Lipids Biological Membranes Biological membranes that define the

Lipids & Biological Membranes Biological membranes that define the boundaries of cells are composed largely of lipid molecules, which form a permeability barrier allowing only certain molecules to enter the cell. Lipids are one of the four important classes of biomolecules that have a variety of structural and functional roles. Harini Chandra

1 Master Layout (Part 1) This animation consists of 4 parts: Part 1 – Fatty acids Part 2 – Membrane lipids Part 3 – Proteins in membrane structures Part 4 – Properties of cell membranes b w 2 w 3 2 a 3 Fatty acid – general structure w-3 double bond Degree of unsaturation Chain length 4 5 Source: Biochemistry by Lubert Stryer, 5 th & 6 th edition (ebook) 1

1 2 Definitions of the components: Part 1 – Fatty acids 1. Fatty acid: Fatty acids, more simply known as fats, are the key components of lipids that play an important role in signal transduction pathways and as structural elements of membranes. They are long hydrophobic chains of different lengths that possess a carboxylate group at one end. Most naturally occuring fatty acids have an even number of carbon atoms with varying degrees of unsaturation. 2. Degree of unsaturation: The number of double bonds present in a fatty acid chain defines its degree of unsaturation. 3 4 5 3. Chain length: The total number of carbon atoms present in a fatty acid chain is its chain length. 4. w-carbon: Fatty acids are numbered starting from their carboxyl group with the second and third carbon atoms being known as the a and b carbons. The carbon atom that is furthest away from the carboxylate group, at the distal end of the chain is known as the w carbon.

1 Part 1, Step 1: Fatty acids – general structure w b w 2 3 Degree of unsaturation w-3 double bond Chain length Carboxylate group (C 1) 3 Saturated fatty acid Action As shown in animatio n. 5 1 a w-carbon 4 2 Short chain length & increased unsaturation enhance fluidity & decrease MP of fatty acids. Description of the action (Please redraw all figures. ) First show the figure on the left appearing with its labels from the right end to the left in parts as depicted in the animation. Next, show the figure on the right with the labels appearing after the figure. Unsaturated fatty acid Audio Narration Fatty acids are long hydrophobic chains of carbon atoms having different lengths and a carboxylate group at one end. Fatty acids that do not contain any double bonds are said to be saturated while those possessing one or more double bonds in their structure are unsaturated. Most naturally occuring fatty acids have an even number of carbon atoms with varying degrees of unsaturation. The carboxylate group is numbered as one and the last carbon atom that is furthest away from the carboxylate group is known as the omega carbon. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

1 2 Part 1, Step 2: Palmitic acid (C 16, saturated) 12 14 16 13 15 3 9 4 7 2 1 3 5 Oleic acid (C 18, monounsaturated) 2 Double bonds referred to by cis/trans- ∆4 number at which the double bond is 15 located in superscript. 17 6 16 5 6 8 10 11 18 4 Systematic name is derived by replacing the final ‘e’ of the parent hydrocarbon with ‘oic’/’oate’. For eg. C 16 fatty acid is hexadecanoate (parent hydrocarbon is hexadecane). Fatty acids - nomenclature 5 13 11 14 12 10 9 8 7 Action Description of the action As shown in animati on. (Please redraw all figures. ) First show the figure on top followed by the green callour located above it. Next show the figure below followed by the two text boxes and then the violet callout shown. 3 1 18: 1 indicative of 18 carbon atoms with 1 double bond. Systematic name: cis-∆9 -octadecenoate Audio Narration The fatty acid names are derived from their corresponding parent hydrocarbons by replacing the ‘e’ at the end with ‘oic’ or ‘oate’. A saturated fatty acid with 16 carbon atoms, for instance, is known as hexadecanoate. If there is one double bond, then it become deceneoate with the position of the double bond being indicated as a superscript after a delta symbol. For instance, a 18 carbon fatty acid with one double bond is known as ocatadecenoate while with two double bonds, it is known as octadecadienoate. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Master Layout (Part 2) 1 This animation consists of 4 parts: Part 1 – Fatty acids Part 2 – Membrane lipids Part 3 – Proteins in membrane structures Part 4 – Properties of cell membranes 2 Cholesterol Fatty acid Sugar unit 3 Glycolipids 4 Fatty acid 5 G L Y C E R O L Phosphate Phospholipids Source: Biochemistry by Lubert Stryer, 6 th edition (ebook) Alcohol

