Transport across cell membrane

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coating formed by carbohydrate chains act as receptor molecules: signalling receptors - recognise messenger molecules like hormones and neurotransmitters endocytosis - bind to molecule to be engulfed by membrane act as cell markers/antigens allowing cell-cell recognition 4) Proteins INTEGRAL (INTRINSIC) PLASMA PROTEINS ↓ TRANSMEMBRANE PROTEIN proteins that are found embedded within the membrane may be found in inner layer, outer layer or spanning the whole membrane (these are transmembrane proteins) helps in movement in and out of cell PERIPHERAL (EXTRINSIC) can be present inside or outside of the cell membrane i.e., intracellular, and extracellular extracellular peripheral proteins communication, receptors, and recognition proteins intracellular peripheral proteins- structural support, attached to the cytoskeleton of the cell www.alevel-notes.weebly.com Function of transmembrane proteins act as gateways and can transform, helping in facilitated diffusion and active transport ● ● Channel proteins phospholipid peripheral protein channel protein ● ● carrier protein DU!!!!! 8 8 8 8 8 8 8 ● integral proteins do not require energy Cell surface antigen 2 cholesterol • transport substances through membrane passively, along their concentration gradient used for both active transport and facilitated diffusion phosphate head- (polar/hydrophilic) (non-polar/hydrophobic) Image: https://o.quizlet.com/MZFY3U-L 4j6xL86C4rWTO0_b.jpg Carrier proteins • require energy go against the concentration gradient take substances from outside and pumps it inside or vice versa used for active transport ← glycoprotein fatty acid tails> Cell surface receptors • present in membranes and binds with particular substances • used for signalling, endocytosis, cell adhesion, cell markers acts as cell identifying markers • each type of cell has its own antigen this enables cells to recognise other cells and behave in an organised way Cell signalling cells detect signals with cell receptors, i.e., glycoproteins and glycolipids, present on their membrane the signalling molecule binds to the receptor as their shapes are complementary to each other • this creates a chain of reactions in the cell, leading to a response a) If the signalling molecules are hydrophobic (e.g., steroid hormones such as oestrogen) ● b) 1) 2) 3) 4) 5) 6) they can diffuse directly across the cell membrane and bind to receptors in the cytoplasm or nucleus. • If the signalling molecule is water-soluble signal arrives at protein receptor in cell membrane the receptor's shape is complementary to the ligand the signal brings about a change in the receptor's shape changing the shape of the receptor allows it to interact with the next component of the pathway so the message gets transmitted ● binding triggers/stimulates reactions within the cell cell signalling results in a response which may be intracellular or extracellular EXTRACELLULAR FLUID 1 Reception Receptor. Km & Signal molecule CYTOPLASM Transduction →6-0- Signal-transduction pathway -Plasma membrane Image: https://croteaubio.wordpress.com/ 3 Response 4.2 Movement of substances into and out of cells Diffusion Activation of cellular responses concentration down a gradient, as the result of the random movement of particles. passive process • molecules tend to reach an equilibrium situation Net movement of molecules or ions from a region of higher concentration to a region of lower Factors affecting diffusion as steepness of gradient increases, diffusion increases as temperature increases, diffusion increases as surface area increases, diffusion increases as distance increases, diffusion decreases smaller and non-polar molecules like fats diffuse much easily across the cell surface membrane as they're soluble in phospholipid tails b) Facilitated diffusion > Diffusion of a substance through transport proteins in a cell surface membrane. www.alevel-notes.weebly.com ● Channel proteins • allow charged substances, usually ions to diffuse can move to open or close the pore, like a gate controlling ion exchange ● Carrier proteins • flip between 2 shapes, as a result, the binding site opens alternatively to each side Extracellular space the proteins provide hydrophilic areas that allow the molecules or ions to pass through the membrane which would otherwise be less permeable to them ● Intracellular space ● 0 Cell membrane ● channel protein, ● 3 O c) Osmosis > Net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane as a result of their random motion. O Water potential > Tendency of water to move out of solution. water always moves down a water potential gradient, this happens until water potential is the same throughout the solution • denoted by psi (4) water potential becomes negative if the solute concentration is very high WATER LOSS WATER GAIN 0 Extracellular space O O Intracellular space Image: https://www.khanacademy.org/. Carrier protein RBC /ANIMAL CELLS crenated haemolysed / lysed d) Active transport > Movement of molecules or ions through transport proteins, across a cell membrane, against their concentration gradient, using energy from ATP. PLANT CELLS plasmolysed, flaccid turgid achieved by carrier and channel proteins these are specific to the type of molecule they're transporting requires energy; supplied by ATP ● energy is used to make the channel/carrier proteins change shape, transferring molecules/ions across the membrane in the process Sodium/Potassium pump EXTRACELLULAR FLUID CYTOPLASM Sodium- potassium exchange pump ENDOCYTOSIS (INSIDE) ATP FOR EVERY ATP MOLECULE USED 3Na* - given out the cell 2K+ taken in the cell Endocytic visicle forming ADP e) Bulk transport > A type of active transport where large molecules are transported across the cell surface membrane, using energy from ATP. -plasma membrane 3 Nat EXOCYTOSIS (OUTSIDE) Exocytic visicle leaving cytoplasm Image: http://lifeofplant.blogspot.com/ 1) Endocytosis > Bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell by the infolding of the cell membrane to form vesicles containing the substance. 2) Exocytosis > Bulk movement of liquids or solids out of a cell by the fusion of vesicles containing the substance with the cell surface membrane. www.alevel-notes.weebly.com