proteins

• What are some limitationa of the lock and key model? (3 points) Suggested Active Site of an enzyme is rigidScientists observed inhibitors could bindHence enzymes shape was being altered by binding molecule
• Recall the function and 3 properties of globular proteins. FunctionalCompactWater solubleMetabolic processes
• Recall function and 2 properties of fibrous proteins. Function: StructuralInsoluble in waterForm long chains
• What monomers make up proteins? Amino acids
• What is a dipeptide? Two amino acids joined together via a condensation reaction
• What is a polypeptide? Formed when more than two amino acids join together
• How are polypeptides formed? Condensation reactions involving amino acids, where water is released Peptide bonds are between the amino acids
• What are the structural levels of proteins? Primary structure Secondary structureTertiary structureQuaternary structure
• List 4 types of protein molecules found in organisms: Enzymes AntibodiesTransport proteinsStructural proteins
• Recall the test for proteins. MS [2] Add Biruet's reagent Positive result is purple/violet
• What does it mean to call enzymes ‘biological catalysts’? They catalyst metabolic reactions at cellular level (respiration) and in the organism as a whole (digestion)
• How do enzymes lower activation energy? [2] Enzymes attach to substrates and can hold the two substrates close together, reducing repulsion and allowing bonding to occur more easilyEnzymes breaks up the substrate more easily as it applies strain on the bonds
• What is the lock and key model for enzyme-substrate action? The substrate fits into the enzyme like a key fits a lockThis was before the induced fit model that came based upon new evidence
• Describe the induced fit model for enzyme action. MS [3] Active site of enzymes is not complementary to substrateShape of active site undergoes a conformational change when substrate binds to form an E-S complexStressing/distorting/bending bonds in substrates leads to reaciton
• What 4 factors can affect enzyme activity? Temperature pHEnzyme concentrationSubstrate concentration
• How does increasing temperature closer to the optimum affect enzyme activity? MS [4] Rate increases when temperature increases More kinetic energy hence moving faster More frequent collisions between enzyme and substrate moleculesMore E-S complexes formed
• How does pH affect enzyme activity? Enzymes have an optimum pH to work inAbove and below the optimum pH, the presence of more/less than ideal numbers of H+ and OH- ions can damage ionic bonds in the enzymes tertiary structureThis causes the enzyme to be denatured
• How does enzyme concentration affect enzyme activity? More enzyme molecules in a solution means they are more likely to collide with a substrate and form an enzyme-substrate complexIncreasing enzyme concentration increases reaction rateIf the amount of substrate is limited, adding more enzyme won’t increase the rate any further
• How does substrate concentration affect the rate of reaction? The higher the substrate concentration, the faster the reaction Collisions between substrate and enzyme are more likely, and so more active sites are used This is limited by the saturation point where all the active sites are full and adding more substrate does not help
• What happens to substrate concentration as a reaction progresses? [ ] decreases with time during the reactionHence rate of reaction will decrease over the course of a reactioninitial rate highest as the most substrates are available
• How can you measure the rate of an enzyme controlled reaction? (2 marks) Two ways: How fast the product of the reaction appearsDisappearance of the substrate
• How can you calculate the initial rate of reaction? Draw a tangent to the graph at t = 0 Calculate the gradient of the lineThis is the rate of reaction
• Give similarities between starch and cellulose. [6] Similarities:Both polysaccharidesContain glucoseContain glycosidic bondsHave 1-4 linksHydrogen bonding within the structure
• Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? MS [2] Double bonds Are present between the carbons
• Maltose is hydrolysed by the enzyme maltase. Explain why maltase catalyses only this reaction: MS [3] The active site has a shape complimentary to the substrate Only maltose is able to bindTo form the enzyme substrate complex
• Whats the test for proteins? (3 marks) The Bierut test for proteins: Add sodium hydroxide solution to make the solution alkalineadd copper (II) Sulfate Purple colour proves protein is present.
• Explain the function and structure of antibodies? (3 marks) Involved in the immune response.Composed of 2 light and 2 heavy polypeptide chains bonded together.Antibodies have variable regions where the amino acid sequence varies greatly.
• What does the enzyme do to speed up the Rate of Reaction? Lower the activation energy by forming an enzyme-substrate complex, where the reaction occurs at a lower tempreature.
• What is the enzyme's active site tetermined by? The enzymes tertiary structure.
• Why are enzymes specific? (3 marks) Enzymes are very specific as they can only catalyse one reaction.This specificity arises from the complementary substrate fitting into the active site.The shape of the active site is determined by the enzyme's tertiary structure.
• What happens if the tempreature is low in a chemical reaction? Less Kinetic energy for the substarte to collide with the enzymeno e-s complex forms.
• What happens if the tempreature is high in a chemical reaction? Causes the enzyme to vibrate moreif above a certain tempreature - vibration breaks bonds between the molecules changes the shape of the active site enzyme is now denatured.
• What will an increase in pH do to the enzyme? Optimum PH is 7 But differnent for each enzymeabove and below optimum the H+ and OH - bonds wil interfere with the hydrogen and ionic bondschange the shape of the active siteenzyme denatured.
• What is the effect of increasing the enzyme concentration on the reaction? the higher the enzyme conc. the more likely a collision will occur with a substrate, forming an ES complexHowever if all substartes are full, an increase will have no further effect.
• What is the effect of increasing the Substarte concentration on the reaction? Increasing the substarte concentration will increase the rate of collisions with enzymesincreasing the chance of ES complexThis is only true until saturation, where all the active sites are full, so an increase has no effect.
• Explain what a competitive inhibitor does: (4 marks) Similar shape to a substrate molecule.Binds to the active site and competes with the substrate molecule.If the concentration of substrate is higher, it is less likely to cause inhibition.Increasing the concentration of the inhibitor will increase inhibition and decrease the ES complex.
• Explain what a non-competitive inhibitor does (3 marks) Binds to the enzyme away from the active site (allosteric site).Changes the shape of the active site, preventing the enzyme from binding.Increasing concentration has no effect.
• What are amino acids? The basic monomer units that combine to make up a polymer called a polypeptide
• General structure of an amino acid
• What are the 4 different chemical groups in an amino acid? Amino group -NH2 Carboxyl group -COOH Hydrogen atom -H R (side) group