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Unit 3 Biological Molecules AS Unit F212 Context Proteins, carbohydrates and lipids are 3 of the key groups of macromolecules essential for life Understanding the structure of these macromolecules allows an understanding of their functions in living organisms Objectives Describe how hydrogen bonding occurs between water molecules, and relate this, and other properties of water to the roles of water in living organisms Covalent Bonding Bonding between non-metals Consists of atoms sharing electrons The electrons are in the outer shell Strong bonds, lot of energy is required to break them The number of covalent bonds is equal to eight minus the group number Hydrogen Bonding Water- a special case Covalent bonding is an electron sharing bond, and in this case the sharing is not equal. The oxygen gets more, giving it a slightly -ve charge δ- . Water as a solvent Water is an excellent solvent. The tiny charges attract other molecules. The other molecules and ions spread around in between the water molecules. This is called dissolving Many reactions, including metabolic reactions will only take place in solution Density and viscosity Water molecules are pulled together by the hydrogen bonds between them, this makes water a relatively dense liquid. Why is it easy for living organisms to swim? How might an organism have adapted to float or sink in water? How have organisms adapted to swim? Cohesion and surface tension Water molecules tend to stick together, this is called cohesion. Even in a tall column of water, forces holding the molecules to each other help to prevent the column from breaking. Within water each molecule is attracted to all the molecules around it. On the surface the uppermost molecules only have the molecules underneath so are pulled downwards. Surface Tension forming a strong layer on the surface of water. How does cohesion help with water transport in a plant? Water moves up each column by mass flow. Cohesion between the water molecules hold the column together. If the column broke, then the pulling force exerted by transpiration in the leaves would not be transmitted to the whole of the column and the water would not move up the plant in this way. Property Key Points Role of water Good solvent for charged and uncharged substances Water molecules are attracted to ions and polar molecules e.g glucose Transport in blood, xylem and phloem Specific heat capacity is high 4.2kj are necessary to increase the temperature of water by 1oC The thermal energy absorbed is used to break the hydrogen bonds Helps prevent changes in body temperature Latent heat of vaporisation is high Much thermal energy is used to cause water molecules to change to water vapour- this happens in transpiration in plants, and in sweating and painting in mammals Coolant- water is used efficiently, as a small amount of water absorbs much thermal energy High cohesion Hydrogen bonds ‘stick’ water molecules together Helps draw up water in xylem Can be reactive Water reacts with other substances Involved in hydrolysis reactions an in photosynthesis Incompressibility Outside pressure cannot force water into a smaller space Hydrostatic skeleton for some animals e.g. earthworms Provides turgidity in plant cells Starter activity Firstly, peer assess each others work using the markscheme provided. Mark with 2 stars and a wish State four functions of water in living organisms Briefly describe a water molecule Briefly describe what is meant by a polar molecule Why is water’s high specific heat capacity useful for living organisms? Starter activity State four functions of water in living organisms Briefly describe a water molecule Briefly describe what is meant by a polar molecule A molecule is polar if it has a negatively charged part and a positively charged part Why is water’s high specific heat capacity useful for living organisms? Exam question Water is essential for life. It makes up a high proportion of the cytoplasm in a cell. Many different compounds can dissolve in it and it is therefore described as an excellent . Water remains in the state over a wide range of environmental temperatures. As it cools below 4 °C it becomes less than warmer water. Ice floats on water, forming a layer that the water beneath with the result that large bodies of water rarely freeze entirely. The bonds that form between water molecules are responsible for its high , which allows small insects such as pond skaters to move on its surface without sinking. Exam question Water is essential for life. It makes up a high proportion of the cytoplasm in a cell. Many different compounds can dissolve in it and it is therefore described as an excellent . Solvent Water remains in the state over a wide range of liquid environmental temperatures. As it cools below 4 °C it becomes less than warmer water. Ice floats on water, forming a layer that the water beneath with the result that dense insulates large bodies of water rarely freeze entirely. The bonds that form between water molecules are hydrogen responsible for its high , which allows small Surface tension insects such as pond skaters to move on its surface without sinking. 