Module 2.4 - Enzymes Flashcards
Define enzymes
Globular proteins with specific tertiary structures
How do enzymes get these specific tertiary structures?
Primary base sequence determines the specific tertiary structure
Do endotherms need enzymes adapted for extreme temperatures?
No as they maintain their own internal body temperature, so maintain the optimum temperatures for enzymes by thermoregulation
How do heterotrophs digest food?
Consume other organisms and digest them inside the body (e.g. animals)
How do saprophytic feeders digest food?
Release enzymes onto food for it to be digested outside the body and then absorb the monomers (e.g. fungi, bacteria)
Define extracellular enzymes
Catalyse outside cells
Most digestive enzymes
Define intracellular enzymes
Catalyse inside cells (within cytoplasm / on membranes)
How do enzymes catalyse a reaction?
Reduce activation energy required by providing a different route for the reaction
Define activation energy
Minimum energy required for reaction to take place
Induced fit hypothesis
As the substrate binds to the active site, the enzyme changes shape slightly.
The active site is tighter around the substrate molecules.
Oppositely charged groups on the substrate and active site interact and hold the substrate molecule in place (ESC).
The enzyme’s shape change puts strain on the bonds in the substrate which destabilises it, causing the reaction to occur more easily.
Enzyme product complex is formed and as it is a different shape to the reactant it’s released from the active site.
Define temperature coefficient
Measure of rate of change of a reaction when the temperature is increased by 10°C
How will a low pH affect enzymes?
A low pH means that there are more H+ ions, which will attract negative parts of the enzyme and repel positive parts
This interferes with the hydrogen and ionic bonds giving the enzyme its tertiary structure and therefore specific active site
Define enzyme inhibitors
Molecules that slow down the rate of an enzyme controlled reaction
Main points about competitive inhibitors
Similar shape to enzymes’ substrate
Complementary to active site so they can bind with it and block it, forming an enzyme-inhibitor-complex
Prevents ESCs forming, slows rate of reaction, no products formed
Do not bind permanently (action is reversible)
Main points about non-competitive inhibitors
Fit into allosteric site on enzyme
Alters tertiary structure of enzyme so changes shape of active site
No ESCs can form, rate of reaction decreases
Bind permanently
Three cofactors
Coenzymes
Prosthetic groups
Inorganic ion cofactors
Define cofactors
Substances that must be present to ensure that an enzyme-controlled reaction takes place at the right rate
Points about coenzymes
Small, organic, non-protein molecules
Able to bind to active site at same time as substrate or just before
Changed by the reaction then converted back to original state (usually by a different enzyme)
E.g. vitamin B12 (nicotinamide) is used to make the coenzyme required for Pyruvate Dehydrogenase
Points about prosthetic groups
Permanent parts of some enzymes (permanent coenzyme)
Vital to 3D shape, function and charges on enzyme
E.g. carbonic anhydride contains Zn2+ prosthetic group, allows red blood cells to combine CO2 and H2O to produce carbonic acid
Points about inorganic ion cofactors
Increase reaction rate
Combine with enzymes or substrates which helps ESC form more easily by altering charge or shape of ESC
E.g. amylase breaks down starch into maltose molecules, and will only function properly if in the presence of chloride ions
Points about potassium cyanide
Non-competitive inhibitor of enzyme cytochrome oxidase needed for respiration
Inhibiting this enzyme decreases use of oxygen so ATP can’t be made
Organism has to respire anaerobically causing build up of lactic acid in blood
Inhibitors used to treat viral infections
Competitive inhibitors
E.g. HIV is treated using protease inhibitors as viruses need protease enzymes to build viral coat and inhibitors prevent this happening
Inhibitors in antibiotics
Treat bacterial infections by killing/stopping growth
E.g. penicillin is an inhibitor of the enzyme that helps build cell walls in bacteria, preventing bacteria reproducing
Inhibitors in alcohol
Ethylene glycol (in antifreeze) is broken down in the liver by alcohol dehydrogenase in oxalic acid which is highly toxic - can lead to death Ethanol acts as a competitive inhibitor of alcohol dehydrogenase
