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Questions and Answers
Vitamin B₃ is also known as Niacin.
Vitamin B₃ is also known as Niacin.
True
Coenzyme Q has a structure that is similar to Vitamin A.
Coenzyme Q has a structure that is similar to Vitamin A.
False
Lipoic acid serves as a carrier of carbon in oxidative decarboxylation.
Lipoic acid serves as a carrier of carbon in oxidative decarboxylation.
False
Pyridoxal phosphate is involved in transamination and decarboxylation of amino acids.
Pyridoxal phosphate is involved in transamination and decarboxylation of amino acids.
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Biotin acts as a carrier of nitrogen in the fixation of CO₂ reactions.
Biotin acts as a carrier of nitrogen in the fixation of CO₂ reactions.
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Hydroperoxidases can use hydrogen peroxide as a substrate.
Hydroperoxidases can use hydrogen peroxide as a substrate.
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Dioxygenases incorporate only one atom of molecular oxygen into the substrate.
Dioxygenases incorporate only one atom of molecular oxygen into the substrate.
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Superoxide dismutase is an enzyme that protects organisms from oxygen toxicity.
Superoxide dismutase is an enzyme that protects organisms from oxygen toxicity.
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Catalase primarily uses organic peroxides as electron donors.
Catalase primarily uses organic peroxides as electron donors.
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L-ascorbate oxidase catalyzes a reaction involving molecular oxygen.
L-ascorbate oxidase catalyzes a reaction involving molecular oxygen.
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All enzymes are proteins except ribozymes, which are types of RNA that catalyze reactions.
All enzymes are proteins except ribozymes, which are types of RNA that catalyze reactions.
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Extracellular enzymes are produced and act inside the cells.
Extracellular enzymes are produced and act inside the cells.
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Enzyme activity is expressed in International Units (IU) by measuring the conversion of one micromole of substrate per minute.
Enzyme activity is expressed in International Units (IU) by measuring the conversion of one micromole of substrate per minute.
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Holoenzymes consist only of a protein molecule.
Holoenzymes consist only of a protein molecule.
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Cofactors can only be organic compounds like vitamins.
Cofactors can only be organic compounds like vitamins.
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Prosthetic groups are small organic molecules bound to enzymes by covalent bonds.
Prosthetic groups are small organic molecules bound to enzymes by covalent bonds.
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Coenzymes are strongly attached to enzymes and do not leave during the reaction.
Coenzymes are strongly attached to enzymes and do not leave during the reaction.
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A katal measures the amount of enzyme that catalyzes the conversion of one mole of substrate per second.
A katal measures the amount of enzyme that catalyzes the conversion of one mole of substrate per second.
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Metal-activated enzymes have a metal that is tightly attached to the apoenzyme.
Metal-activated enzymes have a metal that is tightly attached to the apoenzyme.
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Calcium is used by lipase as an essential metal ion.
Calcium is used by lipase as an essential metal ion.
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Manganese is associated only with the enzyme xanthine oxidase.
Manganese is associated only with the enzyme xanthine oxidase.
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The active site of an enzyme consists solely of binding sites.
The active site of an enzyme consists solely of binding sites.
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Enzymes can accelerate reactions by a factor of 10³ to 10⁸ times compared to uncatalyzed reactions.
Enzymes can accelerate reactions by a factor of 10³ to 10⁸ times compared to uncatalyzed reactions.
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Metalloenzymes can lose their metal ions during purification through dialysis.
Metalloenzymes can lose their metal ions during purification through dialysis.
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Zinc does not participate in the catalytic activity of alcohol dehydrogenase.
Zinc does not participate in the catalytic activity of alcohol dehydrogenase.
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The hydroxyl group of serine can be found in the active site of an enzyme.
The hydroxyl group of serine can be found in the active site of an enzyme.
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The amount of enzyme in a cell is only determined by the rate of enzyme synthesis.
