HL Bio - Molecular Bio (I): C1.1 Enzymes

Define enzymes

Biological catalysts which speeds up chemical reactions by lowering the activation energy and remains chemically unaltered

Define anabolic and catabolic reactions

Anabolic: building up processes (synthesise)
Catabolic: breaking down processes (degrade)

Outline the induced fit hypothesis

1. Substrate has complementary shape to active site (AS) of enzyme

2. Substrate binds to AS of enzyme, results in conformational change of enzyme AS

3. More precise fit, greater effectiveness of catalytic function, easier to break bonds and form new bonds

4. Substrates converted to products, detach from AS

5. Enzyme returns to original state and available for more substrates to bind

How do enzymes lower activation energy?

By providing an alternative mechanism pathway for the reaction to take place.

Define active site

The specific region on an enzyme where the substrate binds

What determines the specific three-dimensional conformation of the active site?

Tertiary/Quaternary structure - ionic, hydrogen, disulfide bonds, hydrophobic interactions

How does an increase in temperature affect rate of enzyme activity?

1. Increase temp - increase KE of E and S

2. Increase frequency of effective collisions between E and S molecules

3. Increase formation of ES complexes - increase in E activity

4. Past optimum temperature, enzymes irreversibly denature - E activity decrease

How does a deviation from optimum pH affect the rate of enzyme activity?

Deviate from optimum pH - enzyme activity decrease

H+ concentration interferes with interactions between amino acids and bonds which give enzyme specific 3D shape - deviate = loses 3D shape, denature

How does substrate concentration affect the rate of enzyme activity?

1. Increase [substrate], increase probability of effective collisions between E and S molecules

2. Increased formation of ES complexes - increased E activity

3. As active sites of enzymes become saturated, E activity plateaus

Define denaturation

The process where enzymes loses its specific 3D conformation of its active site due to external factors (e.g. changes in pH/temperature)

Named example of intracellular catalysed reaction

Glycolysis: break down of glucose into 2 pyruvate molecules catalysed by hexokinase

Named example of extracellular catalysed reactions:

Digestive enzymes: amylase, lipase, protease, secreted by exocytosis to work outside of the cell

Define cyclical and linear metabolic pathways

Cyclical - the product of one step is the reactant of another (Kreb's Cycle)
Linear - reactant is transformed through a series of steps into a final product (Glycolysis)

Define allosteric site and state the type of inhibition which the inhibitor binds with it

Site away from active site

Non-competitive inhibition

In which type of inhibition does the inhibitor compete with the active site of the enzyme?

Competitive inhibition

Describe end-product inhibition

Final product inhibits the enzyme catalysing the first step in the metabolic pathway