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Cell memberane structure,function & machanism
The cell membrane is a thin barrier that separates the living cell from its nonliving surroundings and controls what enters and exits the cell. It is made up of a phospholipid bilayer with embedded proteins and carbohydrates. Membrane proteins and carbohydrates perform important functions like transport, acting as enzymes or receptors, and attaching to the cytoskeleton. There are three main types of transport across the membrane - passive diffusion, facilitated diffusion, and active transport. Passive diffusion moves molecules down their concentration gradient without energy, while active transport moves molecules against their gradient by using ATP.
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Cell memberane structure,function & machanism
- 1. Topic : CellMembrane, its Structure, Function & Mechanisms Submitted To : Dr.Feroza Wattoo Submitted By : Victor Tabassum (11-arid-979) Asma Butool (11-arid-980) Mujahid Hussain (11-arid-981) Nauman Wahid (11-arid-982) =>DVM 1 st Semester<= AP Biology 1
- 2. The Cell Membrane(Introduction) AP Biology
- 3. Overview Cell membrane separates living cell from nonliving surroundings thin barrier = 8nm thick Controls traffic in & out of the cell selectively permeable allows some substances to cross more easily than others hydrophobic vs hydrophilic AP Biology 3
- 4. Plasma membraneof lipid bilayer lined from both sides by globular protein Davson & Danielle proposed sandwich model In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer AP Biology 4
- 5. Structure Of TheCell Membrane AP Biology 5
- 6. Overview Made of phospholipids, proteins & other macromolecules AP Biology 6
- 7. Phospholipids Fatty acid tails hydrophobic Phosphate group head hydrophilic Arranged as a bilayer AP Biology 7
- 8. Phospholipid Bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads AP Biology 8
- 9. Membrane is acollage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Phospholipids Cholesterol Transmembrane proteins Peripheral protein Cytoplasm Filaments of cytoskeleton AP Biology 9
- 10. Membrane Fat CompositionVaries Fat composition affects flexibility membrane must be fluid & flexible about as fluid as thick salad oil % unsaturated fatty acids in phospholipids keep membrane less viscous cold-adapted organisms, like winter wheat increase % in autumn cholesterol in membrane AP Biology 10
- 11. Membrane Proteins Proteins determine membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: peripheral proteins loosely bound to surface of membrane cell surface identity marker (antigens) integral proteins penetrate lipid bilayer, usually across whole membrane transmembrane protein transport proteins channels, permeases (pumps) AP Biology 11
- 12. Function Of Membrane Proteins & Carbohydrates AP Biology 12
- 13. Overview Transport Enzyme Location Receptors,Transport Signals From Outide To Cytoplasm Site For The Attachment With Cytoskeleton AP Biology 13
- 14. Many Functions OfMembrane Proteins Outside Plasma membrane Inside Transporter Enzyme Cell surface activity receptor Cell surface Cell adhesion Attachment to the AP Biology identity marker 14 cytoskeleton
- 15. Membrane Carbohydrates Play a key role in cell-cell recognition ability of a cell to distinguish one cell from another antigens important in organ & tissue development basis for rejection of foreign cells by immune system AP Biology 15
- 16. Types Of Transport Across Cell Membrane AP Biology
- 17. Diffusion 2nd Law Of Thermodynamics governs biological systems universe tends towards disorder (entropy) Diffusion AP Biology movement from high → low concentration 17
- 18. Diffusion Move from HIGH to LOW concentration “passive transport” no energy needed movement of water AP Biology diffusion 18 osmosis
- 19. Diffusion Across CellMembrane Cell membrane is the boundary between inside & outside… separates cell from its environment Can it be an impenetrable boundary? NO! IN OUT food waste carbohydrates OUT ammonia sugars, proteins salts amino acids CO2 IN lipids H2O salts, O2, H2O products AP Biology cell needs materials in & products or waste out 19
- 20. Diffusion Through PhospholipidBilayer What molecules can get through directly? fats & other lipids What molecules can inside cell NOT get through NH3 lipid salt directly? polar molecules H2O ions salts, ammonia sugar aa H2O outside cell large molecules starches, proteins AP Biology 20
