G11 Membrane Structure and Transport PDF

Membrane Structure and Transport  G10 Which substances are transported in and out of cells? Membrane Write down a list of substances that are transported transport throughout the cell- moves inside and outside.  What does polar / non-po...

Membrane Structure and Transport  G10 Which substances are transported in and out of cells? Membrane Write down a list of substances that are transported transport throughout the cell- moves inside and outside.  What does polar / non-polar mean? 1. __________________  Use an example to explain polarity and 2. __________________ non-polarity.  Consider this statement: 3. __________________ "The cell membrane in organisms are like partially open windows and 4. __________________ etc. doors that regulate the transportation of substances.” Discuss.  Which substances are transported in and out of cells? Write down a list of substances that are transported throughout the cell- moves inside and outside. 1. Oxygen 2. Carbon dioxide 3. Water These particles 4. Glucose can be grouped 5. Nitrogen 6. Fats (triglyceride/fatty acids/glycerol into polar and 7. Amino acids non-polar 8. Minerals – Ca2+, PO43-, K+, Na+ (inorganic) 9. Vitamins – C, D, B etc. (organic) 10. Urea Many more…  Polarity of a molecule is to do with electrons. A non polar molecule is a molecule with an equal distribution of electrons. 1. Oxygen 2. Carbon dioxide 3. Nitrogen 4. Fats (triglyceride/fatty acids/glycerol 5. Vitamins A, D, E, K  A polar molecule is a molecule with an unequal distribution of electrons. 1. Ions - Ca2+, PO43-, K+, Na+ 2. Glucose 3. Water 4. Amino acids 5. Urea 6. Vitamin C, B 7. Ethanol  Some of these substances are able to be transported directly through the cell membrane unaided. Some of these substances need cell membrane components to help them be transported, these are called: membrane proteins. 1. Oxygen 2. Carbon dioxide 3. Water 4. Glucose 5. Nitrogen 6. Fats (triglyceride/fatty acids/glycerol 7. Amino acids 8. Minerals – Ca2+, PO43-, K+, Na+ (inorganic) 9. Vitamins – C, D, B etc. (organic) 10. Urea  Non-polar molecules (their charge is evenly Small, Non-polar distributed) , e.g. fats/lipids, oxygen, methane are hydrophobic and CAN dissolve in the lipid bilayer – LIKE with LIKE. No membrane proteins needed.  Ions (e.g. K+/Na+/Cl- and Large polar molecules (means, molecules where the charges are unevenly distributed in some amino acids, ATP etc.) are hydrophilic and CANNOT pass through the hydrophobic core. Need membrane proteins.  Small polar molecules can pass through but only slowly. Selectivity comes with ions and large polar molecules and charged molecules (molecules that are able to ionize) in a pH solution. What does the cell membrane look like? The cell membrane is selective for transportation of substances https://alevelbiology.co.uk/notes/lipids-triglyceride-and-phospholipid-synthesis/ http://www.phschool.com/science/biology_place/biocoach/bioprop/phospho.html https://alevelbiology.co.uk/notes/lipids-triglyceride-and-phospholipid-synthesis/ Polar molecules can interact with other molecules e.g. forming hydrogen bonds  Lipids (fats/oils:Triglycerides) Phospholipids Waxes Steroids - Testosterone - Oestradiol http://telstar.ote.cmu.edu/biology/MembranePage/i ndex2.html Saturated (animal) and Unsaturated (plant) fats Unsaturated fats Singer-Nicolson Model Extracellular matrix (ECM) (membrane proteins such as Integrin in animal cells attach to the matrix) Peripheral Integral cytoskeleton https://www.sigmaaldrich.com/technical-documents/articles/biofiles/ecm-gel-product-protocols.html  http://resources.schoolscience.co.uk/MRC/2/page6.html Structure of the plasma membrane (article) Khan Academy https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/14-membrane-transport/facilitated-diffusion.html  Non-polar molecules (their charge is evenly Small, Non-polar distributed) , e.g. fats/lipids, oxygen, methane are hydrophobic and CAN dissolve in the lipid bilayer – LIKE with LIKE. No membrane proteins needed.  Ions (e.g. K+/Na+/Cl- and Large polar molecules (means, molecules where the charges are unevenly distributed in some amino acids, ATP etc.) are hydrophilic and CANNOT pass through the hydrophobic core. Need membrane proteins.  Small polar molecules can pass through but only slowly. Selectivity comes with ions and large polar molecules and charged molecules (molecules that are able to ionize) in a pH solution.  