Enzyme Nomenclature and Classification

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Questions and Answers

How do sulfa drugs inhibit bacterial growth?

Sulfa drugs inhibit bacterial growth by competitively inhibiting the enzymes that normally react with PABA, preventing the synthesis of folic acid.

What is the main structural difference that allows penicillin to target bacteria but not human cells?

The main structural difference is that bacteria possess a cell wall, while human cells do not.

What role does the enzyme transpeptidase play in bacterial cell wall synthesis?

Transpeptidase cleaves terminal d-alanine and facilitates the cross-linking of peptidoglycan layers in the bacterial cell wall.

How do penicillins act as inhibitory substrates for transpeptidase?

Penicillins act as inhibitory substrates for transpeptidase due to their structural similarity to d-alanyl-d-alanine, allowing them to bind to the enzyme. Signup and view all the answers

Explain why sulfa drugs are ineffective in humans.

Sulfa drugs are ineffective in humans because humans obtain folic acid preformed from dietary sources and do not synthesize it. Signup and view all the answers

What does Km represent in enzyme kinetics?

Km represents the substrate concentration at which the reaction velocity, υ, equals half of the maximum velocity, vmax. Signup and view all the answers

How is Km related to the binding affinity of the substrate to the enzyme?

Km is inversely related to the binding affinity; a greater Km means lower affinity. Signup and view all the answers

Explain the significance of the Lineweaver-Burke plot in determining Km.

The Lineweaver-Burke plot transforms the Michaelis-Menten equation into a linear form, making it easier to estimate Km and vmax. Signup and view all the answers

What happens to Km when the substrate concentration, S, is very low?

When substrate concentration, S, is very low, Km becomes equal to S when the reaction velocity, υ, is half of vmax. Signup and view all the answers

How does the value of vmax relate to the turnover number of an enzyme?

Vmax is equivalent to the turnover number, denoting the maximum rate at which an enzyme converts substrate into product. Signup and view all the answers

What type of reaction does an oxidase catalyze?

An oxidase catalyzes oxidation reactions. Signup and view all the answers

Name one substrate and its corresponding enzyme from the hydrolases class.

One substrate is protein, and its corresponding enzyme is protease. Signup and view all the answers

What do transferases specifically facilitate in biochemical reactions?

Transferases catalyze the transfer of functional groups between two substrates. Signup and view all the answers

Describe the action of lyases and provide an example.

Lyases catalyze the addition or removal of groups to create or eliminate double bonds without hydrolysis. An example is a dehydratase, which removes water from a substrate. Signup and view all the answers

Identify and define one type of enzyme that belongs to the isomerases class.

Racemases are enzymes that convert D isomers to L isomers or vice versa. Signup and view all the answers

What is the primary action of hydrolases in biochemical reactions?

Hydrolases catalyze the addition of a water molecule to break chemical bonds. Signup and view all the answers

Explain how dehydrogenases function in enzymatic reactions.

Dehydrogenases introduce a double bond by removing hydrogen (H2) from a substrate. Signup and view all the answers

How are enzyme names typically structured based on their function and substrates?

Enzyme names often include a prefix indicating the type of reaction followed by the substrate, such as 'glucose oxidase.' Signup and view all the answers

What is the role of protein modification in enzyme activity?

Protein modification can activate or inactivate an enzyme through the addition or removal of phosphate groups. Signup and view all the answers

How do irreversible inhibitors affect enzyme activity?

Irreversible inhibitors bind tightly to enzymes and prevent the formation of the enzyme-substrate complex. Signup and view all the answers

Describe competitive inhibition.

Competitive inhibition occurs when an inhibitor with a similar structure competes with the substrate for the active site on the enzyme. Signup and view all the answers

What distinguishes noncompetitive inhibition from competitive inhibition?

Noncompetitive inhibition involves inhibitors that bind to sites other than the enzyme's active site, affecting the reaction without blocking substrate binding. Signup and view all the answers

What is the role of kinases and phosphatases in protein modification?

Kinases are enzymes that add phosphate groups to proteins, while phosphatases are enzymes that remove them. Signup and view all the answers

What is a structural analog in the context of enzyme inhibition?

A structural analog is a compound that closely resembles a substrate and competes for the active site on an enzyme, acting as a competitive inhibitor. Signup and view all the answers

Explain how chemotherapy relates to enzyme activity.

Chemotherapy uses chemicals to selectively destroy infectious microorganisms without harming the host's cells, often impacting enzyme activities critical for microbial survival. Signup and view all the answers

Give an example of an irreversible inhibitor and its effect.

Diisopropylphosphofluoridate (DIPF) is an example; it binds covalently to enzymes, leading to permanent inhibition. Signup and view all the answers

What is the significance of the slope and intercept in the plot of 1/υ vs. 1/(S)?

The slope represents Km/vmax, while the intercept on the ordinate is 1/vmax, allowing for the calculation of Km. Signup and view all the answers

List the vitamin that acts as a coenzyme in decarboxylation reactions and its deficiency symptoms.

Thiamine (B1); deficiency symptoms include fatigue, anorexia, nerve degeneration, paralysis, and heart failure. Signup and view all the answers

What coenzyme is associated with riboflavin (B2) and what are some symptoms of its deficiency?

Riboflavin is associated with flavin mononucleotide and flavin adenine dinucleotide; deficiency symptoms include dermatitis, glossitis, and cataracts. Signup and view all the answers

Which vitamin is known for its role in numerous redox reactions and name the deficiency it causes?

