Introduction To Enzymes In Physiology Flashcards
What is an enzyme?
- Biological catalysts
- Provide reaction surface (active site)
- Weaken bonds in the reactants ( may provide acid base catalysis)
- Doesn’t change position of equilibrium
Should there be a positive or negative 🔺G and what is the equation to calculate it?
- Negative
- 🔺G = free energy of initial state - free energy of final state
What is the lock and key hypothesis?
- Active site has a rigid shape
- Fit between substrate and enzyme is exact
- E-S complex formed
- Products are different shapes from substrate and are released
What is the Induced Fit Hypothesis?
- Active site is flexible and can change conformation
- Shape of enzyme, active site and substrate adjust to maximise fit
- Greater range of substrate specificity
How does changing pH affect enzymes?
-Alters the ionisation state of amino acid side chains
- Alters ionic bonding, structural stability, shape & functionality of enzyme
- Overall 3D structure
How does changing temperature affect enzyme activity?
- Most active at optimum temperatures
- Show little activity at low temps
- Activity is lost at high temps as denaturalising occurs
What are Cofactors?
-Non protein prosthetic group (metal ions or inorganic group)
- Cofactors bind to enzyme and maintain correct config of active site
What are Coenzymes?
- Organic molecule bound to the enzyme by weak interactions
- Transfer electrons or small groups between substrates
What are the different classifications of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
-Ligases/synthases
What are Oxidoreductases?
- Catalyse transfer of electrons from donors to acceptors
- Catalyse oxidation-reduction pathways
- E.g Dehydrogenases accept and donate electrons as hydride ions or hydrogen atoms
What are Transferases?
- Catalyse transfer of a specific functional group between molecules
- E.g Kinases, Aminotransferases, Glycosyltransferases,
Acyltransferases
What are Kinases and Aminotransferases?
- Kinases: transfer phosphate groups usually ATP to another molecule
- Aminotransferases: transfer amino groups, important in amino acid metabolism
What are Glycosyltransferases and Acyltransferases?
- Glycosyltransferases: transfer carbohydrate residues
- Acyltransferases: transfer fatty acyl groups
What are Hydrolases and describe examples?
- Catalyse cleavage of bonds by the addition of water molecules
- Phosphatases : Hydrolyse phosphoric ester bonds
- Lipases : hydrolyse ester bonds in lipids
- Peptidases : Hydrolyse peptide bonds to form 2 products
What are Lyases?
- Catalyse the addition of water, ammonia or CO2 to double bonds
- Cleave bonds by means other than hydrolysis or oxidation
-Decarboxylases : Remove CO2 - Dehydrases : Remove H2O
- Deaminases : Remove NH3
What are Isomerases?
- Catalyse inter conversion of isomeric forms of a molecule by transferring groups within the same molecule
- Conversion of Cis and Trans
- Conversion of D and L isomers
What are Ligases?
- Catalyse synthesis of new covalent bonds using ATP
Enzymes may recognise and catalyse …
1) A single substrate
2) A group of similar substrates
3) A particular type of bond
What are enzymes that catalyse 1 substrate?
- Absolute
- Urease catalyses only hydrolysis of Urea
What are enzymes that catalyse a group of similar substrates?
- Group
- Hexokinase adds phosphate groups to hexoses
What are enzymes that catalyse a particular type of bond?
- Linkage
- Trypsin catalyses hydrolysis of peptide bonds
What are Isoenzymes?
- Different forms of an enzyme catalysing same reaction in different tissues
- slight variations in aa sequence
- can have different physical attributes & optimal conditions
What is positive & negative allosterism?
- Effector molecules change activity of an enzyme by binding at 2nd size
- Some effectors speed up enzyme action (positive allosterism)
Some effectors slow enzyme action (negative allosterism)
