Enzymes Flashcards
What is an enzyme and what type of protein are they?
Enzymes are globular proteins that act as biological catalysts
Define metabolism
Refers to all the reactions of the body
What is an anabolic reaction?
Building up molecules
e.g protein synthesis
What is a catabolic reaction?
Breaking molecules down
e.g digestion
What is an enzyme- substrate complex?
Enzyme acts on substrate forming temporary bonds at the active site
How are enzymes secreted from cells?
By exocytosis
What are the two models of enzyme action?
The lock and key model
The induced fit model
How do enzymes use induced fit to catalyse a reaction?
- Active site not complementary to substrate
- As substrate binds, active site changes shape to form enzyme-substrate complex
- This stresses bonds in substrate causing reaction to occur
For an enzyme to catalyse a reaction, it must…
Come into contact with substrate
Substrate must be complementary to active site
Must collide with enough energy at the right orientation
How do enzymes actually speed up the rate of reaction?
Lower the activation energy
What is an exergonic reaction?
Energy released
What is an endergonic reaction?
Energy absorbed
What is a catalyst?
A substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction
What is an enzyme inhibitor and what does it do?
Substances that directly or indirectly affect the functioning of the active site of a specific enzyme and so prevent the substrate binding, preventing the formation of enzyme substrate complexes and therefore decrease the rate of reaction
What are the two types of inhibitors?
Competitive and non-competitive
How does a competitive inhibitor work?
Have a similar structure to the substrate, so they can bind to the active site of an enzyme. Binding of a competitive inhibitor to the active site is reversible, so when it leaves the active site, another molecule can enter (substrate or inhibitor)
How does a non-competitive inhibitor work?
Binds to an enzyme at a site that is NOT the active site (allosteric site). Binding of the inhibitor causes a change in the tertiary structure of the enzyme, therefore changing the shape of the active site. This means that the active site is no longer complementary to the substrate so the substrate can no longer bind (so no enzyme substrate complex formed and no reaction)
How can competitive inhibition be overcome?
Increase substrate concentration
What does negative feedback do?
speed up/slow down/stop enzymes to control the metabolic pathway based on the cells demands
What determines the shape of an enzyme’s active site?
Tertiary structure – held in place by selection of bonds – ionic/disulphide/hydrogen
What is pH?
A measure of hydrogen ion
concentration
Define limiting factor
A factor is limiting when an increase in its value causes an increase in the rate of reaction
Name 4 factors that could affect the rate of enzyme action
• Temperature
• pH
• Enzyme concentration
• Substrate concentration
