Enzyme activity Flashcards
What is an enzyme?
- A biological catalyst that increases the rate of metabolic reactions.
- A globular protein with a specific tertiary shape
- lowers activation energy for reactions
Which two theories explain how enzymes work?
The lock and key hypothesis and the induced fit model
Explain the lock and key model
- shape of both the substrate and the enzymes active site are complimentary
- substrate collides with enzyme active site and binds to it
- substrate forms bonds with the AC site called an enzyme substrate complex
- reaction takes place and the bonds in the substrate are broken
- an enzyme product complex is formed
- products unbind from AS and diffuse out
Explain the induced fit model
- substrate and AS of enzyme not complimentary
- substrate molecule collides with enzyme and if its of the correct composition the shape of the enzymes active site will change
- the substrate and enzyme will form and enzyme - substrate complex and the reaction is catalysed
- the enzyme product complex forms
- products diffuse away from enzyme
Which four factors affect the rate of reaction?
- temperature
- pH
- enzyme concentration
- substrate concentration
Explain the effect of temperature
Small increase in temperature can increase enzyme activity as the kinetic energy of the enzyme and the substrate increase. • They are therefore more likely to come into contact with each other. • They also collide with greater force • Therefore are more likely to form an enzyme-substrate complex when they do meet. • As temperature increases, it will approach the enzyme’s optimal temperature: where the enzyme is working at maximum efficiency. • Beyond this temperature, the enzyme becomes denatured. • Bonds responsible for maintaining the enzyme’s tertiary structure become broken and the active site changes shape • Enzyme becomes totally inefficient
Explain the effect of pH
- below optimum means slow RR or denaturing
- optimum produces fastest RR
- Too high mean slower RR or denaturing
- The tertiary structure of an enzyme relies on hydrogen bonding changes in pH from the enzyme’s optimal pH change hydrogen bonding in tertiary structure
Explain the effect of enzyme concentration
- low conc means competition for AS so RR is slow
- optimum conc means faster RR
- High conc means the enzyme is the limiting factor and RR plateaus
Explain the effect of substrate concentration
- low conc means unoccupied AS so low RR
- optimum conc has higher RR
- High conc means enzymes are limiting factor too few AS so RR will plateau At Vmax, all the enzyme active sites are said to be ‘saturated’ or occupied.
What are the three types of inhibition?
- Competitive
- Non-competitive
- Irreversible
How do competitive inhibitors work?
• Can fit into the active site, but does not react • Competes with substrate for access to the active site • Effect is concentration dependent ○ Can be minimized by raising the concentration of substrate • Effects are reversible
How do non competitive inhibitors work?
• Binds to allosteric site • Changes the shape of the molecule, preventing it from working • This is permanent and cannot be rectified • Effect is independent of substrate concentration
How do irreversible inhibitors work?
Binds irreversibly • Even if in high competition with substrate, can eventually inhibit a large proportion of available enzyme • Can have long-lasting effects ○ Until organism generates more enzyme and the inhibitor is outnumbered by enzyme • E.g. aspirin
Why are enzymes important?
to lower the activation energy of a specific reaction so that it is spontaneous. • This might mean it can occur at body temperature while it might normally require higher temperatures
