Question). i) Which carbohydrate storage molecules can be found in the cells of

Question

Question). i) Which carbohydrate storage molecules can be found in the cells of animals and plants, and ii) why do cells use large homopolymers to store energy rather than monosaccharides?

(1 mark)

Question). Could the purity of cellulose be estimated using the same method, acid hydrolysis, as used to estimate the purity of glycogen during practical 5? (no more than 100 words; use key words)

Yes     No

(1 mark)

Question) You are given a drink that you are told is sweetened with either maltose or lactose. Using the following resources explain how you would test if the drink was sweetened with either lactose or maltose? Explain the carbohydrate chemistry behind the test to justify your answer.

The only (!) resources available to you include:

the drink

the enzyme lactase

the Somogyi-Nelson reagents for the determination of reducing sugars.

(2 marks)

i) concisely describe the tests that you would use:

(1.0 marks)

ii) describe the observations that would be made if the drink contained maltose:

(0.5 marks)

iii) describe the observations that would be made if the drink contained lactose

(0.5 marks)

Explanation / Answer

Answer

1

i) The carbohydrates stored in the animals cells is glycogen and in plant cells the stored carbohydrate molecule is starch. These carbohydrates are linear homopolymers of glucose which are linked by alpha-glycosidic bonds.

ii) The cells use large homopolymers to store energy rather than monosaccharides because the monosaccharides can disrupt the osmolarity of cell. Furthermore, the branching allows for quick mobilization and provides a number of ends for which acts as sites for liberation of sugars and quick access for stored sugars.

2

In acid hydrolysis method, glycogen is treated with 2M HCl. By introducing dilute HCl, the alpha-glycosidic bonds of glycogen will be easily hydrolyzed. However, when cellulose is treated with HCl, the beta-glycosidic bonds of cellulose are not hydrlyzed in fact they remained very stable and intact. Therefore, the purity of cellulose cannot be estimated by same method of acid hydrolysis for glycogen.

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