2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 368 questions
shows the breakdown of a molecule of sucrose. HOCH2 H2O HOCH2 T O O O O HOCH2 HOCH2 HO OH α-glucose fructose CH2OH CH2OH O Name the bond indicated by T. State the name given to this type of reaction in which water is involved. State two roles of water within plant cells other than taking part in breakdown reactions. 1. 2. Enzymes are globular proteins. State what is meant by the term globular. The reaction shown in is catalysed by the enzyme sucrase. shows an enzyme-catalysed reaction. U substrate Name the part of the enzyme labelled U. With reference to , explain the mode of action of enzymes.
9700_s10_qp_21
THEORY
2010
Paper 2, Variant 1
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Polysaccharides are synthesised by condensation reactions between monosaccharide or disaccharide subunits . Name the type of bond formed when polysaccharides are synthesised. Disaccharides are formed following synthesis from monosaccharides or as a result of polysaccharide hydrolysis. Cellobiose, maltose, sucrose and trehalose are four different disaccharides found in nature. shows the molecular structure of these disaccharides. Identify the disaccharides, labelled A to D, using the information below. • The disaccharide cellobiose is formed from the hydrolysis of the polysaccharide cellulose. • When cellobiose is hydrolysed, two β-glucose molecules are produced. • One of the disaccharides is sucrose. • Trehalose is a disaccharide that is synthesised from two α-glucose molecules. • The disaccharide maltose is formed from the hydrolysis of amylose, a component of starch. Write the name of the disaccharides in the spaces provided on . In some organisms, trehalose is used as an energy store and gives protection against the harmful effects of very low temperatures. Trehalose is sometimes referred to as a cryoprotectant, allowing organisms to survive in freezing conditions. Freezing temperatures can damage the cell surface membrane and membranes within the cell. Explain the importance of the cell surface membrane to cells. Freezing temperatures can also completely stop enzyme activity by causing the molecules to undergo ‘cold denaturation’. Enzyme activity is not recovered when temperatures are increased to a normal working temperature range. Explain the mode of action of enzymes. Suggest how the molecular structure of the enzyme changes during ‘cold denaturation’. Cryoprotectants, such as trehalose, are of particular interest in their application to preserving cells, tissues or organisms for future use. An investigation was carried out to find the protective effect given by different concentrations of two cryoprotectants, trehalose and glycerol, on a respiratory enzyme. The enzyme was subjected to a freezing temperature and then returned to its optimum temperature. The activity of the enzyme was measured at its optimum temperature. is a graph showing the results of the investigation. cryoprotectant concentration / mmol trehalose glycerol percentage of maximum activity With reference to , describe the results of the investigation.
9700_s13_qp_22
THEORY
2013
Paper 2, Variant 2
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Questions Discovered
368