CHAPTER-3 Flashcards
(23 cards)
What Are Enzymes?
Enzymes are protein molecules that act as biological catalysts.
Enzymes are globular proteins with a 3D shape.
Hydrophilic R-groups on the outside make them soluble in water.
Many enzyme names end with “-ase” (e.g., amylase, ATPase).
Almost every metabolic reaction in living organisms needs enzymes to happen.
What Are Catalyst?
A catalyst speeds up a chemical reaction without being used up in the process.
Intracellular vs. Extracellular Enzymes
Enzymes operate within cells are described as intracellular.
Enzymes that are secreted by
cells and catalyse reactions outside cells are described
as extracellular.
Lock and Key Hypothesis
Enzyme have an active site (a pocket or cleft) where the substrate binds.
Active site has a fixed shape, like a lock.
Only the correct substrate (key) fits perfectly.
Forms an enzyme-substrate complex (temporary bonding via R-groups).
Highly specific—one enzyme usually works on one substrate.
🔹 Example:
Like a key fitting into a lock, only the right substrate binds.
Induced Fit Hypothesis (Updated Version)
Enzymes are not rigid—they can adjust shape slightly when the substrate binds.
The active site molds around the substrate for a tighter fit.
Makes catalysis more efficient than the rigid lock-and-key model.
🔹 Example:
Like a hand in a glove—the glove (enzyme) changes shape to fit the hand (substrate).
Catalase & Lysozyme Examples
Breaks toxic hydrogen peroxide (H₂O₂) into harmless water + oxygen in your cells. [one of fastest enzyme]
Found in tears, saliva, and mucus .
Attacks bacteria by breaking their cell walls (cuts polysaccharide chains). - Induced Fit in Action
What is activation energy
All chemical reactions need extra energy to start This starter energy is called activation energy.
How does Enzymes Lower Activation Energy
Enzymes avoid
this problem because they decrease the activation energy
of the reaction which they catalyse .
They do this by holding the substrate or substrates in such a
way that their molecules can react more easily.
Reactions catalysed by enzymes will take place rapidly at a much
lower temperature than they otherwise would.
What is Initial Rate of Reaction
The speed of the reaction at the very beginning (when substrate is abundant).
Factors that affect enzyme
action
The effect of enzyme concentration
The effect of substrate
concentration
Temperature and enzyme activity
pH and enzyme activity
Substrate Concentration
Effect:
↑ Substrate conc. = ↑ Reaction rate (until Vₘₐₓ).
Graph: Hyperbolic curve (initial rate vs. substrate conc.).
Why? Active sites saturate; extra substrate queues.
Key Term: Vₘₐₓ (maximum rate at saturation).
Temperature Effect
Low temp: Slow reactions (low energy).
Optimum temp: Peak rate (~37°C humans, ~70°C thermophiles).
High temp: Denaturation (irreversible shape loss).
Graph: Bell-shaped curve (rate vs. temp).
pH
Effect:
Optimum pH: Enzyme-specific (pepsin=pH 2, amylase=pH 7).
Extreme pH: Denaturation (H⁺/OH⁻ disrupt bonds).
Graph: Bell-shaped curve (rate vs. pH).
Turnover Rate (Catalytic Efficiency)
Definition: Number of substrate molecules converted to product per enzyme per second.
Examples:
Typical enzyme: ~1,000 molecules/sec
Carbonic anhydrase: 600,000 CO₂ molecules/sec (one of fastest known)
Biological Importance:
Essential for rapid removal of toxic metabolites (e.g., CO₂ buildup would be lethal).
Real-World Example: Ethylene Glycol Poisoning Competitive, Reversible Enzyme Inhibition
Toxic Ingredient: Ethylene glycol (antifreeze) → converted to oxalic acid (kidney damage).
Treatment: Ethanol (alcohol) acts as a competitive inhibitor:
Binds the same enzyme (alcohol dehydrogenase).
Slows ethylene glycol breakdown → body excretes it safely.
What is Non-Competitive Inhibition?
An inhibitor binds to the enzyme outside the active site (allosteric site), altering its shape and disabling the active site.
Reversible (inhibitor can unbind, restoring enzyme activity).
End-Product Inhibition (Feedback Mechanism)
Purpose: Prevents overproduction in metabolic pathways.
Process:
Final product of a pathway binds to allosteric site of an early enzyme.
Blocks pathway → reduces product synthesis.
As product levels ↓, inhibition stops → pathway resumes.
Example:
ATP inhibiting phosphofructokinase (PFK) in glycolysis (stops excess ATP production).
Michaelis–Menten
constant, Km
Definition: [Substrate] at which reaction rate = ½Vₘₐₓ.
Interpretation:
Low Kₘ: High enzyme-substrate affinity (enzyme reaches ½Vₘₐₓ at low [S]).
High Kₘ: Low affinity (needs high [S] for same efficiency).
Analogy:
Kₘ ≈ “Appetite” of enzyme for substrate.
Vₘₐₓ ≈ “Maximum eating speed”.
Calculating Active Site Occupancy
Occupancy = [S] /
[S]+Km
[S] = Substrate concentration
Km = Michaelis constant (substrate concentration at ½Vₘₐₓ)
What is Enzyme Immobilization?
Attaching enzymes to an inert support (e.g., alginate beads, silica gel) to reuse them and improve stability.
Alginate/other matrices hold enzyme shape rigidly, reducing denaturation
How Immobilized Enzymes Make Lactose-Free Milk
Lactase (the enzyme that breaks lactose) is stuck inside tiny beads (like jelly balls).
Milk flows through a column filled with these lactase beads.
break lactose into glucose + galactose
Reuse: Beads can be used over and over (saves money).
No Mixing: Milk stays clean—no enzyme bits floating in it.
Stronger Enzymes: Beads protect lactase from heat/pH changes.