Niacin (B3); its deficiency causes pellagra, characterized by scaly skin, muscle fatigue, diarrhea, and mental disorders. Signup and view all the answers

What is the function of coenzyme A, and is there a known deficiency syndrome for pantothenic acid (B5)?

Coenzyme A is involved in many reactions of fatty acids, and notably, there is no known deficiency syndrome, although it may cause fatigue. Signup and view all the answers

Which coenzyme is linked to amino acid reactions involving transamination and what are the potential deficiency symptoms?

Pyridoxine (B6) is linked to these reactions, with deficiency symptoms including dermatitis, fatigue, and anemia. Signup and view all the answers

Identify the coenzyme for CO2 fixation reactions and its associated deficiency symptoms.

Biotin is the coenzyme for CO2 fixation; its deficiency can lead to dermatitis, fatigue, anemia, nausea, and mental depression. Signup and view all the answers

What role does tetrahydrofolic acid play and what are the consequences of its deficiency?

Tetrahydrofolic acid is involved in various reactions with single carbon compounds; its deficiency can lead to abnormal red and white blood cells and gastrointestinal disturbances. Signup and view all the answers

Cyanocobalamine is known for which specific biochemical processes, and what deficiency does it cause?

Cyanocobalamine is involved in carbon chain isomerization and methyl group transfers; its deficiency can cause pernicious anemia and neurological disorders. Signup and view all the answers

What is the primary function of ascorbic acid (Vitamin C) and what deficiency symptoms may arise?

Ascorbic acid is essential for collagen formation, protein metabolism, and iron absorption; deficiency symptoms include bleeding gums, slow healing wounds, and muscle pain. Signup and view all the answers

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Study Notes

Enzyme Reactions and Nomenclature

Enzymes are categorized by their reaction type, indicated by prefixes; examples include oxidase for oxidation and hydrolase for hydrolysis.
Substrates can also be included in enzyme names, e.g., glucose oxidase and pyruvate carboxylase.
Enzymes are classified into six major classes by the International Union of Biochemistry.

Classification of Enzymes

Oxidoreductases: Catalyze oxidation-reduction reactions.
- Oxidases: Facilitate oxidation.
- Reductases: Facilitate reduction.
- Dehydrogenases: Introduce double bonds by removing H₂, transferring hydrogen to coenzymes.
Transferases: Aid in transferring functional groups.
- Kinases: Transfer phosphate groups.
- Transaminases: Transfer amino groups.
Hydrolases: Add water to break bonds.
- Proteases: Hydrolyze peptide bonds in proteins.
- Carbohydrases: Hydrolyze glycosidic bonds (including sucrase and lactase).
- Lipases: Hydrolyze ester bonds in lipids.
- Nucleases: Hydrolyze sugar phosphate bonds in nucleic acids.
- Phosphatases: Hydrolyze phosphate ester bonds.
Lyases: Remove/add groups to form double bonds without hydrolysis.
- Dehydratases: Remove water.
- Decarboxylases: Remove carbon dioxide.
- Deaminases: Remove ammonia.
Isomerases: Convert substrates into isomers.
- Racemases: Convert D to L isomers.

Enzyme Activation and Regulation

Protein modification, particularly phosphorylation, can activate or inactivate enzymes.
Kinases phosphorylate proteins, while phosphatases dephosphorylate them.

Inhibition of Enzyme Activity

Irreversible Inhibitors: Form covalent bonds with enzymes, blocking activity permanently (e.g., diisopropylphosphofluoridate).
Reversible Inhibitors: Bind non-covalently and can be released.
- Competitive Inhibition: Inhibitor competes with substrate for active sites; can be overcome by increasing substrate.
- Noncompetitive Inhibition: Inhibitor binds elsewhere, altering enzyme activity without blocking substrate binding.

Chemotherapy and Antibiotics

Chemotherapy: Uses chemicals to target infectious microorganisms.
Antimetabolites: Act through competitive inhibition (e.g., sulfa drugs mimic PABA).
Antibiotics: Target bacterial-specific structures like cell walls (e.g., penicillin inhibits cell wall synthesis enzymes).

Michaelis-Menten Kinetics

Vmax: Maximum reaction rate; influenced by substrate concentration.
Km (Michaelis constant): Substrate concentration at which reaction velocity is half of Vmax; indicative of substrate affinity.

Lineweaver-Burke Plots

Linear transformation of Michaelis-Menten equation allows for easier determination of Km and Vmax.
Slope represents Km/Vmax; intercepts provide Vmax and -1/Km.

Coenzymes and Vitamins

Water-soluble vitamins play crucial roles as coenzymes in metabolic reactions.
- Thiamine (B1): Decarboxylation; deficiency leads to beriberi.
- Riboflavin (B2): Redox reactions; deficiency causes dermatitis and glossitis.
- Niacin (B3): Redox reactions; deficiency leads to pellagra.
- Pantothenic Acid (B5): Transfers acetyl groups; no known deficiency.
- Pyridoxine (B6): Key for amino acid reactions; deficiency can cause dermatitis and anemia.
- Biotin: CO2 fixation; deficiency leads to dermatitis and fatigue.
- Folic Acid: Involved in C-compound reactions; deficiency results in abnormal blood counts.
- Cyanocobalamin (Vitamin B12): Isomerization and methyl transfers; deficiency leads to pernicious anemia.
- Ascorbic Acid (Vitamin C): Necessary for collagen formation; deficiency leads to scurvy.

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