enzymes Flashcards
2.1.4 (23 cards)
what is an enzyme?
a biological catalyst (globular protein) with a complex, unique tertiary structure. used to increase the rate of chemical metabolic processes (anabolic/catabolic) without being used up itself by decreasing activation energy. allow reactions to take place at a lower temperature, for example at body temperature
what is an intracellular enzyme?
an enzyme that acts within the cell that produced it, for example catalase catalyses the break-down of hydrogen peroxide into oxygen and water to prevent the accumulation of toxic hydrogen peroxide inside of cells
what is an extracellular enzyme?
an enzyme that acts outside of the cell it was produced and secretes them. for example amylase is secreted by the salivary glands, pancreas and small intestine to break down starch into maltose. another example is trypsin which is secreted by the pancreas into the small intestine to break down proteins into smaller polypeptides
describe the lock and key theory
states that the enzyme has a unique tertiary structure with a specific active sit that is complementary to the substrate and fits perfectly into it, forming an enzyme-substrate complex with temporary bonds forming between the R groups within the active site and substrate.
what is the induced fit hypothesis
an updated version on the lock and key theory, states that the active site of the enzyme slightly changes shape when the substrate enters, as the initial interaction is weak, then this changes the enzymes tertiary structure, strengthening bonds + straining the substrate, weakening its bonds and therefore lowering activation energy
describe enzyme denaturation
a change in temperature/pH can cause the enzyme’s active site to change shape so that the substrate no longer fits, so the enzyme-substrate complexes cannot be formed and the enzyme has denatured
describe enzymes in extreme temperatures
organisms evolve to cope with extreme temperatures, eg hot springs, high altitudes etc. enzymes need to adapt. ones in cold environments are more flexible, less stable structures that will denature at lower temperatures. ones in hot environments (thermophiles) are more stable due to more bonds in the tertiary structure (hydrogen and sulphur bridges),so the active site is more resistant to temperature rises
what are the 4 factors affecting enzyme activity?
-temperature
-pH
-substrate concentration
-enzyme concentration
how does temperature affect enzyme activity?
-as temperature increases, rate of reaction increases because molecules have more kinetic and collide more often, so there is more enzyme-substrate complexes
-maximum rate of reaction is reached at optimum temperature
-as temperature continues to increase past optimum temperature, rate of reaction decreases until 0 because the active site changes shape and so the enzyme has denatured
how does pH affect enzyme activity?
-below optimum pH, rate of reaction is low/0 because in acidic conditions, hydrogen ions break ionic/hydrogen bonds and denatures the enzyme
-at optimum pH, rate of reaction is at its fastest
-above optimum pH, rate of reaction decreases to low/0 because in alkaline conditions, hydroxide ions break ionic/hydrogen bonds and denatures the enzyme
how does substrate concentration affect enzyme activity?
-as substrate concentration increases, so does rate of reaction because there are more substrate molecules to form enzyme-substrate complexes
-as substrate concentration increases further, rate of reaction starts to plateau ( saturation point ) because all active sites are occupied, and enzyme concentration becomes the limiting factor
how does enzyme concentration affect enzyme activity?
-as enzyme concentration increases, so does rate of reaction because more enzymes are able to form enzyme-substrate complexes
-as enzyme concentration increases further, rate of reaction plateaus because all of the substrate molecules available are being used up and substrate concentration becomes the limiting factor
what are the 4 different things an enzyme inhibitor can be?
-reversible
-irreversible
-competitive
-non-competitive
whats the difference between a reversible and an irreversible enzyme inhibitor?
a reversible one forms weak hydrogen/ionic bonds with the enzyme, whereas an irreversible one forms strong hydrogen/ionic bonds with the enzyme
what is a competitive inhibitor
-a molecule that looks similar tot he substrate that binds to the enzymes active site and blocks the substrate for creating an enzyme-substrate complex
-leads to lower rate of reaction
-usually reversible as they temporarily bind to the active site
-as substrate concentration increase, so does rate of reaction because the active site is more likely to collide with a substrate molecule than the competitive inhibitor
what is a non-competitive inhibitor?
-a molecule that binds to the allosteric site of an enzyme, causing a change in it’s tertiary structure and therefore active site, preventing an enzyme-substrate complex
-lowers rate of reaction
-increasing substrate concentration has no effect on rate of reaction because the inhibitor does not block/bind to the active site
what is a coenzyme
-organic cofactors
-usually derived from vitamins
-help enzymes catalyse reactions
-permanently or temporarily bound
-eg vit B3 produces NAD used in hydrogen atom transfer in respiration
what is a cofactor and state the 2 types
-non-protein molecule that binds to an enzyme to increase their activity
-the 2 types are coenzymes and prosthetic groups
-eg Cl- is cofactor for ezyme amylase
what is a prosthetic group
-bind tightly to enzymes permanently
-for example Zn+ is a prosthetic group for the enzyme carbonic anhydrase for the metabolism of carbon dioxide
what is end product inhibition
-when the products of an enzyme-substrate reaction act as an inhibitor to the enzyme that produced it
-non competitive and reversible
-example of negative feedback
-for example ATP binds to the allosteric site on PFK, preventing phosphate binding to glucose to make ATP, so decreases ATP levels, until it’s all used up when it’ll unbind and start making more
what is precursor activation
the process by which an enzyme precursor is permanently converted into an active enzyme.
causes biological change to precursor
what’s the difference between an anabolic and catabolic reaction
anabolic - build complex molecules from simpler ones
metabolic - break down complex molecules into simpler ones
equation for temperature coefficient
Q10= x+10 / x