1 2 3 4 5 Definitions of the components: Part 2 – Membrane lipids 1. Lipids: These are water insoluble biomolecules that readily dissolve in organic solvents like chloroform and have a wide range of biological functions. They are important components of membranes, serve as fuel reserves and signalling molecules. Three important membrane lipids include phospholipids, glycolipids and cholesterol. 2. Phospholipid: Phospholipids are composed of four components – fatty acids, a platform to which the fatty acid is attached, phosphate residue and an alcohol attached to the phosphate. The platform to which the fatty acids are linked is commonly glycerol but in some cases, a more complex alcohol known as sphingosine may also be present. Phospholipids containing glycerol are known as phosphoglycerides, with two OH groups of glycerol being esterified with the carboxylate groups of fatty acids. The fatty acid chains form the hydrophobic tail while the remaining components constitute the hydrophilic head group. 3. Glycolipid: Lipids that have a sugar component in them are known as glycolipids. They are made up of a sphingosine backbone with the amino group acylated by a fatty acid and one or more sugar residues attached to the primary hydroxyl group. The simplest glycolipid is known as cerebroside which contains either glucose or galactose as its sugar residue. 4. Cholesterol: Cholesterol is a steroid molecule whose structure is significantly different from that of phospholipids and glycolipids. Cholesterol is found in varying quantities in animal membranes but is not present in prokaryotes. It is composed of a hydrocarbon chain linked to one end a hydroxyl group at the other end.

Part 2, Step 1: 1 Membrane lipids - phospholipids G L Y C E R O L Fatty acid 2 Fatty acid 3 Phosphatidate (Diacylglycerol 3 -phosphate) Glycerol backbone Phosphate group Shorthand depiction As shown in animation. 5 Alcohol Fatty acids Hydrophobic tail 4 Phosphate Polar head group Ester linkage Description of the action Audio Narration (Please redraw all figures. ) Phospholipids are composed of four components – fatty acids, a First show the coloured block diagram structures on left top. platform to which the fatty acid is attached, phosphate residue and First the blue rectangle must appear followed by the two ovals an alcohol attached to the phosphate. The platform to which the fatty and then the green rectangle and finally the violet parallelogram. acids are linked may be glycerol or sphingosine. Phospholipids Next, the structure on bottom right must appear. First the containing glycerol are known as phosphoglycerides, with two OH central region must appear marked ‘glycerol backbone’. Next, groups of glycerol being esterified with the carboxylate groups of the groups on the left marked ‘fatty acids’ must appear followed fatty acids. The simplest phospholipid, phosphatidate, is made up of by the pink group on the right. The green box must then only the phosphate group and fatty acids attached to the glycerol highlight the region as indicated with the corresponding label. backbone. The figure on bottom left must then appear with the labels. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 2, Step 2: 1 Common phosphoglycerides Glycerol backbone 2 Fatty acids 3 4 Phosphatidyl ethanolamine Phosphatidyl serine Phosphatidyl choline Phosphatidyl inositol Diphosphatidyl glycerol (cardiolipin) Action Description of the action As shown in animation. 5 Audio Narration The important phophoglycerides found in membranes (Please redraw all figures. ) First show the blue and green parts of the are derived from phosphatidate by esterification of the structure with their labels. Next, the red phosphate group with the hydroxyl group of various groups must appear sequentially one after alcohols. The most commonly observed another with their corresponding names appearing below as shown in animation. phosphoglycerides include phosphatidyl serine, choline, ethanolamine, inositol and diphosphatidyl glycerol, also (The red groups are layered one over another – watch in slide show mode only) known as cardiolipin. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 2, Step 3: 1 Phospholipids - sphingomyelin 2 Sphingosine Fatty acid 3 Choline Sphingomyelin 4 Action As shown in animation. 5 Description of the action (Please redraw all figures. ) First show the figure on top with its label followed by the figure below with its labels as shown. Audio Narration Sphingosine is another amino alcohol backbone that serves as a platform for attachment of fatty acids and alcohols. Sphingomyelin, derived from sphingosine , consists of a fatty acid linked to the amino group via an amide bond a choline moiety attached to the primary hydroxyl group via a phosphate group. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 2, Step 4: 1 Membrane lipids - glycolipids Fatty acid 2 SPHINGOSINE Sugar residue(s) 3 4 5 Cerebroside Action Description of the action As shown (Please redraw all figures. ) in First show the box diagrams shown on top animation. left. The green rectangle must appear first follwed by the blue parallelogram and then the brown oval. Next show the structure below in which the blue region must appear first followed by the green region and finally the pink labeled box. Audio Narration Lipids that have a sugar component in them are known as glycolipids. They are made up of a sphingosine backbone with the amino group acylated by a fatty acid and one or more sugar residues attached to the primary hydroxyl group. The simplest glycolipid is known as cerebroside which contains either glucose or galactose as its sugar residue. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 2, Step 5: 1 Membrane lipids - cholesterol 2 Alkyl side chain 3 4 Polar head group Action As shown in animation. 5 D C A B Steroid nucleus Description of the action (Please redraw all figures. ) Show the appearance of the structure above. First ring A must appear followed by ring B, then ring C and then ring D. All the other groups attached at the various positions must appear after all four rings have appeared. Audio Narration Another group of structural membrane lipids is the sterols, found in most eukaryotic cells. The steroid nucleus consists of four fused rings that are oriented in a planar manner. Cholesterol is an amphipathic molecule with a polar hydroxyl head group and a non-polar steroid nucleus and hydrocarbon side chain. In addition to having a structural role in membranes, sterols are precursors for several products such as steroid hormones and bile acids. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 2, Step 6: 1 Micellar arrangement Membrane formation by phosphoglycerides Polar head group Hydrophobic tail 2 Hydrogen bonding, electrostatic attraction Hydrophobic, Van der Waals interactions 3 Random orientation 4 Bilayer arrangement Action As shown in animation. 5 Description of the action Audio Narration The amphipathic nature of the phosphoglyceride molecules consisting (Please redraw all figures. ) of a polar head group and a hydrophobic tail enables them to First show the green structures oriented randomly. Next they must be surrounded by rearrange themselves in an aqueous environment. When they come in contact with aqueous surroundings, they can either reorient to form water (blue clouds). When this happens, the a micellar structure or a bilayer arrangement. In these arrangements, green structures must reorient themselves in the polar head groups are in contact with water by means of hydrogen the two arrangements shown on the right bonding while the hydrophobic tails interact with each other through after the arrows. The arrows and green ovals hydrophobic and Van der Waals interactions. The lipid bilayer with the text must then appear. arrangement is more favoured for phospholipids and glycolipids. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

