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Homework  Enzymes Homework 1

Name:
Mark:     /  27
My targets to improve:

Q1.       (a)     What is an enzyme?
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The diagram shows stages during an enzyme-catalysed reaction.

(b)     Using the letters in the diagram, describe what is happening in this reaction.
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(Total 5 marks)
 Q2.   Gelatine is a protein. When a warm gelatine solution cools, it sets to form a jelly.
Fresh pineapple juice contains an enzyme that digests protein.
A student investigated the effect of pineapple juice on the setting of jelly.
He set up three different tubes of warm gelatine solution and recorded which had set after three hours. The contents of each tube and his results are shown in the table.
 
Tube | Contents of tube | Jelly formed
A | 6 cm^3  gelatine + 2 cm^3  pineapple juice + 2 cm^3  water | No
B | 6 cm^3  gelatine + 2 cm^3  pineapple juice + 2 cm^3  hydrochloric acid | Yes
C | 6 cm^3  gelatine + 2 cm^3  boiled pineapple juice + 2 cm^3  water | Yes
(a)     Explain why 2 cm^3 of  water was added to tubes A and C.
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(b)     Explain the results of
tube A ..........................................................................................................
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tube B ..........................................................................................................
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(c)     What was the purpose of tube C?
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 (3)  (Total 9 marks)
Q3.   The diagram shows the structure of the amino acid serine.

(a)     (i)      Draw a box on the diagram around the R group of serine and label the box with the letter R. (1)
(ii)     Draw a circle around each of the parts of the serine molecule which would be removed when two other amino acid molecules join directly to it. (1)
(b)     (i)      Which two substances are formed when two amino acid molecules join together?
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(ii)     Name the type of bond formed between the joined pair of amino acid molecules.
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(c)     Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure.
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(Total 7 marks)

Q4.   Lactose is a disaccharide sugar which can be broken down by the enzyme lactase into two monosaccharides, glucose and galactose.
lactase
lactose+ water  glucose + galactose
(a)     The formula for galactose is C_6H_12O_6. What is the formula for lactose?
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(2)
(b)     A solution containing the enzyme lactase was added to a lactose solution. The solution was incubated at 40 °C for one hour. Sample A was removed from the tube before incubation. Sample B was removed after one hour.
(i)      Describe a chemical test you could carry out on sample A to show that lactose is a reducing sugar.
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(2)
(ii)     This chemical test was carried out on samples A and B. All experimental variables were the same in the testing of the two samples. Both tubes were left for ten minutes to allow the precipitate to settle. The diagram shows the result.

Is galactose a reducing sugar? ....................
Explain how the results in the diagram support your answer.
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(2)
(Total 6 marks)

Carmel College