Large, non-polar Biology: The Cell: 03: Structure - Structure of the Cell Membrane https://ebsco.smartimagebase.com/biology-the-cell-03-structure-structure-of-the-cell-membrane/view-item?ItemID=81061 1. Why is the phospholipid described as a ‘fluid’ and ‘mosaic’ (see video - https://www.youtube.com/watch?v=Qqsf_UJcfBc https://ebsco.smartimagebase.com/biology-the-cell-03-structure-structure-of-the-cell-membrane/view-item?ItemID=81061 2. Why are the membrane proteins positioned as they are in the phospholipid bilayer? 3. Use this link: https://www.abpischools.org.uk/topic/cellbiology/4/1 to find out the functions of each of the components found in the phospholipid bilayer. Extension: Find out what the previous cell membrane models were using this link: - https://mmegias.webs.uvigo.es/02-english/5-celulas/ampliaciones/3-modelo-membrana.php Draw diagrams to describe the cell membrane models prior to that of Singer Nicolson’s Fluid- Mosaic Model along with the names of the scientists and how they were experimentally deduced and falsified. 1. Why is the phospholipid described as a ‘fluid’ and ‘mosaic’ The fatty acid tails contributes to the fluid movement of the bilayer, as the fatty acid tails are hydrophobic in nature, like that of oil, they do not interact well with water and therefore is ‘fluid’ in movement. Only the hydrophobic regions of the lipid portion of the glycolipids, the cholesterol and membrane proteins are also fluid in nature. The mosaic portions are due to the protruding membrane proteins, e.g. the hydrophilic portions of the integral portions, glycoproteins and ‘glyco’ lipids. 2. Why are the membrane proteins positioned as they are in the phospholipid bilayer? The hydrophobic regions of the membrane proteins do not interact well with water so they are orientated inwards towards the bilayer, whereas, the hydrophilic regions of the membrane proteins do interact well with water so they are orientated outwards. 3. Use this link: https://www.abpischools.org.uk/topic/cellbiology/4/1 to find out the functions of each of the components found in the phospholipid bilayer.  HL only: B2.1.11 – page 220 - 224 What factors increases the fluidity of the phospholipid bilayer? What benefit would there be to increase the fluidity in organisms?  HL only: B2.1.11 – page 220 - 224 What factors increases the fluidity of the phospholipid bilayer? 1. Increase temperature. 2. Limited saturated fatty acids. Presence of unsaturated fatty acids. Must have the ideal ratio between saturated fatty acids : unsaturated fatty acids. 3. The shorter the length of fatty acids, the more fluid the phospholipid bilayer. 4. Lack of cholesterol  What benefit would there be to increase the fluidity in organisms? - Increases membrane permeability. - The presence of cholesterol molecules would decrease membrane permeability, e.g. decreasing diffusion of water molecules external to the cell which would be high in an aqueous environment. The result would be increasing the aqueous environment.  Think butter in the fridge! Lower temperatures:  saturated fatty acids,  straight tails,  compressed,  dense  fairly rigid membrane.  Thicker  Have higher melting points to break the hydrophobic interactions between the fatty acid tails. For higher temperatures:  Unsaturated fatty acids.  "kinks" in their tails.  elbow adjacent This "elbow room" helps to maintain fluidity phospholipid molecules in the membrane at temperatures at which away. membranes with saturated fatty acid tails in  maintains some space their phospholipids would "freeze" or solidify. between the phospholipid molecules.  Many organisms (fish are one example) are capable of adapting to cold environments by changing the proportion of unsaturated fatty acids in their membranes in response to the lowering of the temperature. http://bcs.whfreeman.com/webpub/Ektron/pol1e/Interactive%20Tutorials/it0501/it_0501_lipid_bilayer.html Role of Cholesterol - Type of lipid not a fat or oil. Is a steroid. - Amphipathic - Mostly hydrophobic, therefore will attract to hydrophobic regions of lipid bilayer - The hydrophilic part will be attracted to phosphate head due to hydroxyl group. - Synthesised in the liver. - Carried in the blood as LDLs (increased risk of heart disease/stroke) or as HDLs (removes LDLs to liver and degraded). HL only: B2.1.11 – page 220 - 224 HL only: B2.1.11 – page 220 - 224 4-ringed-carbon compound http://alaskadigitalvisions.com/female See page 194 – hormones/NaturalHistory.htm B1.1.13 Example of a biological steroid is: How many Carbon atoms are here? 17 -The purpose of cholesterol is to reduce the membrane fluidity and permeability to solutes. IB! Membranes have varying amounts of cholesterol. More cholesterol means increase in stability and decrease permeability. Suggest why marine organisms living in polar regions have a very low - no cholesterol in their membranes. Low temperature decreases fluidity - cholesterol Precursor to steroid hormones, e.g. testosterone No cholesterol in plant cells - they depend on saturated or unsaturated fatty acids to maintain proper membrane fluidity.  