The amount of enzyme in a cell is only determined by the rate of enzyme synthesis.
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Positive effectors are molecules that inhibit the catalytic reaction in allosteric regulation.
Positive effectors are molecules that inhibit the catalytic reaction in allosteric regulation.
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Citrate acts as a positive allosteric effector for the enzyme phosphofructokinase1.
Citrate acts as a positive allosteric effector for the enzyme phosphofructokinase1.
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Feedback inhibition occurs when the end products of a metabolic pathway inhibit the activity of the first enzyme.
Feedback inhibition occurs when the end products of a metabolic pathway inhibit the activity of the first enzyme.
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Allosteric enzymes lack a regulatory site separate from the active site.
Allosteric enzymes lack a regulatory site separate from the active site.
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Enzyme turnover number indicates the number of substrate molecules converted to products per enzyme molecule per second.
Enzyme turnover number indicates the number of substrate molecules converted to products per enzyme molecule per second.
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Pepsin is an enzyme that demonstrates absolute specificity for its substrate.
Pepsin is an enzyme that demonstrates absolute specificity for its substrate.
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The Michaelis-Menten equation can apply to allosterically regulated enzymatic reactions.
The Michaelis-Menten equation can apply to allosterically regulated enzymatic reactions.
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The EC number for alcohol dehydrogenases is EC 1.1.1.1.
The EC number for alcohol dehydrogenases is EC 1.1.1.1.
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Reversible covalent modification in enzymes involves the addition or removal of phosphate groups.
Reversible covalent modification in enzymes involves the addition or removal of phosphate groups.
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Urease can catalyze the hydrolysis of both urea and thiourea.
Urease can catalyze the hydrolysis of both urea and thiourea.
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Repressors increase the synthesis of key enzymes in glycolysis.
Repressors increase the synthesis of key enzymes in glycolysis.
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Hexokinase enzymatically facilitates the phosphorylation of disaccharide sugars.
Hexokinase enzymatically facilitates the phosphorylation of disaccharide sugars.
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Carbonic anhydrase is considered one of the fastest enzymes in the human body.
Carbonic anhydrase is considered one of the fastest enzymes in the human body.
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Group specificity allows an enzyme to act on molecules with specific functional groups.
Group specificity allows an enzyme to act on molecules with specific functional groups.
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Lactate dehydrogenase is named for its ability to catalyze the dehydrogenation of lactose only.
Lactate dehydrogenase is named for its ability to catalyze the dehydrogenation of lactose only.
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Study Notes
Enzymes
- Enzymes are protein catalysts that increase the rate of chemical reactions in biological systems without changing themselves.
- All enzymes are proteins except some types of RNA which act as enzymes catalyzing the cleavage and synthesis of phosphodiester bonds. These types of RNA are called ribozymes.
- Substrate: The substance upon which the enzyme acts.
- Cellular distribution of enzymes:
- Intracellular enzymes: Enzymes produced and act inside the cells (e.g., metabolic enzymes).
- Extracellular enzymes: Enzymes produced inside cells but act outside cells (e.g., digestive enzymes).
- Enzymes are mainly synthesized in the cytosol or endoplasmic reticulum (ER), some in the mitochondria. They are present in all body cells and are found in both extracellular fluids (e.g., plasma, CSF) and intracellular compartments (e.g., cell membrane, cytosol, mitochondria, lysosomes, microsomes, nucleus).
- Enzyme activity is expressed in:
- International unit (IU): The amount of enzyme that catalyzes the conversion of one micromole (µmol) of substrate to product per minute.
- Katal: The amount of enzyme that catalyzes the conversion of one mole of substrate to product per second (1 katal = 1 mol s⁻¹).
- Nature of enzymes: Most enzymes are proteins. Enzymes can exist as:
- Simple enzymes: Made up of only a protein molecule.
