Biochemistry: Enzymes and Glycolysis

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 biochemical reactions by lowering activation energy
• Enzymes can catalyze anabolic (synthesis) and catabolic (breakdown) reactions
• Enzymes modify existing molecules or transport them
• Enzymes have specific roles in various metabolic pathways

Glycolysis

• Glycolysis is a metabolic pathway that converts glucose to pyruvate
• Enzymes like hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK) are crucial
• Illustrated diagram showing the steps and involved enzymes

Enzyme Classification

• Enzymes are often categorized using EC numbers (Enzyme Commission numbers)
• Different types of enzymes perform different types of reactions

Activation Energy

• Activation energy is the energy needed for a reaction to start
• Enzymes lower activation energy, allowing reactions to proceed faster
• Catalysts, like enzymes, do not affect the reaction equilibrium, only speed it up

Activation Energy and Catalysts

• Catalysts speed up reactions without being consumed
• Enzymes are biocatalysts that lower activation energy required for biochemical reactions

Enzyme Structure

• Enzymes consist of an apoenzyme (protein portion), and a cofactor (non-protein portion)
• These components combine to form a holoenzyme (complete active enzyme)
• An illustration showing the structure with an active site where substrate binds

Enzyme Active Site

• The active site of an enzyme is a unique region for substrate binding
• Amino acids within the active site are precisely arranged to catalyze the reaction
• A graphic illustration of an active site with key amino acid residues

Enzyme Activity

• Enzyme activity (V) refers to the reaction rate or how quickly a substrate is converted to a product
• One unit (U) of enzyme converts one micromole (µmol) of substrate to product in one minute
• Illustrated with a graphical analogy using a speedometer

Factors Affecting Enzyme Activity

• Enzyme concentration: higher concentration leads to faster reaction
• Substrate concentration: increased substrate initially increases reaction rate, reaching saturation
• Temperature: optimal temperature exists; beyond that, enzyme denatures
• pH: specific pH levels are ideal for optimal activity
• Inhibitors: competitive or non-competitive inhibitors bind to reduce activity

Enzyme Concentration

• Reaction rate increases with increasing enzyme concentration
• Demonstrated in a graph showing reaction rate as a function of time and enzyme concentration

Substrate Concentration

• Substrate concentration affects the reaction rate, as shown in a graph
• Km (Michaelis-Menten constant) is the substrate concentration at half-maximal velocity (Vmax)

Temperature

• Enzymes have optimal temperatures for activity
• Temperature increase affects enzyme activity until denaturation

pH

• Enzymes exhibit optimal pH ranges for activity
• Different enzymes have different optimal pH values

Inhibitors

• Inhibitors decrease enzyme activity
• Reversible inhibitors bind and release, while irreversible inhibitors bind permanently and denature the enzyme
• Competitive inhibitors bind to the active site preventing substrate binding.
• Noncompetitive inhibitors bind elsewhere on the enzyme changing the enzyme's shape.

Reversible Inhibition

• Competitive, noncompetitive, and uncompetitive are types of reversible inhibition
• Graphically showing the effects of various inhibitors on enzyme activity, by affecting Km and Vmax

Enzyme Kinetics and Km

• Km is a measure of affinity between enzymes and substrates
• A higher Km implies a lower affinity, lower Km higher affinity
• Km reflects the affinity of an enzyme towards its substrate
• Illustrated using a reaction rate graph to better understand Km

Km: A Clinical Example

• Km values can be used to understand the toxicity of substances
• Alcohol dehydrogenase, an enzyme, is involved in alcohol metabolism
• Illustrated with various metabolic equations

Regulation of Enzyme Activity

• Enzyme synthesis, degradation, and modification affect enzyme activity.
• Methods such as phosphorylation, negative feedback, and compartmentalization regulate the effectiveness of enzymes.
• The location and modification of an enzyme influence its activity.

Enzyme Regulation: Phosphorylation/Dephosphorylation

• Phosphorylation or dephosphorylation modify enzyme activity.

Regulation of Enzyme Activity: Feed-Back Inhibition

• Negative feedback inhibition, where products regulate the initiating enzyme, controls reaction velocity

Regulation of Enzyme Activity: Feed-Forward Activation

• An earlier reaction activating a later reaction in a metabolic pathway

Isozymes

• Isozymes are related enzymes that catalyze the same reaction with similar but different amino acid sequences.

This quiz covers essential concepts in biochemistry related to enzymes, including their properties, classifications, and the factors influencing their activity. Additionally, it delves into glycolysis, a key metabolic pathway, highlighting the enzymes involved and their roles. Test your understanding of enzyme functions and metabolic reactions.