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What are enzymes and what is their role in biochemical reactions?
What are enzymes and what is their role in biochemical reactions?
Enzymes are proteins that act as biological catalysts, increasing the rate of biochemical reactions by lowering the activation energy.
Explain the term 'activation energy' and its significance in chemical reactions.
Explain the term 'activation energy' and its significance in chemical reactions.
Activation energy is the initial energy required to start a chemical reaction, acting as a barrier that must be overcome for the reaction to proceed.
How do enzymes demonstrate specificity in their reactions?
How do enzymes demonstrate specificity in their reactions?
Enzymes are specific to particular substrates, meaning each enzyme typically catalyzes one specific reaction.
What characteristics of enzymes allow them to act quickly in biochemical processes?
What characteristics of enzymes allow them to act quickly in biochemical processes?
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Describe the historical contributions of Kuhne and Buchner in the study of enzymes.
Describe the historical contributions of Kuhne and Buchner in the study of enzymes.
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What is the significance of the suffix '-ase' in enzyme nomenclature?
What is the significance of the suffix '-ase' in enzyme nomenclature?
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In what ways can enzymes be classified according to the International Union of Biochemistry (IUB)?
In what ways can enzymes be classified according to the International Union of Biochemistry (IUB)?
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What distinguishes ribozymes from other enzymes?
What distinguishes ribozymes from other enzymes?
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Why are enzymes not considered to be damaged during chemical reactions?
Why are enzymes not considered to be damaged during chemical reactions?
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How do enzymes facilitate reversible reactions?
How do enzymes facilitate reversible reactions?
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What suffix is commonly found in the names of enzymes?
What suffix is commonly found in the names of enzymes?
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What does the first digit in an enzyme's EC number represent?
What does the first digit in an enzyme's EC number represent?
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Define coenzymes and provide two examples.
Define coenzymes and provide two examples.
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What is a zymogen?
What is a zymogen?
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How does the induced fit model differ from the lock and key model?
How does the induced fit model differ from the lock and key model?
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What effect does temperature have on enzyme activity?
What effect does temperature have on enzyme activity?
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What happens to an enzyme's activity at extreme pH levels?
What happens to an enzyme's activity at extreme pH levels?
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What is the purpose of the enzyme active site?
What is the purpose of the enzyme active site?
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Differentiate between cofactors and coenzymes.
Differentiate between cofactors and coenzymes.
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What is an isoenzyme?
What is an isoenzyme?
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Study Notes
Enzymes: History and Definition
- Enzymes, in Greek, mean "in living" (en = in, zyme = living).
- Enzymes are biocatalysts or organic catalysts with high molecular weight (except RNA enzymes, Ribozymes).
- The term "enzyme" was coined by Kuhne in 1878.
- The first enzyme was extracted from yeast by Buchner in 1897.
- The first purified enzyme was urease, isolated by James B. Summer in 1926.
Enzyme Definition
- Enzymes are proteins (biological catalysts) that accelerate the rate of a reaction by lowering activation energy.
- Enzymes catalyze nearly all biochemical reactions in cells.
- Enzymes have unique 3-dimensional shapes that fit the shapes of reactants (substrates).
Activation Energy
- Activation energy is the initial amount of energy needed to start a chemical reaction.
- It's often supplied as heat from the surroundings.
- Think of activation energy as the barrier required to form a product.
- The product with the lowest energy is the most stable.
- Most reactions require a "push" or activation energy to initiate the reaction.
Characteristics of Enzymes
- Enzymes generally act quickly, with reaction speed depending on substrate concentration.
- Enzymes are not damaged during a reaction, allowing them to be reused.
- Enzymes can react in both directions.
- Enzymes are specific, binding and catalyzing one type of reaction to a specific substrate.
- Enzymes are generally larger than their substrates.
- All enzymes are proteins, but not all proteins are enzymes.
- Enzymes are complex globular proteins with three dimensions.
Nomenclature and Classification of Enzymes
- Enzyme names usually end in "-ase" (e.g., dehydrogenase).
