Types and Functions of Enzymes — Revision Notes

⚡ 30-Second Revision

Enzymes — Biological catalysts, mostly proteins.
Function — Lower activation energy ($E_a$), speed up reactions.
Specificity — High, due to active site.
Models — Lock & Key (rigid), Induced Fit (flexible).
Classes (IUBMB)

1. Oxidoreductases: Redox reactions. 2. Transferases: Group transfer. 3. Hydrolases: Hydrolysis (add water). 4. Lyases: Cleavage without water/redox. 5. Isomerases: Isomerization. 6. Ligases: Bond formation (with ATP).

Factors — Temperature, pH (optimum, denaturation), Substrate conc. ($V_{max}$), Enzyme conc.
Inhibitors — Competitive (active site, overcome by substrate), Non-competitive (allosteric site, not overcome).

2-Minute Revision

Enzymes are proteinaceous biological catalysts that dramatically accelerate biochemical reactions by lowering their activation energy, without being consumed. They exhibit high specificity due to their unique active sites, which bind specific substrates.

The 'Induced Fit' model, where the enzyme's active site molds around the substrate, is a more accurate representation than the rigid 'Lock and Key' model. Enzyme activity is highly sensitive to environmental factors: each enzyme has an optimal temperature and pH, outside of which it can denature and lose function.

Increasing substrate concentration initially boosts activity until saturation ($V_{max}$), while increasing enzyme concentration linearly increases the rate. Inhibitors, such as competitive (binding active site, reversible by high substrate) and non-competitive (binding allosteric site, not reversible), regulate enzyme activity.

Enzymes are classified into six major groups based on the reaction type they catalyze: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, and Ligases. Understanding these classes and their functions is crucial for NEET.

5-Minute Revision

Enzymes are indispensable biological catalysts, primarily composed of proteins, that significantly increase the rate of biochemical reactions by reducing the activation energy ($E_a$). They are not consumed during the reaction and are highly specific, meaning each enzyme typically acts on a particular substrate or a small group of related substrates.

This specificity arises from the unique three-dimensional structure of their active site, a specific region where the substrate binds. The 'Induced Fit' model best describes this interaction, where the enzyme's active site undergoes a conformational change upon substrate binding to achieve a tighter, more efficient fit.

Enzymes are classified into six main categories by the IUBMB based on the reaction they catalyze:

1
Oxidoreductases — Catalyze oxidation-reduction reactions (e.g., dehydrogenases).
2
Transferases — Transfer functional groups (e.g., kinases transferring phosphate).
3
Hydrolases — Break bonds by adding water (e.g., proteases, lipases).
4
Lyases — Cleave bonds without hydrolysis or oxidation (e.g., decarboxylases).
5
Isomerases — Rearrange atoms within a molecule (e.g., mutases).
6
Ligases — Form new bonds, often coupled with ATP hydrolysis (e.g., DNA ligase).

Enzyme activity is profoundly influenced by environmental factors. Temperature and pH have optimal ranges; deviations lead to denaturation, an irreversible loss of the enzyme's structure and function.

Substrate concentration affects reaction rate, with activity increasing until the enzyme becomes saturated ($V_{max}$). Enzyme concentration is directly proportional to reaction rate (assuming excess substrate).

Inhibitors decrease enzyme activity: competitive inhibitors bind to the active site (can be overcome by high substrate), while non-competitive inhibitors bind to an allosteric site (cannot be overcome).

Understanding these types and functions is fundamental to comprehending metabolic regulation and is a high-yield topic for NEET.

Prelims Revision Notes

Enzymes: The Biological Catalysts

Definition — Biological catalysts, mostly proteins, that speed up biochemical reactions.
Mechanism — Lower activation energy ($E_a$), do NOT change $\Delta G$ or equilibrium constant ($K_{eq}$). Provide alternative reaction pathway.
Nature — Predominantly proteinaceous. Some RNA molecules (ribozymes) also act as enzymes.
Active Site — Specific region on enzyme where substrate binds. Determines specificity.
Models of Action

* Lock and Key: Rigid active site, perfectly complementary to substrate. * Induced Fit: Flexible active site, changes shape upon substrate binding for a tighter fit.

Specificity — Highly specific (absolute, group, stereospecific).
Reusability — Enzymes are not consumed in the reaction.

Enzyme Classification (IUBMB - 6 Classes)

1
Oxidoreductases — Catalyze redox reactions (e.g., Dehydrogenases, Oxidases).
2
Transferases — Transfer functional groups (e.g., Kinases, Transaminases).
3
Hydrolases — Catalyze hydrolysis (cleavage with water) of bonds (e.g., Proteases, Lipases, Amylases).
4
Lyases — Cleave bonds by elimination, forming double bonds (e.g., Decarboxylases, Aldolases).
5
Isomerases — Catalyze intramolecular rearrangements (e.g., Racemases, Mutases).
6
Ligases — Catalyze bond formation coupled with ATP hydrolysis (e.g., DNA Ligase, Synthetases).

Factors Affecting Enzyme Activity

Temperature — Activity increases with temp up to optimum ($37^circ C$ for human enzymes), then rapidly decreases due to denaturation (loss of 3D structure).
pH — Each enzyme has an optimal pH (e.g., Pepsin pH 1.5-2.5, Trypsin pH 8). Extreme pH causes denaturation.
Substrate Concentration — Rate increases with [S] until saturation ($V_{max}$ is reached).
Enzyme Concentration — Rate is directly proportional to [E] (assuming excess substrate).
Inhibitors — Decrease enzyme activity.

* Competitive: Binds to active site, structurally similar to substrate. Can be overcome by increasing [S]. Increases apparent $K_m$, $V_{max}$ unchanged. * Non-competitive: Binds to allosteric site (not active site). Causes conformational change. Cannot be overcome by increasing [S]. Decreases $V_{max}$, $K_m$ unchanged. * Irreversible: Forms strong (often covalent) bonds, permanently inactivating enzyme.

Activators — Enhance enzyme activity.
Cofactors/Coenzymes — Non-protein components required for activity (e.g., metal ions, vitamins).

Vyyuha Quick Recall

To remember the 6 enzyme classes: Over The Hill, Lions In Large Groups.

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases (The 'G' is for Groups, but helps remember Ligases)