2_biomolecules.pdf

2 Biomolecules 2.1 Testing for biomolecules equal volumes of sample and Biuret reagent are mixed Food tests if proteins are present, the co...

2 Biomolecules 2.1 Testing for biomolecules equal volumes of sample and Biuret reagent are mixed Food tests if proteins are present, the colour changes from blue to lilac 1) Reducing sugars instead of biuret reagent, KOH and dil. CuSO4 can be reduce soluble blue copper sulphate containing copper used (II) ions to insoluble brick-red copper oxide, containing copper (I) For extra details on performing food tests, see paper 3 the copper oxide is seen as a brick-red ppt notes. 2.2 Carbohydrates and lipids All living organisms are made of C, H, O + N molecules. add equal volumes of Benedict’s reagent and the food sample to a test tube Carbohydrates heat in a water bath at 80°C composed of C, H, O if reducing sugars are present, the following colour divided into monosaccharides, disaccharides, changes are observed: polysaccharides monomer – one of many small molecules that combine to form a polymer, e.g. – monosaccharides, 2) Non-reducing sugars amino acids, nucleotides e.g., sucrose polymer – large molecule made from many similar disaccharide is first broken down into its 2 repeating subunits, e.g. – polysaccharides, proteins, monosaccharide constituents in a hydrolysis reaction nucleic acids this is done by adding HCl, and then neutralising the acid with an alkali such as sodium bicarbonate macromolecule – large molecule formed due to constituent monosaccharides will be reducing sugars polymerisation of monomers, e.g. – polysaccharides, and their presence can be tested by Benedict’s test proteins (polypeptides), nucleic acids (polynucleotides) 3) Starch Monosaccharides add drops of iodine solution to the sample Molecule consisting of a single sugar unit with the general if blue-black colour is quickly produced, starch is formula C(H2O)n present dissolves in water iodine solution is yellow brown main types of monosaccharides – trioses (3C), pentoses (5C), hexoses (6C) 4) Lipids (emulsion test) glucose, fructose galactose, ribose, deoxyribose sample is shaken with ethanol HEXOSES PENTOSES any lipids present will dissolve mixture of ethanol and sample is poured into a beaker containing water if lipids are present, a cloudy-white suspension is formed due to the lipids being unable to remain dissolved when mixed with water therefore, the lipid molecules form droplets throughout the liquid, this kind of mixture is called the emulsion Image: https://tlamjs.com/2017/01/13/biological-molecules-carbohydrates/ Roles of monosaccharides 5) Proteins (Biuret test) 1) source of energy in respiration – C-H bonds can be all proteins have peptide bonds containing nitrogen broken to release a lot of energy which is atoms which form a purple complex with Cu2+ ions transferred to help make ATP from ADP 1 www.alevel-notes.weebly.com 2) building blocks for larger molecules – glucose is uses chains are shorter than to make the polysaccharides starch, glycogen, and long, unbranching chain amylose and branch out to cellulose; ribose is one of the molecules used to make sides RNA and ATP, deoxyribose is one of the molecules used to make DNA chains are curved and coil into helical branches are formed by 1-6 Disaccharides structures making the linkages final molecule more Sugar molecule consisting of 2 monosaccharides joined compact by a glycosidic bond. 2) Glycogen made of chains of 1-4 linked ⍺-glucose molecules with 1-6 linkages forming branches tend to be more branched than amylopectin molecules many ends due to branching aids in easy addition and removal of glucose compact and insoluble, doesn’t affect the water potential (Ψ) 3) Cellulose → polymer of β-glucose in order to form a glycosidic bond with the 4th carbon Image: https://dopeahmeanbio.wordpress.com/tag/glycosidic-bonds/ atom where the OH group is below the ring; every H2O molecule is removed; the bond formed by other glucose is rotated 180° condensation is called a glycosidic bond so successive glucose molecules are linked 180° to each other Polysaccharides one oxygen is up and the other is down A polymer whose subunits are monosaccharides joined the molecules are still linked 1-4 by glycosidic bonds e.g., starch, glycogen, cellulose (all polymers of glucose) not sugars if glucose itself accumulated in cells, it would dissolve and make the contents of the cell too concentrated which affects its osmotic properties cellulose molecules become tightly cross-linked to storage polysaccharides – convenient, compact, form bundles called microfibrils inert, insoluble microfibrils are held together in bundles called fibres by hydrogen bonding 1) Starch à amylose + amylopectin cellulose fibres have very high tensile strength – this AMYLOSE AMYLOPECTIN makes it possible for a cell to withstand large pressures as a result of osmosis cellulose fibres, despite their strength, are freely permeable Image: http://futurefoodchemist.weebly.com/ Image: https://www.e-education.psu.edu/ made by