Enzymes

Question 1

1. Enzymes (5)

Answer 1

1-Enzymes speed up chemical reactions by acting as biological catalysts.
2-Enzymes are globular proteins.
3-Enzymes have an active site, which has a specific shape that is determined by the tertiary structure.
4-The active site is where the substrate molecules bind to.
5-For an enzyme to work, the substrate`s shape has to be complementary to the active site.

Question 2

2. Intra/extracellular (2)

Answer 2

1. Intra - within cells - catalase is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless O2 and water
2. Extra - outside cells - amylase is secreted by the salivary glands into the mouth, causing hydrolysis of starch into maltose (a sugar)

Question 3

3. Activation energy (4)

Answer 3

1- in a chemical reaction, a certain amount of energy needs to be supplied to the chemicals before the reaction will start - this is called the activation energy
2- the energy is often provided as heat
3- Enzymes reduce the amount of activation energy that’s required, often making reactions happen at a lower temperature, speeding up the rate of reaction
4- The formation of an enzyme-substrate complex causes this because:
4.1- if 2 substrate molecules need to be joined, attaching the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily
4.2 - if an enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate meaning the molecule breaks up more easily

Question 4

4. Lock and key / induced fit (4)

Answer 4

1. Substrate binds with enzyme’s active site to form an enzyme-substrate complex
2. Enzyme-product complex forms
3. Products are released and the enzyme is unchanged.
4. Induced fit shows that as the substrate binds, the active site changes shape slightly to fit the substrate more closely (explains why enzymes are so specific)

Question 5

5. Factors affecting enzyme activity

Answer 5

1. Temperature:
   1a - when temp increases, there is more kinetic energy so molecules move faster. this makes the enzymes more likely to collide with the substrate molecules.
   1b - The energy of collisions also increases, which means each collision is more likely to result in a reaction
   1c - a rise in temp makes the enzyme molecules vibrate more
   1d - if the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzymes in shape
2. pH levels
   2a - all enzymes have an optimum pH value (usually pH 7 in humans)
   2b -above and below the optimum pH, the H+ and OH- ions found in acids and alkalies can mess up the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. This makes the active site change shape, so the enzyme is denatured
3. Enzyme concentration
4. 1 - The more enzymes there are in a solution, the more likely a substrate molecule is to collide with one so increasing the enzyme concentration increases the ROR
5. 1 - If the amount of substrate is limited, there comes a point when there’s more than enough enzymes to deal with all the available substrate so adding more enzyme has no further effect
6. Substrate concentration
7. 1 - more substrate molecules means collisions between substrate and enzyme are more likely and so more active sites will be used
8. 2 - this is only true until a saturation point. After that