Enzymes Flashcards
What is an enzyme?
A globular protein molecule that acts as a biological catalyst and increases the rate of biochemical reactions
How do enzymes increase the rate of reactions?
it forms enzyme-substrate complexes which lowers the activation energy of the reaction it catalyses which means that the reaction requires less energy to start and therefore makes it quicker
What is the active site?
an area of depression in the enzymes’ shape caused by folds due to the enzymes tertiary structure
What is the substrate?
the molecule that the enzyme acts on
Explain and describe the lock and key hypothesis.
- it’s an earlier model used to explain how enzymes work
- the enzyme’s structure is fixed so the active site is specific to the substrate
- the substrate is a perfect fit for the enzyme
Explain and Describe the induced fit model.
- a more recent model used to explain how enzymes work
- the tertiary substrate changes as the subatrate approaches
- as the bonds begin to form the tertiary structure of the active site molds itself around the substrate
- this ensures that the substrate fits perfectly
Why is the enzyme specific to the substrate according to the lock and key theory?
because the enzyme has a fixed structure therefore it’s active site is only complementarty to one substrate
Why is the enzyme specific to the substrate according to the induced fit hypothesis?
- if the substrate isn’t complementary it can’t form the correct bonds with the correct amino acids in the active site
- this means the tertiary strcuture can’t change to become the perfect fit and catalyse the reaction
How does temperature affect enzyme controlled reactions?
- the kinetic energy of enzyme atoms increase
- this increases the rate of reaction first until the optimum temperature
- then the vibrations break the hydrogen bonds
- changes the shape of the protein and therefore the active site
- the active site is no longer complementary with the substrate so rate decreases
What factors affect the rate of enzyme controlled reactions?
- temperature
- pH
- concentration of enzymes
- concentration of substrate
- concentration of competitive inhibitors
- concentration of non-competitive inhititors
How does pH affect enzyme controlled reactions?
- acids and alkalines contail H+ and OH- ions respectively
- these interfrere with the hydrogen and ionic bonds that create the tertiary structure of the active site/enzyme
- this reduces the active site’s ability to bind with the substrate as the shape is no longer complementary
- this causes the rate of reaction to decrease
this happens above the optimum pH
How does enzyme consentration affect enzyme controlled reactions?
- as the concentration increases so does the rate of reaction
- this is because there are more active sites for the substrates to form enzyme-substrate complexes with
- however after a certain point there are more enzymes than substrate so the rate of reaction stays the same
- substrate concentration is now the limiting factor
How does substrate concentration affect enzyme controlled reactions?
- as the concentration increases so does the rate of reaction
- this is because there are more enzyme-substrate complexes forming
- however after a certain point there are more substrates than enzymes this means all the enzymes are occupied
- so the rate of reaction stays the same
- enzyme concentration is now the limiting factor
How does competitve reversible inhibitors concentration affect enzyme controlled reactions?
- it occupies the active site of an enzyme
- this means that the substate can’t form enzyme-substrate complexes which slows down the rate of reaction
What does Vmax represent?
the max rate of reaction
How do competitive reversible Inhibitors work?
- they are molecules that have a similar shape to the substrate of an enzyme
- this means it can attach to the active site of an enzyme and then it eventually detatches
- this means that it occupies the enzyme for a period of time instead of the substrate
How can the affect of competitive reversible Inhibitors be decreases?
by increasing the concentration of the substrate it means that the inhibitor is less likely to occupy the active site
How do competitive irreversible Inhibitors work?
- it perminantly attaches to the active site of an enzyme
- this means that once on the active site it never leaves
- this also means that increasing the substrate concentration is inaffective as the active site is perminantly occupied
How does non-competitve reversible inhibitors concentration affect enzyme controlled reactions?
as the concentration of non-competitve reversible inhibitors increase, the rate of reaction decreases as the shape of the active site is altered and therefore no longer able to catalyse the reaction
How do non-competitve reversible inhibitors work?
- it binds to an alternative site (allosteric site)
- this changes the tertiary structure of an enzyme which changes the active site
- substrate is no longer complementary with the substrate so enzyme-substrate complexes can’t form
- which decreases rate of reaction
Why does increasing substrate concentration not affect non-competitve reversible inhibitors?
even if you increase the consentration, the substrate is still no longer complementary with the altered active site
