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Note On Cell Membrane

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Published in: Biology
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ASlevel Biology Cell membrane

Areesha A / Dubai

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  1. Transport Across the Cell Membrane Cell Membranes and Transport 00 0 Diffusion Passive transport Facilitated diffusion Active transport qijjli
  2. Membranes & Transport Functions Fluid Mosaic Model Components of the plasma membrane Transport across the plasma membrane
  3. Learning Objective- To explore the components of Cell membrane and their roles Success criteria- Able to outline the roles of the plasma membrane Able to describe and explain the fluid mosaic model of membrane structure Able to outline the roles of cell surface membranes including carrier proteins, channel proteins, cell surface receptors and cell surface antigens
  4. Some music please...... https ://www.youtube.com/watch DE9PK 2w
  5. Cell Membrane All living cells have something known as a cell membrane. The phospholipid bi-layer is so thin it can barely even be seen by an electron microscope - a xl 00,000 magnification is required, and only shows a double black line around 7nm wide
  6. Jobs of the cell membrane Isolate the cytoplasm from the external environment Regulate the exchange of substances Communicate with other cells Identification Cell Membrane 00
  7. Extracellular surface of membrane Carbohydrate group of glycoprotein Carbohydrate group of lycolipid Cholesterol Proteins Cholesterol molecules insert themselves into the lipid layer. Membrane splits into layers in freeze-fracture electron microscopy. Intracellular surface of membrane Lipid tails form the interior layer of the membrane. Phospholipid heads face aqueous intracellular and extracellular compartments. Fig. 3-4
  8. phospholipid Bilayer Hydrophilic y rophobic This selectively-permeable membrane controls the exchange of materials, receives hormone messages and is very thin. It can be described as a phospholipid bi-layer - meaning that it is made from phospholipid molecules and has two layers
  9. Fluid Mosaic Model Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Filaments of cytoskeleton Cholesterol Peripheral protein Integral protein EXTRACELLULAR FLUID Glycolipid CYTOPLASM Copyright C' publishing Cummings.
  10. Fluid Mosaic Model "Fluid" refers to the fact that individual phospholipid and protein molecules move around within the layer http://wvvw.susanahalpine.com/anim/Life/memb.htm Plasma Membrane Structural Components Glycoprotein Carboh rate Hyd ilic Side n— Hydrophobic Region Figure I Phospholipid Hydrophobic Region ydroffhilic Reg on Transmembrane Protein
  11. • Mosaic because like a mosaic that is made up of many different parts. The plasma membrane is composed of different kinds of macromolecules, such as integral protein, peripheral protein, glycoprotein, phospholipids, glycolipids, and in some cases cholesterol, lipoproteins.
  12. Features of the mosaic model Extracellular Fluid Protein channel (transport protein) Globular protein Glycoprotein Carbohydrate Hydrophilic heads Phospholipid bilayer Phospholipid molecule Chc*sterol peri tnieOrat ce goby!gep'0teinV • Filamen (Integral protéihv Cytoplasm
  13. Components of the Cell membrane https ://www.youtube.com/watch oos
  14. (a) 000.0 lateral movement flip-flop (rare) (frequent) The lateral movement of a phospholipid occurs rapidly. Flip-flopping across the membrane occurs at a very slow rate cholesterol
  15. Fluid Viscous 0000000 00000000 00900 unsaturated hydrocarbon saturated hydrocarbon tails tails with kinks (b) Unsaturated hydrocarbon tails of phospholipid have double bonds that form kinks. These keep the molecules from packing together, enhancing membrane fluidity (c) At moderately warm temperatures, the cholesterol molecules reduce membrane fludity by preventing free movement of phospholipid molecules. At low temperatures, cholesterol molecules prevent close packing of phospholipids and slow solidification.
