Enzymes I Flashcards
What are enzymes?
Proteins that speed up the rate of chemical reaction
Function of enzymes
○ Digestion of carbohydrates, fats and proteins
○ Blood clotting (thrombin, thromboplastin)
○ Defence-immune system-activation of complement
○ Movement
Nerve conduction
Drug targets
How do enzymes speed up rate of reaction?
Increase rate of reaction by choosing the pathway with a lower activation energy
Properties of enzymes
Specific
Defects in enzymes cause disease
Drug targets
Do not change position of equilubrium
What are Cerebrosides?
Glycosphingolipids which are an important component in animal muscle cells
Active site and the evidence of the way it works
• 3D cavity binds to substrate using forces like electrostatic, hydrogen bonding, hydrophilic and hydrophobic
○ Evidence from X-ray crystallography
Kinetic studies of enzyme activity
Induced fit theory
The active site senses the substrate and the active site changes shape slightly
Substrate binding
- There is a limit to how many substrates an enzyme can process in a given time
- An increase in concentration increases rate at which product is formed eventually reaching a maximum value(Vmax)
- Another parameter used to characterize an enzyme is its Km(the concentration of substrate that allows the reaction to proceed at one-half its maximum rate(0.5 Vmax)
Drug targets in antibiotics example
Penicilin’s inhibit cell wall synthesis
Drug target in anti-inflammatory agents example
Aspirin block prostaglandin
Drug target in anti-cancer drug example
§ Methotrexate is a folate analogue
Interferes with synthesis of DNA precursors
What diseases can enzyme defects cause?
○ Phenylketonuria
Glycogen storage disease
Tay-sachs disease
What happens in phenylketonuria?
Cannot convert Phe to Tyr
What happens in tay sachs disease?
Membrane Cerebroside
What is more favourable and drives a reaction?
Drop in free energy
What is the equation for turnover number?
Vmax/[enz]total
How is enzyme activity regulated?
- Control of gene expression amount
- Compartmentation
- Allosteric regulation
Covalent modification of enzyme
What is feedback inhibition?
End product inhibits one of the enzymes in the chain process to regulate its own production
What is an allosteric enzyme?
A multi-subunit complex
Where are the regulatory and catalytic site on allosteric enzymes located?
On different subunits
How does regulation occur in allosteric enzymes?
Via conformational changes
What are allosteric enzymes involved in ?
In feedback inhibition of metabolic pathways
Km and Vmax in competitive inhibition
Km increases
Vmax remains unaffected
Km and Vmax in uncompetitive inhibition
Km reduced
Vmax reduced
Km and Vmax in non competitive inhibition
Km unaffected
Vmax reduced
What is ATCase regulated by?
Regulated by CTP