1 2 Master Layout (Part 3) This animation consists of 4 parts: Part 1 – Fatty acids Part 2 – Membrane lipids Part 3 – Proteins in membrane structures Part 4 – Properties of cell membranes Glycoprotein Outside Glycolipid Integral protein 3 4 Lipid bilayer Phospholipids Sterol Inside 5 Peripheral protein Source: Biochemistry by A. L. Lehninger, 4 th edition (ebook)

1 2 Definitions of the components: Part 3 – Proteins in membrane structures 1. Lipid bilayer: The flat membrane sheets that form a barrier around cells consisting of two layers of lipid molecules is known as the lipid bilayer. The hydrophobic tail regions are sequestered within the bilayer, away from the aqueous environment while the polar heads face outward and interact with the surrounding molecules. The bilayer is also embedded with proteins that perform specific functions for the cell. 2. Integral proteins: Those proteins that span the membrane and are embedded within the lipid bilayer are known as integral proteins. They interact extensively with the hydrophobic chains of lipids and cannot be easily dissociated from the membrane. 3 4 5 3. Peripheral proteins: Peripheral membrane proteins, however, are only bound to the membrane surfaces by means of electrostatic and hydrogen bond interactions with the polar head groups of the lipids. They can be easily dissociated from the membrane with mild agents such as salts, acids or alkali since they are not embedded within it. 4. Glycoprotein: Carbohydrate groups are often covalently attached to proteins to form glycoproteins. The sugar residues are typically attached to the amide nitrogen atom of the aspargine side chain or to the oxygen atom of the serine or threonine side chain. These glycoproteins are components of cell membranes and have a variety of functions in cell adhesion processes.

