Enzymes

• cellular metabolism is when cells carry out thousands of chemical reactions daily
• catabolic reactions involve the breakdown of substances and the release of energy
• anabolic reactions involve the taking in of energy to build up complex molecules from simple molecules
• enzymes are biological catalysts made of proteins that speed up chemical reactions. They have other properties due to their globular shape
• Enzymes are

  Specific- they catalyse 1 reaction only.

  Not used up- very small amount of enzyme is needed.

  Enzyme/Sub complexes are formed

  Affected by Ph and temp

  cofactor must be present

  Inhibitors stop enzyme based reactions.
• Enzymes are specific because of the 3D tertiary structure of the protein molecules
• Lock and key theory suggests enzymes have a specific 3D shape and are large molecules. They are bigger than the substrate.

  Only a small amount of enzyme comes into contact with the substrate- this is called the active site, which is a exact fit.

  This forms a enzyme/substrate complex

  Once this occurs, and the product is formed, they no longer fit and is therefore repelled
• The induced fit theory is when the active site changes shape to fit the substrate. It essentially moulds itself around the substrate.

  This distorted enzyme molecule inturn distorts the substrate molecule, straining and twisting the bonds. This makes the enzyme less stable, reduces its potential energy, and also lowers activation energy.
• Catalytic activity is affected by pH and temperature
• An example of an enzyme is amylase. Amylase breaks down starch into maltose
• Activation energy is the minimum amount of energy needed for a reaction to occur.
• activation energy- heating molecules means more kinetic energy is produced and therefore they will move faster, collisions will be more frequent, more successful and rate of reaction increases
• activation energy is used to break bonds. This is like a domino effect. This is limited to 37 Celsius as enzymes become dentatured at extreme temperatures
• Enzymes lower the activation energy to make a reaction to happen. This also they don't need heat to work, so they can work at lower temperatures.
• By lowering the activation energy, enzymes reduce the input of energy needed to allow reactions to occur at lower temperatures
• heating increases the rate of chemical reactions as the particles have more kinetic energy so they move more and are more likely to collide
• The change in rate of a reaction for each 10C rise in temp is called Q10
• Q10 = Rate of reaction at X + 10C (divided by)

  Rate of reaction at X_C
• In relation to q10, at suboptimal temps the rate doubles for each 10C rise in temp
• Optimum temperature is the temperature at which the enzyme is most active. The activity of a enzyme will increase with eg, heat. It will increase until a maximum point, called the optimum.
• At suboptimal temps, ( less than 37 ), increasing the temp increases the kinetic energy of the reactants
• Above 40C, the 3D secondary and tertiary structural shape of the enzyme is lost because cross bonds between amino acid side chains break. This means that the enzyme and substrate are no longer complementry
• Optimum pH- enzymes have a narrow pH range. Optimum pH is the pH where enzyme activity is at its highest.
• Deviations in optimum pH cause hydrogen and ionic bonds to break, causing denaturation.
• Acidity and alkalinity can affect the active site of a enzyme. Free H+ an OH- ions can affects the charges of the amino acid side chains on the active site. This means the enzyme loses its activity
• The turnover number is the number of substrate molecules that are converted into products per second.

  
  

  IF CONDITIONS SUCH AS TEMP AND PH ARE SUITABLE AND

  If there is any leftover substrate, the rate of reaction is directly proportional to enzyme concentration.

  In the same way, if the substrate is limited, it limits the reaction even if you add more enzyme.
• substrate concentration - for a given amount of enzyme, the rate of reaction increases with increase in substrate to a certain point.

  AT THAT POINY-

  active sites are filled.

  rate of reaction increases wont go faster if u add more substrate unless amount of enzyme present is increased
• Cofactors make our enzymes work better. For example, they're usually vitamins or minerals.
• Cofactors are non-protein molecules. They modify the chemical structure of the enzyme in some way so that it can function more effectively. Chloride ions act as cofactors for salivary glands by binding with amylase, changing its shape and facilitating enzyme

  substrate complex formation.
• the 3 types of cofactors are

  1. prosthetic groups
  2. coenzymes
  3. activators
• Prosthetic groups are organic molecules that form a permanent attachment to the enzyme.

  Haemoglobin contains the prosthetic group HAEM, which contains iron and bonds PERMANENTLY (a difference) to the protein molecule.
• COENZYMES are small, non-protein organic molecules. They combine with the substrate, changing its shape, making it fit right. They aren't permanently attached to the enzyme like prosthetic groups.

  Coenzymes help enzymes and substrate bond together. The enzyme can only work with the coenzyme.
• Activators are inorganic metal ions, examples include magnesium, iron, calcium and zinc. Activators form a temporary attachment to the enzyme and change its active site so that the reaction is more likely to take place.
• An inhibitor is a substance that can slow down or stop a reaction.

  The inhibitor combines with the enzyme and stops it from attaching to the substrate.

  Inhibitors are either reversible or non-reversible.

  The effects of reversible inhibitors are temporary and when the inhibitor is removed, the enzyme regains its full activity.
• The types of reversible inhibitors include:

  1. Competitive Inhibitors
  2. Non-Competitive Inhibitors
• Competitive inhibitors compete with the substrate for the active site of a enzyme.

  If a inhibitor gets in, substrate can and rate of reaction decreases.

  This means it prevents the formation of enzyme/substrate complexes and reduces rate of reaction.

  INCREASING THE CONC OF SUBSTRATE CAN REDUCE EFFECTS OF A COMPETITIVE INHIBITOR. The more substrate molecules present, its more likely to get into active site instead of inhibitor
• Non-competitive inhibitors do not bind to the active site of the enzyme. It attaches to the binding site/ another part.

  This alters the overall shape of the enzyme molecule, including the active site, and the substrate can no longer bind to the active site.

  The inhibitor and the substrate are not competing for the active site so increasing the amount of substrate will not reduce the inhibition. (DIFFERENCE)
• Allosteric Enzymes have a second site where non substrate molecules can attach. This means they only need 1 cycle/ 1 pathway.

  They also play an important role in the regulation of enzyme activity through negative feedback. (used to turn reactions on/off)

  When the cells have produced enough products for their own needs, these products reach a sufficient quantity to bind to the allosteric site of the enzyme and function as a non-competitive inhibitor.

  This is important as it prevents wasteful metabolic reaction
• Why slow down/ stop a reaction


  waste energy

  switch reactions on/off when u need them

  regulation of enzyme based reactions
• Some enzymes are only active during the process of disease.

  This means they can be used to diagnose the onset disease AND monitor its development.

  They are called Biomarkers.