enzyme pt 2 Flashcards
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 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 water
No
B
6 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 hydrochloric acid
Yes
C
6 cm3 gelatine + 2 cm3 boiled pineapple juice + 2 cm3 water
Yes
(
(4)
(c) What was the purpose of tube C?
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(Extra space) ________________________________________________________
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) For comparison / as a control;
To show that it is an enzyme in pineapple that digested gelatine /
stopped gelatine setting in tube 1;
Boiling denatures enzyme / Can be described but must be
permanent change;
Other components of pineapple still present;
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 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 water
No
B
6 cm3 gelatine + 2 cm3 pineapple juice + 2 cm3 hydrochloric acid
Yes
C
6 cm3 gelatine + 2 cm3 boiled pineapple juice + 2 cm3 water
Yes
(a) Explain why 2 cm3 of water was added to tubes A and C.
To keep concentrations of gelatine constant;
Accept ‘to keep concentration constant’ for /
mark if points 1 and 2 not made
To keep concentration of pineapple extract constant;
Tube 2 had HCI added / to give same volume as B;
Explain why the rate of reaction of enzyme B is low at pH 5.
(change in pH) leads to breaking of bonds holding tertiary structure / changes charge on amino acids;
enzyme / protein / active site loses shape / denatured; substrate will not bind with / fit active site / fewer / no ES complexes formed;
The maximum rate of reaction with an incubation time of 60 minutes is less than the maximum rate of reaction with an incubation time of 5 minutes. Explain why.
Bonds (holding tertiary structure) broken;
More enzyme denatured / tertiary structure destroyed /
active sites lose shape / no longer fit;
Fewer enzyme-substrate complexes formed
What colour would you expect the sample to go when tested with biuret reagent?
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(1)
(iii) Give an explanation for your answer to part (ii)
i In an investigation, the enzyme amylase was mixed in a test tube with a buffer solution and a suspension of starch. The amylase broke down the starch to maltose. When all the starch had been broken down, a sample was removed from the test tube and tested with biuret reagent.
Protein present / the enzyme / amylase is a protein;
Not used up in the reaction / still present at the end of
the reaction;
Catalase is an enzyme. It catalyses the breakdown of hydrogen peroxide in the reaction:
2H2O2 → 2H2O + O2
hydrogen water oxygen
peroxide
In an investigation, samples of different substances were added to hydrogen peroxide in a series of test tubes. The rate of reaction was measured by recording the rate at which bubbles of oxygen were produced. A scale going from 0 for no bubbles to 5 for the maximum rate of bubbling was used to measure this. The results are shown in the table.
Tube
Substance added
Rate at which bubbles of
oxygen were produced
A
Piece of liver
4
B
Ground liver and sand
5
C
Sand
0
D
Piece of cooled, boiled liver
0
(a) Explain the difference between the rate at which bubbles were produced in.
(i) tubes A and B;
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(2)
(ii) tubes A and D.
Explain the purpose of tube C.
test tubes A and B became warmer when the reaction was taking place.
(Grinding) breaks open cells / increases surface area (of liver);
Releases catalase / enzyme / more catalase / allows more hydrogen peroxide into liver;
2
(ii) Heating causes bonds (maintaining tertiary structure) to break;
Denatures / changes tertiary structure so active site changed;
Substrate no longer fits / ES complex not formed;
(Control) to show that sand did not affect reaction (with ground liver);
Energy in products / water and oxygen less than energy in substrate / reactants / hydrogen peroxide;
(Difference) given out as heat / exothermic;
Gout is a painful condition caused by uric acid crystals in the joints. It is often treated with a drug that inhibits xanthine oxidase. The diagram shows a molecule of xanthine and a molecule of this drug.
Xanthine Drug used
to treat gout
Use the diagram to explain why this drug is effective in the treatment of gout.
Xanthine similar shape to drug;
Drug fits active site / competes for active site / is a competitive inhibitor;
Less / no uric acid formed;