Part 3, Step 1: 1 Integral proteins - Bacteriorhodopsin Amino acid sequence of membrane protein AQITGRPEWIWLALGTALMGLGTLYFLVKG 2 MGVSDPDAKKFYAITTLVPAIAFTMYLSMLL GYGLTMVPFGGEQNPIYWARYADWLFTTPL LLLDLALLVDADQGTILALVGADGIMIGTGL VGALTKVYSYRFVWWAISTAAMLYILYVLFF 3 GFTSKAESMRPEVASTFKVLRNVTVVLWSA YVVVWLIGSEGAGIVPLNIETLLFMVLDVSA KVGFGLILLRSRAIFGEAEAPEPSADGAAAT S Membrane spanning a-helices 4 Charged residues Action Description of the action As shown (Please redraw all figures. ) First show the figure on the left. The red box in animation. must then appear which must be zoomed into 5 Residues of the 7 membrane-spanning helices (largely non-polar) to show the figure on the right with the highlighted regions as depicted along with all the labels and the key shown below. Audio Narration Bacteriorhodopsin is an archaeal integral membrane protein that plays a role in energy transduction, using light energy for the transport of protons from inside to outside the cell. It is made of seven membrane-spanning alpha helices that are oriented perpendicular to the plane of the membrane. Determination of the amino acid sequence of this protein revealed that most of the residues within the membrane are non-polar, thereby allowing favorable interactions with the lipid hydrocarbon chains. Very few charged residues were found in the structure. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

1 Part 3, Step 2: Integral proteins – Porins --- Hydrogen bonded b-strands 2 3 Amino acid sequence of porin from Rhodopseudomonas blastica Hydrogen bonds Hydrophobic residues (on surface of structure) Hydrophilic residues (buried inside) 4 5 Action Description of the action Audio Narration Porins are another class of integral membrane proteins that form channels As shown in (Please redraw all figures. ) within the membrane. They are composed entirely of b-strands with animation. First show the structure on top with its label. Then show the dotted arrows and the figure on essentially no alpha helices in their structure. These beta strands are hydrogen bonded to each other to form a beta sheet which folds to form a right top. The brown circles must appear and pass through the blue cylinder. This must hollow cylindrical structure. The folding occurs such that the polar amino happen continuously throughout this animation. acid residues line the inside of the cylinder, thereby making it hydrophilic. Simultaneously, the green box must appear and This allows the channel to be filled with water and also allows passage of this region must be zoomed into and the figure small ions and charged molecules. The non-polar residues facing outside below must be shown with its labels and the key interact hydrophobically with the lipid chains of the membrane. on the left. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 3, Step 3: 1 Peripheral proteins Acid/alkali added – change in p. H Dissociation Integral proteins 2 Peripheral membrane proteins 3 Dissociation 4 Action Description of the action As shown in (Please redraw all figures. ) animation. First show the figure in the middle with the yellow and blue shapes labeled a-e. Next show the blue cloud appearing on the blue shapes with the corresponding label. The blue shapes, d & e, must then dissociate from the figure as shown. 5 Audio Narration Peripheral membrane proteins are attached to either the outside or inside surface of the membrane via electrostatic and hydrogen bond interactions with either the lipid heads of the membrane or with other integral proteins. These polar interactions can be easily disrupted by addition of acids or alkali which modify the p. H or by addition of salts. Source: Biochemistry by A. L. Lehninger, 4 th edition (ebook)

Part 3, Step 4: 1 Each amino acid is associated with a free energy change for its transfer from a hydrophobic to aqueous environment. Prediction of transmembrane helices – Hydropathy index Threshold value for helix detection 3 4 5 ~ 20 amino acid residues ~ 30 Ao Free energy calculations are made for transfer of every 20 amino acid residues (i. e. 1 -20, 2 -21, 3 -22 etc. ) from hydrophobic to aqueous environment. This is plotted as a hydropathy plot. Action Description of the action As shown (Please redraw all figures. ) in First show the long chain like structure animation. shown in the centre with the labels. Next show the dialogue box on the right top followed by the dialogue box at the bottom. Once this is shown, the graph on the right must appear with the arrow mark and text box. Hydropathy index, k. J/mol 2 First amino acid residue in window Audio Narration It is possible to predict transmembrane helix regions of a protein by calculating the free energy changes associated with the transfer of residues from a hydrophobic to aqueous environment. The width of a membrane is typically around 30 Ao, which can fit approximately 20 amino acid residues. Therefore the free energy change for hypothetical alpha helices formed every 20 residues, from residue 1 to 20, 2 to 21, 3 to 22 and so on are calculated until the end of the sequence is reached. These free energy changes are plotted against the first amino acid residue of every 20 -residue window ito obtain a hydropathy plot. A peak above 84 k. J/mol is indicative of a likely membrane spanning helix. This, however does not detect membrane spanning b sheets. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

