Introduction of Cell, Cell Theory and History Chapter 2

CHAPTER: 2 (CHEMICAL COMPONENTS OF THE CELL) ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Living creatures _ merely chemical systems. Till 19th century _ Living organism _ vital force (an animus) _ responsible for distinctive features Chemistry of life _ Special kind: 1- Based on Carbon compounds _ Study of these is organic chemistry. 2- Life depends on chemical reactions _ take place in watery or aqueous solution in narrow range of temperature. 3- Enormously complex 4- Dominated by collection of polymers (chains of chemical subunits) 5- chemistry of life is tightly regulated (control the rate and time of reactions through feedback mechanism). Chemical Bonds: Matter _ combination of elements (substances i.e. H, C that cannot be broken down or interconverted by chemical means) _ Contain Atoms (smallest particle of element that still retain its distinctive chemical properties) Matter → Elements → Atoms Properties of substance _ depends on the type of atoms and way these atoms are linked together in groups to form molecules. Type of Atoms in Cell Structure: Nucleus: Centre, dense, positively charged, surrounded by electrons. = Protons (+) and Neutrons (No charge) Electrons _ Negatively charged and held there via electrostatic attractions to the nucleus. Atomic Number: Number of protons in nucleus Exp: H atom _ 1 proton _ 1 atomic number _ lightest element *Electric charge of Proton is exactly equal but opposite to the electron. * * No. of negatively charged electron is equal to the number of positively charged protons. Neutrons _ same mass _ Protons. * Provide structural stability to the nucleus *If the number of neutrons is too small or large then nucleus will disintegrate by radioactive decay. *But they do not alter the chemical properties of the atom. *So, element can exist in several physically distinguishable but chemically identical forms called isotopes _ Having different number of neutrons but same number of protons. All elements _ have isotopes _ some are unstable _ radioactive _ Carbon 14 _Decay at slow but steadily _ Archaeologist _ Estimate the age of material. Atomic wight: equal to the sum of protons and neutrons (electrons do not make much part of cell) Molecular weight: some of atomic weighs of all atoms. Example: C12 = 12D (6P+6n) * Dalton _ unit for molecular and atomic weight _ 1dalton = equal to mass of hydrogen atom. Its hard to measure the size of an atom _ Approximately its diameter is 0.2nm _ 5 Million atoms in straight line _ Make 1mm. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ No. of grams equal to the atomic or molecular weight = Avogadro’s number (6 x 1023) Example: Atomic weight of H = 1, so 1 gram of H contain 6 x 1023 atoms. Example: C12 = 12 atomic weight = 12 grams contain = 6 x 1023 Carbon atoms. Avogadro’s number = 1 Mole. Naturally occurring elements = 90, but living organisms consist of only few elements (C, O, H, N makes the 96% of an organism’s mass.) Outermost electron: Atoms _ Join _ Molecules? Protons and neutrons only change patterner during extreme conditions _ During radioactive decay, in nuclear reactor or in the interior of sun. Living organisms _ only electrons undergo the rearrangement _ define the rule of chemistry by which atoms combine. Electrons _ continuous motion _ Discrete orbits/shell _ Specific number in each shell. Shell 1: 2 electrons Shell 2: 8 electrons Shell 3: 8 electrons Shell 4 & 5: 18 electrons each Stable atoms: Electrons present in shells near to the nucleus * An atom with outermost complete shell is stable or unreactive. i.e. Helium with 2 electrons in outermost shell. * H _ only 1 electron in its outermost shell _ reactive _ interact with other atoms to gain or lose electrons _ To fill their outermost shell. Strategies for exchange: 1- Transferring electrons from one atom to another 2- Sharing of electrons Chemical bonds are generated as result these strategies. Ionic bond: formed as result of donation of electrons or receiving electrons Covalent bond: formed by sharing electrons. Characteristics of a cell _ depend upon its molecules Molecules _ Cluster of atoms held together by covalent bonds in which electron are shared. H2 _ H-H Electron cloud help to held the atoms together by reducing the repulsive forces of nucleus. Attractive