Many Proteins Are Enzymes Flashcards
Which type of proteins are enzymes?
- globular protein
What is activation energy?
- minimum amount of energy needed for a reaction to take place
What are enzymes?
- tertiary structure proteins which catalyse reactions
Describe the active site of an enzyme
- active site is specific and unique in shape due to the specific folded and bonding in the tertiary structure of the protein
- due to this specific active site, enzymes can only attach to substrates that are complementary in shape
What happens when enzymes attach to the substrate?
- lowers the activation energy needed for the reaction to occur and speed up reaction
What are the two models of enzyme action?
- lock and key
- induced fit
Explain the lock and key model
- enzyme is like a lock and substrate is like a key due to complementary shape
- enzyme active site is a fixed shape and due to random collisions, substrate collides and attaches to enzyme forming enzyme substrate complex
- substrate is distorted to lower activation energy and products released and reused
Explain the induced fit theory
- enzymes active site is not completely complementary to substrate
- shape of active site changes as substrate binds to become complementary to the substrate and forms enzyme substrate complex
- enzyme substrate complex causes stressing and distortion of bonds in the substrate causing bonds to break, lowering the activation energy
- product is formed and released and enzymes active site returns to original shape
What are the factors affecting the rate of enzyme controlled reactions?
- temperature
- pH
- substrate concentration
- enzyme concentration
- inhibitors
What happens if temperature is too low?
- not enough kinetic energy for successful collisions between the molecules and the enzyme and substrate
- less enzyme substrate complexes form
- slows rate of reaction
What happens if temperature is too high?
- enzymes denature
- enzyme molecules vibrate so energetically that (name of bond) begins to break
- tertiary structure unravels
- shape of active site becomes altered and substrate no longer fits
- enzyme substrate complexes cannot form
- slows rate of reaction
What happens when temperature is increasing?
- rate of reaction increases
- kinetic energy increases so substrate and enzyme molecules move faster
- increase in successful collisions between molecules and enzymes active site and substrate
- more enzyme substrate complexes form
- for every 10 degrees Celsius increase rate of reaction doubles
What happens when optimum temperature is reached?
- many successful collisions between molecules and enzymes active site and substrate
- many enzyme substrate complexes form
- strain is put on a substrate molecule and distorts (named 2 bond) and lowers activation energy
What happens if temperature is still increasing after it is too high?
- all enzymes become denatured and reaction stops
What happens if pH is too high or low?
- interferes with the charges in the amino acid in the active site
- break ionic and hydrogen bonds holding the tertiary structure in place and active site changes shape and effects the R group in the active site which temporarily bonds with substrate
- enzyme denatures and fewer enzyme substrate complexes form
- if too high pH, too many hydrogen ions, if too low pH, too many OH- ions
What happens if there is an insufficient substrate concentration?
- slows down reaction
- fewer collisions between enzyme and substrate as fewer substrate molecules available to collide with enzyme
- fewer enzyme substrate complexes available
What happens if there is insufficient enzymes?
- slows reaction
- enzyme active sites will become saturated with substrate and unable to work any faster as fewer active sites available
What happens if you increase substrate concentration?
- if increase substrate concentration, rate of reaction becomes constant
- new limiting factor, enzyme concentration
- eventually enzyme active sites become fully saturated so reaction cannot occur any faster
- substrates have to wait until enzyme substrate complex has dissociated into products
What happens if you increase enzyme concentration?
- rate of reaction plateaus
- new limiting factor substrate concentration
- empty active sites due to insufficient substrate
What happens if enzyme concentration and substrate concentration is both constant?
- more enzyme molecules can react with more substrate molecules
- reaction rate increases due to increase inactive sites and increase in successful collisions
What are competitive inhibitors?
- molecule same shape as substrate and can bind to active site
- forms enzyme inhibitor complex and prevents substrate from binding and reaction occurring
How are competitive inhibitors overcome?
- increasing substrate concentration will knock out competitive inhibitors from active site
What are non competitive inhibitors?
- molecules bind to a site other than the active site causing the active site to change tertiary structure and shape so substrate can no longer bind
- regardless of substrate concentration
Draw rate of reaction on a graph for competitive inhibitor
- rate of reaction is lower than that of one without an inhibitor until very high substrate concentrations is reached
- increase of substrate knock out inhibitor and substrate binds, rate turns normal (meets same end point of no inhibitor)
Draw rate of reaction on a graph for non competitive inhibitor
- lower rate of reaction and plateaus at a lower rate of reaction
- due to substrate concentration having no effect, active site having a different shape so no longer catalysing reaction
- reach maximum rate of reaction at a lower rate
What is end product inhibition?
- if a lot of product is produced at the end of enzyme pathway it acts as a non-competitive inhibitor on the first enzyme, turning off its own production
- if product is being used elsewhere there is less feedback inhibition (more products made)
- self regulates
What is an example of a competitive inhibitor and its properties?
- cyanide
- respiratory inhibitor that stops respiration by stopping ATP production
Describe protein shape
- 3-D conformational shape is precise and critical to enzyme function
- Hydrophobic region inside
- Hydrophilic regions outside in watery
environment of cell ie soluble. - Shape determines function of enzyme
- Denaturation alters tertiary structure:
– Caused by change in pH or temperature
– Changes 3-D shape - non functional as distorts active site
How to calculate rate of reaction from a graph?
- draw tangent at time and draw triangle
- use formula product (change of the amount of product) / time (change of the time)
What are other enzyme inhibitor examples and its effect?
- malathion inhibits nervous system
- penicillin inhibits cell wall formation in bacterial cells, can’t reproduce
What do small changes in pH cause?
- inactivation of enzyme
- reversible
What to large changes in pH cause?
- enzyme to denature
- irreversible
