biological molecules-enzymes

Question 1

what are enzymes

Answer 1

• globular proteins that catalyse metabolic reactions
• anabolic reactions: larger molecules are built up from smaller molecules
• catabolic reactions: larger molecules are broken down/hyrolysed

Question 2

enzymes as biological catalysts

Answer 2

• catalyst: a molecule that speeds up a chemical reaction but remains unchanged at the end of the reaction
• enzymes are biological catalysts made of protein (speed up rate of a chemical reaction)
• requires in small amounts
• remain unchanged at the end of the reaction
• specific in action
• affected by temperature and pH
• enzymes are always present in cells and organisms but some are only produced under particular conditions/at certain stages (allows for cells to control what chemical reactions and when they happen in the cytoplasm)
• for reaction between 2 organisms to occur, there must be an effective collision between them for activation energy to be produced
• must collide with each other in right orientation and speed

Question 3

metabolic reaction

Answer 3

for reaction to take place
- activation energy is needed to raise molecules to an unstable high energy intermediary state prior to formation of product molecules
(because of the extra energy within them, they become unstable)
- an energy barrier needs to be overcome before the reaction takes place thus enzymes lower the activation energy is needed to activate the substrate molecules
- enzymes are highly specific in their action: only catalyse 1 type of reaction due to the specific 3-dimensional conformation and distinctive chemical properties of the active site where the substrate molecule bind

Question 4

lock and key hypothesis

Answer 4

enzyme: lock
substrate: key
- an enzyme binds its substrate molecule at its active site, forming the enzyme-substrate complex
- when an enzyme-substrate complex is formed, the energy level of the substrate is raised to a transition state before it breaks down to form its product with the enzyme remaining unchanged

summary:

1. the shape of the active site of the enzyme is specific and complementary to the shape of the substrate. upon effective collision between enzyme & substrate, the enzyme-substrate complex is formed
2. interactions between enzyme and substrate molecules strain/weaken chemical bonds within substrates, thus lowering activation energy
3. when reaction between substrates finish, products no longer fit into active site and are released

Question 5

factors affecting enzyme reaction

Answer 5

pH:

• all enzymes have optimum pH in which it functions most effectively
• at the optimum pH:
• all bonds within enzyme are intact (maintain its specific 3-dimensional conformation thus enzyme active site is complementary to its substrate)
• maximum number of enzyme-substrate complex to be formed per unit time, converting substrate to products
• changes in pH alter the enzyme bonding pattern (alters 3-dimensional conformation of the active site, substrate is no longer complimentary to the active site –> no enzyme-substrate complex–> no product formed–> thus enzyme is denatured and no product formed)
• effects of pH on active site is normally reversible if not too extreme (unlike temperature changes)

temperature:

• for every 10 degree celsius rise in temperature, rate of enzyme reaction is doubled until optimum temperature is reached
• as temperature increases, KE of substrate and enzyme molecules increase thus increasing the frequency of effective collisions between substrate and enzyme active site
• increases formation of enzyme-substrate complex
• increases rate of reaction/products formed
• enzyme activity is highest at 35-40 degree celsius
• when temperature exceeds optimum temperature of 40 degree celsius:
• high temperature breaks the bonds that hold enzyme active site in its functional conformation (enzyme is denatured–> loses catalytic function