2.5 cell membranes

• phospholipids - phosphate head, fatty acid tails • glycolopids • glycoproteins • intrinsic proteins • extrinsic proteins - channel proteins, gated proteins, carrier proteins • cholesterol

• lipids attached with carbohydrate chains • act as antigens so that cells can be recognised by the cells of immune system

• proteins with carbohydate chains attached • plays a role in cell adhesion and as receptors for cell signaling • when chemical binds to receptor it elecits a response from the cell - cell signaling eg. receptors for neurtransmitters at nerve cells synapses, neurtoransmiiters bind to receptors or receptors used for peptide hormones

• provide a hydrophyllic channel that allow passive movement of polar molecules and ions down a concentration gradient • held in position by intercation between the hydrophylic core of the membrane and the hydrophylic R-groups on the outside of the protiens

• channel can open or close in a reponse to a particular signal

• important in role of passive and active transport • requires energy ATP to release energy to change shape for sepecific molecules • specific types of carrier protiens for different types of molecules

• attach to the fatty acid tails to give stabilty and structure to the membrane • at low temperatures : cholesterol increases fluidity of the membrane stopping the phospoholipid tails packing too close • at high temperatures : cholesterol decreases fluidity of the membrane by making the phospholipid tails packing closer together

• temperature • solvents

• when temp high: phospholipids have gain more kinetic energy so move more therefore make the membrane more fluid and loose structure, permeability increases making it easier for particles to cross it • when temp really high - proteins denature making the membrane even more permeable and destroying the cell structure

• organic solvents dissolve membranes disrupting the membrane structure • if solvent is alcohol - causes damage to the cell membrane sllowing non-polar molecules to enter the cell membrane which disrupts the membrane, when the membrane is disrupted it becomes more fluid and more permeable

movement of molecules or ions through a cell membrsne from a region of lower concentration to a regio of higher concentration using energy from respiration

• reabsorption of useful molecules and ions into blood after filtration in the kidney tubules • absorption of some products of digestion eg. glucose into the blood • loading of sugar from photosynthesis cells of leaves into phloem tissue for transport around plants • loading of organic ions from soil to root hair

• the molecule or ion that needs to be transported binds to receptors in the carrier protein • on the otehr side of the cell ATP binds to the carrier prteisn and is hydrolysed into ADP and P(phsophate) • Binding of P to carrier protein causes the protien to change shape - openign up tot he other side of the membrane • molecule or ion is released to the inside or outside of the cell • phsophate released from carrier protein and recombine with ADP to form ATP • carrier protien returns to original shape

• trasnportz larg quantities of maferials in or out of cells • carry large rnolecules such as protein or pollysacharides • carry parts of cell • carry whole cells eg. bacteria (lysomes)

• endocytosis - phagoctosis for solids or pinocytosis for liquids (includes micropinocytosis and macropinocytosis) • exocytosis • ATP needed for movement of these vesicles along the cytoskeleton

• cell membrane invaginates when it comes into contact with the material that needs to the teansported • the membrane enfolds the material until the membrane fuses forming a vesicle • vescile moves into the cytoplasm to transfer material further for prcoessing

• bulk transport of solid materials • cells that specialise in the process are called phagocytes • vacuoles formed are called phagocytic vacuoles • occurs when engulfing bacteria by phagocytic white blood cells

• bulk intake of liquids • if the vesicle that is formed is extermely small the process is called micropinocytosis, opposite for macropinocytosis

• substances to be transported are pachaged in secretory vesucles formed by the golgi appratis • secretory vesicles move tot he cell surface membrane • the contents gets released outside of the cell

net or overall movement of particles from a region of higher concentration to an area of lower concentration will ocntinue until there is an equilibrium

• temperature • concentration difference • surface area • properties of molecules/ions

the higher temp the higher the difference in conc between 2 regions the faster the rate of diffusion because overall movement from higher to lower conc will be longer

the greater the difference in conc between 2 regions the faster the rate of diffusion bc of overall movment from higher to lower conc will be longer

• the grater the surface area accross which diffsuion takes place the higher the no. of molecules/ions can cross at any one moement therefore facster rate of diffusion