Biochemistry LE 1: Enzymes II

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Questions and Answers

What type of enzyme is hexokinase?

Hydrolase

Kinase

Transferase (correct)

Thiolase

What is the reaction catalyzed by hexokinase?

Glucose + ATP → Glucose 6-phosphate + ADP (correct)

Glucose → Glucose 6-phosphate

Glucose 6-phosphate → Glucose + ATP

ATP → ADP + Phosphate

What is the product formed when glucose reacts with ATP in the presence of hexokinase?

Glucose and ADP

Glucose and ATP

Glucose 6-phosphate and ATP

Glucose 6-phosphate and ADP (correct)

What is the function of kinases in metabolism?

To regulate metabolism by transferring phosphate groups Signup and view all the answers

What is the type of reaction catalyzed by thiolase?

Cleavage of a chemical bond Signup and view all the answers

What is the last step in the beta oxidation of fatty acids?

Cleavage of beta ketoacyl CoA Signup and view all the answers

What type of enzyme is pyrophosphatase?

Hydrolase Signup and view all the answers

Which phosphate group of ATP is transferred by either hexokinase or glucokinase?

Any of the above Signup and view all the answers

What is the type of inhibition that occurs when the inhibitor binds to the active site of the enzyme?

Competitive Signup and view all the answers

What is the term for the process by which an enzyme is converted to its active form?

Zymogen activation Signup and view all the answers

What is the term for the molecules that assist enzymes in their catalytic activity?

Coenzymes Signup and view all the answers

What is the term for the plot used to analyze the kinetics of enzyme-catalyzed reactions?

Lineweaver-Burk plot Signup and view all the answers

What is the term for the process by which an enzyme's activity is regulated through the binding of a molecule to a site other than the active site?

Allosteric modification Signup and view all the answers

What is the term for the molecules that are required for the activity of certain enzymes?

Metal ions Signup and view all the answers

What is the term for the specific binding of an enzyme to its substrate?

Enzyme specificity Signup and view all the answers

What is the term for the energy required for an enzyme-catalyzed reaction to occur?

Activation energy Signup and view all the answers

What is the function of the active site on an enzyme?

To catalyze a chemical reaction Signup and view all the answers

Which of the following is NOT a type of functional group found on the surface of the active site?

Lipids Signup and view all the answers

What is the term for a molecule that binds to an enzyme and enhances its activity?

Allosteric modifier Signup and view all the answers

What is the rate-limiting enzyme in the De Novo Synthesis of Fatty Acids?

Acetyl-CoA Carboxylase Signup and view all the answers

What is the function of HMG CoA Reductase?

To catalyze the reduction of HMG CoA into Mevalonate Signup and view all the answers

What is the effect of insulin on HMG CoA Reductase activity?

It increases the activity Signup and view all the answers

What is the effect of statins on HMG CoA Reductase activity?

It decreases the activity Signup and view all the answers

What is the term for a molecule that binds to an allosteric site on an enzyme and affects its activity?

Allosteric modifier Signup and view all the answers

What is the function of acetylcholinesterase?

Hydrolysis of acetylcholine to choline and acetate Signup and view all the answers

What is the ring structure of penicillin?

Four-membered beta-lactam ring fused to a five-membered thiazolidine ring Signup and view all the answers

What is the target of penicillin in bacteria?

Glycopeptide transpeptidase Signup and view all the answers

What is the result of penicillin binding to glycopeptide transpeptidase?

Impaired bacterial cell wall synthesis Signup and view all the answers

What is the type of inhibition exhibited by penicillin?

Suicide inhibition Signup and view all the answers

What is the basis for the antibacterial activity of penicillins?

Cell-wall synthesis inhibition leading to cell content leakage Signup and view all the answers

What is the name of the enzyme described in the text as responsible for the synthesis of bacterial cell wall?

Glycopeptide transpeptidase Signup and view all the answers

What is the term used to describe penicillin's structural similarity to the transition state?

Transition-state analog Signup and view all the answers

What is the role of cofactors in enzyme-catalyzed reactions?

To increase the rate of enzyme-catalyzed reactions and keep the enzyme in its active form Signup and view all the answers

What happens to the reaction velocity when substrate concentration increases?