This animation consists of 4 parts: Part 1 – Fatty acids Part 2 – Membrane lipids Part 3 – Proteins in membrane structures Part 4 – Properties of cell membranes Bleach Fluorescence Recovery After Photobleaching (FRAP) 2 Recovery Bleach Fluorescence intensity 1 Master Layout (Part 4) Recovery Time 3 Lateral diffusion Very fast 1 mm/s 4 Transverse diffusion (flip-flop) Very slow t 1/2 in days 5 Source: Biochemistry by A. L. Lehninger, 4 th edition (ebook)

1 2 3 4 5 Definitions of the components: Part 4 – Properties of cell membranes 1. Fluorescence Recovery After Photobleaching (FRAP) : This is a technique by which a cell surface component is first labelled by means of a fluorescent molecule and a small region of the cell surface is viewed by means of fluorescence microscopy. The fluorescent molecules in the region being viewed are destroyed by a laser pulse, a process known as bleaching. Once this occurs, the time required for fluorescence to reappear in this region is plotted against the fluorescence intensity. This helps in understanding the movement of molecules across the cell surface. 2. Lateral diffusion: The process by which membrane components move laterally from one region to another in the same plane. This is a quick process and takes place in a matter of microseconds. Proteins exhibit varying degrees of lateral mobility, with some being as mobile as lipids and others being almost immobile. 3. Transverse diffusion (flip-flop): This is a process by which molecules in the membrane transition from one surface of the membrane to the other. The time required for transverse diffusion is significantly more than that for lateral diffusion and can be measured by electron spin resonance techniques. This process is made quicker by the enzyme ‘flippase’. 4. Fluid Mosaic Model: The overall organization and properties of biological membranes were proposed by Jonathan Singer and Garth Nicolson in 1972 as the Fluid Mosaic Model. They proposed that membranes are two-dimensional solutions of oriented lipids and globular proteins, with the lipids serving as a “solvent” for integral membrane proteins and functioning as a permeability barrier. They also hypothesized that membrane proteins undergo lateral diffusion freely but not transverse diffusion.

Part 4, Step 1: 1 Lateral diffusion of membrane components - FRAP Fluorescence intensity 2 Bleach Laser Bleaching Recovery 3 4 Time Region being viewed through microscope Cell surface components labelled with fluorescent molecule Action As shown in animation. 5 Recovery Description of the action Audio Narration (Please redraw all figures. ) Lateral diffusion of membrane components can be proved First show the blue figure with the green spots on it and the using fluorescence recovery after photobleaching corresponding labels. Followed by the red box and its label. Next, show technique. A cell surface component is first labelled by the ‘laser’ and its light falling on the green spot at the bottom. Once this means of a fluorescent molecule and a small region of the happens, the green spot must change color to grey and the label cell surface is viewed by means of fluorescence ‘bleaching’ must appear. Then the laser must be removed and the grey microscopy. The fluorescent molecules in the region being spot should move down and disappear and simultaneously the green spot viewed are destroyed by a laser pulse, a process known as on top must move into the red box as shown in animation. When bleaching occurs, the downward slope of the graph must be shown and bleaching. Fluorescence however reappears in the region when the green spot on top enters the red box, the upward curve must be after a certain time that is dependent on the diffusion coefficient of the molecules. shown to appear. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

1 Part 4, Step 2: Lateral diffusion Vs Transverse diffusion Lateral diffusion Very fast 2 3 4 5 1 mm/s Flippase Transverse diffusion (flip-flop) Very slow t 1/2 in days Action Description of the action Very fast t 1/2 in seconds Audio Narration The Fluid Mosaic model explains the lateral diffusion As shown in (Please redraw all figures. ) animation. First show the green figures on top with the title ‘lateral diffusion’. The blue of membrane components but not the transverse diffusion. Lateral diffusion is a rapid process taking shape must move as indicated by the arrow and reach the position indicated on the right. This must occur quickly. Next show the figure on left place in the range of microseconds. However, bottom with the title ‘transverse diffusion’. The blue shape alone must flip transverse diffusion, also known as the ‘flip flop’ very slowly in the direction indicated by the arrow to reach the position reaction takes place very slowly over a period of shown on the right. Next, the brown oval must appear with its label. When several hours. This reaction is facilitated by the this happens, the flipping must take place quickly in the same way as the enzyme flippase, which carries out transverse previous diagram. diffusion in the time range of few seconds. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

