How does an enzyme function as a catalyst in biochemical reactions?
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An enzyme functions as a catalyst by lowering the activation energy required for a reaction, which in turn increases the rate of reaction. This allows biochemical processes to occur more efficiently at physiological temperatures.
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How does an enzyme function as a catalyst in biochemical reactions?
An enzyme functions as a catalyst by lowering the activation energy required for a reaction, which in turn increases the rate of reaction. This allows biochemical processes to occur more efficiently at physiological temperatures.
What is the induced fit model of enzyme catalysis?
The induced fit model describes how an enzyme changes shape upon substrate binding, allowing for a more precise fit between the enzyme and substrate. This model emphasizes that the active site is flexible and can adapt to the substrate's shape, enhancing the catalytic process.
What are the major classifications of enzymes and the common reactions they catalyze?
| Enzyme Class | Common Reactions |
|---|---|
| Oxidoreductases | Oxidation-reduction reactions |
| Transferases | Transfer of functional groups |
| Hydrolases | Hydrolysis reactions |
| Lyases | Addition or removal of groups to form double bonds |
| Isomerases | Isomerization reactions |
| Ligases | Joining of two molecules with the use of ATP |
What are proenzymes and how do they function in enzymatic activity?
Proenzymes, also known as zymogens, are inactive precursors of enzymes. They require a biochemical change, such as cleavage of a peptide bond, to become active. This mechanism helps regulate enzyme activity and prevent premature action in the body.
What factors affect enzyme activity?
| Factor | Effect/Mechanism |
|---|---|
| Temperature | Enzymes have an optimal temperature; low temperatures slow reaction rates; high temperatures can denature the enzyme |
| pH | Each enzyme has an optimal pH; deviations can affect ionization of residues and disrupt structure |
| Substrate concentration | Increased substrate concentration increases reaction rate until saturation (Vmax) is reached |
| Enzyme concentration | More enzyme increases rate if substrate is available; less enzyme reduces rate |
| Inhibitors | Competitive and non-competitive inhibitors decrease enzyme activity |
| Cofactors and coenzymes | Non-protein molecules that assist catalysis and are required by some enzymes |
What is the mechanism of action of serine proteases in cleaving peptide bonds?
| Step | Description |
|---|---|
| Substrate binding | The substrate binds to the enzyme's active site |
| Formation of tetrahedral intermediate | Serine (Ser195) attacks the peptide carbonyl, forming a tetrahedral intermediate |
| Acyl-enzyme intermediate | The intermediate collapses, releasing the first product and forming an acyl-enzyme complex |
| Deacylation (water attack) | Water attacks the acyl-enzyme, releasing the second product and regenerating the free enzyme |
What is the primary function of enzymes in biochemical reactions?
Enzymes are biological catalysts that increase the reaction rate by lowering activation energy without altering the equilibrium of a reaction.
What is the significance of the suffix '-ase' in enzyme nomenclature?
The suffix '-ase' indicates that the molecule is an enzyme and typically describes its function.
What are the functions of Kinase and Phosphorylase enzymes?
| Enzyme | Function |
|---|---|
| Kinase | Catalyzes the transfer of a phosphate group from a high-energy molecule (usually ATP) to a substrate. |
| Phosphorylase | Adds inorganic phosphate onto a substrate without using ATP; if it uses ATP, it is called phosphatase. |
How do enzymes reduce activation energy in a reaction?
Enzymes stabilize the transition state of reactants, which lowers the activation energy required for the reaction to proceed, thus increasing the reaction rate.
What are the four mechanisms of catalysis performed by enzymes?
| Mechanism | Description |
|---|---|
| Approximation | Brings reactants together in proximity and proper orientation. |
| Covalent catalysis | A reactive group on the enzyme is temporarily covalently bonded to the substrate. |
| Acid-base catalysis | A reactive group on the enzyme acts as a proton donor or acceptor. |
| Metal ion catalysis | Assists in electrophilic or nucleophilic interactions or binds to the substrate. |
What is the role of the active site in an enzyme?
The active site is the region in an enzyme where the enzyme-substrate complex interacts. Substrate binding often induces a conformational change in the enzyme that enhances binding strength.
How does an enzyme provide an alternate reaction pathway?
An enzyme facilitates a reaction by providing an alternate reaction pathway with a lower activation energy (Ea), allowing the reaction to proceed rapidly under cellular conditions. It does not alter the free energies of reactants or products, nor does it change the equilibrium of the reaction, but it accelerates the rate at which equilibrium is reached.
