enzymes

• What are enzymes?


  Every cell requires hundreds of biochemical reactions to survive and carry out its function. Nearly all of these are catalyzed large globular proteins called enzymes. Enzymes can speed up reactions by a factor of many millions, but they cannot catalyze reactions that would otherwise not occur. Enzymes catalyze both anabolic (building up) and catabolic (breaking down) reactions
• structure of enzymes


  All enzymes are globular proteins. they are soluble in water due to the presence of many hydrophilic side groups on their constituent amino acids. most enzymes are very large molecules but only a small part of them is involved in catalysis. this is called the active site and it may consist of just a few amino acids. the remainder of amino acids maintain the precise shape of the enzyme and the active site
• Location of enzyme action


  Enzyme action occurs both intracellularly and extracellularly. DNA replication is an intracellular process that involves many enzymes, such as DNA polymerase and DNA ligase. Some intercellular reactions occur on a membrane. The synthesis of ATP by ATP synthase during respiration. Digestion involves the extracelluar action of enzymes such as pepsin and amylase. These breakdown food particles into small molecules, such as peptides and disaccharides
• enzymes lower the activation energy of a reaction

  A) uncatalysed

  B) catalysed

  
• Substrates and specificity


  The active site of an enzyme binds the substrate molecule of a biochemical reaction, and is critical to its specificity and catalytic activity. many enzymes are specific for just one reaction. for example, catalase only catalyzes the breakdown of hydrogen peroxide, a toxic by-product of metabolism. other enzymes catalyze more general types of reactions
• Lock and Key


  • based on the idea that a key will only fit one ock
  • model proposed by german chemist emil fischer in 1894
• Lock and key model

  A) active site

  B) substrates

  
• Models of enzyme action: induced fit


  It has been found that other molecules can bind to enzymes at sites other than the active site, altering the enzymes activity. this suggests that the structure of an enzyme is flexible and not rigid.
• Induced fit model


  • proposes that the enzyme changes shape slightly
  • mould itself to substrate
  • as enzyme changes shape, it puts on a strain on the substrate. this distorts bonds in the substrate making it easier to break
• what does inhibitor mean


  an agent that interferes or slows with a chemical action
• competitive and non-competitive inhibitors

  A) substrate

  B) inhibitor

  C) alternate binding site

  
• competitive and non-competitive inhibitors

  A) substrate

  B) inhibitor

  C) substrate

  
• competitive inhibitor


  competes for active site with substrate, increasing substrate concentration will increase the rate of reaction
• non-competitive inhibitor


  do not compete for active site. they attach to an alternative site on the enzyme changing the shape of the active site preventing the substrate from binding: non competitive inhibition cannot be overcome by increasing the substrate concentration
• End product inhibition

  A) inhibition