2.5 Enzymes Flashcards
What is a catalyst?
A substance which changes the rate of a chemical reaction without being changed itself.
What is an enzyme? What is an enzyme – substrate complex? What is an active site?
What do they catalyze
A biological catalyst
The enzyme and substrate bound together
The special site in the structure of an enzyme where the substrate binds.
They catalyze metabolic reactions in living organisms
What is activation energy? How do enzymes help?
The energy needed for a chemical reaction to take place.
The use of enzyme lowers the activation energy required
What does the lock and key model suggest?
What does the induced fit model suggest?
This model suggests that the substrate fits into the enzyme’s active site in the same way in which a key fits into a lock. The shape of the substrate and the active site are perfectly complementary to each other.
The induced fit model suggests that the shapes of the enzyme’s active site and its substrate are not exactly complementary, but when the substrate enters the active site, a conformational change (change of shape) occurs which induces catalysis. Places strain on the substrate bonds which break
What kinds of proteins are enzymes?
What structure does it have?
Soluble?
Globular proteins that act as biological catalysts
Enzymes have a specific tertiary structure
Globular proteins are generally soluble in water
How specific are enzymes? (4)
- They are a results of the complex primary, secondary and tertiary structure (and sometimes quaternary structure) of the protein
- Specific action is due to the presence of an active site in the enzyme
- very individual, has a specific shape and usually formed by fewer then 10 amino acids
- Only bonds to certain types of substrates
How do enzymes work?
- the substrate has a complementary structure to the active site
- any individual enzymes can only catalyze one particular reaction
- way in which substrate and enzyme bond is called induced fit
- induced fit brings chemical groups of the active site into positions that enhance their ability to work on the substrate and catalyze the chemical reaction – lowering the activation energy needed to break the bond.
- by bonding with the substrate, the enzyme to stabilize the bond in the substrate thereby creating the process of bond breakage
Where do enzymes work?
Enzymes can either be intracellular or extracellular
- intracellular enzymes - catalyze reactions inside the cell
e. g. enzymes found in cytoplasm or attached to the cell membrane, lysosomes, mitochondria, chloroplast - extracellular enzymes - catalyze reactions outside the cell
e. g. digestive enzymes, spider digest flies using enzymes they secrete, saprophytic fungi secrete enzymes to digest food
What factors affect enzymes?
1) temperature – both low (collision) in high (denature)
2) pH (denature)
3) enzyme concentration (collisions)
4) substrate concentration (collisions)
5) inhibitors - competitive (collisions) and non-competitive (denature)
How does temperature affect enzymes?
Increase temp = increase kinetic energy of the molecules -> more movement = more collision (increased liklihood of enzyme-substrate complex formation)
Increased temp = increase kinetic energy -> put strain on the bonds holding the enzyme together -> the shape of the active site changes
How does pH affect enzymes?
pH is a measure of H+ ion concentration. Acids are sometimes know as proton donors as they have excess H+ ions (protons). Some enzymes function optimally at different pHs.
If too many H+ ions are floating around in solution - they interfere with the delicate balance and can change the shape of the active site
These H+ ions cluster around the side chains of amino acids and interfere with the binding of the substrate - rate of reaction declines
What does buffer solutions do?
They counteract the effects of large pH swings - a mixture of 2 chemicals which counteract the effect of acids and alkalis
How does enzyme concentration affect the rate of reaction?
What happens if substrate is kept in excess?
What happens if substrate is limited?
If the amount of substrate is kept in access – the reaction will continue indefinitely and the rate of reaction about increase in proportion to the amount of enzyme
If the amount of substrate is limited – there are only so many collisions that can occur – the rate is capped by the amount of substrate
Why are enzymes usually kept at low concentrations?
For re-use and control
What is an immobilised enzyme? What is enzyme immobilization?
An example? What is the limitation of immobilizing enzyme?
Enzymes whose movement in space has been restricted either completely or to a small limited region.
A process of confining the enzyme molecules through a solid support over which is substrate is passing converter to products.
e.g. alginate gel beads -> small beads with enzyme immobilized inside
Limitation: difficult to make the same sized beads, cant ensure same concentration of enzyme, substrate has to enter the beads as well