  16. Features of the Mosaic Model The membrane primarily consists of a bilayer of phospholipid molecules. These molecules can move about by diffusion in their own layer. Width is about 7nm on average Some of the phospholipids are saturated and some are unsaturated. This affects the fluidity of the membrane, a heavily unsaturated membrane means a more fluid membrane. This is due to the kink in saturated tails causing the molecules to not sit closely together.
  17. • Phospholipid tails point inwards, facing each other, meaning that inside the membrane it is non-polar hydrophobic. The protein molecules within the structure can move around although some are fixed to structures inside the cell and do not move. Many proteins and lipids have short carbohydrate chains attached to them, forming glycoproteins and glycolipids. Contains cholesterol.
  18. Roles of the components of the cell membrane Phospholipids Cholesterol Proteins Glycolipids and glycoprotein
  19. Roles of the components of the cell membrane gel phase--low temperatures hydrocarbons are tightly packed at higher temperatures--moves to fluid phase bilayer "mel&", movement is allowed
  20. Phospholipids: basic structure of plasma membrane. Tails are non-polar, difficult for polar molecules, or ions, to pass through them. Act as barrier to most water-soluble substances. hydro" I-obi c fatty acid tails Phospholipid Bilayer
  21. Roles of the components of the cell membrane of cell) membrane protein cholesterol (cytoplasm inside of cell) glycoprotein phospholipid plasma membrane
  22. • Cholesterol: has hydrophobic tail and hydrophilic head. Help to regulate the fluidity of the membrane, preventing it from becoming too fluid or too rigid. Provide mechanical stability.
  23. Roles of the comoonents of the PerivAieral Carbohydrate membrane protein uuuguuuå Integral membrane prc*ein Peripheral membrane protein
  24. • Proteins: act as transport proteins. Provide hydrophilic channels or passageways for ions and polar molecules to pass through the membrane. Control types of substances that are allowed to enter or leave the cell.
  25. Roles of the components of the cell membrane carbohydrate group of glyc opro tein carbohydrate group c peripheral Of protein protein rane proteins ohydrate group of glycolipid extracellular face - phospholipid amino acid carbohydrate oplasmic face
  26. Glycolipids and glycoproteins: carbohydrate chains project out into the watery fluids which can form hydrogen bonds with water molecules to help to stabilize the membrane structure. Acts as receptor molecules, binding with particular substances such as hormones or neurotransmitter.
  27. Transport across the plasma membrane The phospholipid bilayer is an effective barrier especially against the movement of water- soluble molecules and ions. The aqueous contents of the cell are prevented from escaping. Exchange between the cell and its environment is necessary.
  28. Quiz time joinmyquiz.com To play this quiz 1. Use any device to open join my quiz.com 2. Enter join code 613572 Dianne Chabira
  29. Learning Objective • Describe and explain the processes of diffusion, osmosis, active transport, facilitated diffusion, endocytosis and exocytosis.
  30. Recap (i) A student measured the line and calculated the actual width ot the membrane in Fig. 6.1. State the unit that the student should use tor the actual width ot the membrane. state how to identify the external surface of the cell surface membrane. Name R and S in Fig. 6.1 and describe their roles in the membrane.
  31. Answers a)(i) a)(ii) i(b) nanometres / nm ; A ora throughout (presence of) carbohydrate I sugar, chains I residues, on, (glyco)proteins / (glyco)lipids A there are no sugar chains on the inner surface A (presence of) glycoproteins / glycolipids (on external surface) A (presence of) cell surface antigens I receptors (on external surface) A (presence Of) glycocalyx 1 cholesterol : one from 2 3 4 maintains / regulates, fluidity of, membrane I phospholipid bilayer at low temperatures, maintain / increase fluidity / prevents close packing A prevents hydrophobic •tails' interacting at low temperatures at high temperatures, stabilises the membrane I decreases fluidity ; prevents passage (across membrane) Of, hydrophilic / polar, substances ; phospholipid (monolayer) ; R phospholipid bilayer
  32. Substances move in and out of cells by: Transport Passive transport Active transport Bulk transport Diffusion Facilitated diffusion Osmosis Phagocytosis Endocytosis Pinocytosis Exocytosis
  33. Exchange between cell & environment Simple Diffusion Facilitated Diffusion Mechanism Osmosis Active Transport Bulk Transport
  34. Passive Transport Movement of ions and molecules down their concentration gradient. Does not require ATP and energy expenditure.
