Enzymes

Question 1

What are enzymes

Answer 1

Enzymes are biological catalysts made of protein
-Enzymes speed up metabolic reactions by lowering the activation energy (energy needed to start the reaction)
-They remain unchanged at the end of the reaction

Question 2

Active site

Answer 2

-The active site is a small part of the enzyme where the substrate binds
-The shape of the active site is determined by the tertiary structure of the enzyme
-There are complementary R groups within the active site that help the substrate to bind, via hydrogen, ionic, or hydrophobic interactions

Question 3

Models of enzyme activity

Answer 3

LOCK AND KEY MODEL
-The lock and key model is an older idea that states that the enzyme is a perfect match for the substrate
-This explains specificity but does not explain flexibility
INDUCED FIT MODEL
The induced fit model (better-accepted model) states that the active site of an enzyme slightly changes to better fit around the substrate
-This explains how some enzymes can bind more tightly or flexibly to specific substrates

Question 4

How enzymes lower activation energy

Answer 4

-Enzymes lower activation energy by binding to the substrate via the active site
-Enzymes stabilise the transition phase (making it easier for the intermediate reaction to be set up)
-Enzymes also make it easier to break or form bonds
-This reduces the amount of energy needed to start the reaction (activation energy)

Question 5

Intracellular enzymes

Answer 5

-Intracellular enzymes are enzymes that work inside of the cell where they were produced
-Intracellular enzymes catalyse metabolic reactions inside cells, and are often found in the cytoplasm or organelles

Question 6

Example of an intracellular enzyme

Answer 6

-Catalase is an example of an intracellular enzyme
-Catalase breaks down hydrogen peroxide (waste product of metabolism) into water and oxygen

Question 7

Extracellular enzyme

Answer 7

-Extracellular enzymes are enzymes that are secreted out of the cell to work on the surrounding environment
-Extracellular enzymes are often used by organisms to break down large molecules outside of the cell so they can be absorbed into the cell
-They are common in digestive systems and decomposers

Question 8

Examples of extracellular enzymes

Answer 8

For example- Amalyse, produced in the salivary glands, breaks down starch into maltose and trypsin, which breaks down proteins into smaller peptides

Question 9

Core practical 4 investigating effect of enzyme or substrate concentrations on rate of reaction

Answer 9

AIM
-Aim is to investigate the effect of different enzyme or substrate concentrations on the rate of an enzyme-catalysed reaction
METHOD
-Label test tubes with different concentrations of substrate (hydrogen peroxide) or enzymes (catalase from potato extract)
-Use a gas syringe to collect the oxygen produced from the break down of hydrogen peroxide
-Place the test tubes into a water bath to maintain a constant temperature (e.g 25 degrees)
-Add the enzyme to the substrate and immediately start the timer
-Measure the amount of oxygen produced between 10-30 seconds (this is the initial reaction)
-Repeat this at least three times for each concentration of substrate/enzyme
CONTROL VARIABLES
-use a water bath to keep the temperature constant
-Use the same substrate concentration
-Use the same enzyme concentration (if the substrate is the dependent variable)
-Use the same equipment
-Keep the time the reaction is measure for the same