- Sometimes, the enzyme name identifies the reacting substance (e.g., sucrase catalyzes reactions of sucrose).
- Sometimes, the enzyme name describes its function (e.g., oxidases catalyze oxidation).
- Some common names exist, particularly for digestive enzymes (e.g., pepsin, trypsin).
- A systematic nomenclature system exists based on International Union of Biochemistry (IUB) recommendations.
-Enzyme names have 2 parts:
- The first part denotes the substrate, The second part indicates the reaction type catalyzed. This suffix ends in the suffix -ase.
- For instance, Lactate dehydrogenase and Pyruvate carboxylase.
IUB Enzyme Classification
- Enzymes are categorized based on the reactions they catalyze.
- Example categories include:
- Oxidoreductases (oxidation-reduction reactions).
- Transferases (transfer groups of atoms).
- Hydrolases (hydrolysis reactions).
- Lyases (add/remove atoms from double bonds).
- Isomerases (rearrange atoms).
- Ligases (combine molecules using ATP).
EC Numbers
- EC numbers are four-digit codes for enzymes, assigned by the Enzyme Commission.
- a: class of the enzyme
- b: functional group of the enzyme works
- c: coenzyme(NAD, FAD)
- d: substrate
Enzyme Terminologies
- Enzyme: proteins produced by cells of living organisms acting as biological catalysts.
- Substrate: the substance upon which the enzyme acts in a biochemical reaction.
- Coenzyme: small organic molecules that transport chemical groups. Examples include NAD and FAD.
- Cofactor: nonprotein, heat-stable, small-MW substances with the same function as coenzymes. Examples include Mg²⁺, Fe²⁺, and Cu²⁺.
- Ribozymes: RNA molecules that catalyze chemical reactions.
Enzyme Active Site
- The enzyme active site is a region in the enzyme that fits the shape of the substrate.
Zymogen
- Zymogens are inactive forms of enzymes (also called proenzymes) that become activated when the active site is unmasked via the removal of polypeptide chains.
Isoenzymes
- Isoenzymes are enzymes that catalyze the same reaction but are found in different tissues.
Mechanism of Enzyme Action
- The substrate (S) binds to the enzyme's active site, forming an enzyme-substrate complex(ES).
- Reaction occurs within the enzyme-substrate complex, converting the substrate into a product(P).
- The product is released, and the enzyme is recycled and ready to catalyze another reaction.
Enzyme Models
- Lock-and-key model: The active site's shape is rigid and only a specific substrate fits.
- Induced-fit model: The active site adjusts its shape to fit the substrate, improving the fit and catalysing the reaction.
Factors Affecting Enzyme Action: Temperature
- Enzymes show their optimal activity at a specific temperature (usually 37°C in humans).
- Lower temperatures decrease enzyme activity as substrate interaction decreases, denaturation occurs at high temperatures.
Factors Affecting Enzyme Action: pH
- Enzymes demonstrate optimal activity at a specific pH.
- Deviations from the optimum pH can disrupt the enzyme's 3D structure (denaturation), reducing activity.
Factors Affecting Enzyme Action: Enzyme Concentration
- Increasing enzyme concentration (with constant substrate) increases the reaction rate.
- At higher enzyme concentrations, the more substrates bind to the enzyme and increase catalysis.
Factors Affecting Enzyme Action: Substrate Concentration
- Increased substrate concentration (with constant enzyme) initially increases the reaction rate.
- Maximum activity is reached when all enzyme active sites are occupied by substrates, limiting further increase of activity.
Enzyme Inhibition
- Inhibitors are substances that decrease the velocity of enzyme-catalyzed reactions (decrease or stop enzyme action).
- Competitive inhibitors compete with the substrate for the active site.
- Non-competitive inhibitors bind to another site on the enzyme (allosteric site), altering the active site's shape and preventing substrate binding.
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Description
This quiz explores the history and definition of enzymes, including their roles as biological catalysts. Learn about the origins of the term 'enzyme' and how they function to lower activation energy in biochemical reactions. Discover key historical milestones in enzyme research.
