digestion (enzymes)

Question 1

Amylase and maltase are involved in the digestion of starch in the small intestine. Where are the enzymes producedand what are the products of the reaction catalysed by the enzymes

Answer 1

1. (Amylase) pancreas, produces maltose;2. (Maltase) in/on epithelium (of small intestine), produces glucose;

Question 2

Cholera bacteria produce toxins which increase secretion of chloride ions into the lumen of the intestine.Explain why this results in severe diarrhoea (watery faeces).

Answer 2

1. Water lost into gut/water moves into gut/ water leaves cells;2. Low(er) water potential of intestine/gut (lumen);3. Osmosis/movement down a WP gradient;4. Less/not enough water (re)absorbed;

Question 3

Some people cannot digest lactose when they are adult. They could digest lactose when they were children.Use your knowledge of water potential to explain why these adults get diarrhoea when they drink milk.

Answer 3

1. Low(er) water potential in lumen / intestine / gut; 2. Water enters lumen / leaves (body) cells / by osmosis;

Question 4

The equation shows the reaction catalysed by the enzyme lactase. Complete this equation.Lactose + ……………………………….. ——>Glucose + ………………………………..Name the type of chemical reaction shown in this equation.

Answer 4

(Lactose +) Water——->(Glucose +) GalactoseHydrolysis

Question 5

Lactase is an enzyme. Lactose is a reducing sugar.(i) Describe how you could use the biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose.(ii) Explain the result you would expect with the enzyme.

Answer 5

1.Lactase / enzyme will give purple / lilac / mauveLactose / reducing sugar will not give purple / lilac / mauve / will remain blue;2. Lactase / enzyme is a protein with peptide bonds so not reducing

Question 6

The equation shows the breakdown of lactose by the enzyme lactase.lactose and water———>galactose + monosaccharide XWhat type of reaction is it?Name monosaccharide X.

Answer 6

hydrolysis alpha glucose

Question 7

Describe how you would use a biochemical test to show that a reducing sugar is present.

Answer 7

Add Benedict’s (reagent) and heat / warmRed

Question 8

Lactose, galactose and alpha glucose are all reducing sugars.After the lactose has been broken down there is a higher concentration of reducing sugar. Explain why.

Answer 8

2 products / 2 sugars produced

Question 9

A high concentration of galactose slows down the breakdown of lactose by lactase. Use your knowledge of competitive inhibition to suggest why

Answer 9

1. Galactose is a similar shape / structure to lactose/both complementary2. (Inhibitor / Galactose) fits into / enters / binds with active site (of enzyme)3. Prevents/less substrate fitting into / binding with (active site) / fewer or no E-S complexes

Question 10

People who are lactose intolerant are not able to produce the enzyme lactase. Explain why these people get diarrhoea when they drink milk containing lactose.

Answer 10

Low / decreased water potential (in gut)Water enters gut / lumen / leaves cells by osmosis;

Question 11

Gluten is a protein found in wheat. When gluten is digested in the small intestine, the products include peptides. Peptides are short chains of amino acids. These peptides cannot be absorbed by facilitated diffusion and leave the gut in faeces.Some people have coeliac disease. The epithelial cells of people with coeliac disease do not absorb the products of digestion very well. In these people, some of the 5 peptides from gluten can pass between the epithelial cells lining the small intestineand enter the intestine wall. Here, the peptides cause an immune response that leads to the destruction of microvilli on the epithelial cells.Scientists have identified a drug which might help people with coeliac disease.It reduces the movement of peptides between epithelial cells. They have 10 carried out trials of the drug with patients with coeliac disease.Use the information in the passage and your own knowledge to answer the following questions.1. Name the type of chemical reaction which produces amino acids from proteins2.Explain why the peptides cause an immune response

Answer 11

1. Hydrolysis2. Foreign/(act as) antigen /non-self

Question 12

The peptides released when gluten is digested cannot be absorbed by facilitated diffusion . Suggest why

Answer 12

1. Too big/ wrong shape2. To fit/ bind/ pass through (membrane/ into cell/through carrier/ channel protein)3. Carrier / channel protein

Question 13

The epithelial cells of people with coeliac disease do not absorb the products of digestion very well . Explain why

Answer 13

1. Villi /microvilli damaged/ destroyed2. Reduced surface area 3. For (facilitated) diffusion/ active transport

Question 14

Scientists have carried out trials of a drug to treat coeliac disease - Suggest two factors that should be considered before the drug can be used on patients with the disease.

Answer 14

1. Dose to be given2. No (serious) side effects3. How effective4. Cost of drug