1.4.2 proteins & enzymes

Question 1

Enzymes

Answer 1

Lowers activation energy, speeding up rate of reaction

Biological catalysts

Question 2

Intracellular

Answer 2

Synthesised in the cell & react in the cell

Question 3

Extracellular

Answer 3

Synthesised in the cell & react outside of cell

Question 4

Lock & key

Answer 4

Active site is a fixed shape; complementary to one substrate

After a successful collision, an E-S complex is formed leading to a reaction

Question 5

Induced fit model

Answer 5

Before reaction, enzyme active site not complementary to substrate

Active site shape changes as substrate binds and E-S complex forms

Stresses/distorts bonds in substrate leading to a reaction

Question 6

Specificity of enzymes

Answer 6

Have a specific tertiary structure and active site

Sequence of amino acids (primary structure) determines tertiary structure

Active site is complementary to a specific substrate

Only this substrate can bind to active site, inducing fit and forming E-S complex

Question 7

Enzyme conc effect

Answer 7

Increasing substrate conc > rate of reaction increases

Enzyme conc = limiting factor

More successful E-S collisions and E-S complexes

At certain point, rate plateaus: substrate conc limiting factor (all substrates in use)

Question 8

Substrate conc effect

Answer 8

Increasing substrate conc > rate of reaction increases

Substrate conc = limiting factor (too few enzyme molecules to occupy all active sites)

More successful E-S collisions and E-S complexes

At certain point, rate plateaus

Enzyme conc = limiting factor (all active sites saturated)

Question 9

Temperature effect

Answer 9

Increasing temp up to optimum > rate increases

Increase in kinetic energy

More successful E-S collisions and E-S complexes

Increasing temp above optimum > rate decreases

Enzymes denature; tertiary structure & active site change shape (hydrogen/ionic bonds break)

Fewer E-S collisions and E-S complexes (substrate no longer binds to active site)

Rate of reaction 0 when all enzymes denature

Question 10

pH

Answer 10

Above/below optimum > rate decreases

Enzymes denature; tertiary structure change & active site changes shape (hydrogen/ionic bonds break)

Complementary substrate can no longer bind to active site

Fewer E-S collisions & E-S complexes

PH = -log10(H+)

Question 11

Competitive inhibitor

Answer 11

Decreases rate of reaction

• similar shape to substrate
• binds to active site so substrate can’t bind
• fewer E-S complexes
• increasing substrate conc reduces effect of inhibitor

Question 12

Non-competitive inhibitor

Answer 12

Decreases rate of reaction

• binds to allosteric site
• enzyme tertiary structure / active site change shape so substrate cannot bind
• fewer E-S complexes
• increasing substrate conc has no effect on rate as causes permanent change to active site shape

Question 13

pH

Answer 13

pH= -log10(H+)