Enzymes and Metabolic Pathways

Learning Objectives

• Describe enzymes and their common properties
• List enzyme classifications in correct order
• Describe factors that change enzyme activity
• Explain the relationship between Km and activity
• Explain enzyme inhibition and inhibition types

Metabolic Reactions

• Enzymes facilitate metabolic reactions
• Enzymes speed up reactions by lowering activation energy
• Enzymes alter the rate and change the classic biochemical reaction
• Enzymes facilitate transport of molecules

Glycolysis

• Glycolysis is a metabolic pathway for glucose breakdown
• Enzymes like hexokinase and phosphofructokinase are key in glycolysis
• Chemical reactions in glycolysis are shown in diagrams.

Activation Energy

• Activation energy is the energy needed for a reaction
• Catalysts, like enzymes, lower the activation energy, increasing reaction rates.
• Enzymes do not cause a chemical or nuclear reaction, but rather speed up an existing one.

Activation Energy and Catalysts

• Catalysts increase reaction rate without being consumed
• Catalysts decrease activation energy, making reactions easier
• Enzymes are biological catalysts

Enzymes

• Enzymes are biological catalysts
• Enzymes increase reaction rate by lowering activation energy
• Enzymes bind to substrates—reactants—to make products.

Properties of Enzymes

• Most enzymes are proteins
• Ribozymes are RNA enzymes
• Enzymes change reaction rate
• They are specific for substrates and reactions.

Efficiency

• Enzyme-catalyzed reactions are much faster than uncatalyzed reactions
• Carbonic anhydrase is a very fast enzyme, hydrating CO2
• Enzymes are highly efficient

Specificity

• Reaction specificity means enzymes catalyze specific reactions
• Substrate specificity means enzymes work on specific substrates or related molecules

Enzyme Nomenclature: Classification

• Enzymes are classified using an EC number
• Classification groups enzymes by function
• This classification system provides a hierarchical structure for enzymes.

Enzyme Kinetics and Km

• Km is a measure of enzyme affinity for substrate
• High Km means low affinity
• Enzymes work quickly and efficiently at high substrate concentration.
• Affinity and binding power are affected by substrate concentration.

Km, A Clinical Example

• Km is used to assess the efficiency of enzymes in clinical situations.
• Enzymes efficiency is relevant to the toxicity of substances.

Regulation of Enzyme Activity

• Enzyme activity can be regulated through multiple mechanisms.
• Enzyme amount (synthesis and degradation)
• Enzyme modification (covalent and non-covalent)
• Isozymes and compartments
• Feed-forward activation and feedback inhibition are important regulatory processes.
• These regulatory mechanisms allow the body to adjust enzyme activity based on cellular needs.

Enzyme Structure

• Apoenzyme: protein part of an enzyme
• Cofactor: non-protein part of an enzyme
• Holoenzyme: complete catalytically active enzyme
• Active site: where substrates bind and reactions occur.

Enzyme Structure: Active Site

• Active sites are highly specific for substrates
• Amino acid residues in the active site interact with substrates

Enzyme Activity

• Enzyme activity is measured by the rate of product formation
• One unit of enzyme activity converts one µmole of substrate to product
• Reaction speed depends on the number of substrates that change into products.

Factors Effecting Enzyme Activity

• Enzyme concentration affects the speed of a reaction
• Substrate concentration affects how quickly substrates move into reactants
• Temperature changes enzyme structure, and affects activity
• pH changes can affect enzyme activity
• Inhibitors can decrease reaction speed and are important to understanding enzyme functions.

Enzyme Concentration

• Enzyme concentration directly impacts reaction speed
• Increasing enzyme concentration increases the rate at which substrates can be converted to products

Substrate Concentration

• Increasing substrate concentration increases reaction speed until maximum rate is reached
• Km, the substrate concentration at half maximum reaction rate, reflects enzyme affinity for a substrate

Temperature

• Temperature affects enzyme shape and activity
• Enzymes have optimal temperatures for maximum activity
• Extreme temperatures can denature enzymes, stopping reactions.

pH

• pH affects enzyme shape and activity
• Enzymes have optimal pH ranges
• Extreme pH values can denature enzymes

Inhibitors

• Inhibitors decrease enzyme activity
• Reversible inhibitors bind temporarily
• Irreversible inhibitors bind permanently

This quiz covers the essential concepts of enzymes, their properties, classifications, and roles in metabolic pathways like glycolysis. It also explores the concepts of activation energy and enzyme inhibition. Test your understanding of how enzymes facilitate biochemical reactions and influence metabolic processes.