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What does the word "enzyme" mean in Greek?
What does the word "enzyme" mean in Greek?
in living
What are the two main categories that enzymes fall into?
What are the two main categories that enzymes fall into?
biocatalyst or organic catalyst
Enzymes are always proteins.
Enzymes are always proteins.
False
Who coined the term "enzyme"?
Who coined the term "enzyme"?
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What was the first enzyme to be purified?
What was the first enzyme to be purified?
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How do enzymes accelerate chemical reactions?
How do enzymes accelerate chemical reactions?
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Enzymes can only catalyze one specific biochemical reaction.
Enzymes can only catalyze one specific biochemical reaction.
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What is the initial amount of energy required to start a chemical reaction?
What is the initial amount of energy required to start a chemical reaction?
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The product of a reaction is always the most stable when it has the lowest energy level.
The product of a reaction is always the most stable when it has the lowest energy level.
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Why is activation energy sometimes referred to as a "push"?
Why is activation energy sometimes referred to as a "push"?
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Enzymes are damaged during a reaction.
Enzymes are damaged during a reaction.
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Enzymes are limited to a single direction of reaction.
Enzymes are limited to a single direction of reaction.
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What makes an enzyme specific?
What makes an enzyme specific?
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Enzyme molecules are generally smaller than their substrates.
Enzyme molecules are generally smaller than their substrates.
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All proteins are enzymes.
All proteins are enzymes.
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What are the two main categories of enzyme names?
What are the two main categories of enzyme names?
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The traditional names of enzymes often end in the suffix ______.
The traditional names of enzymes often end in the suffix ______.
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How do enzyme names sometimes indicate the substance they act on?
How do enzyme names sometimes indicate the substance they act on?
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What is the primary purpose of the systematic nomenclature system for enzymes?
What is the primary purpose of the systematic nomenclature system for enzymes?
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What are the two components of an enzyme's systematic name?
What are the two components of an enzyme's systematic name?
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What suffix indicates the reaction type in an enzyme's systemic name?
What suffix indicates the reaction type in an enzyme's systemic name?
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Which of the following enzymes are classified as oxidoreductases? (Select all that apply)
Which of the following enzymes are classified as oxidoreductases? (Select all that apply)
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What is the primary reaction catalyzed by hydrolases?
What is the primary reaction catalyzed by hydrolases?
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What is the primary function of lyases? (Briefly describe how they act.)
What is the primary function of lyases? (Briefly describe how they act.)
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What type of reaction do isomerases facilitate?
What type of reaction do isomerases facilitate?
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What is the primary role of ligases in the context of chemical reactions?
What is the primary role of ligases in the context of chemical reactions?
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What is the general structure of an EC number?
What is the general structure of an EC number?
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What does the first digit (a) in an EC number represent?
What does the first digit (a) in an EC number represent?
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What does the second digit (b) in an EC number represent?
What does the second digit (b) in an EC number represent?
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Ribozymes are composed of proteins.
Ribozymes are composed of proteins.
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What is the active site of an enzyme?
What is the active site of an enzyme?
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What is a zymogen?
What is a zymogen?
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What are isoenzymes?
What are isoenzymes?
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The lock-and-key model of enzyme action suggests that enzymes are rigid and inflexible.
The lock-and-key model of enzyme action suggests that enzymes are rigid and inflexible.
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The induced-fit model of enzyme action suggests that enzymes are flexible and can change their shape in response to substrate binding.
The induced-fit model of enzyme action suggests that enzymes are flexible and can change their shape in response to substrate binding.
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The optimum temperature for enzyme activity is generally around 37 degrees Celsius.
The optimum temperature for enzyme activity is generally around 37 degrees Celsius.
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Enzymes tend to be more active at very high temperatures.
Enzymes tend to be more active at very high temperatures.
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Enzymes are most active at their optimum pH.
Enzymes are most active at their optimum pH.
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Increasing enzyme concentration generally leads to a decrease in the rate of a reaction.
Increasing enzyme concentration generally leads to a decrease in the rate of a reaction.
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The rate of a reaction can increase indefinitely with increasing substrate concentration.
The rate of a reaction can increase indefinitely with increasing substrate concentration.
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What is an inhibitor?
What is an inhibitor?
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How does a competitive inhibitor affect an enzyme?
How does a competitive inhibitor affect an enzyme?
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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 extracted was from yeast by Buchner in 1897.
- The first purified enzyme was urease, isolated by James B. Summer in 1926.
Definition
- Enzymes are proteins (biological catalysts).
- They increase the rate of reactions by lowering activation energy.
- Enzymes catalyze nearly all biochemical reactions in cells.