  35. Diffussion Diffusion can be defined as the net movement of molecules (or ions) from a region of higher concentration and to a region of lower concentration. Molecules move down a concentration gradient Molecules move in the Brownian movement Achieve equilibrium where there is an even spread of molecules within a given space.
  36. DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural kinetic energy. Blue liquid particles concentrated edge
  37. Diffusion of Bromine
  38. Diffusion of Bromine
  39. Diffusion through a membrane Inside cell Cell membrane Outside cell
  40. Diffusion through a membrane O Inside cell O Cell membrane diffdsion Outside cell
  41. Diffusion through a membrane Inside cell Cell membrane Outside cell EQUILIBRIUM
  42. How Molecules Cross the Membrane Diffusion • Molecules move constantly and randomly • Over time, they will distribute hemselves evenly Small, hydrophobic molecules can diffuse in & out of cell*
  43. How Molecules Cross the Membrane Diffusion • Molecules move constantly and randomly • Over time, hey will distribute hemselves evenly Small, hydrophobic molecules can diffuse in & out of cells
  44. What determines the rate of diffusion? 1. 2. e?s.4. The steepness of the concentration gradient The bigger the difference between the two sides of the membrane the quicker the rate of diffusion. Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster. 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. The type of molecule or ion diffusinq. Large molecules need more energy to get Them to move so they tend to diffuse more slowry. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.
  45. Molecules that diffuse through cell membranes lipid-soluble molecules. 02. C02. H20 (outside) (inside) 1. 2. 3. Oxygen - Non-polar so diffuses very quickly. Carbon dioxide - Polar but very small so diffuses quickly. Water - Polar but also very small so diffuses quickly.
  46. Facilitated Diffusion How Molecules Cross the Membrane Facilitated diffusion Molecule is too large or charged to diffuse on ib own Can diffuse if here is a specific tansport protein (channel) Stops when concentrations are equa inside & out (still diffusion! )
  47. Facilitated diffusion: Transmembrane proteins form channels or act as transport proteins to facilitate and to increase the rate of diffusion across cell membrane. Example of transmembrane proteins are protein channels and carrier proteins. Each type allowing only one kind of molecules or ion to pass through it. Hydrophilic substances, eg. Na+, HC03-, Cl-, , diffuse across membranes with the help of transport proteins.
  48. Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na+ or Cl- cannot pass. These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION. Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.
  49. •plSt.lt Pidqoqdsoqd
  50. Facilitated Diffusion through a membrane O Inside cell O Cell membrane Protein channel Outside cell
  51. Facilitated Diffusion through a membrane Inside cell Cell membrane di usion Protein channel Outside cell
  52. Facilitated Diffusion through a membrane Inside cell Cell membrane di usion Protein channel Outside cell EQUILIBRIUM
  53. Facilitated Diffusion: Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.
  54. OSMOSIS Describe and explain the process of osmosis(C) List the factors effecting osmosis in plant and animal cell( B) Explain the movement of water between cells and solutions with different water potentials( A) Dianne Chabira
  55. Osmosis The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane.'
  56. Water potential: The tendency of water molecules to move from one place to another is called water potential, v. (PSI) Factors effecting water potential: Solute potential Pressure potential
  57. The amount that the solute molecules lower the water potential of a solution is called the solute potential. Vs. is always negative. Pressure potential, Vp, is the pressure exerted on a fluid by Its surrounding. In plants + Vp Dianne Chabira
  58. Osmosis DILUTE SOLUTION Sugar molecule O O O o Inside cell O CONCENTRATED SOLUTION Cell membrane artial ermeable. VERY Low conc. of water molecules. Hi h water potentia . Outside cell VERY High conc. of water molecules. Hi h water potentia .
