(todo 1.10-11,14B,16-17) Biological Molecules and Transport in Cells - Key Concepts

Question 1

What are enzymes and how do they act?

Answer 1

Enzymes are biological catalysts. They have a uniquely shaped active site which can only bind to a complementary substrate by the lock & key hypothesis. So enzymes only catalyse one specific reaction.

Question 2

What is a catalyst?

Answer 2

Something that speeds up a reaction.

Question 3

How can changes in the shape of its active site cause an enzyme to become denatured?

Answer 3

Enzyme active sites are uniquely shaped to fit a certain type of substrate by the lock & key model. If the shape changes, that type of substrate will no longer fit, so the enzyme has become denatured.

Question 4

How does temperature affect enzyme activity?

Answer 4

At first, increasing temperature increases rate of reaction as with all reactions. Above the optimum temperature, enzymes begin to become denatured as their bonds break.

Question 5

Why does increasing temperature increase rate of all reactions at first?

Answer 5

The reactants have more energy, so they move about more and collide more often.

Question 6

What temperature tends to be optimal for enzymes in the human body?

Answer 6

37°C

Question 7

At what temperature to enzymes in the human body tend to become denatured?

Answer 7

45°C

Question 8

How does substrate concentration affect enzyme activity?

Answer 8

At first, increasing substrate concentration increases rate of reaction as enzymes collide with substrates more often. At some point the enzymes have about as much as they can cope with (all the active sites are full), and further increasing substrate concentration makes no difference.

Question 9

How does pH affect enzyme activity?

Answer 9

All enzymes have an optimum pH. If the pH strays too far it may interfere with the bonds in the enzyme, causing it to become denatured.

Question 10

How do enzymes aid synthesis of carbohydrates?

Answer 10

They catalyse the joining of simple sugars.

Question 11

How do enzymes aid synthesis of proteins?

Answer 11

They catalyse the reactions needed to join amino acids.

Question 12

How do enzymes aid synthesis of lipids?

Answer 12

They are heavily involved in synthesis from fatty acids and glycerol.

Question 13

How do enzymes aid breakdown of carbohydrates?

Answer 13

Carbohydrases convert carbohydrates into simple sugars by breaking the chain bonds. For example, amylase breaks down starch.

Question 14

How do enzymes aid breakdown of proteins?

Answer 14

Proteases catalyse the conversion of proteins into amino acids by breaking the chain bonds.

Question 15

How do enzymes aid breakdown of lipids?

Answer 15

Lipases catalyse the conversion of lipids into fatty acids and glycerol by breaking each fatty acid’s bond to the glycerol.

Question 16

How do you prepare a solid food sample if testing for reducing sugars, starch or proteins?

Answer 16

1. Get a piece of your food and break it up using a pestle and mortar.
2. Transfer the ground up food to a beaker and add some distilled water.
3. Give the mixture a good stir with a glass rod.
4. Allow the mixture to settle out and then use a pipette to transfer it.

Question 17

How do you test a food sample for reducing sugars?

Answer 17

The Benedict’s test:
1. Transfer 5cm3 of a food sample to a test tube.
2. Prepare a water bath at 75°C.
3. Add some Benedict’s reagent (which is blue) to the test tube (about 10 drops) using a pipette.
4. Place the test tube in the water bath using a test tube holder and leave it for 5 minutes.
5. During this time, if the food sample contains reducing sugars, a green, yellow or brick-red precipitate will form - further with increasing concentration.

Question 18

How do you test a food sample for starch?

Answer 18

The iodine test:
1. Transfer 5cm3 of a food sample to a test tube.
2. Add a few drops of iodine solution (iodine dissolved in potassium iodide solution) and gently shake the tube. If the food sample contains starch the colour of the solution will change from orange-brown to blue-black.

Question 19

How do you test a food sample for proteins?

Answer 19

The biuret test:
1. Transfer 2cm3 of a food sample to a test tube.
2. Add 2cm3 of potassium hyroxide solution to make the solution alkaline.
3. Add a few drops of copper (II) sulfate solution (which is bright blue).
4. If the food sample contains protein, the solution will change from blue to pink or purple.

Question 20

How do you test a food sample for lipids?

Answer 20

An emulsion test:
1. Get a piece of your food and break it up using a pestle and mortar.
2. Transfer some of the food sample into a test tube.
3. Add 2cm3 of ethanol to the test tube.
4. Shake the test tube well for about 1 minute until the food sample dissolves.
5. Pour the solution into a test tube containing 2cm3 of distilled water.
6. If the food sample contains lipids, they will precipitate out of the liquid and show up as a milky emulsion - more noticeable with more lipid.

Question 21

What is diffusion?

Answer 21

Diffusion is the spreading out of particles from an area of higher concentration to an area of lower concentration. It is a passive process, meaning it does not require energy to work.

Question 22

How is diffusion different across cell membranes?

Answer 22

Cell membranes are partially permeable, meaning only very small molecules can diffuse across.
Movement is of course random, but there can be a net movement of particles if there is a large difference in concentration.

Question 23

What is osmosis and how does it relate to diffusion?

Answer 23

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. It is a special case of diffusion for water molecules across a partially permeable membrane.

Question 24

What is active transport and how does it differ from diffusion?

Answer 24

Active transport is the movement of particles from an area of lower concentration to an area of higher concentration using energy transferred during respiration. Unlike the passive diffusion, active transport requires energy.