It increases until the maximal velocity is reached Signup and view all the answers

Why does the reaction velocity decrease after reaching the maximal velocity?

Because the substrate molecules are competing for active sites on the enzyme surfaces Signup and view all the answers

What is the significance of enzyme levels in clinical diagnosis?

They are used to diagnose diseases of specific tissues Signup and view all the answers

What happens to enzyme levels during cell necrosis due to disease or trauma?

They increase Signup and view all the answers

Which of the following tissues can be diagnosed using enzyme levels?

Heart, liver, skeletal muscles, and other tissues Signup and view all the answers

What is the primary function of enzymes in clinical diagnosis?

To diagnose diseases of specific tissues Signup and view all the answers

Why are enzymes released into the blood during normal cell turnover?

Because they are part of the normal cell turnover process Signup and view all the answers

What is the relationship between substrate concentration and enzyme activity?

Substrate concentration increases enzyme activity up to a point Signup and view all the answers

Study Notes

Enzyme Kinetics

Michaelis-Menten kinetics describes the rate of enzymatic reactions, characterized by parameters like Vmax and Km.
The Lineweaver-Burk plot is a double reciprocal representation of the Michaelis-Menten equation, useful for calculating Vmax and Km.
Enzyme kinetics can be affected by various factors such as temperature, pH, and substrate concentration.

Coenzymes and Metal Ions

Coenzymes are organic molecules (e.g., NAD+, NADP+, Biotin, Thiamine, Flavin Adenine Dinucleotide) that assist enzymes by participating in the chemical transformations of substrates.
Metal ions like K+, Fe²⁺, Mg²⁺, and Zn²⁺ serve as cofactors to enhance enzymatic activity and maintain enzyme structure.

Types of Enzyme Inhibition

Competitive inhibition occurs when a substrate and inhibitor compete for the active site of an enzyme.
Non-competitive inhibition reduces enzyme activity without affecting substrate binding.
Irreversible inhibition leads to permanent loss of enzyme activity, often via covalent bonding.
Allosteric sites modulate enzyme activity by causing conformational changes, impacting substrate affinity.

Enzyme Activity and Regulation

Enzymes lower activation energy, thus increasing reaction rates.
Feedback inhibition regulates enzyme activity, where the end product of a pathway inhibits an upstream process.
Allosteric regulation can be positive or negative and can significantly affect the rate-limiting step in metabolic pathways.

Enzyme Specificity

Enzyme specificity refers to the ability of an enzyme to select substrate molecules based on shape, charge, or hydrophobic/hydrophilic characteristics.
Lock and Key Model and Induced Fit Model explain how substrates bind to enzymes, influencing reaction rates.

Enzymes in Clinical Diagnosis

Certain enzymes are released into the blood during normal cell turnover and can indicate tissue health.
Elevated enzyme levels in the blood can be markers for diseases, particularly in organs such as the heart and liver.

Cardiac Enzymes as Diagnostic Markers

Cardiac enzymes are utilized as biomarkers to diagnose myocardial infarction and other heart conditions.
Key cardiac enzymes include creatine kinase (CK) and troponin.

Key Reactions Involving Enzymes

Kinases transfer phosphate groups from ATP to specific substrates, crucial in metabolic regulation.
Hexokinase and glucokinase phosphorylate glucose in glycolysis, a vital metabolic pathway, resulting in glucose-6-phosphate.
Thiolase catalyzes the cleavage of beta-ketoacyl-CoA, a step in fatty acid metabolism, producing acetyl-CoA.

Penicillin and Enzyme Interactions

Penicillin inhibits bacterial cell wall synthesis by irreversibly binding to glycopeptide transpeptidase, a serine protease, disrupting bacterial growth.
Acetylcholinesterase hydrolyzes acetylcholine, a neurotransmitter, using serine residues to form a covalent intermediate.

Factors Affecting Enzyme Activity

Temperature and pH can significantly influence enzyme activity, with each enzyme having optimal conditions.
Substrate concentration impacts reaction velocity, which increases with substrate availability until Vmax is achieved, at which point all enzyme active sites are occupied.

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