosaic model of the cell surface membrane

- fluid- because the individual phospholipid molecules can move relative to one another

-mosaic- because the proteins that are embedded in the phospholipid bilayer vary in shape, size and pettern in the same ways as stones in mosaic

temperature and permiability

below 0 degrees- rigid bilayer, ice crystals, increase the permeability

from 0-45 degrees -phospholipids can move/flow, partially permeable

above 45 degrees- phospholipid bilayer will break down, proteins will denature.

diffusion

- does not require ATP but uses the kinetic energy from the motion of particles,

what are the factors affecting the rate of diffusion

- concentration gradient- difference in concentration between 2 areas, proportional relationship

-thickness of exchange surface - is inversely proportional

-surface area- proportional

which substances can diffuse in simple diffusion

-small

-lipid soluble

-non polar

-non charged

facillitated diffusion

-use protein channels and carriers

-passive process

-down a concentration gradient

channel proteins

- the channels are selective

-channel proteins are gated

-allow specific, charged or polar substances

what is diffusion

net movement of particles from an area of high concentration to an area of lower concentration until evenly distributed

What is osmosis

the net movement of water from any area of high water potential to low water potential until equally distributed

What does hypertonic mean

water moves out of the cell in this solution

-this is because the solution has a lower water potential/greater solute concentration

-flaccid, plasmolysed

what does hypotonic mean

water means into the cell

- the solution has a greater water potential so water moves into the cell

what does isotonic mean

there is no net movement of water

-

plasmolysed

the protoplast shrinks and completely detatches from the cell wall

How does active transport differ from passive forms of transport

- needs ATP

-goes against the concentration gradient

- always require carrier proteins

-very selective

Active transport

the movement of large, polar, charged, non-lipid soluble

fro an area of low concentration to high concentration using ATP and carrier proteins

What happens when ATP is hydrolysed

it turns into ADP

Sodium phosphate pump

- 3 Na ions come through the carrier protein

-there is a conformational change

-Na + ions diffuse out and K + ions come in

- an ATP molecule turns into a phosphate and it diffuses out the carrier protein

factors that effect the rate of active transport

- the speed of individual carrier proteins

-the number of carrier proteins present

the rate of respiration in the cell and the availability of ATP