Membranes Flashcards
(33 cards)
Function is membranes
Separating cell components from outer environment
Unique compartments within cells
Site of cell signalling and recognition
Control and regulation of reaction sequences
Regulate transport of materials in and out
Three formations of phospholipids
Bilayer- where tails point inwards away from water
Micelles - single layer of phospholipids forming sphere with tails pointing to centre
Liposomes
Thickness of membrane
7-10nm
Other components in membrane (list)
Cholesterol, glycolipids, integral and peripheral proteins
Description of fluid mosaic model
Bilayer of phospholipids forms basic membrane structure
Various proteins floating in bilayer, some others are bound one one side within the cell
Extrinsic proteins are partially embedded, intrinsic span the bilayer
Constant fluidity and lateral movement allows…
Protein movement
Role of cholesterol in membrane
Small, flat molecule which fits between fatty acid tails
Increases hydrophobic tendencies making the barrier more solid.
Generally membrane stability and fluidity regulation.
Channel proteins roles
allow movement of small polar substances across the membrane. Many are also gated so allow one way, or controllable transport, such as in neurons.
Carrier proteins roles
Move substances across the membrane.ms
Edification shaped so a certain molecule fits at which point they change shape to allow the molecule through.
Receptor site
Allow hormones to bind causing a cell response. Specifically shaped.
Diffusion
The net movement of molecules or ions I’m a gas or liquid from an area of high concentration to an area of low concentration.
Factors affecting the rate of diffusion
Thickness of exchange surface Concentration gradient Surface area to volume ratio Size of molecules Temperature
Fick’s law
Rate of diffusion is proportional to (surface area X difference in concentration) / thickness of exchange surface
Things which can diffuse straight across the membrane
Small, non-polar molecules.
Ie. Lipid based molecules as can pass straight through the bilayer or gases which can pass between phospholipids
Molecules requiring channels or protein carriers
Small charged particles, eg. Sodium ions through protein channels
Larger molecules eg. Glucose through carrier proteins
Larger quantities of water, through aquaporins
Active transport
The transport of molecules or ions from a region of their lower concentration to a region of their higher concentration requiring energy and carrier proteins.
Differences between carrier proteins used in facilitated diffusion and those used in active transport.
In active transport:
Carry specific molecules one way across the membrane
Use ATP
Work against the concentration gradient
Can carry molecules at a faster rate than could be done using diffusion
Can accumulate molecules in one place.
Bulk transport or cytosis
Another form of active transport, either in or out of a cell, where large quantities of material are enrolled in the membrane and then pinched off into a vesicle, requiring ATP to move membrane and vesicles on the cytoskeleton.
Exocytosis
Movement out of the cell
Difference between pinocytosis and phagocytosis
Pino = transport of liquid material Phago = transport of solid material
Osmosis
The movement of water molecules from an area of higher water potential to an area of lower concentration across a partially permeable membrane.
Hypotonic solution
Concentration of solutes is less, hence concentration of water is greater
Isotonic solution
Concentration of solutes is equal, therefore no net movement.
Hypertonic solution
Concentration of solutes is greater in solution, hence concentration of water is less.