- Holoenzymes: Made up of a protein part (apoenzyme) and a non-protein part (cofactor). Cofactors can be organic compounds (e.g., vitamins) or inorganic metal ions (e.g., Fe²⁺, Zn²⁺, Mg²⁺).
- Organic molecules are divided into prosthetic groups and coenzymes.
- Prosthetic group: Small organic molecule covalently bound to the apoenzyme.
- Coenzyme: Small organic molecule non-covalently bound to the apoenzyme. Coenzymes are derivatives of vitamins.
- Coenzymes are categorized as:
- Codehydrogenases
- Group transferring coenzymes
Enzyme Nomenclature
-
Trivial names: Names that don't describe the source, function, or catalyzed reaction.
-
Recommended names: Typically end in "-ase" and describe the substrate or the reaction.
-
Enzyme Commission (EC) number: A classification system that uses four numbers to identify enzymes. The first number indicates the reaction type, the second number indicates the functional group, the third number identifies the coenzyme, and the fourth number identifies the substrate.
-
Specificity: Enzymes are specific for their substrates.
- Absolute specificity: One enzyme only catalyzes on one substrate.
- Group specificity: Enzymes act on molecules with specific functional groups.
- Optical specificity: Enzymes are specific for one optical isomer.
- Dual specificity: Acts on two substrates in the same reaction
Enzyme Kinetics
- Enzyme kinetics: Study of reaction rates involving enzymes.
- Velocity of reaction: The increase in product concentration or decrease in substrate concentration over time.
- Initial velocity: The reaction velocity measured at the start.
- Michaelis-Menten equation: Describes the relationship between reaction velocity and substrate concentration.
- Km: Michaelis constant, numerically equal to the substrate concentration at which the reaction velocity is half of the maximum velocity (Vmax). Km reflects enzyme-substrate affinity.
- Vmax: Maximum velocity, the maximum rate of reaction achievable.
Enzyme Activity Factors
- Temperature: Enzyme activity increases with temperature until an optimum temperature (around 37°C for many human enzymes).
- pH: Enzyme activity is optimal at a specific pH range.
- Enzyme concentration: Increasing enzyme concentration increases the reaction rate up to a point.
- Substrate concentration: Increasing substrate concentration increases the reaction rate up to a saturation point (maximum velocity).
- Inhibitors: Substances that decrease enzyme activity (competitive and non-competitive, irreversible).
Enzyme Classification
- Enzymes are classified based on the reactions they catalyze into six major classes:
- Oxidoreductases (oxidation-reduction reactions)
- Transferases (transfer a group from one molecule to another)
- Hydrolases (hydrolysis reactions)
- Lyases (addition or removal of groups to form double bonds)
- Isomerases (isomerization reactions)
- Ligases (joining two molecules using ATP)
Isoenzymes
- Isoenzymes: Different forms of an enzyme that have the same catalytic function but differ in amino acid sequence, physical properties, and/or organ distribution.
- Isoenzyme variations are important in clinical diagnosis.
Enzyme Inhibition
- Inhibitors: Substances that decrease enzyme activity, either reversibly (competitive, non-competitive, uncompetitive) or irreversibly.
- Irreversible inhibition: The inhibitor forms a permanent bond with the enzyme.
- Reversible inhibition: The inhibitor forms a temporary bond with the enzyme.
Enzyme Regulation
- Regulation of enzyme activity: Occurs through amount of enzyme, allosteric regulation, feedback inhibition, covalent modification.
- Allosteric regulation: Enzymes that have an active site and an allosteric site that accepts effectors, which change the enzyme's shape and therefore activity.
- Feedback inhibition: End products inhibit the enzyme.
- Covalent modifications: Phosphate addition or removal modifies enzyme activity.
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Description
Test your knowledge on key biochemicals such as vitamins and enzymes. This quiz covers topics like Coenzyme Q, Lipoic acid, and various enzymatic functions in biochemical reactions. Perfect for students studying biochemistry at any level!
