Enzymes Flashcards
What are enzymes ?
They are biological catalyst made of proteins with a specific active site .They speed up reactions whilist remaining unchanged
Active site
Indented area on the surface on the enzyme molecule with a shape that is complementary to the shape of the substrate molecule
Catalyst
Chemical that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction
Metabolic/metabolism
Sum of the chemical reaction that takes place inside living cells of organisms
Product
Molecule produced from substrate molecules by an enzymes cataylsed reaction
Substrate
molecule that is altered by an enzymes controlled reactions
metabolites
reactants intermediates and products in enzymes controlled reactions
Key thing to remember
- small number of enzymes molecules are able to convert a large number of substrate molecules into products molecules
- number of reactions that an enzyme molecules can catalyse per second is its turnover number
- Enzymes affect metabloish at a cellular level as well as a whole organism level
Features of enzymes
- catalysts that speed up the rate of reactions
- globular proteins
- specific 3D tertiary structure providing the active site where the reaction occurs
- affected by temperature and ph
- work best at optimum
- lose their specfic 3d tertiary structure and shape they are unable to catalyse reactions and are said be denatured
- specific
- speed up reactions by lowering the activation energy for a reaction
Intracellular enzymes
enzymes that work inside cells
* catalase - breaks down hydrogen peroxide into water and oxygen ( 6 million reaction in a second )
* ATP synthase - enzyme that catalyzes the formation of the enrgy storage molecule in to ADP + pi
* DNA polymerase - responsible for replicating DNA
* Carbonic anhydrase - catalyze a reaction fundemental for life
Extracellular enzymes
enzymes that work outside the cells
* amylase - salivary glands - acts in the mouth to digest starch into maltose
* trypsin - pancreas - acts in the small intestine to digest proteins into smaller peptides
* lipase - breaks down fats in food in order to be absorbed pancreas, mouth and stomach
How do enzymes work
speed up metabolic reactions by converting substrates into products. This is done by randomly colliding with substrate molecules. the substrate is held in a way that encourages the products to be formed
Enzymes reactions
- catabolic reactions - substrate are broken down
- anabolic reactions - substrates joined together to make a larger product
Enzymes specificify
- the active site is complementary to the shape of the substrate
- the specific shape is maintained by the tertiary structure of the protein and means that usually each enzyme will only catalyse one reaction
Activation energy
- the minimum amount of extra energy required by a reacting molecule to get converted into a product
- enzymes decrease activation energy by providing an active site where a reaction can occur more easily then elsewhere
Lock and key theory
- The shape of the enzyme’s active site is complementary to the shape of the substrate molecule
- the complementary shape of the active site and substrate molecle are like lock and key
Induced fit theory
- the enzymes active site changes slightly upon collision , making the ctive site fit closer to the substrate. there may also be changes to the amino acids in the active site that conttibute to holding the substrate in place
Effect of temperature
An increase in temp increases the rate of reaction due to increasing kinetic enegry of the molecules. there are therefore more collisons between molecules
Kinetic energy and collision theory
If the kinetic energy of both molecules is increased by heating there will be more collisions between them and with more force. this will lead to an increased rate of reaction and more product is formed
Rate of reaction
ROR = 1/ time taken to reach end point
Q10= rate of reaction at (T +10)/ rate of reaction at T
Optimum temperature
- gives the enzymes maximum rate of reaction it is a balance between increasing the kinetic energy of the molecules and increasing the vibration of the enzyme molecule
- 3 examples of environments of optimum temperature - space, hypeethermal vents, geothermal active water ( springs)
Denaturation
- This is when the tertiary structure of the enzyme us changed to the point where the enzyme no longer works. this change is not reversible
- Applying heat makes vibrate and there vibrations put strain on the bonds holding a molecule together
- The vibrations break the weker hydrogen bonds and ionic bonds
- lots of bonds in the enzyme and vital in maintaining tertiary structure hence the shape of the active site
- As the heat increase , more bonds are broken and the active site is held less and less in the shape needed for it to work
- rate of reaction decrease and if enough bonds are broke the whole tertiary structure will unravel and the enzyme will stop working altogether
pH
- a measure of H+ ion concentration
- the higher the H+ ions, the lower the pH value
- H+ ions affect the ionic and hydrogen bonds the tertiary structure
The effect of pH affects the tertiary structure of protein and enzyme action
- If the tertiary structure is disrupted the active site can be altered affecting the rate of reaction
- the induced fit theory states than importana part of enzyme function is that the active site relies on charged and cluster around them. this interfers with binding of the substrate to the active site
Why is there an optimum pH
- This pH gives the enzyme’s maximum rate of reaction. it is where the concentration of H+ ions gives the tertiary structure the best overall shape - the shap that makes the active site complementary to the substrate molecule.
- Enzymes generally have a narrow pH range in which they work , small changes in pH can lead to a fall in reaction rates because the shape of the enzyme is so disrupted.
- Each enzyme has its own optimum pH
pH and denaturation
- MInor changes in pH do not denature enzymes
- the bonds are disrupted can reform if the pH returns towards the optimum pH.
