Cell membrane

• Controls what substances enters and leaves the cell • Allows cell signaling/ cell recognition • Site of chemical reactions

• Compartementialisation (separates organelles from cytoplasm) • Controls which substances leaves and enters the cell->selective permeability • Can form vesicles to transport substances • Site of chemical reactions • Provides surface for attachment (of enzymes + ribosomes)

• Fluid mosaic model • Fluid-> components of the membrane that can move->phospholipids • Mosaic->made up of lots of different shape +position-> proteins in the bilayer

• Phospholipids • Glycoprotein • Glycolipids • Proteins • Cholesterol

• Have a hydrophilic phosphate head • Have a hydrophobic fatty acid tail • Doesn’t allow water soluble (ions+ polar substances) to diffuse through • Fat soluble can pass throug

• Are between the phospholipids-> bind with hydrophobic tails • Stabilises membrane structure and regulated fluidity

• Are lipids attached with carbohydrate chains • Sticking out from surface • are antigens - cell surface involved in self recognition and immune response

• Sticking out from the surface • Protein molecules with carbohydrate chains attached • Responsible for cell adhesion, cell signaling, receptor sites

• Release of signal molecule by exocytosis/secretion • Glycoproteins/Glycolipids have receptors • The receptor/signal is specific • Shape of receptor and signal are complementary • Attachment of signal molecules causes a change (inside the cell/on cell surface)

• Many drugs bind to the receptors in the cell membrane - This either triggers a response in cell or block the receptors from working

• Go through both layers of the membrane - Have amino acids with hydrophobic R group on the external surfaces

-Go through one side of the membrane

• Allows passive movements of polar molecules/ions down the concentration gradient • Held by the hydrophobic part of membrane and hydrophobic R group outside the protein

• Role in both passive transport(down the concentration gradient)->involves in protein changing shape • Uses ATP to transport molecules • Moves large ions and molecules

• Temperature - Concentration

• When they have energy, phospholipids can move around+ aren’t tightly packed-> partially permeable • Increasing temperature, increases KE-> membrane becomes more ‘leaky’ and more permeable • Phospholipids bilayer starts to melt and membrane becomes MORE PERMEABLE • Channel +Carrier proteins denature-> can’t control movement-> increases permeability

• Some solvents dissolves the lipids in the cell membrane, so membrane loses its structure • Increasing concentration of solvent will increase permeability

-Diffusion +Facilitated diffusion

• Movement of molecules from an area of higher concentration to an area of lower concentration( down CG) • Will happen till equilibrium reached

• Temperature-> higher temp, faster rate of diffusion bc molecules have more energy • Concentration gradient->Steeper CG (more molecule on 1 side) faster diffusion • Surface area->Large SA, faster rate of diffusion • Distance of diffusion pathway-> narrow the diffusion pathway the faster rate of diffusion

• Small, non polar can diffuse easily - Polar ions + larger molecule cannot diffuse easily-> cell is partially permeable

• Movement of molecules from an area of higher concentration to an area of lower concentration via channel/carrier proteins • Diffuses large/charged molecules

1- Large molecules attaches to the carrier protein in the membrane 2-Protein changes shape 3-Releases molecules to other side of membrane DOESN’T INVOLVE ATP IN FACILLITATED DIFFUSION

• Movement of substances against their concentration gradient(low-high) across a cell membrane, using ATP+ carrier protein • Requires energy in the form of ATP • Active process