- 21. What Determines TheRate Of Diffusion? 1. The steepness of the concentration gradient: The bigger the difference between the two sides of the membrane the quicker the rate of diffusion. 2. Temperature: Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster. 3. The surface area: The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment. 4. The type of molecule or ion diffusing: Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails. AP Biology 21
- 22. Molecules That DiffuseThrough Cell Membranes 1. Oxygen – Non-polar so diffuses very quickly. 2. Carbon dioxide – Polar but very small so diffuses quickly. 3. Water – Polar but also very small so diffuses quickly. AP Biology 22
- 23. Channels Through CellMembrane Membrane becomes semi-permeable with protein channels specific channels allow specific material across cell membrane inside cell H2O aa sugar NH3 AP Biology salt 23 outside cell
- 24. Facilitated Diffusion Diffusion through protein channels channels move specific molecules across cell membrane facilitated = with help no energy needed open channel = fast transport high low AP Biology 24 “The Bouncer”
- 25. Active Transport Cells may need to move molecules against concentration gradient shape change transports solute from one side of membrane to other protein “pump” conformational change “costs” energy = ATP low ATP high AP Biology 25 “The Doorman”
- 26. Active Transport Many models & mechanisms ATP ATP antiport symport AP Biology 26
- 27. Getting Through CellMembrane Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids high → low concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel high → low concentration gradient Active transport diffusion against concentration gradient low → high uses a protein pump ATP requires ATP AP Biology 27
- 28. Transport Summary simple diffusion facilitated diffusion active ATP transport AP Biology 28
- 29. How About LargeMolecules? Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” exocytosis AP Biology exocytosis 29
- 30. Endocytosis fuse with phagocytosis lysosome for digestion pinocytosis non-specific process triggered by receptor-mediated molecular endocytosis signal AP Biology 30
- 31. The Special CaseOf Water Movement Of Water Across The Cell Membrane (OSMOSIS) AP Biology
- 32. Osmosis Is DiffusionOf Water Water is very important to life, so we talk about water separately Diffusion of water from high concentration of water to low concentration of water across a semi-permeable membrane AP Biology 32
- 33. Concentration Of Water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water water hypotonic hypertonic AP Biology net movement of water 33
- 34. Managing Water Balance Cell survival depends on balancing water uptake & loss AP Biology freshwater balanced 34 saltwater
- 35. Managing Water Balance Isotonic animal cell immersed in mild salt solution example: blood cells in blood plasma problem: none no net movement of water flows across membrane equally, in both directions volume of cell is stable AP Biology 35 balanced
- 36. Managing Water Balance Hypotonic a cell in fresh water example: Paramecium problem: gains water, swells & can burst water continually enters Paramecium cell solution: contractile vacuole ATP pumps water out of cell ATP plant cells turgid AP Biology 36 freshwater
- 37. Managing Water Balance Hypertonic a cell in salt water example: shellfish problem: lose water & die solution: take up water or pump out salt plant cells plasmolysis = wilt AP Biology 37 saltwater
- 38. Osmosis… .05 M .03 M Cell (compared to beaker) → hypertonic or hypotonic Beaker (compared to cell) → hypertonic or hypotonic flow? → in or out of cell AP Biologyway does the water 38 Which
- 39. AP Biology 39
Editor's Notes
- #10 The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
- #15 Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made.
- #16 The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.
- #18 Movement from high concentration of that substance to low concentration of that substance .
- #25 Donuts! Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaporins , facilitate massive amounts of diffusion.
- #26 Some transport proteins do not provide channels but appear to actually translocate the solute-binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule. This is model for active transport.
- #27 Plants: nitrate & phosphate pumps in roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer Supplying these nutrients to plants Replenishing the soil since plants are depleting it