and repulsive forces are in balance when the nuclei are separate by a characteristic distance called bond length. Some atoms share 2 electrons so they develop double covalent bond Some share 3 electrons _ they develop triple covalent bonds Ionic Bonds form by gaining and losing electrons. Ionic bonds: Formed by atoms which can easily gain or lose electron in outermost shell. Due to the movement of electrons atoms becomes charged and called ions. Na – lose electron – Increase in 1 net proton – net + charge _ cations Cl – gain electron – Increase in 1 net electron – net – charge _ anions ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Na and Cl will attract each other due to opposite charges _ held together by ionic bond *Ions held together by solely by ionic bonds are called salts. *Due to charges, ionic compounds i.e. salts are high soluble in water. In water _ ions dissociate into ions _ each surrounded by a group of water molecules Importance of non-covalent bonds: Ionic bonds _ weak in solution (10100 times) In biological system _ molecules are held together via non-covalent bonds _ Quite week _ sum of energies can create effective force. The ionic bond between Na and Cl _ an example of electrostatic interaction. _ strong when involved atoms are fully charged. Electrostatic attractions are week _ between molecules contain polar covalent bonds. Large molecule _ Many polar groups _ Pattern of partial positive and negative charges on surface _ encounter a second molecule with a complementary set of charges _ the two will attract via electrostatic attractions H-Bonds Water _ 70% of cell’s weight _ medium for reactions Water _ O-H-O (H2O) _ O-H _ highly polar _ O (strongly electronegative and attract electrons) but H (weakly electronegative and attract electrons weakly) _ unequal distribution of electrons _ partial + charge on H and partial – charge on O. +vely charged H will interact with -vely charged regions or atoms of other molecules and develop weak attraction called H bond. H bond _ very weak _ broken by thermal motion Each water molecule _ 2 H bonds All water molecules make a network of molecules via H bonds _ liquid at room temperature with high boiling point and surface tension. *H bonding _ not limited to water _ any molecule with positively charged H will develop H bond with negatively charge atom in another molecule, particularly O and N. Hydrophilic (water loving6) molecules: molecules carrying positive or negative charges likewise dissolve readily in water. Examples: DNA, RNA, majority of proteins. Hydrophobic (water fearing) molecules: molecules which are uncharged and for few or no H bonds and do not dissolve in water. Examples: Hydrocarbons (in these H binds with C with non-polar bond, hence H has no charge and do not make H bond) _ perform structural role in cells (cell membrane) Small molecules in Cell A cell is formed of carbon compounds Except water, nearly all molecules in a cell are based on carbon. Carbon: have ability to form larger compounds Carbon: small, four electrons in outermost shell, four valency, four covalent bonds with other atoms. C-C bond is a stable covalent bond _ Help in making long chains and rings. Compounds made by carbon are called organic molecules. Compounds which do not have carbon as an essential component are called inorganic compounds. Major families of small organic molecules: → less abundant then macromolecules ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Small organic molecules _ 100-1000 molecular weight and up to 30 carbons_ found free in cytoplasm _ account only 1/10 of the total organic molecules of cell. Functions: 1- monomers: use to construct polymers or macromolecules i.e. proteins, nucleic acid, carbs 2- source of energy 3- some act as both; as monomers and source of energy. These are synthesized and broken down into smaller monomers by the same chemical reactions. Families: Sugars, Fatty acids, amino acids and nucleotides. These basic compounds make larger compounds by the process called condensation/polymerization. SUGARS Both _ energy source and subunits of polysaccharides Simplest sugars _ Monosaccharides (CH2O)n _ n=3,4,5,6 _ larger molecules are called carbohydrates. Glucose _ C6H12O6 _ C/H/O are the basic elements _ it can be converted into different sugars i.e. mannose or