8 marks You have been given an a sample of an unknown solution. Your task is to find out what biological molecules have been dissolved in the water. You must write a method for each biological test you carry out and a table of the results you collect. Condensation and hydrolysis reactions Objectives Describe with the aid of diagrams, the molecular structure of alpha-glucose Beta glucose Maltose Amylose Glycogen Cellulose Learning outcomes Describe, with the aid of diagrams, the molecular structure of alpha glucose as an example of a monosaccharide carbohydrate State the structural difference between alpha and beta glucose Week 13 Subunit structure of amylose and glycogen © Pearson Education Ltd 2008 This document may have been altered from the original Key terms Monosaccharide Disaccharide Polysaccharide Monomer Polymer Condenastion Hydrolysis Learning outcomes Describe, with the aid of diagrams, the formation and breakage of glycosidic bonds in the synthesis and hydrolysis of a disaccharide (maltose) and a polysaccharide (amylose) Compare and contrast the structure and functions of starch (amylose) and Cellulose Learning Outcomes Explain how the structures of glucose, starch (amylose), glycogen and cellulose molecules relate to their function in living organisms describe, with the aid of diagrams, the structure of an amino acid describe, with the aid of diagrams, the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides; explain, with the aid of diagrams, the term primary structure; Amino Acid structure H H N H Amine Group C R O C OH Carboxylic Acid group R group Changes for each amino acid H H N C H O N H + C R H H OH H N C H H H2O O H H C C C N R Peptide Bond R R O C OH O C OH Condensation Reaction Objectives explain, with the aid of diagrams, the term quaternary structure, with reference to the structure of haemoglobin; describe, with the aid of diagrams, the structure of a collagen molecule; Description or Diagram Primary structure Secondary Structure Tertiary Structure Quaternary Structure Examples Haemoglobin 4 polypeptides in each haemoglobin 2 x α globin subunits 2x β globin subunits Secondary structure- α helix Tertiary structure- further folding of polypeptide stabilised by hydrophobic interactions Quaternary structure An example of a Globular protein Made of 4 polypeptide chains which fit together and are held in place by hydrogen bonds and ionic bonds between R groups In the middle of each subunit is a haem group. Each haem group can combine with 1 molecule of oxygen so each molecule of haemoglobin can combine with 4 molecules of oxygen Collagen 3 identical chains per molecule of collagen All wound around each other forming a triple helix Each chain consists of about 1000 amino acids Primary structure- every 3rd a.a. is glycine, smallest Rgroup (1H) An example of a fibrous protein Collagen doesn’t show secondary, tertiary, or quaternary structure in the same way as globular proteins The sequences are staggered to allow glycine to be found at every position This allows the 3 chains to pack closely together, forming many hydrogen bonds Collagen The triple helix is left handed αhelix has a right hand turn No further folding to give 3d shape Adjacent molecules form covalent bonds between Rgroups Collagen forms fibres Crosslinks and hydrogen bonds give collagen its strength Globular and fibrous proteins Globular proteins Examples Haemoglobin, enzymes, Fibrous proteins Collagen, keratin, elastin antibodies, transporters in membranes, some hormones (e.g. insulin) Primary structure Very precise, usually made of a non-repeating sequence of amino acids forming a chain that is always the same length Often made up of a repeating sequence of amino acids, and the chain can be of varying length Solubility Often soluble in water Insoluble in water Functions Usually metabolically active, taking part in chemical reactions in and around cells Usually metabolically unreactive, with a structural role Lipids Include fats which tend to be solid at room temp Oils which tend to be liquid Produced mainly by animals Produced mainly by plants There are many exceptions to this rule Lipid structure Made of carbon, hydrogen and oxygen Higher proportion of hydrogen than carbohydrates Triglycerides 3 fatty acids attached to a molecule of glycerol Fatty acids contain a Carboxyl group -COOH hence their name Carboxyl groups of fatty acids are able to react with –OH (hydroxyl) groups of glycerol forming ester bonds Ester bonds involve covalent bonds and are very strong Condensation reaction Triglycerides Insoluble in water None of the atoms carry an electrical charge so are not attracted to water As they are not attracted to water they are said to be hydrophobic Saturated fat- the fatty acids all contain as much hydrogen as they can. Each carbon atom in the tail is linked to its neighbouring carbon atom by single bonds, whilst the other two bonds are linked to hydrogen atoms Unsaturated fat- one or more fatty acids in which at least 1 carbon atom is using 2 of its bonds to link to hydrogen. This double carbon-carbon bond forms a kink in the chain Cholesterol Cholesterol can be classified as a lipid. Not formed the same as triglycerides and phospholipids 4 carbon-based rings Found in all biological membranes Small narrow structure and has a hydrophobic nature Cholesterol and other chemicals with similar structures are called steroids Cholesterol Huge numbers of different kinds of steroids are found in the body Steroid hormones- testosterone, oestrogen and vitamin D As steroids they can pass directly through the phospholipid bilayer Also able to pass through the nuclear envelope (also made of a lipid bilayer) Many cells are able to produce cholesterol as it is vital to living organisms Triglycerol Saturated Unsaturated Saturated Unsaturated Diagram Composed of Any special bonds Reaction used to join components Role in body Hydrophobic/ Hydrophillic Phospholipid Cholesterol & Steroids Enzymes