A level Bio 1.4 Proteins& Enzymes Part II

Hydrolysis of ATP is catalysed by the enzyme ATP hydrolase. box A student investigated the effect of ATP concentration on the activity of ATP hydrolase. She used shortening of strips of muscle tissue caused by contraction as evidence that ATP was being hydrolysed.

• She took four slides A, B, C and D, and added strips of muscle tissue of the same length to each slide.

• She then added the same volume of ATP solutions of different concentrations to the four slides and left each slide for five minutes.

• She then recorded the final length of each strip of muscle tissue. Her results can be seen in Table 1.

Other than those given, name two variables the student should have controlled. (2)

Species/organism the muscle tissue came from (1)

Temperature of the muscle tissue (1)

Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. (2)

Endopeptidases hydrolyse internal (peptide bonds) (1)

More ends or increase in surface area (for exopeptidases) (1)

Scientists have investigated the effects of competitive and non-competitive inhibitors of the enzyme maltase.

Describe competitive and non-competitive inhibition of an enzyme. (6)

Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex (1)

(Competitive inhibition)
Inhibitor has a similar shape to substrate (1)

It binds into active site (of enzyme) (1)

(Inhibition) can be overcome by more substrate (1)

(Non-competitive inhibition)

Inhibitor binds to the allosteric site of an enzyme (1)

enzyme’s active site changes (1)

The scientist used the same concentration of endocellulase and exocellulase in the mixtues. The rate of digestion of cellulose is greatest when both enzymes are present. Suggest why (2)

Endocellulose creates more ends/increases surface area (1)

for exocellulose to act on (1)

Yarrow is a herbaceous plant which grows in California at altitudes from 1500 m to 3000 m. The mean height of the stems of plants growing at 3000 m is smaller than that of plants growing at 1500 m.

The higher the altitude, the lower the mean temperature. Explain how the lower temperature at high altitude reduces the growth of plants. (4)

lower enzyme activity (1)

decrease in rate of photosynthesis so less carbohydrate formed (1)

Lower respiration (1)

lower rate of protein synthesis (1)

The relative contribution of environmental and genetic factors on the growth of the plants was investigated. Samples of young plants were taken and grown outdoors in prepared plots at altitudes of 1500 m and 3000 m.

 

Altitude at which young	Mean maximum height of stems of plants / cm
plants were collected / m	Grown at 1500 m	Grown at 3000 m
1500	80.4	35.3
3000	31.5	24.7

Describe the evidence from the table that the variation in height is partly genetically determined (1)

differ in height when plants from different altitudes grown
in same environment (1)

The relative contribution of environmental and genetic factors on the growth of the plants was investigated. Samples of young plants were taken and grown outdoors in prepared plots at altitudes of 1500 m and 3000 m.

 

Altitude at which young	Mean maximum height of stems of plants / cm
plants were collected / m	Grown at 1500 m	Grown at 3000 m
1500	80.4	35.3
3000	31.5	24.7

Describe the evidence from the table that the variation in height is partly environmentally determined (1)

plants from 1500 / 3000m differ in height when grown at different

altitudes

In an investigation, the rate at which phenol was broken down by the enzyme phenol oxidase was measured in solutions with different concentrations of phenol. The experiment was then repeated with a non-competitive inhibitor added to the phenol solutions. The graph shows the results.

Explain why an increase in concentration of phenol solution from 2.0 to 2.5 mmol dm^-3 has no effect on the rate of reaction without inhibitor (2)

maximum rate at which enzyme can combine with substrate / form enzyme-substrate complexes (1)

(active site of) enzyme saturated with substrate (1)

Doctors investigated babies who were bottle-fed with baby-formula milk and suffered from colic. Colic is a condition that affects the gut and makes babies cry.

Each mother was given two solutions to add to her baby’s milk. One solution contained the enzyme lactase, the other did not. The mother did not know which solution contained lactase. The mother added one of the solutions to her baby’s milk for a week and recorded how long it cried each day. The mother then used the other solution for the second week.

	Mean crying time / hours day–1
Milk with lactase	1.43
Milk without lactase	2.57

 Suggest an explanation for the results (2)

Babies may have lactose intolerance (1)

Lactose (in milk) causes colic/crying/discomfort (1)

Doctors investigated babies who were bottle-fed with baby-formula milk and suffered from colic. Colic is a condition that affects the gut and makes babies cry.

Each mother was given two solutions to add to her baby’s milk. One solution contained the enzyme lactase, the other did not. The mother did not know which solution contained lactase. The mother added one of the solutions to her baby’s milk for a week and recorded how long it cried each day. The mother then used the other solution for the second week.

The table shows the results.

	Mean crying time / hours day–1
Milk with lactase	1.43
Milk without lactase	2.57

Suggest one variable the doctors would have to control in this study to make it a fair test. Explain your answer. (2)

Same age of children (1)

Change in enzyme production with age (1)

Doctors investigated babies who were bottle-fed with baby-formula milk and suffered from colic. Colic is a condition that affects the gut and makes babies cry.

Each mother was given two solutions to add to her baby’s milk. One solution contained the enzyme lactase, the other did not. The mother did not know which solution contained lactase. The mother added one of the solutions to her baby’s milk for a week and recorded how long it cried each day. The mother then used the other solution for the second week.

The table shows the results.

	Mean crying time / hours day–1
Milk with lactase	1.43
Milk without lactase	2.57

The doctors concluded that adding lactase to milk was, ‘A major breakthrough for babies with colic.’

Evaluate the evidence for this conclusion. (3)

Could be other causes/symptoms of colic (1)

Babies might cry for reasons besides colic (1)

Don’t know number of babies in trial/need a larger study
So don’t know how reliable mean is (1)

  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  gelatin + 2 cm3  pineapple juice + 2 cm3  water	No
B	6 cm3  gelatin + 2 cm3  pineapple juice + 2 cm3  hydrochloric acid	Yes
C	6 cm3  gelatin + 2 cm3  boiled pineapple juice + 2 cm3  water	Yes

Explain why 2 cm³ of  water was added to tubes A and C. (2)

To keep concentrations of gelatine constant (1)

To keep concentration of pineapple extract constant (1)

  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.

Explain the results of tube A and B (4)

Tube A

Enzyme (in pineapple) has digested gelatin (1)

so no gelatin/ protein to form a jelly (1)

Tube B

Enzyme denatured/inhibited/change of tertiary structure (1)

by change of pH (1)

Methotrexate is a drug used in the treatment of cancer. It is a competitive inhibitor and affects the enzyme folate reductase (1)

Methotrexate / drug is only similar shape to specific substrate / only fits this active site (1)