condensation reactions between 1,4 also made of 1,4 linked ⍺- linked ⍺-glucose glucose molecules molecules Image: unknown 2 www.alevel-notes.weebly.com Dipoles and hydrogen bonds Alcohols & Esters unequal distribution of charges in a covalent bond is alcohols contain hydroxyl group (–OH) attached to C called a dipole atom molecules which have groups with dipoles are polar reaction between (fatty) acid (–COOH) and alcohol (– OH) produces an ester the chemical link between acid and alcohol is called an ester linkage/bond and is formed by a condensation reaction Image: https://alevelbiology.co.uk/notes/dipoles-of-water-molecules/ in water, oxygen atom gets more electrons due to it being more electronegative and therefore gets a small negative charge denoted by delta (𝛅-) hydrogen atoms get less electrons and therefore get small positive charges (𝛅+) Image: https://revisionscience.com/ glyceride is an ester formed by a fatty acid combining with the alcohol glycerol (C3H8O3) glycerol has 3 hydroxyl groups; each one is able to undergo a condensation reaction with a fatty acid Image: https://courses.lumenlearning.com/cheminter/chapter/hydrogen-bonding/ triglycerides are insoluble in water due to the non- negatively charged oxygen of one molecule is polar nature of hydrocarbon tails – they don’t have attracted to a positively charged hydrogen of uneven distribution of charges and are hydrophobic another, this attraction is called a hydrogen bond Roles of triglycerides Molecules which have groups with dipoles are polar energy reserves they’re attracted to H2O molecules as they also insulator have dipoles and are considered to be hydrophilic protect vital organs (water-loving) soluble in water e.g., glucose, amino acids, NaCl 2.3 Proteins and water Proteins Molecules which do not have dipoles are non-polar All proteins are made from the same monomer - amino acids. they’re not attracted to water and hydrophobic (water-hating) insoluble in water e.g., oils, cholesterol Lipids → 3 Fatty Acids + 1 Glycerol Fatty acids contain the acidic group –COOH Image: https://beautiflworid.com/do-protein?print=print larger molecules in the series have long hydrocarbon tails attached to the acid which are 15- 17 carbon atoms long Amino acids of two types: saturated and unsaturated All have a central carbon atom bonded to – unsaturated fatty acids have C=C double bonds an amine (–NH2) group therefore don’t have maximum amount of hydrogen a carboxylic group (–COOH) atoms a hydrogen form unsaturated lipids a R-group that determines what type of amino acid it mostly liquid is 3 www.alevel-notes.weebly.com The peptide bond Image: https://www.khanacademy.org/ Bonds in the tertiary structure Image: https://www.drawittoknowit.com/ a molecule made up of many amino acids linked together by peptide bonds is a polypeptide polypeptides can be broken down to amino acids by Image: By WikiComTD - Own work, CC BY-SA 4.0, breaking the peptide bonds in a hydrolysis reaction https://commons.wikimedia.org/w/index.php?curid=79148318 this happens naturally in the stomach and small intestine during digestion PROTEINS Structures of proteins GLOBULAR FIBROUS spherical/balled shaped curl up so that their non- polar, hydrophilic R- groups point to the centre of the molecule away proteins that form long from watery surroundings strands polar, hydrophilic R- groups are on the outside which makes mixing + dissociating in water easier usually not soluble in usually soluble water precise shape, have roles in metabolic activities and are have structural roles specific in nature e.g., enzymes, haemoglobin, e.g., keratin, actin, myoglobin myosin, collagen 4 www.alevel-notes.weebly.com Haemoglobin: a globular protein helical polypeptides are wound together creating a triple helix made of 4 polypeptide chains therefore they have a quaternary structure strands are held together by hydrogen and some covalent bonds 2 of the haemoglobin chains, ⍺-chains, are made of ⍺- globin every 3rd amino acid in each polypeptide chain is glycine the other 2 chains, β-chains, are made of β-globin each 3 stranded molecule interacts with other each polypeptide chain has a haem group attached collagen molecules running parallel to it (prosthetic group) to it covalent bonds form between R-groups of amino haem contains charged particle of iron acids the haem group is also responsible for the colour of these cross-links hold many collagen molecules side haemoglobin by side forming fibrils many fibrils lie alongside each other forming strong bundles called fibres collagen is flexible but has tremendous tensile strength collagen fibres line up according to the forces they withstand each polypeptide chain can carry one molecule of oxygen therefore, in total, haemoglobin can carry 4 molecules of oxygen or 8 oxygen atoms Collagen: a fibrous protein found in skin, tendons, cartilage, bone, teeth, etc. a structural protein collagen molecule consists of 3 polypeptide chains, each in a helical shape Image: https://rosemarycottageclinic.co.uk/ 5 www.alevel-notes.weebly.com