2.4 ENZYMES Flashcards
What is an enzyme?
An enzyme is a globular protein containing an active site which catalysis a reaction by lowering the activation energy
What is the structure of an enzyme?
Structure of enzymes:
- globular protein
- 3D structure made of a folded polypeptide (tertiary or quaternary)
- contains an active site which is complimentary to the substrate
What do enzymes do?
Enzymes catalyse reactions by lowering the activation energy by stretching or compacting substrate bonds, making them easier to make or break
What do catabolic and anabolic enzymes do.
Catabolic- break things down
Anabolic- build things up
What is the lock and key theory?
The lock and key theory states the active site and substrate are complimentary and fit perfectly to form and ESC, until the substrate is completely used up
What is the induced fit model:
The induced fit model suggests the active site may reconfigure and change shape to fit certain substrates and once products are formed and substrate is used up, the active site with revert back to its original form
What does it mean when an enzyme is denatured?
When an enzyme is denatured the tertiary structure (active site) is altered so that it no longer fits the substrate
Measuring enzyme activity.
Enzyme action = rate of reaction.
rate = 1 / time taken to reach end point (s)
Calculating temperature coefficient (Q10).
Q10 = rate of reaction at (T + 10) / rate of reaction at T
What is the optimum pH?
The optimum pH:
- more acidic = more H+ ions
- more alkaline = more OH- ions
- pH only temporary when H+ ions present
- H+ stimulate tertiary structure to change shape , no bonds formed
- optimum pH is when enzymes are in the perfect configuration
What are inhibitors?
Inhibitors are chemicals that selectively inhibit the action of specific enzymes- can be reversible or irreversible
What are compitetive inhibitors?
Competitive inhibitors:
- competes with substrate for active site
- similar shape to substrate (blocks active site)
- forms enzyme-inhibitor complex
- do not react with active site and usually leave (usually reversible)
- reduces rate of reaction but do not reduce v-max
e.g statins- reversible
- synthesis of cholesterol
e.g aspirin- irreversible
- inhibits active site of cox enzymes
- prevents synthesis of chemicals (prostaglandins and thromboxane) responsible for pain and fever
What do non-competitive inhibitors do?
Non-competitive inhibitors:
- bind to the allosteric site (anywhere on enzyme) which alters the active site
- does not compete with substrate
- prevents substrate from binding so rate of reaction decreases
- can be reversible or irreversible
e.g organophosphates- irreversible
- inhibit acetyl cholinesterase (used in nerve impulse transmission)
- leads to muscle cramps and paralysis
e.g protein pump inhibitors- irreversible
- treat indigestion by irreversibly blocking an enzyme that secretes hydrogen ions in the stomach
What is end-product inhibition?
End-product inhibition is inhibition that occurs when the products of a reaction act as an inhibitor to the enzyme that produces it
Multi-step production of ATP in respiration.
Multi-step production of ATP in respiration:
- ATP is an end product inhibitor
- binds to the allosteric site of the phosphofructokinase enzyme and prevents glucose being broken down- if ATP is being used up, less bind to the enzyme and therefore, more glucose is then broken down
