A Level Biology: Enzymes 1 - Structure
Hi! Welcome to my first video about Enzymes. Today, we are going to be looking at Enzyme
Structure and the Induced Fit theory.
Here are the key terms that go along with the topic to do with enzymes:
1. Anabolic reaction – is a reaction that builds up molecules. That’s where you’re
taking two things and putting them together;
2. Catabolic reaction - is where you break down the molecule;
3. Metabolism – is basically those reactions; a series of anabolic and catabolic reactions;
4. Catalyst – is a substance that speeds up the reaction without changing the produced
substances and that’s what enzymes are;
5. Metabolic pathway – the sequence of enzyme-controlled reactions. So most metabolic reactions that
happen within the body have a specific number of different reactions and they’re controlled
by different enzymes;
6. Specificity – that refers to being only able to catalyze specific reactions so enzymes
are very, very specific;
7. Substrate – is the molecule that an enzyme works on and again, they’re very, very specific;
8. Product - the molecule that is produced by the enzymes.
There are some other terms that you might need to know:
Intracellular enzymes – the enzymes that work inside cells. An example of that would
be polymerase. It is one that forms DNA.
Extracellular enzymes – the enzymes that work outside the cells. Pepsin and amylase,
which works in the mouth and in the small intestine.
Recommended names - a short name, usually enzymes end in the ‘ase’, so therefore
you can tell what it breaks down.
A systematic name - can tell you something about the process that is involved. Sometimes
they can be classified with the series numbers like this 2, 7, 3, 2.
So what we have here is an example of a structure of enzymes. They have these four different
types of structures: primary, secondary, tertiary and quaternary.
The primary structure of enzymes, because enzymes are proteins, your primary structure
is therefore the order of amino acids and so each of these red dots here represents
a different amino acid or maybe not a different one, but a separate amino acid joined together.
Within the primary structure, the amino acids are held together by peptide bonds and so
every time you hear the word peptide that refers to a protein.
The secondary structure is the repeat in pattern in the peptide chain. The two examples of
this might be a pleated sheet or an alpha helix, like in some cases, similar to the
shape of a DNA. That secondary structure then folds on itself to make a complex 3D structure
and that’s held together, usually by hydrogen bonds and sometimes by disulfide or ionic
bonds and that’s known as the tertiary structure.
The quaternary is different and the quaternary is when you have more than one polypeptide
chain and they are joined together to form a certain structure and that can be usually
the example of that is hemoglobin. It is this complex 3D structure that makes enzymes so
very, very specific and so they have a very, very specific shape that only a certain substrate
can fit into and therefore, they can only catalyze certain reactions.
This diagram shows you what exactly enzymes do. They technically reduce the level of activation
energy that is required for the reaction.
What you have here is the energy level of the molecules and so, in order for an uncatalysed
reaction to take place, the activation energy required has to be quite high and so what
the enzymes do is they reduce the level of activation energy that is required for a reaction
to take place and therefore, it could take place at much, much lower temperatures. Generally
speaking, to get the activation energy up to here, you need to heat the reactors to
very, very high levels in order to get there. Whereas, with an enzyme-controlled reaction,
they don’t need to be heated to such an extent and therefore, it lowers the activation
energy.
Enzymes work by lower of activation energy and they form something called an enzyme substrate
complex and that’s essentially where the enzyme in the substrate joins. These are the
stages involved. You have the enzyme and the substrate. That forms an enzyme substrate
complex and then once the product has been produced, that forms the enzyme product complex
and therefore, you have the product and the enzyme separate.
If you join me on the next video, I’ll be looking at Induced Fit and Lock & Key theories.
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