Enzymes Flashcards
All enzymes are proteins. True or false?
False, but almost all are
Which enzymes are not proteins?
Ribozymes - catalytic RNA molecules
The reactant in an enzyme catalyzed reaction is called…
…a substrate
What is the active site of an enzyme?
The small part of the molecule responsible for its catalytic action
Enzymes work by…
…changing the rate of a chemical reaction. They speed up metabolic reactions by reducing the activation energy needed for the uncatalyzed reaction.
Characteristics of enzymes
- Chemically unaltered, equilibrium constant too
- Operate under standard physiological conditions
- High specificity
- High catalytic efficiency
- Form complexes
- Reusable
Modes of enzyme action
- Lock and key
- Induced fit
Lock and key enzyme action
Both enzyme and substrate have corresponding shapes that lets them fit
Induced fit model
Enzyme and substrate change shapes to produce fit
Factors affecting enzyme action
Temperature
pH
Concentration
Co-factors
Temperature and pH higher than the optimal value will lead to…
Denaturing of the enzyme
Optimal temperature for enzymes in the human body
37oc
Optimal pH for enzymes in the human body
~8
Effect of high temperature on enzyme
Shape change, midfolding and denaturing
What are co-factors?
Small organic, inorganic, metallo-organic molecules or metal ions required by some enzymes for activity
Examples of prosthetic co-factors
Heme in haemoglobin
What are prosthetic groups?
Co-factors that are tightly bound to enzymes and remain associated with then between reaction cycles.
What are co-substrates?
Weakly bound co-factors that can associate and dissociate between cycles, behaving like substrates.
Biotin (CE)
Carboxylation
Cobalamin (CE)
Alkylation, intramolecular rearrangements and ribonucleotide reduction
Acyl transfer
Co-enzyme A, Lipoic acid (CE)
Flavin (CE)
Redox
Nicotinamide co-enzymes
Redox
Amino group transfer
Pyridoxal phosphate (CE)
One carbon transfer
Tetrahydrofolate (folic acid) (CE)
Aldehyde transfer
Thiamine pyrophosphate (CE)
Sugar transfer
Uridine diphosphate (CE)
Classes of enzymes
6 - OTHLIL
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
Levels of enzyme specificity
Absolute - Just 1 substrate
Group - One group of substrate
Steroisomeric - One stereoisomer
Oxidoreductases function and examples
Electron transfer or remove and addition of H atoms, eg alcohol dehydrogenase
Transferase function and examples
Functional group transfer, eg hexokinase
Hydrolase function and examples
Hydrolysis reactions, eg trypsin
Lyases function and examples
Cleavage of bonds to form double bond, eg pyruvate decarboxylase
Isomerases function and examples
Transfer of groups within molecules, isomerisation, eg Maleate isomerase
Ligases or synthases function and examples
Bond formation, ATP hydrolysis, eg pyruvate carboxylases
Parts of a protein enzyme structure
Active site
Allosteric site
Organic and inorganic co-enzymes are called…
Co-enzymes and Activators
Apoenzyme
No covalently bound prosthetic group
Holoenzyme
Apoenzyme + Prosthetic group
Proenzyme or Zymogens
Require enzymes to lyse portions of their peptide bonds for activation
Examples of proenzymes
Angiotensin, Chemotrypsin, Pepsinogen
Isoenzymes
Enzymes that exist in different forms but can be differentiated based on solubility, activation, electrophoretic mobility, etc
Characteristics of isoenzymes
- Catalyze same reaction but with different potencies
- Tissue specificity
- Multiple genetic origin
Isoforms
Different form of an enzyme resulting from posttranscriptional modifications but same genetic origin.
Where is a substrate oriented for catalysis?
The binding site of the active site
Effects of residues at binding sites
- H-bond formation
- Hydrophobic interactions
- Temporart covalent interactions (Van Dar Waals)
Active sites ate affected by environmental conditions. True or false?
True
