structure, amino acids, inhibition, enzymes

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Key Facts

Protein = structural e.g. hair, bone...
Enzymes= Hormones, anitbodies ...
Amino acids make up all proteins there are 20 essential amino acids and they make endless combos, all amino acids have the same basic structure:

  • Carboxyl Groups
  • Amine Groups
  • R Groups


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2 amino acids are bonded my a covalent peptide bond.

Lots of amino acids are polymerised to form a polypeptide.

All proteins have levels of structure:

Primary= which amino acids and in which order

Secondary- the shape the polypeptide takes (most common alpha helix)

Tertiary = how the secondary structures make themselves into a 3D shape (globular, fibrous)

I will now go into more detail ...

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Secondary Structure

This is the alpha helix, as you can see the R Groups will determine the structure of the helix (if they were large the coils would be bigger). Weak hydrogen bonds hold the coils in place. The ALPHA helix is folded or twisted to give the tertiary structure.(

The beta pleated sheet is less common.

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Tertiary structure

3D shape the poly peptide takes. Could be Fibrous protein- where the ALPHA helix coils into a long strand- this makes structural insoluble protein e.g. hair, collagen...

Most Tertiary structures are GLOBULAR this is when the helix is wound into a specific ball or globe shape. The shape is held into place by:

  • Ionic bonds
  • Sulphur bridges (in polypeptides where cystine is present)

Hydrophobic Rgroups twist the chain in on itself
Hydrophillic outwards.
Globular proteins specific to shape to carry out certian functions in the organism. E.G. and enzyme as an active site will only let a certain substrate fit.


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Prosthetic Groups

At the Tertiary and Quaternary level of proteins some may CONJUGATE

These have an additional section which is a non-protein (the iron in Haemoglobin)

This is known as a prosthetic group.

They are normally essential to carry out certain functions.

4 polypeptides each with iron to make Haemoglobin, this allows the protein to carry 2 O2

whereas a single strand of the same protein is myoglobin that stores oxygen in muscles.

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Testing for Protein


Animal protein= first class protein

Copper sulphate + Sodium Hydroxide

Purple is protein is present.

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Enzymes- Globular Proteins


  • Biological catalyst
  • changes rate of reaction but doesn't get changed itself
  • so it can get used over and over again

All reactions that occur in living organisms but would happen too slow with out Enzymes.
The enzymes reduce the activation energy so allow reactions to happen at the temp of the organism.

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Induced fit- Lock and Key

You will know the lock and key method of the active site of an enzyme breaking the substrate however:

The enzyme will flex slightly  as the substrate enters the active site, this slight change will put pressure on the substrate causing the bonds to be broken.


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Temperature & Enzymes

Low temps= slow activity but not zero - low kinetic energy
Raise it and it will increase the Kinetic Energy as all the molecules will collide frequently and more often with enough force for enzyme/substrate complex to form. increase RATE OF REACTION.

However too high temperature will cause too much KE = break weak hydrogen bonds in enzymes= change shape in active site = denatured enzymes= reaction 0

Optimum temp= 37 C

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PH & Enzymes

PH will change Enyme activity
R Groups in the enzyme
the ph - free H+ ions in an acid or OH- ions in an alkali react with the ionic and hydrogen bonds holding the enzyme in place.

Even slight change in PH can STOP a reaction!!!

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all enzymes have a max turnover rate- no. of substrates mole can catalyse in a second.

Catalase= fastest can break down 83 000 hydrogen peroxide molecules per second.

VMAX tells how fast an enzyme can work
They can only reach vmax in a very concentrated solution of substrate, so there is always enough substrate to break down.

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Enzyme Inhibition

Competitive inhibitor:
they are shaped like the real substrate and can move into the active site and block it, so that enzyme is cannot now break down the substrate - normally reversible (goes back out) but sometimes irreversible which in effect denatures the enzyme.(

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non competitive inhibition

These combine with the enzyme outside of the active site but cause the enzymes shape to change so the substrate can no longer fit.

They are normally irreversible.


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