Enzymes
LO: Discuss the role of enzymes in catalysts and describe enzyme kinetics
Enzymes
- Catalysts, increase rate of reaction but not changed themselves so reusable
- Most metabolic pathways would occur too slowly without enzymes
- Nearly all enzymes are proteins
- Small number are RNA
Usage
- Digestion
- Metabolism
- Cellular communication
- Cellular energy storage and delivery
- Movement
- Drug metabolism
- Lower Ea so less energy needed to convert substrates into products
- Large globular proteins with complex 3D structure
- Specific active site that binds with substrate and catalyses the reaction
Selectivity
- Active site only bind to specific molecules
- Shape of active site and susbtrate
- R groups of amino acids at interaction site
- Cofactors in active stie
Lock and key model
- Enzyme - lock
- Substrate - key
- Substrate binds to enzyme only as shape is complementary
Induced fit model
- Shape of active site changes on substrate binding
- Help orientate substrates correctly, provide favourable microenvironment and strain substrate bonds
Enzyme kinetics
- How enzymes accelerate reactions and the factors that affect it
- Substrate Enzyme
Enzyme Product - Linear part of curve - product increases over time and gradient used to calculate initial rate of reaction
- Plateau - running out of substrate, enzyme denaturation, product inhibition
Temperature
- Most human enzymes work best at ~37
C - At high temperatures - hydrogen bonds disrupted and 2
and 3 structure is lost
pH
- Optimum between 6-8
- Outside of range: hydrogen bonds are disrupted causing denaturation and change in shape of the active site
- Some enzymes have an acidic pH optimum
Cofactors
- Helper molecules that interact with enzymes and required for their activity
- Inorganic ions and organic molecules (co-enzymes)
LO: Describe the role of enzymes in the diagnosis and management of disease
- Enzymes make up 30% of clinical drug targets
- Myocardial infarction - increase in blood levels of CK-MB, LDH, troponin
- Liver disease - alanine aminotransferase (ALT) and aspartate aminotransferase (AST)
- AST > ALT can indicate alcohol related liver injury
Biomarkers
| Enzyme | Tissue source | Diagnostic use |
|---|---|---|
| Creatine Kinase (CK) | Skeletal muscle, heart | Muscular dystrophy, myocardial infarction |
| Lactate dehydrogenase (LDH) | Heart, liver, erthrocytes | Lymphoma, hepatitis, myocardial infarction |
| Alanine aminotransferase (ALT) | Liver | Liver disease |
| Aspartate aminotransferase (AST) | Heart, skeletal muscle, liver | Liver disease |
| Gamma glutamyl-transferase (GGT) | Liver | Hepatitis, alcohol excess |
| Amylase | Pancreas, salivry glands | Acute pancreatitis, biliary obstruction |
| Lipase | Pancreas | Acute pancreatitis, biliary obstruction |
| Alkaline phosphatase | Osteoblast | Bone disorder, bone tumours |
Mutations
- Can cause inherited diseases