Biological Molecules and Transport in Cells - Key Concepts Flashcards
(27 cards)
What are enzymes and how do they act?
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.
What is a catalyst?
Something that speeds up a reaction.
How can changes in the shape of its active site cause an enzyme to become denatured?
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.
How does temperature affect enzyme activity?
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.
Why does increasing temperature increase rate of all reactions at first?
The reactants have more energy, so they move about more and collide more often.
What temperature tends to be optimal for enzymes in the human body?
37°C
At what temperature to enzymes in the human body tend to become denatured?
45°C
How does substrate concentration affect enzyme activity?
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.
How does pH affect enzyme activity?
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.
Devise an experiment to investigate the effect of pH on enzyme activity.
- Set up a beaker of water being heated by a Bunsen burner and adjust the flame to keep the water at about 35°C.
- Put two drops of iodine solution into each spot of a spotting tile.
- Add 2 cm3 of amylase enzyme solution, 2 cm3 of starch solution and 1 cm3 of pH solution to a test tube.
- Mix the solution in the test tube and place it into the beaker of water.
- Use a dropping pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile.
- Repeat until the iodine solution stops turning black.
- Record the time this takes.
- Repeat with different pH solutions.
How do enzymes aid synthesis of carbohydrates?
They catalyse the joining of simple sugars.
How do enzymes aid synthesis of proteins?
They catalyse the reactions needed to join amino acids.
How do enzymes aid synthesis of lipids?
They are heavily involved in synthesis from fatty acids and glycerol.
How do enzymes aid breakdown of carbohydrates?
Carbohydrases convert carbohydrates into simple sugars by breaking the chain bonds. For example, amylase breaks down starch.
How do enzymes aid breakdown of proteins?
Proteases catalyse the conversion of proteins into amino acids by breaking the chain bonds.
How do enzymes aid breakdown of lipids?
Lipases catalyse the conversion of lipids into fatty acids and glycerol by breaking each fatty acid’s bond to the glycerol.
How do you prepare a solid food sample if testing for reducing sugars, starch or proteins?
- Get a piece of your food and break it up using a pestle and mortar.
- Transfer the ground up food to a beaker and add some distilled water.
- Give the mixture a good stir with a glass rod.
- Allow the mixture to settle out and then use a pipette to transfer it.
How do you test a food sample for reducing sugars?
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 10 drops of Benedict’s reagent to the test tube using a dropping 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.
How do you test a food sample for starch?
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.
How do you test a food sample for proteins?
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.
How do you test a piece of food for lipids?
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.
Explain how the energy contained in food can be measured using calorimetry.
In calorimetry small samples of material are placed in the calorimeter which burns them. The energy given off when the material burns is measured.
Define diffusion
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.
How is diffusion different across cell membranes?
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.