galactose _ by switching the orientation of -OH groups Forms of Sugars: D-form and L-form _ mirror images of each other. _ Optical isomers. Isomers: Same chemical formula but different structural formula. Monosaccharides _ linked _ Glycosidic bond _ Carbohydrates 2 Monosaccharides _ Disaccharide _ Sucrose (glucose + fructose)/maltose (2 glucose) Large sugar polymers: Oligosaccharides (2-10 monosaccharides): Trisaccharides, tetrasaccharides and so on Polysaccharides: Up to thousands of monosaccharides Bond Formation: -OH of one sugar react with -OH of other sugar _ condensation reaction _ Expel water molecule. Nucleic acid, proteins also formed by condensation. The bonds formed by condensation could be broken down by hydrolysis. Monosaccharides _ several -OH groups _ Also attached branches _ increase complexity Difficult to determine the sequence of monosaccharide units. Functions: Glucose _ broken down _ ATP _ cellular activities. Glycogen and starch _ made up of glucose _ act as reservoir of energy production Structural role: Cellulose _ cell wall Chitin _ polymer of N-acetyl glucosamine_ insects exoskeleton and fungal cell wall Oligosaccharides _ covalently linked to proteins _ glycoproteins or to lipids _ glycolipids _ cell memb. _ protect cell membrane, adhesion to surface. Fatty acids and Cell membrane Structure: 2 regions: Hydrophilic head containing -COOH group _ donate H+ in solution and highly reactive hydrophobic tail of hydrocarbons_ less reactive ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Molecules—such as fatty acids—that possess both hydrophobic and hydrophilic regions are termed amphipathic. Tails of fatty acids: Saturated: single bonds – Palmitic acid (no double bond) Unsaturated: double bonds – Oleic acid (1 double bond) Make cell membrane _ lipid bilayer Fatty acids along with alcohol join to make lipids which are insoluble in water but soluble in non-polar solvent like benzene, chloroform. Act as energy reserve and store 6x energy as compared to same amount of glucose. Stored form of fats in body are triglycerides: 1 glycerol and 3 fatty acids Fats or triglycerides tails or chains are broken down into 2 subunits similar to the units produce by the break down of glucose which enters the kreb’s cycle. Phospholipids: Glycerol + 2 fatty acids + Phosphate group + Nitrogenous base Head _ Phosphate _ hydrophilic Tail _ fatty acids _ Hydrophobic They are amphipathic Along with phospholipids, cell membrane also contains glycolipids Amino Acids and Proteins Amino acids: Small organic molecules contain -COOH and -NH2 attached to the alpha carbon. Side chain will define the nature of amino acids. Amino acids join via peptide bonds and make long chains called polypeptides which fold upon itself and make 2D proteins. Polypeptide always have amine terminus and carboxylic terminus called N and C terminus. 20 type of amino acids Amino acids also exit in L and D forms _ L form is common _ D form is only found in cell wall of bacteria and in some antibiotics D-serine _ signal molecule in brain. Nucleotides, DNA and RNA ▪ Nucleotides _ building blocks of DNA and RNA _ Nucleoside + Phosphate groups ▪ Nucleoside _ Sugar (ribose or deoxyribose) + Nitrogenous base ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Ribonucleotides (Ribose) & Deoxyribonucleotide (Deoxyribose) Nitrogenous bases: Pyrimidines: Cytosine, Thymine, Uracil – single ring bases (6 membered ring) Purines: Guanine, Adenine – Double ring bases (6 membered and 5 membered rings) Carrier of Energy: Nucleotides can store short term energy _ ATP _ synthesized during reactions which release energy like in the breakdown of foodstuff. 3 phosphates are linked together via phosphoanhydride bonds Release of terminal phosphate release energy Storage of biological information: Building blocks of nucleic acid _ linked via phosphodiester bond _ between sugar of one nucleotide and phosphate group of another nucleotide. Type of nucleic acid: RNA: Ribose sugar, A/G/C/U, usually single stranded Carrier of molecular information DNA Deoxyribose (lack -OH group on carbon 2), A/G/C/T, Double helix (2 polynucleotide chains which run in opposite direction) ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Repository for hereditary information Macromolecules of Cell: Most abundant in cell Polymers _ Build by linking