Q.Describe the important properties of enzymes.

Enzymes are biological catalysts, and they have several important defining properties:

• Protein nature: almost all enzymes are proteins, so each has a primary, secondary and especially a three-dimensional tertiary structure. A few nucleic acids called ribozymes are the exception that can also act as enzymes.
• Active site: the folded chain forms a pocket or crevice, the active site, into which the substrate fits and where the reaction is catalysed.
• Lowering activation energy: an enzyme brings down the energy barrier (the activation energy) that a reaction must cross, which is how it speeds the reaction up.
• Enormous catalytic power: enzymes accelerate reactions by huge factors — carbonic anhydrase, for instance, speeds the making of carbonic acid by about ten million times.
• Unchanged and reusable: the enzyme emerges from the reaction completely unaltered, so it can bind fresh substrate and repeat the cycle again and again.
• Sensitivity to conditions: each enzyme has an optimum temperature and optimum pH; low temperature only slows it reversibly, but high temperature (usually above about 40 degrees Celsius) denatures the protein and destroys its activity. …

Enzymes are what make the chemistry of life run at the speeds cells need, and their behaviour follows from a set of characteristic properties.

They are proteins (with a rare exception). Almost every enzyme is a protein, which means it possesses the full range of protein structure — a primary sequence of amino acids, local secondary folding, and an overall three-dimensional tertiary shape. That tertiary fold is where the catalytic ability lives. The one important exception is that some nucleic acids, called ribozymes, can also act as enzymes, so catalytic power is not the exclusive property of proteins.

They have an active site. When the protein chain folds into its tertiary shape, it criss-crosses over itself and creates pockets and crevices on the surface. One special pocket is the active site. The substrate — the molecule the enzyme acts on — fits into this site, and it is here that the enzyme grips the substrate and catalyses its conversion.

They lower activation energy. For any reaction the substrate must climb an energy barrier, passing through a high-energy transition state before it can become product. The height of that barrier is the activation energy. The secret of an enzyme is that it lowers this barrier, providing an easier route through the transition state, so the change from substrate to product happens far more readily.

They are astonishingly fast. Because they lower the barrier, enzymes accelerate reactions by enormous factors. Carbonic anhydrase, which joins carbon dioxide with water to form carbonic acid, makes only a couple of hundred molecules an hour possible without help but around six hundred thousand molecules a second with the enzyme — roughly a ten-million-fold speed-up.

They are unchanged and reusable. An enzyme lets go of its products at the end of the reaction and emerges completely unaltered. Being regenerated every cycle, a single enzyme molecule can carry out the same transformation over and over on a fresh substrate each time.

They are sensitive to their conditions. Because activity depends on the delicate protein fold, enzymes respond strongly to their surroundings:

• Each enzyme has an optimum temperature and an optimum pH at which it works best, with activity falling away on either side.
• Low temperature does not usually harm an enzyme; it merely slows it into a temporarily inactive state from which it recovers on warming. …

Method: Organizing a List of Properties Around the Enzyme's Working Cycle

"Describe the properties of X" questions are much easier to write and to remember if you don't just list facts in random order, but instead organise them around the natural sequence of what the thing actually does — for an enzyme, that sequence is: what it's made of, how it grips its substrate, how it speeds the reaction, how fast it really is, what happens to it afterward, and what conditions affect it.

Follow that working cycle when you write the answer: first state what enzymes ARE (mostly proteins, with the ribozyme exception), then WHERE the action happens (the active site, formed by the folded tertiary structure), then WHAT the enzyme actually does chemically (lowers the activation energy barrier), then HOW WELL it does it (an enormous rate acceleration, with a concrete example like carbonic anhydrase), then WHAT HAPPENS to the enzyme afterward (it is released unchanged and can be reused), and finally what EXTERNAL FACTORS affect all of the above (temperature and pH o …