What are transition state inhibitors and how do they function?
Transition state inhibitors are drugs that bind tightly to the transition state of a reaction, resembling it closely. This binding inhibits the enzyme's activity. For example, Oseltamivir (Tamiflu) is a transition-state inhibitor of the influenza virus neuraminidase, while penicillin inhibits the bacterial enzyme glycopeptide transpeptidase, acting as a suicide inhibitor by forming irreversible inhibitors in the active site.
What is the induced-fit model in enzyme activity?
The induced-fit model posits that the binding of an enzyme to its substrate results in a release of binding energy, causing a small change in the enzyme's shape. This change enhances the enzyme's affinity for the substrate, leading to a more complementary conformation. Initially, the active site and substrate are not perfect matches; the substrate induces the shape change in the enzyme.
What are coenzymes and provide examples?
| Coenzyme | Role/Typical reactions |
|---|---|
| FAD | Involved in redox reactions |
| NAD+ | Functions in oxidation-reduction reactions |
| Coenzyme A (CoA) | Carries acyl groups |
| Pyridoxal phosphate (PLP, B6) | Functions in transamination reactions |
| Thiamine pyrophosphate (TPP) | Coenzyme for branched-chain dehydrogenases and decarboxylation reactions |
| Tetrahydrofolate (THF) | Involved in one-carbon transfer reactions |
What are the roles of cofactors in enzyme activity?
| Cofactor | Role / Example enzyme |
|---|---|
| Magnesium (Mg2+) | Involved in kinase activity (stabilizes ATP) |
| Zinc (Zn2+) | Found in alcohol dehydrogenase and superoxide dismutase; structural/catalytic roles |
| Copper (Cu2+) | Present in oxidases (electron transfer) |
| Iron (Fe2+/Fe3+) | Found in cytochromes; electron transfer |
| Selenium (Se) | Component of glutathione peroxidase (redox activity) |
What is a prosthetic group in relation to enzymes?
A prosthetic group is a nonprotein component that forms a covalent bond with a protein and is essential for its biological function. These groups can be organic or inorganic but are not composed of amino acids. Examples include heme, flavin, and retinal.
What are the effects of temperature and pH on enzyme activity?
| Parameter | Effect at low | Effect at high | Optimal |
|---|---|---|---|
| Temperature | Low temperatures slow reaction rates | High temperatures can increase rates but may denature enzymes | Enzymes have an optimal temperature range (often near physiological temperature) |
| pH | Deviations from optimal pH can reduce activity | Deviations from optimal pH can denature or disrupt activity | Each enzyme has an optimal pH dependent on its environment and function |
How does enzyme concentration affect enzyme activity?
| Condition | Effect | Notes |
|---|---|---|
| Increased enzyme concentration | Increases reaction rate | More active sites available if substrate is not limiting |
| Decreased enzyme concentration | Decreases reaction rate | Fewer active sites available |
| Regulation | Synthesis and degradation rates, inducers/repressors alter enzyme levels | Cellular control of enzyme concentration affects long-term activity |
What role does histidine play in enzyme catalysis?
Histidine is important in enzyme catalysis, particularly in acid-base reactions. Its pKa is close to physiological pH, making it versatile for catalysis. It is frequently found in enzyme active sites, facilitating the transfer of protons during reactions.
What are proenzymes and how do they function?
Proenzymes, or zymogens, are inactive precursor forms of enzymes. They become active through the cleavage of a specific peptide bond within the proenzyme, resulting in the mature enzyme. Examples include pepsinogen converting to pepsin and trypsinogen to trypsin.
What distinguishes isozymes from regular enzymes?
| Feature | Isozymes | Typical enzymes |
|---|---|---|
| Amino acid sequence | Different sequences between isozymes | A single enzyme has its characteristic sequence |
| Kinetic properties | Differing Km and Vmax values | Specific kinetics for a given enzyme form |
| Tissue distribution | Often tissue-specific isoforms (e.g., glucokinase in liver) | May be more ubiquitously expressed |
| Regulation and subunit composition | Different regulation and subunit makeup | Regulation specific to that enzyme form |
What are the characteristics of serine proteases?
Serine proteases, such as chymotrypsin, trypsin, and elastase, are a family of enzymes that cleave peptide bonds between specific amino acids. They share a common 'catalytic triad' active site configuration involving three reactive amino acids: His 57, Asp 102, and Ser 195. Each enzyme has specific substrate preferences based on the characteristics of their binding pockets.
