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Why do we need enzymes?

Reactions in cells must:

• Be controlled

• Occur under mild conditions

• Occur quickly

• Be specifically catalysed- only one product, only one substrate

• Be regulated by external factors

• Often be coupled to make them thermodynamically favourable (possible)

How are proteins held in their three dimensional conformation?

Covalent disulphide bridges                                                                       

• Between cysteine amino acids

Electrostatic interactions

• F=q₁q₂/Dr²

• D is dielectric constant- in air D=1, in water D=80

• Ion-ion interactions between like and different charges

• Ion-dipole interactions

• Dipole-dipole interactions (e.g. hydrogen bonds)

Hydrogen bonds

• The one electron of hydrogen is strongly attracted by a highly electronegative atom

• This leaves the H nucleus very exposed

• Forms strong interactions with other electronegative atom

• Highly directional linear geometry helps maintain structural specificity

Van der Waal’s forces

• Instantaneous-induced dipoles

• Drop off as a function of r^-6

• In dense core of globular protein help hold it together

Repulsive interactions

• Electrons repel one another at short distances

• Varies as a functions of r^-12

• May consider atoms as hard balls which bounce off each other

The hydrophobic effect

• Polar and non-polar substances don’t mix

• This is because van der Waal’s forces are better optimised in the separated aqueous and non-polar phases than they are in a solution of one in the other

For the rest of this summary, please download the Enzymes Summary Revision Sheet