Eduqas Biology for A Level Book 1: 2nd Edition

It is usual to show the arrangement of the atoms using a diagram known as a structural formula. Structural formula of Structural formula of ribose, a pentose, C 5 H 10 O 5 a triose, C 3 H 6 O 3 Structural formulae of straight chain and ring forms of glucose, a hexose Monosaccharides have several functions and can act as: ▪ A source of energy in respiration. Carbon–hydrogen and carbon–carbon bonds are broken to release energy, which is transferred to make adenosine triphosphate (ATP). ▪ Building blocks for larger molecules. Glucose, for example, is used to make the polysaccharides starch, glycogen, cellulose and chitin. ▪ Intermediates in reactions, e.g. trioses are intermediates in the reactions of respiration and photosynthesis. ▪ Constituents of nucleotides, e.g. deoxyribose in DNA, ribose in RNA, ATP and ADP. H C C 1 2 O Fig 01 OH H C 3 H HO C 4 OH H C 5 OH H CH 2 OH 6 6 CH OH 5 C O H H OH 4 C or, more simply α -glucose H OH 1 C OH 3 C H H 2 C OH O OH OH OH OH CH OH 6 CH OH 5 C O H H OH 4 C or, more simply β -glucose OH H 1 C OH 3 C H H 2 C OH O OH OH OH OH CH OH glucose straight-chain form with C atoms numbered C C H H O OH H OH C H drawn more simply H H H OH OH CH 2 OH C H C C C O OH OH OH CH 2 OH O OH Stretch & challenge A molecule is a three-dimensional structure but a structural formula is in two dimensions on the page. When a bond is drawn pointing upwards, it means that the group it is attached to is above the plane of the drawing, and if it is drawn pointing downwards the group is below the plane. Look at the atoms attached to carbon atom 1 (C1) on α -glucose and on β -glucose and describe the difference. Link You will learn about the reactions of respiration and photosynthesis in the second year of this course. Exam tip You will not be asked to draw the structural formulae of carbohydrates in an examination, but you may be asked to identify them and be asked questions about them, so it is important to understand them. Eduqas Year 1/AS Biology 16