Part 4, Step 3: 1 Factors determining membrane fluidity 3 4 Fluid-like Solid-like 2 Presence of cholesterol – greater cholesterol, higher Tm Tm Temperature Action Description of the action As shown in (Please redraw all figures. ) animation. The graph must appear gradually. As the graph is appearing in the centre, the text around it must appear sequentially as shown. 5 Length of fatty acyl chain – longer chain, higher Tm Degree of unsaturation – Saturated fatty acids increase Tm Audio Narration The fluidity of any biological membrane is dependent on the properties of the fatty acid chains present in it. Transition of the membrane from a rigid state to a fluid state occurs abruptly as the temperature is increased and crosses the melting temperature, Tm. This melting temperature is a function of the length of fatty acyl chains present and their degree of unsaturation. Increase in length of fatty acyl chain increases the Tm while increase in the degree of unsaturation decreases the Tm. In other words, greater number of double bonds disrupts the packing order achieved by saturated fatty acids thereby decreasing the Tm. In animals, the cholesterol content is another regulator of fluidity. Greater the amount of the bulky steroid, higher is the Tm. Source: Biochemistry by Lubert Stryer, 6 th edition (ebook)

1 2 Interactivity option 1: Step No: 1 Membrane lipids are useful for designing lipid vesicles known as liposomes, which consist of small aqueous compartments surrounded by a lipid bilayer. These liposomes are increasingly being used as drug delivery systems in hydrophobic environments. Shown below is an example formation of a glycine-containing liposome. Click on the green phospholipid layer to view liposome formation and then answer the question below. Glycine in water Sonication 3 4 Phospholipid (Click here) Interacativity Type 5 Gel filtration Click to view experiment & then choose the correct answer. Options (Please redraw all figures. ) User must click on the green layer at the bottom of the first figure to view the animation after which the question with 4 options must appear and user must be allowed to choose any 1 option. Results When the user clicks on the green layer, the animation must be shown. The green layer shown at the bottom must gradually form green circles as shown in the middle panel and must surround a few red dots. Once this happens, the arrow saying ‘gel filtration’ must be shown and the red dots must disappear leaving only the green circles enclosing the red circles. The user must then answer the question shown in the next slide. Correct answer is C. If user gets it right, ‘correct answer’ must be displayed otherwise ‘wrong answer’ must be displayed.

1 Interactivity option 1: Step No: 1 What property of membrane lipids allows them to form such liposome vesicles? 2 A) Their low melting temperature B) The presence of cholesterol 3 C) Their self-sealing nature D) The presence of glycerol in the phospholipids 4 Interacativity Type 5 Click to view experiment & then choose the correct answer. Options (Please redraw all figures. ) User must click on the green layer at the bottom of the first figure to view the animation after which the question with 4 options must appear and user must be allowed to choose any 1 option. Results When the user clicks on the green layer, the animation must be shown. The green layer shown at the bottom must gradually form green circles as shown in the middle panel and must surround a few red dots. Once this happens, the arrow saying ‘gel filtration’ must be shown and the red dots must disappear leaving only the green circles enclosing the red circles. The user must then answer the question shown in the next slide. Correct answer is C. If user gets it right, ‘correct answer’ must be displayed otherwise ‘wrong answer’ must be displayed.

1 Questionnaire 1. How many double bonds would be present in a fatty acid having the systematic name “all-cis-∆9, ∆12, ∆15 -Octadecatrienoate”? 2 Answers: a) 1 b) 2 c) 3 d) 4 2. Which of the following is a saturated fatty acid with 18 carbon atoms? 3 Answers: a) cis- ∆9 -Octadecenoate b) Octadecanoate d) Tetradecanoate c) Eicosanoate 3. Which of the following components is not present in Phosphatidyl inositol? Answers: a) Sphingosine b) Glycerol c) Phosphate d) Inositol 4 4. If the degree of unsaturation of fatty acyl chains increases, what happens to the Tm? Answers: a) Tm increases b) Tm remains same c) Tm decreases d) None of the above 5. The threshold value of hydropathy index for detection of alpha helices is? Answers: a) -22 k. J/mol b) +22 k. J/mol c) +67 k. J/mol d) +84 k. J/mol 5

Links for further reading Books: Biochemistry by Stryer et al. , 6 th edition Biochemistry by A. L. Lehninger et al. , 4 th edition Biochemistry by Voet & Voet, 3 rd edition Research papers: Singer, S. J. & Nicolson, G. L. The Fluid Mosaic Model of the Structure of Cell Membranes. Science 1972, 175 (4023), 720 -731.