OCR txt book: Enzyme - questions & answer included (with some popular exam questions)

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  • Created on: 12-06-13 21:49
Preview of OCR txt book: Enzyme - questions & answer included (with some popular exam questions)

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Enzymes
Enzymes
Summary question
Pg.32 topic 2.6
What is a catalyst?
A substance that alters the rate of a chemical reaction without undergoing
permanent change
Why are enzymes effective in tiny quantities?
They are not used up in the reaction and so can be used repeatedly.
Explain why changing one of the amino acids that make up the active site could
prevent the enzyme from functioning.
The changed amino acid may no longer bind to the substrate which will then not be
positioned correctly, if at all, in the active site.
Why might changing certain amino acid that is not part of the active side also
prevent the enzyme from functioning?
The changed amino acid may be one that forms hydrogen bonds with other amino
acids. If the new amino acid does not form hydrogen bonds the tertiary structure if
the enzyme will change, including the active site, so that the substrate may no longer
fit.
Pg. 35 topic 2.7
Explain why enzymes function less well at lower temperatures.
To function enzymes must physically collide with their substrate. Lower temperature
decrease the kinetic energy of both enzymes= and substrate molecules, which then
move around less quickly. They hence collide less often and therefore react less
frequently.
Explain how high temp. may completely prevent enzyme from functioning.
The heat causes hydrogen and other bonds in the enzymes molecule to break. The
tertiary structure of the enzymes molecule changes, as does the active site. The
substrate no longer fits the active site.
Enzymes produced by microorganisms are responsible for spoiling food. Using this
fact and your knowledge of enzymes, can you suggest a reason why the following
procedures are carries out?
a) Food is heated to a high temp. before being canned
High temperatures denature the enzymes and so they cannot spoil the food
b) Some foods, such as onions, are preserved in vinegar.
Vinegar is very acidic and the low pH will denature the enzymes and so preserve
the food
Pg.37 topic 2.8
1

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Enzymes
Distinguish between a competitive and a non-competitive inhibitor.
Competitive inhibitors occupy the active site of an enzyme while non-competitive
inhibitors attach to enzyme at a site other than the active site.
An enzyme-controlled reaction is inhibited by substance. Suggest a simple way in
which you could tell whether substance is acting as a competitive of non-competitive
inhibitor.
Increase the substrate concentration. If the degree of inhibitor is reduced it is a
competitive inhibitor, if it stays the same, it is a non-competitive inhibitor.…read more

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Enzymes
Explain why glucagon will only bind to one particular type of receptor molecule. [2]
Protein molecules have a different sequence to form a different tertiary shape (1)
The receptor molecule has a specific complimentary shape to protein to bind to. (1)
Suggest why glucagon is able to bind to liver cells but not to cells in other parts of
the body. [1]
Because the pH of the liver cell is different to other cells in body.…read more

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Enzymes
Changes shape of the enzyme (1)
Less successful collision and less enzyme-substrate complex form (1)
Some people are lactose intolerant because they don't produce enough lactase
enzymes in the small intestine. Lactose accumulates in the intestines and either
remains unhydrolysed or is converted to other soluble substances be bacteria in the
intestine. Explain how this lead to diarrhea in a lactose-intolerant individual.…read more

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