HL only: B2.1.11 – page 221 Answer Qs 1-4 of the DBQ on page 221: “Frost hardiness and double bonds in chickpeas” Draw your own version of the Singer Nicolson Phospholipid Bilayer Include the following *annotated labels: - (*brief description)  Phospholipid  Fatty acid tails  Phosphate head  Hydrophobic/ hydrophilic / polar/non-polar  Phospholipid bilayer  Transmembrane protein  Peripheral protein  Integral protein  Glycoprotein  Glycolipid  Cholesterol  Channel protein  Carrier protein/pump  Oligosaccharide chain https://www.youtube.com/watch?time_continue=100&v=f7ZSsoYqy8I Draw your own version of the Singer Nicolson Phospholipid Bilayer (Should be drawn more on the surface of the phosphate heads). (Transmembrane protein) Something like this! Draw your own version of the Singer Nicolson Phospholipid Bilayer Label A-I components of a cell membrane https://www.abpischools.org.uk/topic/cellbiology/3/1 Extension only From a mono layer to the Fluid- Mosaic Model - Gorter & Grendel 1920s - Monolayer - Davson Danielli 1930s – Protein layer - Singer-Nicolson Fluid-Mosaic Model – Proteins within the layer – 1970s  https://microbenotes.com/sandwich-davson-danielli-model-of-cell-membrane/ https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/13-membrane-structure/membrane-models.html Extension only https://amit1b.wordpress.com/the-molecules-of -life/about/amino-acids/ There are 20 different amino acids with different polarities. Look at the non-polar, aliphatic R groups (sometimes called Hydrophobic amino acid side chains), why wouldn’t Davson-Danielli’s model be correct chemically? - Having Davson-Danielli’s model wouldn’t work…. Chemically not possible…. - The hydrophobic amino acids (R-side chains) would not allow bonding with polar molecules like water. Can you think what would happen if some hydrophobic amino acids were positioned outside the layer of the phosphate heads?  The non-polar protein portions would separate the polar portions of the phospholipids from water, causing the bilayer to dissolve. Non-polar & Polar do When the membrane proteins would cover the lipid bilayer, their hydrophobic regions would be in contact with water, which destabilizes this construct. Even if they would be oriented towards the membrane, they would face towards the hydrophilic heads of the phospholipids causing the same effect. Additionally the proteins would also separate the hydrophilic phospholipid heads from the water. So there is no real stable solution in embedding the membrane with proteins. NOS: Curriculum link NOS: Curriculum link NOS: Curriculum link What are the bumps signified here in the cytoplasmic layer? Problems with the Davson-Danielli model 1. Freeze-etched electron microscopy. 2. Structure of membrane proteins. 3. Fluorescent antibody tagging. NOS: Curriculum link The cell membrane model proposed by Davson–Danielli was a phospholipid bilayer sandwiched between two layers of globular protein. Which evidence led to the acceptance of the Singer–Nicolson model? A. The orientation of the hydrophilic phospholipid heads towards the proteins B. The formation of a hydrophobic region on the surface of the membrane C. The placement of integral and peripheral proteins in the membrane D. The interactions due to amphipathic properties of phospholipids Extension only The cell membrane model proposed by Davson–Danielli was a phospholipid bilayer sandwiched between two layers of globular protein. Which evidence led to the acceptance of the Singer–Nicolson model? A. The orientation of the hydrophilic phospholipid heads towards the proteins B. The formation of a hydrophobic region on the surface of the membrane C. The placement of integral and peripheral proteins in the membrane D. The interactions due to amphipathic properties of phospholipids Markscheme C  Selection of membrane transport animations https://highered.mheducation.com/sites/9834092339/student_view0/chapter5/how_diffusion_works.html 6 membrane transport mechanisms you will need to know: 1. Simple diffusion: passive 2. Facilitated diffusion: passive 3. Osmosis: passive 4. Endocytosis: active https://www.abpischools.org.uk/topic/cellbiology/6/1 5. Exocytosis: active https://www.abpischools.org.uk/topic/cellbiology/3/1 6. Active transport: active https://www.ncbi.nlm.nih.gov/books/NBK9847/  Facilitated Diffusion https://www.youtube.com/watch?v=gWLqXEyEWM0 - The Potassium channel is narrow (0.3nm) allows only Potassium, hence Channel Proteins are selective. - Example of channel proteins: Na+ and K+ - There is a potential difference (electrical charge) between inside and outside of an axon. - Higher [K+ ions] inside the cell (the cytoplasm) than outside (extracellular) - Higher [Na+ ions] outside the cell (extracellular) than inside (cytoplasm).  