Enzymes and Co-Enzymes

Wow! I cant believe I made it to post 300. Back to chemistry notes again, sorry but its really basic so it should make sense I hope, my handwriting is illegible sometimes so trying to type it up is always not fun. Check out General, Organic and Biological Chemistry by K.C Timberlake, that’s where the majority of my notes come from.


Enzymes and Co-Enzymes

Nature of Enzymes as Catalysts

Enzymes are proteins. They catalyse (Speed Up) most chemical reactions taking place in cells.

The increase the rate of reaction by lowering the amount of energy needed. They also have a unique 3D shape that fits reactants. Enzymes don’t affect the equilibrium as it increases the speed of both forward and reverse reactions.

Enzymes may recognise and catalyse:

  •  Absolute (1 substrate)
  • Group (A group of similar substrates)
  • Linkage (A certain type of bond )


  • Catalyse the same reaction in different places in the body
  • Can be used to identify the organ or tissue involved in damage or disease

Diagnostic Enzymes

  • The levels of diagnostic enzymes determine the amount of damage done in the tissue.
  • For example, to look at pancreatic disease, there would be higher levels of Amylase and cholinesterase lipase

System of Classifying Enzymes

The name of an enzyme is their identification, they mainly end in –ase. The name categorizes them by the reacting substance – sucrose for sucrose. The name also describes the function: oxidase = oxidation. But it can be a common name for example the digestive enzymes.

Class Reaction Catalysed
Oxidoreductases Oxidation Reduction
Transferases Transfer group of atom hydrolysis
Hydrolases Hydrolysis
Lyases Add/Remove atms to/from a double bond
Isomerases Rearrange atoms
Ligases Use ATP to combine molecules

This table is from Timberlake, Pearson Education


Enzymes and Substrate Interactions

Active Site:

  • A place in an enzyme that fits the shape of the molecule (Substrate)
  • Contains Amino Acid R groups that align and bind the substrate to it.
  • Releases product when the reaction is complete

Lock and Key Model:

  • The active site has a rigid shape (Lock)
  • Only a substrate with a matching shape will fit (Key)

Lock and Key fit is an Enzyme(E)-Substrate(S), the ES complex

  • E+S= ES
  • ES = E+P (Product)
  • The Substrate is converted to Product, the product is released from active site when it is no longer attracted to it.

Induced Fit Model:

  • Active site is flexible
  • The active site and substrate move to fit with each other
  • Has a bigger range of substrate specificity


Enzyme Activation and Inhibition

Enzyme and Substrate Concentration:

  • The enzyme, substrate and the environment all play a role in the Enzyme activity.
  • As the rate of enzyme concentration increases, so does the rate of reaction. More substrate binds with enzymes.
  • As the rate of substrate concentration increases, so does the rate of reaction. When the enzyme is saturates, maximum activity occurs.

Enzyme Action:

  • Temperature affects enzymes, most are active at 37 Degrees Celsius  (regular body temp), at lower temperatures, Enzymes lower in activity (like they go to sleep) but can recover as they return to their optimum temperature. At higher temperatures above optimum , the enzyme will denature and no longer be useful.
  • The same applies with pH levels, most enzymes are most active at 7.4pH (regular body pH). They lose activity at higher and lover pH and denature as they can no longer function in their environment. But in different parts of the body the optimum pH can be higher or lower.

Inhibitors: can prevent substrates from fitting into the active site or can cause a lesser catalyst effect. For example: Enzyme + Substrate = ES = Enzyme + Product, with an inhibitor: Enzyme + Inhibitor = EI = No product.

Enzyme Regulation

Rate of reaction that controls the amount of product  is controlled by Zymogens and Allosteric Enzymes.

Zymogens (pro-enzymes):

  • Are inactive enzymes
  • Activated when a peptide is removed
  • Proteases are in zymogen form
  • Digestive Enzymes: are produced as zymogens in a organ and transported to another when they are needed.

Allosteric Enzymes:

  • Is an active enzyme that is solely protein
  • A positive regulator: increases the binding of substrate and enzyme = makes the rate of reaction faster.
  • A negative regulator: stops the binding of substrate and enzyme = slows the rate of reaction.

Enzyme Cofactors

  • A simple enzyme is active and a protein
  • Lots of enzymes are only active when they combine with a cofactor (metal ions or small molecules)
  • COENZYME = cofactor that is a small organic molecule
  • A coenzyme prepares the active site for catalyst

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