- Enzymes have unique 3-dimensional shapes that fit the shapes of reactants.
Activation Energy
- Activation energy is the initial energy needed to start a chemical reaction.
- It's often supplied as heat from the surroundings.
- Think of activation energy as a barrier to making a product.
- The most stable product has the lowest energy.
- Most reactions require a "push" to get started, which is activation energy.
Characteristics of Enzymes
- Enzymes generally act quickly.
- The reaction speed depends on the substrate amount.
- Enzymes are not damaged during the reaction, so they can be reused.
- Enzymes can react in both directions.
- Enzymes are specific, limited to one particular reaction for a specific substrate.
- Enzyme molecules are typically 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
Trivial Names
- Enzyme names typically end in "-ase" (e.g., dehydrogenase).
- Sometimes, the enzyme's name identifies the reacting substance (e.g., sucrase catalyzes sucrose reactions).
- Other times, the name describes the enzyme's function (e.g., oxidases catalyze oxidation).
- Some enzyme names are common, particularly for digestion enzymes (e.g., pepsin, trypsin).
Systemic Nomenclature
- According to the International Union of Biochemistry (IUB), an enzyme has two parts:
- The first part is the name of the substrate.
- The second is the reaction type, ending with the suffix "-ase" (e.g., lactate dehydrogenase, pyruvate carboxylase).
IUB Classification
- Enzymes are classified by the reactions they catalyze.
- Different classes have unique examples shown in the table.
EC Numbers
- EC numbers are four-digit codes for enzymes.
- The first digit represents the enzyme class.
- Subsequent digits specify the functional group, coenzyme, and substrate.
- (e.g., alcohol: NAD oxidoreductase EC number 1.1.1.1).
Enzyme Terminologies
- Enzymes: Proteins produced by living cells that act as biological catalysts, accelerating biochemical reactions by lowering activation energy.
- Substrate: The substance upon which an enzyme acts in a biochemical reaction.
- Coenzymes: Small organic molecules that transport chemical groups (e.g., NAD, FAD).
- Cofactor: Non-protein, heat-stable, small-MW substances with the same function as coenzymes (e.g., Mg2+, Fe2+, Cu2+).
Ribozymes
- Ribozymes (RNA enzymes) catalyze chemical reactions by hydrolyzing their own phosphodiester bonds or bonds in other RNAs.
Enzyme Active Site
- The active site is a region within the enzyme that fits the shape of the substrate.
Zymogen
- Zymogens (proenzymes) are inactive forms of enzymes.
- The active site is masked by a polypeptide chain.
- (e.g., pepsinogen→pepsin, trypsinogen→trypsin).
Isoenzymes
- Isoenzymes catalyze the same reaction in different tissues.
- (e.g., lactate dehydrogenase has 5 isoenzymes).
Mechanism of Enzyme Action
- The substrate (S) fits into the enzyme's (E) active site.
- An enzyme-substrate complex (ES) is formed.
- The reaction occurs in the ES complex, converting S to product (P).
- The product (P) is released from the enzyme.
- The overall reaction converts substrate to product.
Example of an Enzyme-Catalyzed Reaction
- Description of sucrose binding catalyzing sucrose hydrolysis.
Models of Enzyme Action
Lock-and-Key Model
- The active site is rigid.
- Only substrates with the exact shape fit.
- Only one substrate fits.
Induced Fit Model
- The active site is flexible.
- The enzyme's and substrate shapes adjust to improve the fit.
- There's a greater range of substrate specificity.
Factors Affecting Enzyme Activity
Temperature
- Enzymes are most active at optimal temperatures (usually 37°C in humans).
- Enzyme activity decreases at low temperatures; at high temperatures.
- Enzyme activity is lost due to denaturation.
pH
- Enzymes are most active at optimum pH.
- Enzyme activity is lost due to disruptions in tertiary structure in low or high pH.
Enzyme Concentration
- Reaction rate increases with enzyme concentration (at constant substrate concentration).
- Higher enzyme concentration = more substrate binds to the enzyme.
Substrate Concentration
- Reaction rate increases with substrate concentration (at constant enzyme concentration).
- Maximum activity with saturated enzymes.
Enzyme Inhibition
- Inhibitor is any substance that diminishes enzymatic reaction velocity.
- Types of inhibition:
- Competitive: Inhibitor binds directly to the active site.
- Noncompetitive: Inhibitor binds to an allosteric site, changing the active site's shape.
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Description
Explore the fascinating world of enzymes, their historical context, and their fundamental role as biological catalysts. This quiz will cover the origins of the term 'enzyme,' notable discoveries, and the concept of activation energy. Test your knowledge on how enzymes influence biochemical reactions and their unique structures.
