the role of membranes and structure and role of molecules across membranes

cell surface membrane

the partially permeable barrier between a cell and its environment

controls what enters and leaves the cell

site of chemical reactions

site of cell communications (cell signalling)

partially permeable

only some substances can pass through

compartmentalisation

membranes keep the insides of the organelles sperate from the cytoplasm

cell signalling

communicating between cells and cell recognition

a molecule released by one cell attaches to another and causes a response

seven features of the fluid mosaic model

glycoprotein

glycolipid

cholesterol

carrier protein

intrinsic protein

channel protein

phospholipid bilayer

label the phospholipid bilayer

phospholipid bilayer

7nm thick

provides a barrier to large polar molecules

fat soluble substances or very small molecules can pass straight through the membrane (steroids, H2O CO2, fats cholesterol and fat soluble vitamins

cholesterol

stabilises the membrane

regulates fluidity by binding to phospholipids

reduces the permeability to charged particles

glycolipids and glycoproteins

glyco- = carbohydrate attached

glycolipids = carbohydrate and lipid

glycoproteins = carbohydrate and protein

stabilise the membrane by forming H bonds with surrounding water molecules

Receptors - for messenger molecules in cell signalling, drugs, hormones and antibodies

Antigens - for self recognition and the immune response

intrinsic proteins

span the width of the membrane

transport water soluble charged particles

• channel proteins

• carrier proteins

channel proteins

intrinsic proteins

passage way for water and charged substances to diffuse down a concentration gradient

carrier proteins

intrinsic proteins

change shape to move substances from one side of the membrane to the other

this can be down a concentration gradient or against (facilitated diffusion)

extrinsic proteins

AKA peripheral proteins

Present in one side of the bilayer

Normally have hydrophilic R-groups on their surface

diffusion

the net movement of atoms or molecules from an area of high concentration to an area of low concentration

passive- no energy required

simple diffusion

particles pass directly through the phospholipid bilayer

membrane must be permeable to the particles

e.g. non-polar, small

facilitated diffusion

large or polar molecules pass through the cell surface membrane with the aid of a protein

proteins are specific to the molecule that they carry

passive - no energy required

increasing the rate of diffusion

greater difference in concentration (higher concentration gradient)

increase temperature (more kinetic energy)

thinner membrane (shorter diffusion pathway)

Agar jelly membrane testing - method

1. cut agar into 3cm length cubes, 2cm and 1cm

2. place each into boiling tube

3. add 10cm³ hydrochloric acid per tube, leave 10 mins

4. agar contains indicator phenolphthalein - turns pink in presence of an alkali and some sodium hydroxide - changes colour of the indicator in agar

5. remove blocks and measure distance diffused - distance colour has changed

equation of sphere

• surface area

• volume

sa= 4 π r ²

vol= ⁴⁄₃ π r ³

active transport

movement of molecules against a concentration gradient (low to high)

uses a carrier protein and ATP energy (stores energy in bonds → triphosphate)

each carrier protein is specific

types of active transport

endocytosis -

pinching off from the membrane

→ enters pockets in the membrane

creates vesicles into the cytoplasm

exocytosis-

fuse membrane bound vesicle with the membrane

to release outside of cell

impact of solvents on membranes

solvents like alcohol → break down membranes + prevent normal functioning

alcohol= non-polar molecule → disrupts cell membranes and prevents normal functioning

water= no disruption → its a polar solvent + phospholipids wont dissolve in it

impact of temperature on membranes

phospholipids in cell membrane = constantly moving

increase in temperature = increase in kinetic energy = membrane is more fluid → breaks down completely

HAVENT DONE SERIAL DILUTIONS