Biological molecules

• Properties of water: 71% of the worlds surface (great habitat), 2H 1O, joined by covalent bonds, water is a dipole due to unevenly shared charge and is also polar, hydrogen bonds form between water molecules (these are weak as there are few of them), solvent, high specific heat capacity, high latent heat of vaporisation, less dense when solid, high surface tension and cohesion, acts as a reagent.
• Properties of water: as it is a solvent ions and substance dissolve which allow them to be more chemically reactive, 4200j/kgC are required to break the hydrogen bonds means it is a suitable habitat and maintains a constant temperature, optimal for enzyme activity. high latent heat acts as a coolant. water forms hydrogen bonds with other molecules creating adhesion (binding to cellulose allows water to move up the xylem, cohesion also aids this
• monomer: single subunit, polymer: repeating subunits, macromolecule: large molecules containing repeating subunits that may also contain other atoms.
• Covalent bonds: sharing of two or more electrons, shared equally (nonpolar) shared unequally (polar), unsaturated (have a double bond) carbohydrates= glyosidic, proteins=peptide, lipids=ester, nucleic acids=phosphodiester.
• Condensation: when monomers combine and form covalent bonds to form polymers and water is removed. Hydrolysis: covalent bonds between polymers are broken through the addition of water.
• monosaccharides: single sugar monomer, all are reducing sugars, e.g. ribose, glucose, source of energy in respiration, building blocks for polymers.
• Disaccharides: two monosaccharide joined by a glyosidic bond in a condensation reaction, maltose= two alpha glucose, sucrose= alpha glucose + fructose, lactose= alpha glucose + B-galactose.
• Polysaccharides: a polymer formed by many monosaccharides joined by glyosidic bonds in a condensation reaction, cellulose (B-glucose), starch (a-glucose) in the form of amylose and amylopectin, glycogen (a-glucose), energy storage and structural.
• Lipids: all contain C, H, O, types include triglycerides, phospholipids, steroids. functions: storage of energy, source of energy and insulating layer and essential compound of biological membranes.
• Proteins: all contain C, H, O can contain N and S. functions include: required for cell growth and repair, structural importance, and acting as carrier molecules
• Nucleic acids: all contain C, H, O can contain N and P. one function carrying the genetic code which enables the control of cellular processes including protein synthesis.
• Reducing sugars: can donate electrons, can be detected using a Benedict's test as they reduce soluble copper sulphate to insoluble copper oxide, glucose, fructose and galactose. Non-reducing sugars cannot donate electrons and so cannot be oxidised, so they must first go through hydrolysis
• Benedict's test is used to test for reducing sugars: Add Benedict's solution to sample then heat in waterbath at 80C for 10 minutes. Dependent on the type of sugar present, the solution will turn different colours. For non-reducing sugars the solution needs to undergo hydrolysis so HCL need to be added then the solution is heated. Sodium hydrogencarbonate is then used to neutralise the solution, then the Benedict is added again.
• Starch (plant): two different polysaccharides: amylose and amylopectin. Amylose- 10-30% of starch, unbranched helix shape with 1,4 glycosidic bonds between a-glucose. Amylopectin- 70-90% of starch 1,4 glycosidic but also 1,6 between glucose, branched.
• Glycogen (animal): A polysaccharide made of alpha glucose molecules, 1,4 glycosidic between a glucose molecules, 1,6 between glucose molecules creating a branched molecule. similar to amylopectin but more branched.
• Cellulose: a polysaccharide found in plants, consists of long chains of b-glucose joined by 1,4 glycosidic bonds, molecules are rotated 180 to each other. Due to the inversion many hydrogen bonds form between the long chains giving cellulose its strength.
• Polysaccharide function: (starch and glycogen) are storage polysaccharides because they are compact and insoluble. Starch is the storage in plants it is stored as granules in plastids such as amyloplasts and chloroplasts, starch takes longer to digest than glucose, but due to amylopectin being branched its ends are easily hydrolysed for use during cellular respiration.
• Polysaccharide function: (cellulose and glycogen) Cellulose- main structural component of cell walls, cellulose fibres and lignin form a matrix increasing the strength of the cell walls, this provides support for the plants. Glycogen- highly branched, stored in liver and muscle cells, more compact so can store large amounts- hydrolysis can occur rapidly.
• Iodine test for starch: add a few drops of orange/brown iodine to the sample, if starch is present the sample will turn blue/black.
• Lipids: non-polar and hydrophobic, insoluble in water. Two groups (triglycerides and phospholipids). Lipids play an important role in energy yield, energy storage, insulation and hormonal communication)
• Triglycerides: monomers= glycerol and fatty acids, Fatty acids can vary in two ways (length of the hydrocarbon tail, the fatty acid may be saturated (animal fat) or unsaturated (mainly vegetable oil))
• Phospholipids: 1 glycerol, 2 fatty acids, 1 phosphate group. As the phosphate is polar it the hydrophilic phosphate head, and hydrophobic fatty acid tails. are amphipathic (both polar and non-polar) can also form monolayers of bilayers in water.
• Esterification: The process that forms triglycerides, an ester bond forms when a hydroxyl group bonds with a carboxyl group, a H from the glycerol combines with OH from the fatty acid to make water. this is a condensation reaction that releases 3 water molecules.