small monomers by covalent linkages Versatile functions: Nucleic acid: Store hereditary information Proteins: Enzymes, Structural compounds, Specific sequence of subunits in macromolecules: 1- monomers in polymers are slightly different from each other like amino acids and nucleotides 2- subunits are added in a precise order or sequence * Biological functions of macromolecules depend upon the precise sequence of monomers * by varying the sequence of monomers, cell can enormous diversity of macromolecules. Example: protein contain 200 amino acids may have 20200 possible combinations. Example: 10000 nucleotide long stretch may have 410000 different combination. Non-Covalent Bonds specify the SHAPE: Single covalent bond _ allow rotation of the atoms _ flexibility in chain _ it can adapt any shape or conformation. Non-covalent bonds that form between the parts of molecule _ Help the molecule to adapt particular shape _ unique conformations _ determine the chemistry and activity of these molecules Main non-covalent interactions: Electrostatic attractions, H bonds, van der waals attractions and hydrophobic interactions. CHAPTER: 11 (MEMBRANE STRUCTURE) ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Plasma membrane: outermost boundary _ 5nm tick _ not visible with light microscope Protect internal environment from outside environment. No membrane _ No existence of cell. Structure: 2 sheets of lipids into which proteins are embedded. (Fluid mosaic model) Highly selective channels and transporters _ proteins which help the molecules to move in and out of the cell. Certain proteins: receptor proteins _ receive changes in environment It also changes shape when cell grow or move (in enlarges by adding new membrane and deform without tearing). If it pierced, it neither collapses like balloon nor remains torn, instead, it quickly reseals. Eukaryotic cell _ plasma membrane and internal membranes Prokaryotic cell _ only plasma membrane All membranes have same basic framework _ two lipid layers _ lipid bilayer _ Act as permeability barrier for most water-soluble molecules. Proteins perform various other functions and five distinctive characteristics to the membrane of different cells. LIPID BILAYER: Interior and exterior of cell is filled with water _ lipids determine the structure of membrane _ depending upon their behavior with water. Membrane lipids _ Phospholipids Phospholipids: Hydrophilic head (phosphate containing) Hydrophobic tail (hydrophobic tail) Phosphatidylcholine _ Choline containing phospholipids Amphipathic Other amphipathic lipids in cell membrane include cholesterol and glycolipids. Hydrophobic molecules neither develop hydrogen bonding nor electrostatic attractions with water, hence they are not soluble in water and try cover themselves from water by other molecules and displace water. Phospholipids _ hydrophilic head _ attract water while hydrophobic tails run away from water and aggregate with hydrophobic molecules. _ this is resolved by making lipid bilayer. In lipid bilayer _ heads face towards the on both surfaces but tails are present in the interior These forces also help in self sealing of membrane. Any tear in membrane will expose the hydrophobic part, so hydrophilic molecules immediately rearrange and seal the membrane. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Large tears or breaks: membrane fold upon it self to make large vesicles. LIPID-BILAYER is a flexible 2D fluid Aqueous environment inside and outside the cell prevent the lipids from escaping from lipid bilayer. But, instead of this, they continuously change and shuffle their position with in lipid bilayer. So, it behaves like 2D fluid. It is also flexible_ can bend _ this sets the lower limit of vesicles which form from it up to 25nm in size. Pure phospholipids form liposomes (lipid vesicles) when added to water of 25nm to 1mm in size. * lipids continuously exchange their places with neighbors _ allow rapid bilateral diffusion of lipid molecules * the flip-flop movement of lipids molecules (movement from one lipid layer to the other) is rare (once per month). Fluidity of Lipid bilayer depends upon composition. *movement of lipid molecules in lipid bilayer facilitate the functioning of membrane Fluidity of membrane depends upon the nature of phospholipids or particularly on the