Enzymes Flashcards
Give examples of processes enzymes are used for.
- Digestion
- DNA and RNA synthesis
- Energy production
What are the characteristics of enzymes?
- Proteins
- Biological Catalysts
- Lower activation energy
- Not altered or consumed during reaction
What are the two functional groups within the active site?
- BINDING SITE - where substrate binds
- CATALYTIC SITE - where reaction catalysed
Describe the enzyme-substrate complex.
- Transiton state at high energy state
- Intermediate between substrate and product
- Reaction occurs by making/breaking bonds to form product
What are three types of specificity and what contributes to enzyme specificity?
- ABSOLUTE - Catalyse one reaction type for single substrate
- GROUP - Similar to absolute - for similar substrates
- LINKAGE - Similar to absolute - for specific bond type
- Tertiary structure contributes to specificity
Do enzymes alter ΔG?
No
Describe the lock-and-key model
- Active site has a rigid shape
- Only substrates with matching shape fit active site
Describe the induced fit model.
- Active site is flexible
- Shapes of enzyme, active site and substrate adjust to maximise fit, improving catalysis
Why is the optimum temperature for most enzymes 37 degrees?
- Temperature at which enzymatic reaction occurs fastest
What occurs when pH increases to physiological pH?
- Ionisation of functional groups
- Optimum pH is usually 7
- Varies depending on level of acidity of environment
When does Vmax occur?
Vmax - maximal activity
- Occurs when enzyme is saturated - all enzymes have bound substrate
What is the difference between an apoenzyme and holoenzyme?
- APOENZYME - Inactive enzyme without its cofactor
- HOLOENZYME - Active enzyme with its cofactor
What are cofactors?
- Inorganic/organic non-protein components
- Bound covalently or loosely to enzyme
What are coenzymes?
- Organic non-protein components
- Loosely bound to apoenzyme by non-covalent bonds
- EXAMPLE: NAD and FAD
What are prosthetic groups?
- Permanent part of tertiary structure
- Tightly bound to apoenzyme by covalent bonds
- EXAMPLE: Haem group in Hb
What is the purpose of ADH in the liver?
- Oxidation of ethanol to acetaldehyde
- Contains NAD
Describe irreversible inhibition.
- Covalent interaction with enzyme
- Leads to modification of active site
- Modified enzyme needs to be replaced
Give example of irreversible inhibitors.
- Neurotoxins
- Inhibit acetylcholinesterase in synapses
Define competitive inhibition.
- Similar shape and chemical properties to substrate
- Binds to and blocks active site
- Greater inhibitor concentration = greater inhibition
- Inhibition overcome by increasing [substrate]
Define non-competitive inhibition.
- Binds to site on enzyme other than active site
- Reduced enzyme activity - no effect on substrate binding
- Inhibition is reversible
How does cyanide behave as a non-competitive inhibitor?
- Binds to allosteric site of cytochrome C
- ATP synthesis blocked due to inhibition of ETC
- Cells respire anaerobically and lactic acid builds up
Define uncompetitive inhibition.
- Binds to ES complex
- Increases enzyme affinity for substrate
- Forms ES-inhibitor complex - inactive
Define allosteric inhibition.
- Inhibitor binds to modulator site
- Enzyme conformation altered
- Decreased catalytic activity of substrate at active site
Define feedback inhibition
- Enzyme inhibited by end product in biochemical pathway
- Occurs with buildup of product
- Negative feedback slows down production