  59. Osmosis O o O Cell membrane partially permeable. O O O Inside cell O OSMQSIS O O O Low conc. of water molecul s. High water potential. O Outside cell High conc. of water molecules. High water potential.
  60. Osmosis Inside cell Cell membrane partially permeable. OSMQSIS Outside cell EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water
  61. How Molecules Cross the Membrane Osmosis Water can diffuse across a membrane Water ties to dilute out molecules hat cant move across he membrane until he concentation is equal
  62. How Molecules Cross the Membrane Osmosis Water can diffuse across a membrane Water ties to dilute out molecules hat cant move across he membrane until he concentration is equal
  63. Concentrated sugar solution sugar Dilute sugar solution water molecu les water molecules passes through not sugar partial permeable mernbr ane Osmosis Selectwely Permeable Mend»rane Saline Solution Solvent Osmotic Osmosis Equilibriun Osmotic Pressu.le Head Forte Piston Reverse Osmosis
  64. lsotonic solution (?) (?) Hypotonic solution ?20 ??? ??? ?20 ??? ??? Hypertonic solution ?20 ???
  65. Exchange between cell & environment Simple Diffusion Facilitated Diffusion 4 Mechanism Osmosis Active Transport Dianne Chabira Bulk Transport
  66. ACTIVE TRANSPORT Movement of ions or molecules across a cell membrane (aided by protein pump) against their concentration gradient. Transport of ions or molecules from a lower to a higher concentration. Requires energy expenditure provided by Example of ions which undergo active transport, Na+, K+.
  67. How Molecules Cross the Membrane Active transport • Cells must maintain very high or low levels of some molecules • Passive transport can't do this! O Inside Outside Sodium Potassium Glcium
  68. How Molecules Cross the Membrane Active transport • Cells must maintain very high or low levels of some molecules • Active tansport proteins use energy to "pump" a molecule in or out of he cell
  69. How Molecules Cross the Membrane Active transport • Cells must maintain very high or low levels of some molecules • Active tansport proteins use energy to •pump" a molecule in or out of he cell
  70. Active Transport Low Conc O ATP ADP + Pi membrane protein pumps High Conc ACTIVE TRANSPORT Minerals, some sugars, and most amino acids move against a concentration gradient with an input of energy ATP
  71. How Molecules Cross the Membrane Diffusion Osmosis Facilitated Diffusion Active Transport Active/ Passive Passive Passive Passive Active Molecules that Move small, hydrophobic water any (specific transporter) any (specific transporter) Energy Protein Direction Needed? Needed? down gradient (toward low conc.) toward high conc. of solutes down gradient (toward low cons.) specific: in QC out, dep. on t:ransporter no yes no no yes yes
  72. Substances move in and out of cells by: Transport Passive transport Active transport Bulk transport Diffusion Facilitated diffusion Osmosis Phagocytosis Endocytosis Pinocytosis Exocytosis
  73. Bulk Transport Bulk transport can be defined as the movement of large quantities of materials into or out of cells Requires energy endocytosis and exocytosis, respectively.
  74. ENDOCYTOSIS The engulfing of the material by the plasma membrane to form a small sac, or endosytotic vacuole. Phagocytosis ("cell eating"): Bulk uptake of solid material. Eg. the engulfing of microbe by lysosome. ("cell drinking"): Pinocytosis Bulk uptake of liquid. Small vacuoles formed are often extremely small, the process is called micropinocytosis.
