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Cell Membranes + Transport 1.3 - Coggle Diagram
Cell Membranes + Transport 1.3
CELL MEMBRANE
STRUCTURE
PHOSPHOLIPIDS
Hydrophilic phosphate head with phosphate group
2 Hydrophobic fatty acid tails
Forms bilayer - Basis of membrane structure
Allows lipid-soluble molecules to enter + leave
Prevents water soluble molecule from entering + leaving
PROTEINS
Arranged randomly
INTRINSIC
Span bilayer
channels or carriers to facilitate diffusion of polar molecules
Others form pumps + carry out active transport against a concentration gradient
EXTRINSIC
Occur on surface of bilayer, or partly embedded
Provide structural support
Form recognition sites by identifying cells
FUNCTIONS
Boundary separating living cell from non-living surroundings
Controls which substance pass in + out
Controls uptake of nutrients
Allows waste products to pass out
Responsible for secreting substances, enzymes + glycoproteins
Cell recognition
Cholesterol - Found in animal cells, Fits between phospholipid molecules, Increasing rigidity + stability
Glycolipids - Lipids which combine with ploysaccharide, found in outer layer of membrane + involved in cell to cell recognition
Glycoproteins - Proteins combined with polysaccharide, stick out of some membranes
SINGER + NICHOLSON
Fluid mosaic model
Fluid - Lateral movement of molecules in membrane
Mosaic - Random pattern of proteins
PERMEABILITY
MEMBRANE AS BARRIER
Selectively permeable to water + some solutes
Lipid-soluble substances can move through membrane more easily than water-soluble substances
NON-POLAR MOLECULES
Small uncharged molecules, oxygen + carbon dioxide, freely pass through membrane by simple diffusion
Lipid-soluble molecules, glycerol, pass through membrane through bilayer
POLAR MOLECULES
Hydrophobic core impedes transport of ions + polar molecules
Charged particles, ions, + relatively large charged molecules, glucose, can't diffuse across non-polar centre of bilayer as they're insoluble in lipid
FACTORS AFFECTING
INCREASING TEMP
Stable up to 40°C.
Temps above - become increasingly unstable
Increased heat energy - Increased kinetic energy
Phospholipids vibrate more + move further apart
Increases permeability
Proteins denature at high temps, allows betelains to diffuse out more readily
As temps increases permeability increases due to increased disruption
INCREASING ETHANOL CONC
Organic solvents, ethanol, dissolve phospholipids
Greater the conc of ethanol - More permeable membrane becomes
INCREASING SODIUM CHLORIDE CONC
Sodium ions attach to oxygen atoms on hydrophilic heads of bilayer
Reduces mobility of phospholipid molecules so less betelain released
Sodium chloride conc increases - Permeability decreases
INCREASING DETERGENT CONC
Detergents reduce surface tension of phospholipids + disperse membrane
Conc of detergent increase - permeability of membrane increase
PASSIVE TRANSPORT
DIFFUSION
Random movement of particles from region of high concentration to region of low concentration until equally distributed
SIMPLE
Happens through bilayer + limited to small, non-polar or lipid soluble molecules
Oxygen, carbon dioxide + fat-soluble vitamins cross membrane
As concentration gradient increases - rate of diffusion will also increase
Rate of uptake is directly proportional to concentration difference across membrane
RATE
SURFACE AREA
Higher - More places which diffusion can happen + increases rate
Folds increase SA
LENGTH OF PATHWAYS
Shorter diffusion pathway, faster it can happen
Falttened cells, thinner membranes + less layers of cells decrease pathway
STEEPNESS OF CONC GRADIENT
Larger difference between high + low conc, faster diffusion happens
Circulation + ventilation increase conc gradient
TEMP
Higher the temp, more kinetic energy particles have + faster they move
Increases rate
FACILITATED
CO-TRANSPORT
Type of facilitated diffusion, brings molecules + ions into cells together on same carrier protein
Sodium-glucose co-transport is significant in absorbing glucose + sodium ions across cell membrane + into blood in ileum + kidney nephron
CHANNEL
Pores lined with polar groups
Allows charged ions to pass through
Each channel protein specific for one type of ion
Can also open + close depending on needs of cell (gated)
CARRIER
Allows larger molecules, sugars + amino acids across membrane
Particular molecule attaches to carrier protein at binding site + causes protein to change shape or rotate within membrane
This action releases molecule on other side of membrane
Channel + carrier proteins increase rate of diffusion along concentration gradient
Initial increased rate of diffusion as concentration gradient becomes steeper
Due to channel + carrier proteins facilitating process
Rate of diffusion levels off at higher concentration differences
Due to channel + carrier proteins being occupied - Limits rate of diffusion
Facilitated diffusion not affected by respiratory inhibitors
Concentration gradient - Difference in concentration between 2 areas
Unless molecule is used up by cell, equilibrium will be reached
Equilibrium - Concentration of molecules is equal either side of membrane
ATP/energy from respiration not required
Respiratory inhibitors that inhibit ATP production don't affect methods
Movement is from high conc to low conc
OSMOSIS
Isontonic - Equal
Hypotonic - low solute - high water potential
Hepyertonic - high solute - low water potential
Passage of water from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
Pure water - highest water potential of zero
All water potentials have a -ve water potential value
A higher water potential implies a greater tendancy of water to leave a system by osmosis
WATER POTENTIAL
Solute Potential - concentration of dissolved substances inside cell vacuole
Pressure Potential - As outward pressure builds up the cell wall develops an opposing force
EXTERNAL MEDIUM
HYPOTONIC
Cause cell to swell
Animal - no cell wall, burst - Lysis
Plant - Cells become turgid, cell contents push against cell wall
HYPERTONIC
cause cell to shrink
Animal - cell will simply shrink
Plant - Plamolysis, vacuole + cytoplasm shrink causing cell membrane to pull away from cell wall
Plant cell in this condition - plasmolyed + flaccid (floppy); whole plant will wilt
ACTIVE TRANSPORT
ATP requiring process
Ions + molecules moved across membrane against a concentration gradient
Move in opposite direction to diffusion
Combines with specific intrinsic protein - pump
Pump changes shape + transports ions pr molecule across membrane
Ion or molecule released into cell
USES
Protein synthesis
Muscle contraction
Nerve impulse transmission
Absorption of minerals, nitrates by plant root hair cells
Initial increased uptake as concentration gradient increases
Rate of active transport levels off at higher concentration differences
Due to pumps being full - limits rate of active transport
Affected by respiratory inhibitors; rate of transport sharply drops after addition of a respiratory inhibitor, cyanide
ENDOCYTOSIS
Large particles enter cells by endocytosis
Cell membrane engulfs particles or liquid forming a vesicle which enters cytoplasm
Phagocytosis (cell eating)
Pinocytosis (Involves entry of liquid into cell)
Certain types of white blood cell, phagocytes, engluf microbes by phagocytosis
EXOCYTOSIS
Substances leave cell after being transported through cytoplasm in transport vesicles (from rough ER) to Golgi body + then to cell membrane via secretory vesicles
Secretory vesicles fuse with cell membrane + contents are secreted outside cell