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SECTION 4 TRANSPORT ACROSS MEMBRANES (4.1 CELL MEMBRANES (PHOSPHOLIPIDS…
SECTION 4 TRANSPORT ACROSS MEMBRANES
4.1 CELL MEMBRANES
WHAT ARE THEY
Plasma membranes are all membranes
within and around a cell
The cell surface membrane is the outermost one
They are a boundary between the environment, controlling movement
FUNCTIONS AND FEATURES
Flexible and can fuse easily
Cellular compartments to allow different conditions and reactions to happen at the same time
Selective barrier
FLUID MOSAIC MODEL
How the molecules are combined
Fluid as they move mosaic as different shapes and sizes
PHOSPHOLIPIDS
Form a phospholipid bilayer
Lipid soluble material can move through
Prevents water soluble entering
Flexible and self sealing
CHOLESTEROL
Strength
Very hydrophobic to prevent water loss
Pull together fatty acid tails to limit lateral movement
Less fluid at high temperatures
PROTEINS
Extrinsic proteins occur in the bilayer for support,
to act as receptors and to help cells to stick
Intrinsic proteins span the whole bilayer
Some intrinsic proteins are protein channels that allow water soluble material to pass
Others are carrier proteins for active transport
GLYCOLIPIDS
Carb plus lipid
Carb outside cell as a receptor
Recognition, stability and attach cells
GLYCOPROTEINS
Carb chains attached to extrinsic proteins
Recognition sites and to attach cells to form tissues
Recognise one another
PERMEABILITY
Large, insoluble in lipids, same charge or polar molecules do not diffuse across
4.5 CO TRANSPORT
Increase by density of proteins and microvilli
Two substances simultaneously transported by a protein without using ATP
Soidum ions actively trasnported out by pump
Concentration in lumen higher
So they diffuse into epithelial cells through a co trasnport protein whilst attached to a glucose or amino acid molecule
These are then transported further by facilitated diffusion
4.3 OSMOSIS
Passage of water from an area of high water potential to low, through a selectively permeable membrane
WATER POTENTIAL
Pressure created by water molecules, the ability of them to move about in kPa
Addition of solute lowers it
Pure water is zero aka highest wp possible
More solute added equals more negative
ANIMAL CELLS
Red blood cell in a solution of lower water potential is burst in lysis as it draws water in
In higher water potential solution it draws out water so crenates
This is why blood plasma is the same wp
Solute is the substance dissolved
Solvent what its dissolved in
Solution the result
4.2 DIFFUSION
SIMPLE DIFFUSION
Net movement from an area of high concentration to low
Passive
Motion random due to kinetic energy
Eventually reach equilibrium
FACILITATED DIFFUSION
Passive
Proteins aid diffusion
Goes with concentration gradient
PROTEIN CHANNELS
Water filled channels for water soluble ions
Specific
Ion binds to open it
This is so concentration is maintained
CARRIER PROTEINS
Specific
Binds to protein to change its shape and releases on other side
Passive
4.4 ACTIVE TRANSPORT
WHAT IS IT
Movement of molecules into or out of a cell from an area of low to high concentration, using ATP and proteins
ATP used
Active process
Carrier proteins bind to molecule, which binds to receptor sites
ATP binds on the inside so it splits into ADP and a phosphate
Molecule changes shape to open on the other side, phopshate changes it back
Phosphate recombines with ADP in respiration
SODIUM POTASSIUM PUMP
Soidum actively removed whilst potassium taken in at the same time