biology 2.4

• what is the role of enzymes in reactions?


  living organisms need to be built and maintained. this involves the synthesis of large polymer-based components

  the chemical reactions required for growth are anabolic and are all catalysed by enzymes

  catabolic reactions are also catalysed by enzymes
• what are enzymes?


  biological catalysts - speed up reactions

  they are globular proteins that interact with substrate molecules causing them to react at much faster rates
• what is metabolism?


  the sum of all the different reactions and reaction pathways happening in a cell or an organism

  can only happen as a result of the control and order imposed by enzymes
• what is the mechanism of enzyme action?


  for a reaction to happen, molecules need to collide in the right orientation not randomly

  when high temps and pressures are applied, the speed of the molecules will increase therefore so will the number of successful collisions and the overall rate of reaction
• what is activation energy?


  the energy needed to start a reaction
• what happens if the reaction needs a large amount of energy?


  sometimes the energy needed is so large, it prevents the reaction from happening under normal conditions. enzymes help the molecules collide successfully therefore reducing the activation energy required
• what are the two hypotheses for how enzymes help reduce energy needed?


  lock and key hypothesis

  induced-fit hypothesis
• what is the lock and key hypothesis?


  only a specific substrate will 'fit' in the active site of an enzyme

  when the substrate is bound to the active site and the enzyme-substrate complex is formed

  the substrates then react and the product(s) are formed in an enzyme product complex, they are released leaving the enzyme unchanged
• what is the active site?


  an area within the tertiary structure of the enzyme has a shape that is complementary to the shape of a specific substrate molecule
• how does the active site react with the substrate to release a product?


  the substrate is held In such a way that the right atom-groups are close enough to react.

  the r-groups within the active site will also interact with the substrate forming temporary bonds

  these put strain on the bonds within the substrate helping the reaction along
• what is the induced fit hypothesis?


  research shows that the active site of the enzyme changes shape slightly when the substate enters

  modified version of the lock and key
• what happens during the induced fit hypothesis?


  initial interaction between the enzyme and substrate is relatively weak

  these weak interactions rapidly induce changes in the enzyme tertiary structure that strengthen binding

  this puts strain on the substrate molecule which can weaken a particular bond(s) therefore lowering activation energy
• what are intracellular enzymes?


  enzymes that act within cells

  eg: making polysaccharides from glucose requires enzymes
• what is a product of many metabolic pathways and how is it broken down?


  hydrogen peroxide

  the enzyme catalase endures hydrogen peroxide is broken into oxygen and water therefore preventing its accumulation found in both plant and animal tissues
• why does hydrogen peroxide need to be broken down?


  its toxic
• what are extracellular enzymes?


  enzymes that act outside of cells
• what are nutrients made of?


  often in the form of polymers such as proteins and polysaccharides

  these large molecules need to be broken down to enter the cell
• how are large molecules broken down?

  in the process of digestion, enzymes are released from cells to break down the large nutrients into smaller ones

  these enzymes are called extracellular enzymes
• why are extracellular enzymes important?


  • both single-celled and multicellular organisms rely on extracellular enzymes to make use of polymers for nutrition
• what supplies the reactions with the substrates?


  • all the reactions happening in cells need substrates (raw materials) to make products needed by the organism
  • these materials need to be constantly supplied to keep up with the demand
  • nutrients (necessary for growth and survival) present In the diet or environment of the organism supply these materials
• why do single-celled organisms rely on extracellular enzymes?


  single-celled organisms eg: bacteria and yeast release enzymes into their immediate environment.

  the enzymes break down larger molecules and the smaller ones produced such as amino acids and glucose are absorbed by the cells
• why do multi-cellular organisms rely on extracellular enzymes?


  many multi-cellular organisms eat food to gain nutrients

  although the nutrients are taken into the digestive system the large molecules can be absorbed into the bloodstream

  they are transported around the body to be used as substrates in cellular reactions
• what are examples of extracellular enzymes involved in digestion?


  amylase and trypsin
• how is starch digested?


  the digestion begins in the mouth and continues into the small intestine

  it is digested in two steps involving two different enzymes
• why are two different enzymes needed for the digestion of strarch?


  each enzyme only catalyses one specific reaction
• what is the first step of starch digestion?


  starch polymers are partially broken down into maltose (a disaccharide)

  the enzyme involved at this stage is called amylase
• where is amylase produced?


  Pancreas and salivary glands.

  it is released as saliva into the mouth and in pancreatic juice into the small intestine
• what is the second step of starch digestion?

  maltose is broken down into glucose (a monosaccharide)

  the enzyme involved in this stage is called maltase

  glucose is small enough to be absorbed by the cells lining the digestive system and subsequently absorbed into the bloodstream
• where is maltase present?


  small intenstine
• what is the enzyme that catalyses the digestion of proteins?


  trypsin is a protease that catalyzes the digestion of proteins into smaller peptides which can be broken down further into amino acids by other proteases
• where is trypsin produced?


  pancreas and released with the pancreatic juice into the small intestine where it acts on proteins

  the amino acids that are produced by the proteases are absorbed by the cells lining the digestive system and then absorbed into the bloodstream
• what biological molecule is an enzyme made from?


  each enzyme is made from proteins made of these twisting and folding amino acids, therefore it has a unique shape

  held together by weak forces between the amino acid molecules in the chain
• what factors affect enzyme activity?


  temperature

  PH

  substrate and enzymes concentration
• how can temperature affect enzyme activity?


  • as temp increases, the particles move faster leading to more successful and frequent collisions (more kinetic energy)
  • in an enzyme-controlled reaction, an increase in temp results in more frequent collisions between substrate and enzymes increasing the rate of reaction
• what is the temperature coefficient?


  the temp coefficient, Q10, of a reaction is a measure of how much the rate of reaction increases with a 10 degrees rise in temp
• how does temperature cause enzymes to denature?


  • as enzymes are proteins their structure is affected by the temp
  • at higher temps, the bonds holding the protein together vibrate more
  • as the temp increases, the vibrations increase until the bonds strain and then break - resulting in a change in the tertiary structure of the protein which means it has denatured
• why do enzymes denature at high temperatures?


  as enzymes are proteins their structure is affected by temperature

  at higher temps, the bonds holding the protein together vibrate more until the bonds strain and then break

  results in a change in the precise tertiary structure of a protein

  the enzyme changes shape and is said to have denatured
• what is optimum temperature?


  optimum temperature is the temp at which he enzyme has the highest rate of activity
• what is the optimum temperature for enzymes?


  enzymes in the human body have optimum temperatures of around 40 degrees

  thermophilic bacteria (found in hot springs) have enzymes with an opt temp of 70 degrees

  psychrophilic organisms (live in cold areas) have enzymes with an opt temp below 5 degrees
• do enzymes denature quickly?


  yes

  there only needs to be a slight change in the shape of the active site for it to no longer be complementary to the substrate

  at this point in an enzyme-controlled reaction the temp coefficient doesn't apply anymore as the enzymes have denatured