Active Transport https://www.youtube.com/watch?v=bFonzS22xN8 - Uses ATP (adenosine triphosphate). - ATPase hydrolyses ATP HL only - B2.1.15: Sodium-potassium pumps as an example of exchange transporters– pages 226 HL only - B2.1.15: Sodium-potassium pumps as an example of exchange transporters– pages 226 Phosphorylation: the addition of a phosphate group to an organic molecule Phosphorylation: the addition of a phosphate group to an organic molecule Summary  Endocytosis: requires ATP. The movement of large molecules into cells through vesicle formation. The fluid nature of the cell membrane makes it possible to form vesicles.  Exocytosis: requires ATP. The movement of large molecules out of cells by the fusing of a vesicle containing the molecules with the surface cell membrane. HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. vesicle HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. HL only: pages 222 – 224: Membrane fluidity and the fusion and formation of vesicles. Extension only Extension only  Which one is a micelle and a vesicle? 2013 Nobel Prize in Physiology/Medicine - James Rothman, Randy Schekman, Thomas Sudhof - Discoveries of Machinery Regulating Vesicle Traffic, a Major Transport System in Our Cells Extension only Extension only Make notes on the 6 methods of membrane transport. Produce a comparison table to help you understand the similarities and differences of the 6 methods of membrane transport. 1. Simple diffusion: Net random passive movement of particles, down the concentration gradient, from a high concentration to a low concentration until equilibrium is reached. Energy is NOT required, hence it is passive. Examples: non-polar particles, oxygen, carbon dioxide, water. https://en.wikipedia.org/wiki/Diffusion No membrane proteins are required. No conformational change within membrane proteins because there are no membrane proteins required.  2. Osmosis Specialized passive diffusion of the net movement of water molecules from a high water potential (low solute concentration) to a low water potential (high solute concentration) across a selectively-permeable membrane until equilibrium is reached. Channel protein, aquaporin is sometimes found in certain membranes such as in kidney cells. No conformational change exists in aquaporins. 3. Facilitated Diffusion is the passive movement of molecules from a high concentration to a low concentration through membrane proteins (carrier or channel). Examples: Large polar particles. ATP, amino acids, glucose. Conformational change with only carrier proteins. 4. Active Transport uses energy in the form of ATP, to transport particles against their concentration gradient, low to high, using carrier membrane proteins/pumps. Examples: Ions. Cl-, Na+, K+, SO42-. Conformational changes in carriers and pumps. 5. Endocytosis Definition: movement of large molecules into cells through vesicle formation. Energy, ATP, is required. Examples: Bacteria, parts of cells, liquids, dissolved substances. 5. Exocytosis movement of large molecules out of cells by the fusing of a vesicle containing the molecules with the surface cell membrane. The process requires ATP. Examples: Bacteria, parts of cells, liquids, dissolved substances.  Passive transport: takes place as a result of concentration, pressure or electrochemical gradients and involves no energy from a cell.  Diffusion: the movement of the particles in a liquid or gas down a concentration gradient from an area where they are at a relatively high concentration to an area where they are a relatively low concentration.  Osmosis: a specialized form of diffusion that involves the movement of solvent molecules down a concentration gradient.  Facilitated diffusion: takes place through carrier proteins or protein channels.  Active transport: the movement of substances into or out of the cell using ATP produced during cellular respiration.  Endocytosis: movement of large molecules into cells through vesicle formation.  Exocytosis: movement of large molecules out of cells by the fusing of a vesicle containing the molecules with the surface cell membrane. The process requires ATP.  