2.5 Biological Membranes ✓

-theory that fabric of membrane consists of phospholipid bilayer with proteins floating in it (mosaic)
-lipid molecules can change places with eachother and some proteins move (fluidity)

lipid/ phospholipid with chain of carbohydrate molecules attached

protein with chain of carbohydrate molecules attached

cell surface membrane

ability to let substances pass through

-very small molecules diffuse through cell membrane in between its structural molecules
-dissolve in lipid layer and pass through
-pass through protein channels or carried by carrier proteins

do not let all substances through

-separates cell components from external environment
-regulates transport of materials in and out cell
-contain enzymes
-has antigens so immune system recognises it as its ‘self’
-release chemicals to signal other cells
-receptors for chemical signals (hormones + drugs bind to receptors)
-site of chemical reactions

folded inner membranes of mitochondria

give large SA for aerobic respiration and localise enzymes needed for it

inner membranes of chloroplasts

house chlorophyll and on membranes some reactions of photosynthesis

catalyse final stages in breakdown of some sugars

heads: contact with watery exterior and interior
tails: centre of membrane away from water

hydrophilic amino acids

gives mechanical stability and flexibility and resist effects of temp changes on membrane structure

help attract water (due to being hydrophilic) with dissolved solutes so cell can interact with environment and obtain dissolved substances

channel and carrier proteins which span whole lipid bilayer

hydrophobic region of phospholipid bilayer

act as channels to allow ions with electrical charge and surrounded by water through

change shape and carry specific molecules across membrane

act as enzymes, antigens or receptor sites

eukaryote

enable specific functions

proteins allow entry and exit of ions which bring about conduction of electrical impulses

more lipid

flattened cells wrapped around several time giving several layers of cell membrane

recognise antigens on foreign cells

to actively transport nitrate ions from soil to cells

contain many electron carriers made of protein and H+ ion channels associated with ATP synthase enzymes

movement of molecules from high concentration to low concentration of that molecule until equilibrium reached, does not require energy and may of may not pass through membrane

diffusion across a partially permeable membrane via protein channels or carriers (still doesnt require energy

processes like diffusion that do not require energy (ATP) as they only use kinetic energy of molecules

molecules in high concentration area bump into each other as they move randomly until spreading out further into areas of lower concentration until evely dispersed

yes like oxygen and carbon dioxide

yes by dissolving in lipid bilayer like steroid hormones

polar and insoluble in lipid

water present in very large concentrations

specific water channel proteins to make water movement easier present where theres a very high rate of water movement

molecules pass into organelles and are used for metabolic reactions (eg photosynthesis and aerobic respiration)

-temperature
-diffusion distance
-surface area
-size of diffusing molecule
-concentration gradient

as temp increases more kinetic energy so rate of diffusion increases

thicker membrane means slower rate of diffusion

larger surface area means more diffusion

smaller ions or molecules diffuse more rapidly than larger

steeper the gradient the faster the diffusion

insoluble in lipid as cant interact with hydrophobic tails of bilayer

through water-filled protein channels

reduce permeability of membranes to small water soluble molecules

bind to transmembrane carrier protein which opens to allow glucose to pass out other side because cant diffuse through water-filled protein channel due to size

control types of molecule that pass in and out of specific cell

channels specific to potassium and sodium ions (which are important for conducting nerve impulses) and calcium and chloride ion channels at synapses

chloride ion channels which regulate composition of mucus

passage of water molecules down water potential gradient across a partially permeable membrane

measure of tendency of water molecules to diffuse from one region to another

the liquid which solute molecules dissolve in, in a solution

yes

aquaporins

molecules dissociated into ions because as molecules dissociate into ions number of particles in solution doubles

kilopascals (kPa)

when a lot of water molecules enter, cell swells and bursts as plasma membrane breaks

when animal cells shrivel

metabolism cannot proceed as enzyme-catalysed reactions need to be in solution

movement of substances against concentration gradient across a cell membrane using ATP and protein carriers

bulk transport of molecules too large to pass through cell membrane via channel or carrier proteins into a cell

bulk transport of molecules too large to pass through cell membrane via channel or carrier proteins out of a cell

hydrolysis of ATP

-have specific regions that combine reversibly with only certain molecules or ions
-ATP binds to protein and hydrolysis happens to produce energy
-the energy causes a conformational shape change which carries ion from one side of membrane to other

endocytosis with intake of solid matter where protrusion called pseudopodium extends and wraps around particle to create vesicle

endocytosis with intake of liquids where membrane invaginates (folds inwards and forms a pocket) and fuses to create vesicle

provide energy to form vesicles and move them (using motor proteins) along cytoskeleton threads into cell interior

to fuse membranes together and move vesicles (1 molecule ATP needed per step motor protein takes along cytoskeleton thread)

1) membrane-bound vesicle containing substance secreted moved towards cell surface membrane
2) cell surface membrane and vesicle membrane fuse
3) fused site opens releasing contents

saturated fatty acids compress which reduces fluidity

-unsaturated fatty acids have kinks in tail which when compressed push apart phospholipids maintaining fluidity
-cholesterol prevents phospholipid molecules from packing too close together buffering effect of lowered temp on fluidity

proportions of unsaturated and saturated fatty acids

change composition of fatty acids in membranes

-phospholipids gain kinetic energy and move around more increasing membrane fluidity

increases

affects position and function, proteins acting as enzymes drift sideways altering rate of reaction they catalyse

-affects infolding of plasma membrane during phagocytosis
-change ability to signal other cells by releasing chemicals by exocytosis

cholesterol by reducing increase in membrane fluidity

no

-atoms within large molecules vibrate breaking H bonds amd ionic bonds that hold structure together (unfold)
-tertiary structure changes and cannot change back once cooled (denatured)

plasma membrane falls apart and holes appear making it more permeable

dissolve lipids, acetone amd ethanol

having higher osmotic pressure than a particular fluid (higher concentration of solute)

having higher osmotic pressure than a particular fluid (lower concentration of solute)