B1 Enzymes

Question 1

State the order of amino acids coded for by this sequence of DNA

Answer 1

MET VAL LYS

Question 2

during which stage of protein synthesis will this take place

Answer 2

translation

Question 3

explain the role of the active site of an enzyme

Answer 3

• to bind to substrate and form enzyme substrate complex

- for reactions to take place

Question 4

explain why phenolphthalein turns colourless when lipase breaks done lipids in milk

Answer 4

• fatty acids formed when lipids are broken down by lipase

- fatty acids are acidic

Question 5

describe effect of temperature on on activity of lipase

Answer 5

• as temp increases from 20-37c rate of lipase activity increases

rate of lipase activity is optimal at 37c

• above 37c rate of lipase decreases from 0.8-0.1

Question 6

explain why activity of lipase changes above temperature of 40

Answer 6

• increase in temp above 40 causes change in shape of active site of the enzyme
• so enzyme becomes denatured, cannot fit substrate and changes irreversibly

Question 7

rate of reaction when only time is given

Answer 7

1/time

Question 8

investigation was done at 37c

state one variable that student should have controlled

Answer 8

• concentration of the enzyme

Question 9

explain why enzymes only catalyst at specific reactions

Answer 9

• active site of enzyme has a specific shape because of order of the amino acids
• substrate must have a shape which is complementary to the active site

Question 10

explain how the lock and key hypothesis shows how enzymes work

Answer 10

• enzyme and substrate have complementary shapes
• substrate fits into enzymes active site to form enzyme substrate complex
• causes reactions to occur
• products leave enzyme so enzyme can be used again

Question 11

describe how named factors affect rate of enzyme catalysed reactions

Answer 11

Temperature:

• too low =not enough energy for reaction to occur
• optimum temperature means fastest rate of reaction
• over optimum means enzyme active site irreversibly changes shape
• cannot fit substrate so rate of reactions slows down and eventually stops
• denatures

pH:

• as above but with pH

Substrate/Enzyme concentration:

• higher concentrations = faster reactions
• more collisions because of more particles
• more frequent = more successful until all enzymes used up