Enzymes Flashcards
What are enzymes?
Globular proteins with complex tertiary structures (some are quaternary)
What are intracellular enzymes and example?
Enzymes that act inside the cell
CATALASE
- catalase converts hydrogen peroxide into water/oxygen preventing damage to cells , as H2O2 is product of metabolic reactions
What are extracellular enzymes?
Enzymes that catalyse reactions outside cells
AMYLASE - hydrolyses starch into simple sugars
- secreted by salivary glands/pancreas
TRYPSIN - secreted by pancreas/enter SI
- breaks proteins into amino acids/peptides
What makes the enzyme have a specific active site?
Active site shape determined by complex tertiary structure of the protein
- Proteins are formed from chains of amino acids held together by peptide bonds
- The order of amino acids determines the shape of an enzyme
- If the order is altered, the resulting three-dimensional shape changes
What is the locks and key theory?
That enzymes have a complementary active site to the substrate
- they are rigid structure that lock into each other very precisely
What is the induced fit theory?
The enzyme’s active site can change shape slightly as substrate enters enzyme - conformational changes
How do enzymes lower activation energy? What is activation energy?
Provide alternative energy pathway with lower activation energy
- otherwise extreme high temps/pressure would be needed
ACTIVATION ENERGY: amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed
How do enzymes speed up chemical reactions ?
Reduce the stability of the bonds in reactants
- destabilisation of bonds makes substrate more REACTIVE
How does pH effect enzyme activity?
Below /above optimum pH , solutions with excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause HYDROGEN AND IONIC bonds to break , which hold the tertiary structure
- breaking of bonds alters shape of active site, so ESC forms less easily —> denatured enzyme
How does temperature affect enzyme activity?
LOWER TEMPS :
- molecules have less KE
- less frequent successful collisions between substrate/active site , so less frequent ESC formation
- substrate/enzymes also collide with less energy - less likely for bonds to form/break
HIGHER TEMPS:
- Molecules have more KE, so more frequent successful collisions
- more frequent ESC formation
- substrate/enzyme collide with more energy - more likely for bonds to form/break (reaction occurs)
What happens when temp is too high ?
increased kinetic energy of enzyme = a strain on enzyme
- causing the weaker hydrogen and ionic bonds ,that hold the precise shape of enzyme, to break
- changes tertiary structure of enzyme
- active site damaged/not complementary to substrate anymore
Temp coefficient Equn / what is it?
The temperature coefficient is the ratio between the rates of that reaction at two different temperatures
- rate of the reaction doubles for every 10 °C increase in temperature
Q10 = 2
Equn: Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
How does enzyme conc affect enzyme activity?
Higher the enzyme conc , greater no. Active sites available
- more ESC formation
If substrate conc is constant - rate of reaction increase LINEARLY
If substrate conc is limited , increasing enzyme conc has no effect/ rate will plateau
How does substrate conc affect enzyme activity/rate of reaction?
greater the substrate concentration, the higher the rate of reaction
- more likely for ESC formation
Substrate increased until all active cites become saturated
- so increasing substrate conc will no longer have any effect - plateaus
What are the reversible inhibitors? What effect will be cause by increasing conc of this inhibitor ?
Competitive- similar shape to enzyme’s substrate , so blocks active site
Non competitive - bind to enzyme at an alternative site , so changes shape of active site
Increasing conc of inhibitor - reduces rate of reaction and will stop reaction completely eventually
