Enzyme
Definition
An enzyme is a biological catalyst, typically a protein, that speeds up chemical reactions in living organisms without being consumed in the process. Enzymes lower the activation energy required for reactions and are highly specific, each acting on a particular substrate. They are essential for metabolism and virtually all cellular processes.
Key Points for NEET
- 1Most enzymes are proteins (some are RNA - ribozymes)
- 2Highly specific due to lock-and-key or induced fit model
- 3Have an active site where substrate binds
- 4Affected by pH, temperature, substrate concentration
- 5Can be inhibited competitively or non-competitively
Example
Amylase in saliva breaking down starch into sugars
Asked in NEET
Common Mistakes to Avoid
- ✗Thinking enzymes are consumed in reactions — they are catalysts and are reused
- ✗Confusing competitive inhibition (binds active site) with non-competitive (binds allosteric site)
- ✗Assuming all enzymes are proteins — ribozymes are RNA molecules with catalytic activity
Quick Revision Notes
- ⚡Lock-and-key model: rigid active site; Induced fit model: flexible active site molds around substrate
- ⚡Km (Michaelis constant) = substrate concentration at half Vmax; low Km = high enzyme affinity
- ⚡Optimal pH: pepsin (pH 2), trypsin (pH 8), salivary amylase (pH 6.8)
- ⚡Enzyme inhibitors in NEET: competitive (resembles substrate), non-competitive (changes enzyme shape)
Related Terms
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More Cell Biology Definitions
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Meiosis
Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four haploid daughter cells from one diploid parent cell. It occurs in germ cells and is essential for sexual reproduction, introducing genetic variation through crossing over and independent assortment.
Osmosis
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