Archive for the ‘Biology Notes’ Category

Biology Notes Week 3

Posted: November 18, 2014 in Biology Notes

The reason we start at week 3 is because normally this is where students begin having trouble. If you want weeks 1 and 2, please contact me.



Spontaneous reactions need energy to start. Remember “You can’t start a fire without a spark”. The energy for the reaction to occur is called ‘activation energy’.

Enzymes are proteins that increase the rate of a chemical reactions without changing themselves. They reduce the activation energy needed for a chemical reaction, and they can never be used up.

The chemicals that can be effected by enzymes are called ‘substrates’. Every enzyme has a place called the ‘binding site’ which is meant to receive and hold a substrate. When the enzyme first contacts a substrate, it adjusts until the substrate is secure. Think of clasping hands.

An enzyme works by changing shape. Once the substrate is secure, the enzyme bends and shifts shape until the substrate is unstable, thus making covalent bonds more likely to break. Once the bond is broken, the enzyme goes back into shape.

Besides chemical reaction assistants, enzymes can also strengthen chemical bonds. If you have a lot of enzymes and less substrates, then the reaction happens very quickly. Sometimes instantaneously. As long as you have more enzymes, you can add as many substrates as you want, and the reaction speed won’t slow down.

If there are more substrates than enzymes, then the  reaction is slower, because the enzymes can only handle one substrate at a time, and the other substrates have to wait their turn. The only way to speed up the reaction at this point is to add more enzymes.

The more heat there is, then the faster the reaction will happen. But there is such thing as too much heat. Looking at the fact that there can be such thing as too much heat, there can also be such thing as a situation where it’s too cold for a chemical reaction.

That’s the basics of enzymes.