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Plasma membranes and movement across membranes (Osmosis (The net movement…
Plasma membranes and movement across membranes
Plasma Membranes
Primarily made up of phospholipids
Bilayer
Make membrane flexible and self sealing
Hydrophobic tails attract between layers
Hydrophilic heads attract to water outside and inside cell
Barrier to preventing water soluble materials from entering and leaving the cell
Allows Lipid soluble material to pass through easily
Cholesterol
Prevents leakage of water from cells
Reduces lateral movement of membrane
Provides structural support
Glycoproteins
Carbohydrate chains attached to extrinsic proteins in the membrane
Help cells attach to form tissues
Allow immune system to recognise bodies own cells
Glycolipids
Carbohydrate chain attached to lipid
recognition sites
maintain membrane stability
Protein channels
Used to transport non lipid soluble material across the membrane
water filled to hydrophilic channels
selective opening to a specific ion
Protein carriers
Span the plasma membrane
bind to a specific molecule (glucose) changes shape accordingly allowing the molecule to pass into the cytoplasm
Proteins
Mechanical support or cell receptors for molecules (hormones)
act as channels and carriers to allow movement of molecules
Occur in Bilayer, some spread over both layers.
Cell surface receptors for identification
Help cells join together
Diffusion
Passive process
The net movement of molecules or ions from a region of high concentration to low concentration until it is evenly distributed (concentration gradient)
All particles in motion due to kinetic energy
motion is random
Facilitated diffusion
Movement of particles via a protein channel or protein carrier
Passive process
Movement of non lipid soluble and charged molecules pass across the membrane
Osmosis
The net movement of water from a region of high water potential to a region of low potential via a semi-permeable membrane
Semi permeable membrane only allows water to pass across it solute molecules are too big
Water potential measured in kilopascals (pressure produced by water molecules under standard conditions
0 water potential is pure water
water potential is always negative -20kpa -30kpa
Solute is the substance that is dissolved
Solvent is the liquid which dissolves solute
more solute the lower the water potential
occurs via a water potential gradient
Active transport
Co-Transport
Movement of two molecules across a membrane as a result of the gradient of another ion
Sodium ions out on one side of membrane with potassium in
Sodium actively brought in along with glucose
The movement of molecules or ions into or out of a cell from a region of low concentration to an area of high concentration using ATP and carrier proteins
Direct movement of molecules
Metabolic energy in the form of ATP required
selective process using carrier proteins as pumps to transport the molecules
Process
ATP binds to the carrier causing it to split and release energy molecule changes shape and opens up the other side of the membrane
molecule is then released to other side of the membrane
carrier protein binds to ion/molecule (receptor sites)
phosphate molecule and ATP reforms
Sodium potassium pump is an example of molecules being actively transported in and out of the membrane at the same time