Biomolecules Tutorial answers (H1)

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 1 Full Name: Civics group: 21S Index no.: Date: Core Idea 1: The Cell and Biomolecules of Life Tutorial 2 Biomolecules - Carbohydrates MCQ 1 2 3 4 5 6 B B C A D A 9700 / 2010 / Nov - adapted 1 The equation shows a reversible reaction. In this reaction, what enzyme catalyses reaction 1 and what types of reaction occur at 1 and 2? enzyme reaction at 1 reaction at 2 A sucrase condensation hydrolysis B sucrase hydrolysis condensation C sucrose condensation hydrolysis D sucrose hydrolysis condensation 9700 / s2016 / QP12 / Q7 2 The diagrams show four monosaccharides with the formula C6H12O6. Which diagram shows α-glucose? ANS: B Thinking question: What is the term that describe these 4 monosaccharides having the same formula C6H12O6 but different structural arrangements? disaccharide monosaccharides = simple sugars β-glucose -OH group at the plane different from the α-glucose and β-glucose And β-glucose For general info only: (D) α-mannose For general info only: (C) α-allopyranose α-glucose Note: Remember for α-glucose =  

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 2 ANS: ISOMERISM Class Activity: Three monosaccharides condensed together to form a trisaccharide. How many glycosidic bonds does a trisaccharide have? Ans: Draw the condensation reaction of 2 α -glucose to self-check if you are able to understand and apply the concept of LO1(h)(i) ie the formation of glycosidic bonds. Note: Draw a disaccharide consisting of 2 β–glucose for a challenge. Ans: 9700 / 2005 / Nov 3 Which molecule in the key is sucrose? ANS: C 4 Which statements about amylopectin and cellulose are correct? 1 Both contain 1-4 glycosidic bonds. 2 Amylopectin contains β-glucose while cellulose contains α–glucose. 3 Both have cross-linkages. 4 Both are branched molecules. A 1 only B 1 and 2 only C 2 and 3 only D 3 and 4 only 5 carbon sugar 6 carbon sugar Note: Sucrose is a non-reducing sugar, that you must know. It is also comprised of 2 hexose sugars (Glucose & Fructose).

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 3 5 Which statement describes how the molecular structure of starch is suited to its function? A Amylose has a branched structure and amylopectin is coiled to give a compact molecule for transport.  amylose is coiled while amylopectin is coiled and branch. Further, amylose & amylopectin for storage, not for transport purpose B In the breakdown of amylose and amylopectin, many condensation reactions release stored energy.  breakdown is hydrolysis reaction C The helical s tructure of amylose and amylopectin gives starch high tensile strength. D The amylose-amylopectin complex is insoluble and does not affect the water potential of the cell. Correct! Suited for storage function N90/Q3 6 Five disaccharides were each hydrolysed with dilute acid , and the purified products were separated by one -dimensional chromatography. The final chromatogram is shown in the diagram below. If spot 1 represents the products obtained from the hydrolysis of sucrose, which one of the following indicates the results obtained from the hydrolysis of lactose and maltose ? Lactose Maltose A 2 3 B 2 4 C 5 2 D 5 3 glucose fructose galactose 1) You should know that: Sucrose = Glucose + Fructose Lactose = Glucose & Galactose Maltose = Glucose + Glucose 3) You should be able to deduce this 2) From results 2 to 5, you need to deduce which monosaccharide each spot in result 1 represents

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 4 STQ QUESTION 1 Starch grains in plant cells contain both amylose and amylopectin. (a) Explain how both of these substances are formed from glucose in plant cells. ………………………………………………………………………………………………. [2] 1 Condensation reaction whereby -glucose monomers are linked by (1, 4) glycosidic bonds in both, with the release of 1 water molecule per condensation reaction to form linear chains in amylose and amylopectin 2 Amylopectin is branched with its branch points linked by (1, 6) glycosidic bonds ; (b) 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. Fig. 4.1 shows the molecular structure of these disaccharides. Identify the disaccharides, labelled A to D, using the information below.  Cellobiose is formed from the hydrolysis of the polysaccharide cellulose . You can inferred from the mentioned of hydrolysis of polysaccharide [which has only β(1,4) glycosidic bond] that cellobiose has β(1,4) glycosidic bond.  When cellobiose is hydrolysed, two β-glucose molecules are produced.  One of the disaccharides is sucrose.  from content knowledge, sucrose is made up of glucose and fructose.  Trehalose is synthesized from two α-glucose molecules.  Maltose is formed from the hydrolysis of amylose, a component of starch.  from content knowledge, maltose is made up of α-glucose and α-joined together to form α(1,4) glycosidic bond. You can inferred from the mentioned of hydrolysis of amylose [which has only α(1,4) glycosidic bond] that maltose has α(1,4) glycosidic bond.

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 5 Write the name of the disaccharides in the spaces provided on Fig. 4.1. [4] Fig. 2.1 trehalose maltose cellobiose sucrose α-glucose α-glucose α-glucose α(1,1) glycosidic bond β(1,4) glycosidic bond β-glucose fructose is a 6C sugar but unique hexose which has pentagonal shape instead of hexagonal shape like glucose α-glucose

St Andrew’s Junior College The Cell and Biomolecules of Life / Carbohydrates 2021 H1 Biology 6 QUESTION 2 (2020 JC1 Common Test) Agarose forms part of a more complex carbohydrate called agar, which is used as a growth medi um for bacteria. Bacteria cannot use agarose in agar as a respiratory substrate. Fig. 2.1 shows a representation of part of the carbohydrate molecule called agarose, which is made up of repeating units of galactose. Fig. 2.1 (a) Identify the class of carbohydrate of which agarose is an example. ………………………………………………………………………………………..……... [1] 1. Polysaccharide; (b) Plants contain a carbohydrate called amylose. Compare the structures of agarose and amylose. ………………………………………………………………………………………..……... [4] Similarities: 1. monosaccharides of both agarose and amylose are held together by glycosidic bonds; 2. both agarose and amylose are unbranched; (R: large molecule unless mentioned linked by glycosidic bonds) Differences: 1. agarose is made up of galactose but amylose is made up α glucose (R: glucose); 2. coiled/helical structures in amylose but linear/straight structures in agarose; 3. alternate glucose is not inverted 180 o / same orientation in amylose but alternate galactose is inverted 180o in agarose; 4. α(1,4) glycosidic bond is present in amylose but different types of glycosidic bonds are present in agarose; Examiner’s Comments - Many students incorrectly stated the monomer of agarose is β-glucose despite the question stem stating it is made of repeating units of galactose. (precision) - Students incorrectly numbered the carbons in each sugar molecule hence were not able to deduce the correct nature of the glycosidic bond. (accuracy) - Students unable to identify the β glycosidic bond. As the –OH group of C1 of the sugar is point upwards, it is a β sugar molecule. (