2.1.4 - Enzymes Flashcards
What are enzymes?
biological catalysts
What properties do all enzymes have?
- are globular proteins
- specific (only have one substrate)
- have an active site
- affected by temperature and pH
What are anabolic reactions?
reactions that construct molecules from smaller units
- require energy
eg. protein synthesis, building biological molecules
What are catabolic reactions?
reactions that break molecules down into smaller units
- release energy
eg. digestion, respiration
What are intracellular enzymes?
enzymes that react within a cell
eg. catalase, DNA polymerase
What are extracellular enzymes?
enzymes released from cells, which work outside of cells
eg. amylase, trypsin
Describe the lock and key hypothesis
- active site is complementary to a specific substrate
- when substrate binds to active site, enzyme-substrate complex is formed
- enzyme-product complex is formed after the substrate has reacted and products have formed
- enzyme holds substrate so that the right atom groups are close enough to react
Describe the induced fit hypothesis
- when the substrate enters, the active site changes shape slightly
- initial interactions are weak but they change the enzyme’s tertiary structure, which strengthens the interactions and puts a strain on the substrate
- this weakens bonds and therefore lowers the activation energy
What factors affect enzyme action?
- temperature
- pH
- substrate concentration
- enzyme concentration
- presence of inhibitors
- presence of cofactors
How does an increase in temperature affect the rate of enzyme action?
-increase in temp increases kinetic energy
-enzymes and substrates move faster
-active site and substrate collide more frequently
-more enzyme-substrate complexes
increases rate of reaction
- past 38°C the rate decreases
- enzyme denatures
- active site no longer a complementary shape to substrate
What is the temperature coefficient?
Q10
for enzyme controlled reactions, the rate of reaction doubles with each 10°C increase
∴ Q10 = 2
What is denaturing (of an enzyme)?
change in tertiary structure of an enzyme (because bonds are broken)
the active site irreversibly changes shape and no longer has a complementary shape to the substrate
What is an optimum pH (for enzymes)?
the pH (/certain concentration of hydrogen ions) where the enzyme’s active site remains the correct shape
Why do too acidic/too alkali conditions affect enzyme action?
- H+ ions interact with polar R-groups of amino acids
- when the concentration of H+ (pH) changes, the degree of interactions between R-groups change
- the more H+ ions (low pH) present, the less R groups can interact
- bonds break and the active site changes shape
- the less H+ ions (high pH) present, the more R groups can interact
- more bonds form and the active site changes shape
What is an enzyme inhibitor?
a substance/molecule that slows down the rate of an enzyme-controlled reaction by affecting the enzyme somehow (usually by causing the active site to change in some way)
Why do enzymes need to be inhibited?
- to regulate enzyme-controlled reactions
- to regulate amount of products produced
What are the two types of enzyme inhibitors?
competitive inhibitors
non-competitive inhibitors
What is a competitive inhibitor?
a molecule that has a similar shape to the substrate so can fit into the enzyme’s active site
-blocks the substrate from entering the active site
How does a competitive inhibitor affect the rate of reaction?
- reduces rate of reaction (because it reduces how many substrates can bind to the active sites)
- does not change Vmax (takes longer to get there but does not reduce it -if the substrate concentration is increased enough there will be more substrates than inhibitors)
What is a non-competitive inhibitor?
a molecule that binds to the allosteric site on an an enzyme (location other than the active site)
-causes the tertiary structure of the enzyme to change so changes the shape of the active site, meaning the active site no longer has a complementary shape to the substrate
How does a non-competitive inhibitor affect the rate of reaction?
- reduces rate of reaction and causes rate to plateau sooner
- lowers Vmax
- increasing enzyme or substrate concentration won’t affect the inhibitor’s affect
- level or inhibitation depends on number of inhibitors
What is end product inhibitation?
when the product of a reaction acts as an inhibitor to the enzyme that produced it
-are reversible + non-competitive
Why can end product inhibitation be a good thing?
- excess products aren’t made
- resources aren’t wasted
What are enzyme cofactors?
non-protein components on enzymes that help them catalase reactions
How are enzyme cofactors obtained?
from diet
- inorganic cofactors are from minerals (eg. iron, zinc, calcium)
- coenzymes are from vitamins (eg. vitamin B3 and B5)
What are coenzymes?
cofactors that are organic molecules
What is the cofactor for amylase?
chlorine ions (Cl-)
What is the prosthetic group of carbonic anhydrase?
zinc ions (Zn2+)
What are precursor enzymes?
enzymes produced in inactive form
-they need to undergo a change in shape/tertiary structure to be activtaed
Why are some enzymes produced in inactive form?
- they only need to be active in certain conditions
- they can damage cells/tissues
What is an apoenzyme?
precursor enzyme before cofactor is added
What is a holoenzyme?
precursor enzyme with added cofactor
How is a holoenzyme made?
apoenzyme + cofactor -> holoenzyme
What are zymogens/proenzymes?
precursor enzymes that are made active by another enzyme, a change in temperature or a change in pH
How is inactive pepsinogen activated?
by acidic conditions (low pH) in stomach
- transforms into active pepsin (which digests proteins in stomach)
- as activation only occurs in acidic conditions, the rest of the body tissues are safe from being digested
What is a biological catalyst?
a protein used in metabolism that alters the rate of reaction (by lowering the activation energy) without being used up or changed