nature of hydrocarbon tails. Closer and more regular packaging _ viscous and less fluid the bilayer will be Properties of hydrocarbon tail which effect the tight packing of lipid bilayer: 1- length of tail 2- number of double bonds Short chain _ reduce tendency of tails to interact _ increase fluidity of membrane. * tails of membrane phospholipids vary between 14 to 24 carbon atoms but 18-20 being the most usual range. Chains _ double bonds _ no maximum number of Hydrogen atoms _ unsaturated with respect to Hydrogen atoms. Chains _ no double bonds _ maximum number of hydrogen atoms _ saturated with respect to hydrogen atoms. Double bond _ create kink in tail _ make difficult for the tails to pack Lipid bilayer with large proportion of unsaturated hydrocarbon tails are more fluid then with lower proportions. Examples: bacteria and yeast cells: adapt to variable temperatures _ both the lengths and the unsaturation of hydrocarbon tails in the bilayer are constantly adjusted to maintain the membrane at a relatively constant fluidity At high temperature _ membrane lipids with tails that are longer and that contain fewer double bonds. Vegetable oils _ unsaturated _ liquid at room temperature _ hydrogenation of oils _ double bonds are removed_ Margarine Fats and butter _ saturated _ solid at room temperature Animals _ membrane fluidity _ modulated by the inclusion of sterol/ cholesterol (20% in membrane) _ fill the spaces created by the kinks of unsaturated molecules _ stiffen the bilayer _ making it less flexible _ less permeable ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Importance of cell fluidity: Enable many membranes to diffuse rapidly and interact with one another It helps in the transport of lipids and proteins to the target location. It also helps in fusing of molecules Membrane assembly in ER ER _ attached enzymes to the cytosolic surface _ use free fatty acids _ deposit new phospholipids in the cytosolic half of bilayer. Scramblases: randomly select phospholipids from one half of lipid bilayer and insert them in the other _ scrambling _ redistribution of newly made phospholipids evenly in cell membrane between layers of ER. Bits of membrane _ pinched off continuously from ER in the form of small vesicles _ fuse with other membranes i.e. Golgi and plasma membrane Membranes → Asymmetrical → both layers of lipid bilayer contain chemically different sets of phospholipids. Golgi _ flippases _ phospholipids handling enzyme_ flip the phospholipids which are facing the exterior to the cell and flip them towards the cytosol. Fippases and other enzymes in membrane maintain asymmetric arrangement of phospholipids All the membranes have distinct inside and outside faces. Location of proteins is also important for proper functioning Glycolipids _ only in non-cytosolic half of cell membrane. Sugar groups face the exterior _ Part of carbohydrate coat around the cell _ Protection to animal cells Glycolipids _ Acquire carbohydrates in Golgi _ Contain enzymes for this modification ** there are no filappase that transfer the glycolipids to the cytosolic side. Glycolipids _ Golgi _ Transfer _ Plasma membrane _ Exposed to the exterior surface of cell. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Inositol Phospholipids _ Minor component of plasma membrane _ Relay signals from the cell surface to the cell interior _ concentrated in the cytosolic half of lipid bilayer. MEMBRANE PROTEINS: Lipid bilayer _ Basic framework _ Permeability barrier to hydrophilic molecules Animal cell _ 50% mass of plasma membrane _ Proteins Quantity _ Lipids are small molecules _ Have high number as compared to proteins. Functions of membrane proteins: 1- Transport nutrients, metabolites, ions across lipid bilayer 2- some anchor macromolecules in the membrane 3- Receptors _ Detect signals from the environment and relay them into the interior of cell. 4- Enzymes ** Each cell membrane contains specialized proteins which perform specific functions and provide specialty the membrane. Binding of Membrane proteins with Lipid Bilayer: Ways: 1- Transmembrane proteins _ extend through bilayer – part of mass on either side - Amphipathic: - Hydrophobic region lie in the interior along with hydrophobic tails of the lipids. - Hydrophilic regions exposed to the aqueous environment. 