Comparison between simple, facilitated and active transport Simple Facilitated Active Energy utilized No No Yes Conc. Gradient High >> Low High >> Low Low >> High Membrane proteins No Yes: Channel & Pumps or Carrier Carrier Type of molecules Oxygen, carbon Larger particles + Ions. Cl-, Na+, K+, dioxide, water polar. ATP, a.a, SO4 2-. pyruvate, glucose. Membrane protein No Yes – charged lined Yes – pumps and undergoing carrier protein. carriers. conformational No – channel, e.g. ion channel channels K+/Na+,gated channels, aquaporins Cell membranes job is to keep ions and hydrophilic molecules out. How do they do this? Use membrane proteins - creates mosaic effect 1. Hormone-binding sites (hormone receptors): e.g. Insulin receptor 2. Immobilized enzymes, e.g. small intestine. Active site positioned outside 3. Cell adhesion: form tight junctions between groups of cells in tissues and organs. 4. Attachment to the ECM & cytoskeleton. 5. Cell-to-cell communication, for identification,e.g. receptors for neurotransmitters at synapses. 6. Channels for passive transport by facilitated diffusion. 6. Pumps for active transport. NOS: Curriculum link SL and HL: B1.1.7: Roles of glycoproteins in cell-cell recognition– page 187 HL only - B2.1.17: Adhesion of cells to form tissues – pages 227 - 228 HL only - B2.1.16: Sodium-dependent glucose cotransport as an example of secondary active transport (indirect) active transport – pages 227 HL only - B2.1.14: Gated ion channels in neurons – pages 224-225 NOS: Curriculum link SL and HL - B1.1.7: Roles of glycoproteins in cell-cell recognition– page 187 NOS: Curriculum link HL only - B2.1.17: Adhesion of cells to form tissues – pages 227 - 228 - Without cell adhesion, tissues and organs would fall apart - Cell adhesion is brought about by cell adhesion molecules (CAM), e.g. cadherin. - CAM are proteins. - CAM prevents tumours from one localized area spreading to another. - CAM can adhere to leukocytes (white blood cells) during the immune inflammatory response to allow white blood cell attack of pathogens. HL only - B2.1.16: Sodium-dependent glucose cotransport as an example of secondary active transport (indirect) active transport – pages 227  HL only - B2.1.16: Sodium-dependent glucose cotransport as an example of indirect active transport – pages 227 - selective reabsorption of glucose in the proximal convoluted tubule of the kidney nephron, allows osmoregulation (balance of water and ions in tissues). - absorption of glucose in the ileum of the human digestive system. 3 Na+ out - Glucose moves against its concentration due to High > low its ‘partner – the Na+ ion’ moving down its concentration gradient. - Na+ conc. Gradient maintained by the sodium- potassium pump, located on the basal side of the cell (inner side).  illi rov ic M 2. 2K+ in, 3Na+ out 3b. 3a 1. 1.  HL only - B2.1.14: Gated ion channels in neurons – pages 224-225 - Voltage-gated ion channels (Na+ and K+ channels) in neurons allow facilitated diffusion to be turned on and off, due to their ability to open and close their channels. - Highly ion specific The specific mechanism of the voltage-gated K+ and Na+ ion channels will be taught alongside C2.2 – Neural signalling (pages 438-439). In addition, the nicotinic acetylcholine receptor will also be covered when learning about the synapse – p436/6 [5 marks] Compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes. [5 marks] Compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes. [5 marks] Describe the process of endocytosis. Markscheme - endocytosis occurs when a membrane encloses a target particle; - fluidity of membrane permits movement of membrane; - membrane sinks inwardly/forms pit/invaginates to enclose particle; - membrane seals back on itself / edges fuse; - one membrane layer / two phospholipid layers enclose particle making vesicle; - inner phospholipid layer of (original) membrane becomes outer phospholipid layer of vesicle membrane; - outer phospholipid layer of (original) membrane becomes inner phospholipid layer of vesicle membrane; - vesicle breaks away from membrane/moves into cytoplasm; - changes in membrane shape require energy; - specific example of endocytosis (e.g. pinocytosis, phagocytosis); Accept any of the above points in an annotated diagram. Examiners report This question was generally well answered. Many good answers used annotated diagrams to illustrate the process of endocytosis. 1. Define osmosis in terms of solute concentration and water potential. 2. Tissues or organs used on medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis. Explain. 3. How are plant structures such as the leaves and stem able to be firm?