- Only occurs at extremes of pH away from the optimum , at these extremes the bonds become permanently broken
How cells modify enzyme concentration
- enzyme concentration or availabilty depends on the rate of synthesis ( to make something) of the enzyme and its rate of degradation which is directly controlled by the cell
- enzyme synthesis - depending on the cell’s needs, genes for synthesisng particular enzymes can be switched on or off
- enzyme degradation -in cells protein are broken down into their amino acids and used to make new proteins . this is good because it removes any proteins that could accumulate and damage the cell and regulates metabolism
Initial reaction rate
- Gives the maximum possible rate for am enzyme under the condition of the experiment
- to calculate : plot a tangent of the steepest part of the curve and calculating the gradient (x/y = rate)
Limiting factors
- Plateaus occurs because either enzyme or substrate concentration limit any further increase in the rate of reaction
How to measure rate of reaction
- measure how much product appears over a period of time
- measure how much substrate disapears over a period of time
Temperature
- As the temp increases the enzyme activity increases because there is more kinetic energy and therefore more collisions and more enzyme acticity - more enzyme + substrate activity
- At optimum temp this is the peak so highest on the graph
- after optimum temp and the temp increases the enzyme activity decreases rapidily this is because the enzymes start to undergo denaturation so by high temps ut is completely denatured and losts its shape the enzyme activity has stopped
pH
- As the pH increases the enzyme activity increases this is beacuse the H+ ions decreases
- at optimum there is the best concentratioon of H+ ions that gives the tertiary structure the best shape and therfore the enzyme shape its complementary active site to the substrate
- As the pH continues to increases the enzyme activity decreases this is beacuse the enzyme has a narrow pH range and once out of range they begin to denature due to the H+ ions altering the shape of the active site
Substrate concentration
- As the substrate concentration increases do does intial rate of reaction and this because there is more collision taking place between the substrate and enzyme active site
- The graph levels off because the rate of reaction has reached a maximum value as all the active sites are occupied so any further increase insubstrate concentration will have no effect as no enzyme- substrate complexes can form
Enzyme concentration
- AS the enzyme concetration increases so does the intial rate of reaction this is because more collsions are taking place as there are more active sites available for enzyme- substrate complexes
- At a point the graph being to level off as all the substrate will be binded at the same time so there will no further increase in intial rate of reaction as all the substrate will be used
Co factors
- some enzymes only work with a non protein substance bound to them
Inorganic factors
- ions not permanently bound to the enzyme
- helps by binding substrate and enzymes together
- dont participate in the reaction so arent used up or changed
- forms e-s complex more easilty
- tempoary
- eg - ions and amylase
Co enzymes
- small non-protein molecules that bind temporarily to the active site
- act as carriers
- temporary + binds to active site
- vitamin b3
Prosthetic group
- permanent parts of an enzyme molecule
- permanent and covalent
- carbonic anhydrase contains a zinc ion
Medicinal drugs that inhibit enzymes
- aspirin
- ATPase inhibitors
- antivirals
Metabolic poisons
- cyanide - non comeptive inhitor of cytochrome oxidase
- melonate - competitve inhibitor of succinate dehydrogenase
- venom - non competitve inhibitor of pyruvate dehydrogenase
What are enzyme cofactors ?
ions, non-protein parts and prosthetic group that are not used up in a reaction as they dont participate in the reaction
How do viatmins work as coenzymes?
Many vitamins are enzyme cofactors that can be synthezied by the organisms and must be obtained from the diet
Enzyme inhibitors
- Any substance that slows down the rate of an enzyme-controlled reactions by affecting the enzyme molecule in some way.
- there affects are reversible or irreverisble and they affect the active site directly or another part of the enzyjme molecule
Reversible inhibition
- not permanently binds to the enzyme
- if the bonds are hyrogen or ionic (weaker) the inhibitor can be removed and inhibition is reversible
irreversible inhibition
- bind permanently to an enzyme - effectively denaturing it
- if the bonds are covalent , the inhibitor cant be easity removed and inhibition is irreversible
Competitive inhibition
- similar shape to the substrate molecules. They compete with the substrate molecule to bind to the active site so no further reactiuon take place.
- they block the active site so no substrate molecules can fit
- the level ih inhibition depends on relative concentrations of inhibitors and substrate
- high concentration of inhibitors will take up nearly all the active sites and no substrate will get into the enzyme
- they are complementary shape too the active site
non competitive inhibition
- bind to the enzyme away from its active site in a region called the allostertic site
- causes a change in the tertiary structure of the protein causing the active site to change shape so the substrate molecules can no longer bind to it
- this decreases the rate of reaction as a result
- increasing the substrate of the substrate woint make a difference as the enzyme wil still be inhibited
venom
- phosphodiesterases - interfere with the heart causing a drop in blood pressure
- Inhibitor of acetylcholinesterase - inolved in nerve transmission and inhibition causing paralysis
- ATPases- breaks down ATP disrupts prey use of energy
Control of metabloic sequences
- the product of one enzyme controlled reaction is the substrate for the next enzyme controlled reaction - metabolic pathways
Feedback inhibition ( end-product inhibition)
- The end product binds to an enzyme earlir in the sequence
- this changes the active site reduction the rate of reaction ( reversible , non competitive inhibition
- less product is made
Enzyme activation
- some enzymes are synthesised in an active precursor form
- before they carry out their function the protein has to alterned so the active sites assumes the correct shape and is exposed
- by adding phosphate, removing some of their amino acids, adding a cofactor
- example os this is trypsin and pepsin
