2.1.4- Enzymes

enzymes definition

biological catalysts; globular proteins that react with substrate molecules to increase the rate of reaction by providing an alternative activation energy pathway

what are the two types of reactions enzymes can catalyse and what is the difference between them with examples

• anabolic reactions= building up, growth, creating something new e.g. glycogen synthesis, protein synthesis, photosynthesis

• catabolic reactions= involved in the breakdown of molecules e.g. respiration, breakdown of hydrogen peroxide

what is activation energy

energy required for a reaction to start

what are the two types of enzymes and the difference between them

• intracellular= work inside the cell e.g. catalase, hydrolase

• extracellular= work outside of the cell e.g. amylase, trypsin etc

what is the active site

• area of enzymes tertiary structure that is complementary in charge and shape to the substrate it reacts with; specific to only one substrate

what are the two hypotheses for how enzymes work and what do they suggest

• lock and key= shape of the substrate fits perfectly into the active site of the enzyme causing reaction and release of products

• induced fit= active site changes slightly as the substrate enters; tertiary structure adapts as the substrate bonds to it, adjusting to fit perfectly

what is it that allows the enzyme to decrease activation energy

temporary bonds form between the substrate and the active site’s amino acids on the surface and these bonds decrease the activation energy

what factors affect enzymes

• temperature

• pH

• substrate and enzyme concentrations

how does temperature affect enzymes; explain the shape of the graph as well

• as temperature increases, so does rate of reaction until the optimum temperature is reached

  • this is because higher temperatures mean higher kinetic energy so more movement and collisions to form ESCs

• however, past this optimum, enzymes denature and rate of reaction decreases rapidly

  • this is because higher temperatures causes the bonds in the tertiary structure to break (the weaker ones) which changes the shape of the active site so it is no longer complementary to the substrate

  • cannot renature

what is the temperature coefficient and how to calculate

• Q10

• is the rate or reaction at temperature x+10C / temperature x

• usually around 2

how does pH affect enzymes

• enzymes work fastest at a specific optimum pH; the further from this optimum, the slower the rate of reactiob

• at lower pH (more H+ ions)= they can react with the tertiary structure of the enzyme e.g. ionic bonds, hydrophobic/philic interactions

  • this changes the active site shape or the tertiary structure and the molecule falls apart as is breaking the bonds and forming new ones in different positions

• at higher pH (less H+ ions)= less H+ ions interfering means not the correct shape and bonds that would’ve been there are no longer present

  • means the tertiary structure and active site shape changes and cannot form an ESC

how does substrate concentration affect enzymes

• increased substrate concentration means a higher chance of successful collisioins with enzymes to form ESCs

• then plateaus at the saturation point (Vmax) as all active sites are filled so enzymes are the limiting factor and no more increase in substrate changes this

how does enzyme concentration affect enzyme rate of reaction

• more enzymes means more active sites for substrates to bind to to form ESCs

• then plateaus at saturation point/Vmax as substrate concentration limited and max substrates reacting at once

why is rate of reaction initially rapid

higher concentration of substrates to higher chance of collision

why does the graph eventually plateau and the rate slow

as there is a higher product concentration and a lower substrate concentration so less ESCs are being formed as less substrate available

what are the two types of inhibitor

• competitive

• non-competitive

how do competitive inhibitors work

• have a similar shape to the substrate and binds to the active site, blocking substrates from entering and reacting

• less ESCs are therefore formed so the rate decreases

• usually temporary

what does the graph for substrate concentration with competitive inhibitors look like and why

• has a slower rate compared to without the inhibitor

• however eventually reaches the same Cmax as normal due to an increasing substrate concentration being able to cancel out the effects of competitive inhibitors

• at the start the inhibitor to substrate ration is higher so there is a higher chance of collision with the inhibitor

• as substrate concentration increases, more chance of successful collision and more ESCs so higher rate of reaction

how do non-competitive inhibitors work

• bind to the allosteric site of the enzyme, causing the tertiary structure of the enzyme to change so the active site shape changes and the substrate cannot bind so rate of reaction decreases

• can be reversible or non-reversible

describe the graph of substrate concentration and rate of reaction for non-competitive inhibitors

• rate of reaction still starts relatively high

• then plateaus at a much lower Vmax compared to normal

• cannot reach the same Vmax despite increasing substrate concentration as the active site shape is still changed and the substrate physically cannot bind to the enzyme anymore

purposes of inhibitors

• can be used as medicines e.g. statins, penicillin, aspirint

what are precursors and why are they used

• some enzymes produced in inactive precursor form

• means the amino acids need to be removed to have the correct active site shape; can be through temperature change, pH change etc

• used when would cause damage to cells and tissues when working

what is end-product inhibition

• where the final product of a metabolic pathway inhibits an early enzyme and therefore decreases the rate of the whole metabolic pathway

• negative feedback loop

why does end-product inhibition take place

• the body doesn’t want to waste energy and resources when not required

• don’t want to produce an excess of something that could clog cells

what are cofactors and coenzymes and the difference between them

• cofactors= inorganic, non protein molecules that help enzymes to carry out their function by binding to them

  • e.g. minerals, ions etc that form part of the active site

  • temporary

• coenzymes= organic, derived from vitamins and help enzymes to carry out their function by binding to them

• difference is whether they’re organic or inorganic

what are prosthetic groups

cofactors that permanently bind to enzymes to aid function e.g haem