• Lipids function: triglycerides are fats and oils (important for energy storage, insulation, buoyancy and protection) Energy storage (the long hydrocarbon chains are oxidised during cellular respiration causing bonds to break releases energy) insulation (triglycerides form parts of the myelin sheath and the adipose tissue layer which acts to insulate), Buoyancy (the low density of fat tissue increase the ability of animals to float),protection (the adipose tissue in mammals contains stores triglycerides and this tissue protects organs)
• Cholesterol: lipid found in the plasma membrane, have hydrophobic and hydrophilic regions, it affects the permeability and fluidity of the plasma membrane, it disrupts the close-packing of phospholipids increasing the rigidity of the membrane, it acts as a barrier to prevent water-soluble substances from diffusing across the membrane. Cholesterol is used to produce steroid-based hormones.
• Test for lipids: the emulsion test, lipids don't dissolve in water but can dissolve in ethanol, add equal amounts of ethanol and water and shake the solution, if lipids are present an milky emulsion will form, if no lipids are present the emulsion remains clear.
• Amino acids: 20 amino acids found in all proteins common to all living organisms. The general structure of all amino acids is a central carbon atom bonded to: an amine group (NH2), a carboxylic acid group (COOH), a hydrogen atom, an R group.
• Peptide bonds: covalent bonds formed between amino acids, a hydroxyl group is lost from one of the carboxylic group of one amino acid and a hydrogen atom is lost from the amine group. The remaining carbon bonds to the nitrogen atom of the second amino acid. This is a condensation reaction as water is released.
• Protein structure: 4 levels of structure: primary, secondary, tertiary, quaternary. Primary structure: sequence of amino acids in a polypeptide chain. Secondary structure: the folding of the polypeptide chain into a specific shape. Tertiary structure: the folding of the polypeptide chain into a specific shape. Quaternary structure: the folding of the polypeptide chain into a specific shape with other molecules.
• Secondary structure: forms when the weakly charged nitrogen and oxygen atoms interact with the weakly formed hydrogen atoms to form hydrogen bonds. Can form two shapes a-helix or b-pleated sheets. A-helix forms when when hydrogen bonds form between every 4th peptide bond, b-pleated sheet forms when two parts of the polypeptide chain are parallel to each other.
• Tertiary structure: further conformational change of the secondary structure lead to additional bonds forming between the R groups. The additional bonds are: hydrogen, disulphide (only for cysteine) , ionic and weak hydrophobic interactions.
• Quaternary structure: exists in proteins that have more than one polypeptide chain working together as a functional macromolecule. Each polypeptide chain in the quaternary structure is referred to as a subunit of the protein.
• Globular protein: are compact, roughly spherical in shape and soluble in water, non-polar hydrophobic R groups are orientated towards the centre of the protein, their polar hydrophilic R group orientate themselves on the outside of the protein, some are conjugated proteins that contain a prosthetic group.
• Examples of globular proteins: haemoglobin (4 polypeptide chains, with a prosthetic haem group, held by disulphide bonds, changes in the arrangement of the R group can result in properties changes- this causes sickle cell anaemia.), enzymes ( biological catalysts, catalyse- converts hydrogen peroxide to water and oxygen, amylase- hydrolyses starch into simple sugars.) insulin (control of blood glucose concentration, two polypeptide chains, three disulphide bridges)
• Fibrous proteins: long stands of polypeptide chains that have cross-linkages, insoluble (due to hydrophobic R groups), limited number of amino acids, due to repeated structure they are very strong which makes them suitable for structural roles.
• Example of fibrous proteins: Keratin (makes up hair, nails, horns and feathers), elastin (found in connective tissues, tendons, skin and bone), collagen (component of connective tissue, tendons, bones and cartilage, 3 polypeptide chains)
• inorganic ions: CATIONS Hydrogen (control pH, lots of H+ lower the pH, few H+ higher the pH), calcium ions (regulate the transmission of electrical impulses, can also stimulate muscle contract, is also essential in the formation of blood clots), iron II ( binds to oxygen in the haemoglobin, similar to myoglobin is muscles), iron III ( in respiration the iron ion switches between iron 3 to iron 2 to allow electrons to be accepted and donated.)
• Inorganic ions: CATIONS Sodium (required for co-transport of glucose and amino acids across plasma membranes, also transmission of nerve impulses), potassium (nerve transmission for repolarisation, reabsorption of water in the kidneys and the opening of the stomata), ammonium (forms in the deamination of proteins in the liver and kidneys)
• inorganic ions: ANIONS: nitrate (present in the soil, source of nitrogen for protein synthesis, required for growth and repair of plants), hydrogen carbonate (work alongside hydrogen ions in the transport of CO2 in the blood), Chloride ions (transport of CO2 in the blood, helps to maintain pH), phosphate (attach to molecules to form phosphate groups), hydroxide ions (bonding between biochemical molecules, electronegative charge of the oxygen allows for the formation of hydrogen bonds)
• Tests for proteins: biuret solution, contains an alkali and copper sulphate, the copper sulphate reacts in the presence of peptide bonds, add sodium hydroxide to ensure the solution is alkaline, then add the biuret solution. If proteins are present the sample will turn blue/ lilac.