2- Some _ located almost entirely in the cytosol _ associated with cytosolic half of membrane _ remain attached with membrane via an amphipathic alpha helix. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ 3- Some _ lie entirely outside the bilayer _ on one side or the other _ attached to membrane only by one or more covalently attached lipid groups. 4- Some bound indirectly _ on either side of the membrane _ attached via weak interactions with other proteins in membrane. **** transmembrane proteins can only be removed by disrupting the bilayer. Also called Integral membrane proteins. **** Remaining proteins are called as peripheral membrane proteins. _ these can be extracted from membrane without breaking lipid bilayer. Structure of proteins is Function orientated → Orientation of proteins in membrane – essential for function → example – transmembrane protein – outside of cell – receive signals – cytosolic part – transmit signals to the cytosol. → Structure – the portions of transmembrane protein on either side of the membrane are connected by a specialized membrane spanning segments of polypeptide chain. – these are hydrophobic segments – interact with hydrophobic pat of lipid bilayer. *** the peptides bonds → join the successive amino acids → polar → Backbone of peptide is hydrophilic. As water is absent in the interior of cell membrane – hydrophilic backbone will develop hydrogen bonds with its different parts – H- bonding is maximum – alpha helix – hydrophobic side chains of alpha helix – exposed – contact with hydrophobic zone of lipid tails. Functions of transmembrane proteins: Receptors Channels (aqueous pores, allow small water-soluble molecules to cross) – multiple alpha helices cross the membrane and make pores – multipass transmembrane proteins *** in multipass transmembrane proteins – one or more membrane spanning regions are amphipathic – alpha helices with both hydrophobic and hydrophilic regions – hydrophilic parts arranged on one side and hydrophobic parts on the other side – hydrophilic part forming the lining of the aqueous pore. *** alpha helices are the common structure by which most proteins cross the lipid bilayer. Some proteins – cross lipid bilayer – Beta sheets which rolled into a cylinder (keglike structure called beta barrel). → inside of the barrel face hydrophilic amino acids → outer region contains hydrophobic regions which face the lipid bilayer. EXAMPLE: Large porin proteins – form large, water filled pores in mitochondria and bacterial membranes. Porins – allow exchange of small nutrients, metabolites inorganic ions and prevent the exchange of large molecules. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Effect of Detergents on Proteins: Study a protein – separate from other proteins – needs solubilization of lipid bilayer with an agent that destroy lipids Detergents: Small, amphipathic, lipid-like molecules differ from membrane phospholipids in that they have only one hydrophobic tail. Use to disrupt hydrophobic interactions between lipid molecules in membrane. Have one hydrophobic tail – water – aggregate into small clusters called micelles When added in excess – hydrophobic tail – interact with – hydrophobic regions of transmembrane proteins and lipid tails – disrupt the membrane and separate the protein. Hydrophilic heads bring the protein detergents complexes in solution Role of Cell Cortex Cell membrane – extremely thin 10,ooo membranes _ achieve the thickness of this paper. It is supported by the framework of proteins attached via transmembrane proteins. Bacteria/ Yeast/ Plants – Cell wall – cell shape and provide mechanical support. Cell cortex – meshwork of fibrous proteins – attached underside of membrane. Components of cortex in RBCs: Spectrin: dimeric protein, long, thin flexible and about 100nm long. Abnormality in spectrin meshwork – anemia Cortex of other cells: Other cells cortex is rich in actin and motor protein myosin. Complex cortex then RBCs Involved in changing cell shape, providing mechanical support, help in endocytosis Control on Movements of membrane proteins: Proteins can move in lipid bilayer/ocean of lipids freely EXAMPLE: Fusion of mouse and human cell – large hybrid cell – initially proteins was confined to the separate halves of cell – later or after half hour proteins distributed equally on surface of hybrid cell.