Enzymes

Question 1

Enzymes

Answer 1

• GLOBULAR PROTEIN
• hydrophillic amino acids at surface and hydrophobic amino acids at centre
• Soluble
• Biological catalysts that speed up the rate of reactions
• They lower the activation energy by providing an alternative pathway for molecules
• remain uchnaged and reuseable at the end of the reaction

Question 2

Substrate

Answer 2

Any molecule that can have a reaction catalysed by an enzyme
* molecule on which enzyme acts on
* they bind to an enzymes active site
* has a specific enzyme
* will only bind to an active site if its the correct shape

Question 3

Enzyme-substrate complex

Answer 3

part of the enzyme surface that has an active site to attach to the substrate
* active site forms small depressions on enzyme molecule so susbstrate can fit into it forming the complex
* the tertiary structure of the active site is complementary to the substrate

Question 4

Active site

Answer 4

Enzymes can only catalyse a reaction if a substrate binds to its active site
* they contain reactive molecules that carry out steps in a controlled way
* it can also apply physical pressure to a substrate to lower the activation energy

Question 5

Lock and Key model

Answer 5

Only the molecule (substrate) fits into the active site when its broken down
* Active site is specific to substrate
* enzyme= lock, substrate= key
* They fit into eachother due to their complementary shape
* Enzyme active site is a fixed shape, but substrate can collide and attach to enzyme through random collisions
* It distorts the substrate shape
* Lowers activation energy
- Suggests that enzyme is a rigid structure

Question 6

Induced fit model

Answer 6

enzyme changes shape around its active site to let a substrate enter
* Active site becomes induced/moulds around substrate
* A change in the environment of an enzyme (proximity of substrate) leads to a change in the enzymes active site
* General shape of enzyme alters in presence of substrate
* A forced fit happens when there is pressure/a strain on the substrate from enzyme
* Strain distorts bonds in substrate
* Lowers activation energy

Question 7

Activation energy

Answer 7

minimum amount of energy required to start a reaction
* For a reaction to occur, molecules collide with sufficient energy
* A reaction with a lower activation energy will happen faster

Question 8

Enzyme structure

Answer 8

• specific 3-D shape as a result of their sequence of amino acids (primary protein structure)
• Specific functional region: ACTIVE SITE- forms a small depression in large enzyme molecule

Question 9

Changes measured in enxzyme reactions

Answer 9

1. the formation of the products of the reaction
2. the disappearanceof the substrate

Question 10

.. How do the products and the substrates in enzyme-catlysed reactions change overtime?

Answer 10

1. At first theres a lot of substrate, but no product
2. Substate molecules come into contact with the active site easily
3. All active sites are filled and substrate is broken down into products
4. Amount of substrate decreases and is broken down, increasing the amount of product
5. Its more difficult for substrate molecules to come into contact with enzyme molecules because there are fewer substate molecules and product molecules may get in the way
6. It takes longer for the substrate molecules to be broken down by the enzyme so its disapperance rate and the formation of product slows
7. Rate of reaction continues to slow until there is little substrate so its concentration cant be measured
8. The graphs flatten out because all the substrate has been used up

Question 11

Factors affecting enzyme action

Answer 11

1. Temperature
2. pH

Question 12

Temperature on enzyme action

Answer 12

• If temperature increases, there is more kinetic energy, increasing the rate of successful collisions so there is a high rate of reaction
• Enzyme and substrate molecule come together more often
• More substrate-enzyme complexes are formed
• If temp is too high, then the enzymes active site changes shape and the substrate fits less easily into the active site
• Enzyme becomes denatured

Question 13

Denaturation

Answer 13

a permanent change that doesnt allow the enzyme to function again
* High temperatures causes the enzyme to be disrupted that it stops working altogether

Question 14

Effect of pH on enzyme action

Answer 14

• The rate of reaction is fastest at the optimum pH that is specific to the enzyme
• A change in pH away from the optimum affects the rate of enzyme action and could cause the enzyme to be denatured
• If there are more H bonds, this makes acidic bonds and if the conditions are alkaline these produce OH- bonds that mess with the primary structure of the protein
• A change in pH alters the charges on the amino acid that make up the active site

Question 15

Effect of enzyme concentration on rate of reaction

Question 16

Effect of substrate concentration on rate of reaction

Question 17

Competitive inhibitors

Answer 17

physical barriers that prevent the formation of enzyme-substrate complexes
* have a molecular shape similar to the subtrates so it allows them to occupy the active site of an enzyme
* Substrate and inhibitor compete for the active site
* it binds reversibly so it can move in + out again
* if the substrate concentration is increased the effect of the inhibitor is reduced
* Examples: malonate, transpeptidase

Question 18

Non-competitive inhibitors

Answer 18

Molecule that binds to the allosteric site (anywhere but active site) causing a change that alters the shape of the active site so its no longer complementary
* Creates chemical changes indirectly
* Substrate and inhibitor are not competing for the same site so incresing substrate concentration does not decrese the effect on the inhibitor