  75. PHAGOCYTOSIS AND EXOCYTOSIS Microbe or other particle Plasma membrane O Cytoplasm Lysosome Digestive enzymes Partially digested microbe Phagosome (phagocytic vesicle) Phagolysosomes Residual body material O Chemotaxis and adherence of microbe to phagocyte. O Ingestion of microbe by phagocyte, Formation of a phagosome. O Fusion Of the phagosome with a lysosome to form a phagolysosome. O Digestion of ingested microbe by enzymes. O Formation Of residual body containing indigestible Discharge Of waste
  76. Pinocytosis Extracellu'ar flute] Vesicle Plasma membrane cytoplasm
  77. EXOCYTOSIS The reverse of endocytosis and is the process by which materials are removed from cells. For example, lysosome in pancreatic cell carries the indigestible material to the cell surface and releases its contents.
  78. Environment Exocytosis of waste/ Products of digestion S. Food particle taken in by endocytosls Food particles digested Fusion forms secondary lysosome Dianne Chabira
  79. Cell siqnallinq Cells have proteins called 'receptors' that bind to signaling molecules and initiate a physiological response. Different receptors are specific to different molecules. For example, dopamine receptors bind dopamine, insulin receptors bind insulin, and so on
  80. Signaling pathway Signaling pathway includes: Receptor receiving a stimulus or signal Transduction: Converting the signal to a message that is readable Transmission of message/signal to effector (target) The effector making an appropriate response O Recepti-m
  81. Signalling includes both electrical (nerves) and chemical (hormones). Stimuli can be from inside (hormones) as well as outside (light). The cell surface membrane is a important component of most signalling pathways because it controls what molecules move in and out of the cell. 1)Hydrophobic signalling molecules eg. steroid F- hormones It can diffuse directly through the cell surface membrane and bind to geqegtgrs in the cytoplasm
  82. Types of signaling 1)Hydrophobic signaling molecules e.g. steroid hormones It can diffuse directly through the cell surface membrane and bind to receptors in the cytoplasm or nucleus. 2)Hydrophilic signaling molecules-e.g. Protein hormones like insulin. It cannot diffuse through the cell membrane. Binds to receptors on the cell membrane.
  83. Water soluble signaling molecules Membrane receptors fall into three major classes: G-protein-coupled receptors • ion channel receptors • enzyme-linked receptors. G pt otein•coupled receptor Second Cellular responses
  84. G-protein-coupled receptors Signal arrives at a protein receptor in the cell surface membrane Receptor is a specific shape which recognizes the signal. Signal changes the shape of the receptor, and since this spans the membrane, the message is in effect passed to the inside of the cell (signal transduction). Changing the shape of the reactor allows it to interact with the next component of the pathway, so the message gets transmitted. The next component is usually a G-protein - a small molecule which diffuses through the cell relaying the message, like a switch to bring about the release of a 'second messenger'. After 1 receptor molecule is stimulated, many second messenger molecules can be made in response - amplification, a key feature of signalling. Second messenger usually activates an enzyme, which in turn activates further enzymes, increasing amplification at each stage. Signaling cascade: Amplification triggered by G-protein. Response is produced.
  85. Other ways receptors alter activity of the cell: Opening an ion channel, resulting in change of membrane potential Acting directly as a membrane-bound enzyme Act as a intracellular (inside the cell) receptor when initial signal passes through https ://www.youtube.com/watc h?v=VatdTJka3 M&feature=e mb loqo
  86. Surface area to volume ratio: As a cell, grows, its surface area increases and its volume increases. if we divide surface area by volume we can find the surface area-to-volume ratio, which reduces. Therefore, large organisms have smaller surface area-to- volume ratios than small organisms. This has important implications for the rate of diffusion between a cell and its external environment. It also means that there is a limit to the size that cells can grow. This is because after a certain size, the rate of diffusion becomes too low for the cell to function The smaller the object the bigger the surface area to volume ratio. This means that there is a smaller diffusion pathway which increases the metabolic rate.
  87. VIRTUAL EXPERIMENT TIME https ://learning.cambridqeinternational.org/class room/course/view.php?id=3965

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