Biological Molecules: Enzymes Flashcards
what are enzymes?
- globular proteins
- biological catalysts
- 3D tertiary structure
how do enzymes catalyse a reaction?
lowers the activation energy
why are enzymes highly specific?
tertiary structure
where do enzymes work?
- at a cellular level to the whole organism
what types of reactions do enzymes catalyse(wide range)?
- intracellular: e.g. photosynthesis and respiration
- extracellular: e.g. salivary amylase, pepsin
explain the induced fit model of enzyme action.
- substrate binds to the active site, ESC forms
- as the substrate binds the active site changes shape slightly so that it is complementary to the substrate
what are the properties of enzymes related to?
- its tertiary structure
what are the properties of enzymes?
- they are specific and only catalyse one reaction
why are enzymes specific?
only one complementary substrate will bind to the active site
what happens if the substrate shape isn’t complementary to the active site?
no ESC is formed, thus the reaction isn’t catalysed
what determines the shape of the active site?
the tertiary structure (and this is determined by primary structure)
why do enzymes differ?
- each different enzyme has a different tertiary structure so different shaped active site
what could cause changes to an enzyme and its active site?
- alteration of the tertiary structure (can be caused by a change in pH or temperature)
- primary structure of a protein is determined by a gene, and if a mutation occurs in that gene, the tertiary structure of the enzyme produced changes
what factors affect the rate of enzyme-controlled reactions?
- enzyme concentration
- substrate concentration
- concentration of competitive and non- competitive inhibitors
- pH
- temperature
how does enzyme concentration affect the rate of enzyme-controlled reactions?
- increasing enzyme concentration, increases ROR
- more enzyme molecules in a solution = more likely substrate molecule is to bind with one and form ESC
- if substrate is limited then adding more enzymes would have no effect at some point
how does substrate concentration affect the rate of enzyme-controlled reactions?
- higher the substrate concentration, faster the reaction = more substrate molecules that are available to bind to the active site
- this occurs until the saturation point , after that there are too many substrate molecules and all the active sites are occupied
how does temperature affect the rate of enzyme-controlled reactions?
- rate of enzyme-controlled reactions increases as temperature increases
- higher temps = more kinetic energy = faster reactions
- ESC forms at faster rates
- at higher temps the enzyme denatures
how does pH affect the rate of enzyme-controlled reactions?
- all enzymes have different optimum temperatures
- above or below the optimum pH, the H+ or OH- ions found in acids and alkalis disrupt the ionic bonds and hydrogen bonds that hold enzymes tertiary structure in place
- thus the enzyme becomes denatured and the active site changes shape
how does competitive inhibitors affect the rate of enzyme-controlled reactions?
- they compete with the substrate molecules as they are similar shapes and bind to the active site
- this reduces the forming of ESC
what is a competitive inhibitor?
- molecules with a similar shape to that of substrate molecules
what are non-competitive inhibitors?
- molecules which bind to the enzyme away from its active site
how does non-competitive inhibitors affect the rate of enzyme-controlled reactions?
- non-competitive inhibitors bind away from the active site and this causes the shape of the active site to change so substrate molecule no longer binds to it
- prevent ESC forming
what are the models of enzyme action?
- induced-fit model
- lock and key model
what is the lock and key model?
- substrate binds to active site of enzyme as they are complementary to each other
- ESC forms
- chemical reaction takes place and products are formed
