Enzymes
- Created by: victoria123!!!
- Created on: 06-04-16 12:16
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- Enzymes
- Enzymes are globular proteins with a tertiary structure folded into a spherical shape
- Enzymes are held together by ionic bonds, hydrogen bonds and disulphide bridge
- The active site is a small area with a 3D shape
- The enzyme acts on the substrate by making temporary bonds on the active site
- Enzymes have a hydrophilic R group which makes enzymes soluble
- Each enzyme has a unique sequence of amino acids
- The elements in the R group determine the bonds between the amino acids
- Site of enzyme action
- Some enzymes are extracellular- they are secreted from cells by exocytosis and catlyse extracellular reaction
- Intracellular enzymes in solution, these are enzymes within the cell in a solution
- Intracellular enzymes in solution breakdown glucose in the cytoplasm
- Membrane bound extracellular enzymes, these are enzymes attached to membranes e.g on the cristae of the mitochondria
- How they work
- Lock and key model
- The unique shape of the active site means enzymes catalyse only one type of reaction, it is enzyme specific
- Induced fit model
- The enzyme shape is altered by the binding of the substrate
- This suggests the enzyme is flexible and not rigid
- The enzyme shape is altered by the binding of the substrate
- Lock and key model
- Activation energy
- The minimum amount of energy needed for molecules to react
- Increasing kinetic energy by increasing the temperature increases the number of successful collisions
- But if the heat is too high (usually above 40 degrees Celsius) the enzyme denatures
- As the kinetic energy increases the bonds vibrate, the bonds vibrate so much that they eventually break. The enzyme changes shape and is denatured
- But if the heat is too high (usually above 40 degrees Celsius) the enzyme denatures
- The rate of reaction of an enzyme controlled reaction can be measured by the amount of product formed or substrate used up in a given time
- Initially there are many substrate molecules but the concentration decreases as the reaction progresses and the form products
- Factors affecting rate of reaction
- Temperature
- Increasing kinetic energy by increasing the temperature increases the number of successful collisions
- But if the heat is too high (usually above 40 degrees Celsius) the enzyme denatures
- As the kinetic energy increases the bonds vibrate, the bonds vibrate so much that they eventually break. The enzyme changes shape and is denatured
- But if the heat is too high (usually above 40 degrees Celsius) the enzyme denatures
- Increasing kinetic energy by increasing the temperature increases the number of successful collisions
- pH
- Enzymes will have an optimum pH- the pH which enzymes work best at
- Small changes in pH cause reversible changes to the enzyme and therefore reduce its activity
- Extreme changes in pH cause the enzyme to become denatured
- There are charges on the amino acid chain which are affected by the H+ and OH- ions
- At high pH the excess OH- ions neutralise the H+ ions and therefore disrupt the hydrogen bonds within the enzyme and cause it to become denatured
- There are charges on the amino acid chain which are affected by the H+ and OH- ions
- Substrate concentration
- When the enzyme concentration is constant the rate of reaction increases as substrate concentration increases
- When there is a low concentration of substrates enzymes only have a few substrates to collide with, they are not working to their full potential. Substrate concentration is the limiting factor
- When all active sites are filled the enzyme is saturated and cannot go any faster
- Enzyme concentration
- when the product is released from the enzyme it can be reused
- Only a low concentration of enzymes are needed to catalyse a large number of reactants
- Turn over is the number of substrate and enzyme can turn into productsin a given time
- As enzyme concentration increases
- Temperature
- Enzyme inhibition
- Decreases the rate of reaction of an enzyme contolled reaction
- competitive inhibition
- The competitive inhibitor will have a complementary shape to the active site
- The substrate and inhibitor compete for the active site
- Increasing substrate concentration decreasesthe affect of competitive inhibitors
- The competitive inhibitor will have a complementary shape to the active site
- Non-competitive inhibiton
- They bind to a site other than the active site
- They affect bonds within the enzyme and alter its overall shape so the substrate can no longer bind
- They don't compete with the substrate
- They bind to a site other than the active site
- Immobilised enzymes
- Advantages of immobilised enzymes
- Increased stability as they are able to function over a wider range of temperatures and pH
- Products are not contaminated wtih enzymes
- Easily recovered for reuse
- Enzymes are easily added or removed
- Can have a sequence of columns at different pH and temperatures
- Enzymes which are fixed or bound to an inert matrix
- Uses
- lactose free milk
- milk is poured down column containing lactase
- milk binds to the enzymes active site and is hydolysesd into glucose and galactose
- milk is poured down column containing lactase
- lactose free milk
- Advantages of immobilised enzymes
- Biosensorors
- Turns a chemical signal into an electrical signal
- Rapidly and accurately detects concentrations of molecules e.g blood glucose
- Glucose oxidase, immobilised on a selectively permeable membrane is placed in a blood sample and binds to the glucose and produces a small electrical crrent
- Enzymes are specific and select one type of molecule
- Enzymes are globular proteins with a tertiary structure folded into a spherical shape
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