Topic B Biomolecules H1H2 2015 Lecture(Teachers)

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules J1/2015 1 TOPIC B: BIOMOLECULES Learning Outcome Candidates should be able to Core Topic 1 – Cellular Functions (c) Describe the formation and breakage of a glycosidic bond. (d) Analyse the molecular structure of a triglyceride and a phospholipid, and relate these structures to their functions in living organisms. (e) Describe the structure of an amino acid and the formation and breakage of a peptide bond. (f) Explain the meaning of the terms primary structure, secondary structure, tertiary structure and quaternary of proteins, an d describe the types of bonding ( hydrogen, ionic, disulfide and hydrophobic interactions) which hold the molecule in shape. (g) Analyse the molecular structure of a protein with a quat ernary structure e.g. haemoglobin, as an example of a globular protein, and of collagen as an example of a fibrous protein, and relate these structures to their functions. Core Topic 6 – Cellular Physiology and Biochemistry (f) Compare the storage and structural forms of starch, glycogen and cellulose and their roles in plants and animals. Content Outline 1. Introduction 2. Carbohydrates (a) Monosaccharides (b) Disaccharides (c) Polysaccharides 3. Lipids (a) Triglycerides (b) Phospholipids (c) Steroids and Sterols 4. Proteins (a) Amino acids (b) Structure of protein (c) Types of protein (d) Denaturation References 1. Campbell, N. A. and Reece J.B. (2008) Biology Eighth edition. Chapter 5: The Structure and Function of Large Biological Molecules. Pearson Education, Inc 2. Clegg, C. J. and MacKean, D. J. (2000) Advanced Biology, Principles and Applications. Second edition. Chapter 6: The Chemistry of Living Things. John Murray (Publisers) Ltd. 3. Jones, M. and Jones, G. (20 04) Advanced Biology. Chapter 1: The Molecules of Life. Cambridge University Press. 4. Voet, D. and Voet, J.G. (2004) Biochemistry Thrid edition. Chapter 8: Three -dimensional Structures of Protein. John Wiley and Sons, Inc. 5. Taylor, D. J. , Green, N. P. O. an d Soper, R. (2001) Biological Science 1. Third Edition. Chapter 3: Chemicals of Life. Cambridge University Press. 6. Roberts, M. , Reiss, M. and Monger, G. (2000) Advanced Biology. Chapter 2: The Chemicals of Life. Nelson.

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 2 1. Introduction Cells and their contents are built up by many biomolecules. The structure and function of these molecules are essential to the working of the cell and life itself. Some important biomolecules and their functions are:  Carbohydrates: main energy source and storage  Lipids: main component of cell membrane and energy storage  Proteins: structural and enzymatic function  Nucleic acids: store and transmit hereditary information The monomers (basic units) of important biomolecules 2. Carbohydrates Carbohydrates are the most abundant class of biomolecules. They contain the eleme nts carbon, hydrogen and oxygen in the ratio of C:H:O = 1:2:1 . Their general formula is (CH2O)n, where n = number of carbon atoms. There are three main classes of carbohydrates namely: (a) Monosaccharides  Glucose  Fructose (b) Disaccharides  Maltose (glucose + glucose)  Sucrose (glucose + fructose)  Lactose (glucose + galactose) (c) Polysaccharides  Starch (monomer: α-glucose)  Glycogen (monomer: α-glucose)  Cellulose (monomer: β-glucose) Biomolecules Monomers (the basic units) Carbohydrates Sugars (saccharides) Lipids Fatty acids and glycerol Proteins Amino acids Nucleic Acids Nucleotides

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 3 (a) Monosaccharides Monosaccharides are simple sugars, which are the monomers that make up disaccharides and polysaccharides. They are classified according to the number of carbon atoms such as trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C). They function mainly as energy sources as they contain many carbon -hydrogen bonds (C—H), which release energy when they are oxidised. They also act as building blocks for the synthesis of larger molecules. Biologically Important Monosaccharides (i) Structure of monosaccharides  General formula: (CH 2O)n, where number of C atoms present, n > 3. E.g. Glucose: C6H12O6  Has a carbonyl group (C=O) and multiple hydroxyl groups (-OH). The C=O group is part of the aldehyde group or ketone group.  A monosaccharide is either an aldose (with aldehyde group) or ketose (with ketone group). No. of C atoms General Name Chemical Formula Examples Functions 3 Triose sugar C3H6O3 Glyceraldehyde Intermediate compound in respiration and photosynthesis 5 Pentose sugar C5H10O5 Ribose Component of RNA and ATP Deoxyribose Component of DNA 6 Hexose sugar C6H12O6 Glucose Main source of energy for cellular respiration. Fructose An energy source. Component of sucrose. Galactose Component of lactose. Found in dairy products.

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 4 Structures of monosaccharides Aldoses (aldehyde sugars): Carbonyl group at the end of carbon skeleton. Ketoses (ketone sugars): Carbonyl group within carbon skeleton. (ii) Properties of monosaccharides  Physical properties: Monosacch arides are sweet, soluble and have crystalline structures.  Chemical Properties: All monosaccharides are reducing sugars meaning they can carry out a chemical reaction called reduction.  They contain either a free aldehyde or ketone group that donates electrons to reduce Cu2+ to Cu+ in the Benedict’s test.  Carbonyl carbon is oxidized to carboxyl group. Ionic equation: Cu2+ + e-  Cu + Orange-red suspension Blue solution

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 5 Sugars as reducing agents Oxidation of the glucose and other sugars is the basis for Benedict’s reaction. The copper (Cu +) produced under alkaline conditions forms a red oxide precipitate. In the ring form, C-1 of glucose cannot be oxidised by Cu 2+. However, the open -chain form is in equilibrium with the ring form, and eventually the oxidation reaction goes to completion. (iii) Benedict’s test  Add 2cm3 of Benedict’s solution to 2cm 3 of sample solution in a t est tube and mix.  Place test tube in a boiling water bath for 2 minutes.  If reducing sugar is present, the blue solution turns varying from green, yellow - orange, orange to orange-red suspension as the concentration of reducing sugar increases.  By measuring the amount of oxidising agent reduced by a solution of a sugar, it is also possible to estimate the concentration of that sugar.  Therefore, Benedict’s test is both a qualitative and quantitative test. Range of colours for the Benedict’s test corresponding to the relative amounts of reducing sugar

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 6 (iv) Examples of Monosaccharides  Glucose It is the most abundant hexose sugar and the main respiratory substrate for all living things.  Structure o Chemical formula of C6H12O6 o In solution, glucose alternates between straight chains and ring structures freely. It exists mainly in the ring structures (more stable) and only a small proportion of the molecules exist in the straight chain at any one time. o The ring structure is the form in which glucose molecules combine to form maltose (disaccharide) and starch or glycogen (polysaccharides). Structures of the open chain form and α and β ring structures of glucose The three forms exist in equilibrium in aqueous solution, with 0.02% open chain, 36% α glucose and 64% β glucose.

NANYANG JUNIOR COLLEGE H1/H2 Biology Biomolecules Carbohydrates J1/2015 7 o There a