2.1.4 enzymes Flashcards
function of enzymes
they are biological catalysts
they function in living system and speed up the rate of chemical reactions without being used up or undergoing permanent change
structure of enzymes
globular proteins with complex tertiary structures
- some formed from a single polypeptide
- others made up of two or more polypeptides - quaternary structure
what do enzymes control in a reaction?
- metabolic pathways are controlled by enzymes
- every metabolic reaction in a living organism is catalysed by an enzyme
- enzymes are essential for life
how are enzymes produced?
enzymes are proteins that are produced via protein synthesis inside cells
how can enzymes work?
intracellularly and extracellularly
what are intracellular enzymes?
produced and function inside the cell
what are extracellular enzymes
secreted by cells and catalyse reactions outside cells
what is the temperature coefficient?
the ratio between the rates of that reaction at two different temperatures
temperature coefficient for enzyme-catalysed reactions
the rate of the reaction doubles for every 10oC increase in temp
Q10 = 2
temperature coefficient equation
temperature coefficient = (rate of reaction at (x+10) oC / (rate of reaction at xoC)
what happens when enzymes are denatured at extreme pH?
- hydrogen and ionic bonds hold the tertiary structure of the protein together
- below and above the optimum pH of an enzyme, solutions with an excess of H+ ions and OH- ions causes these bonds to break
- the breaking of bonds alters the shape of the active site so that the enzyme-substrate complex forms less easily
- then it can no longer form and complete denaturation has occurred
explain how pepsin functions
pepsin is found in the stomach, an acidic environment at pH 2 - due to the presence of HCl in the stomach
pepsin’s optimum pH is pH 2
how can you use buffer solutions to measure the rate of reaction at different pH values?
- buffer solutions have a specific pH
- they maintain this pH
- a measured volume of the buffer solution is added to the reaction mixture
- this same volume should be added for each pH value that is being investigated
investigating the effect of pH on enzyme reaction rates
- use the enzyme amylase to breakdown starch at different pH values, using iodine as an indicator for the reaction occurring
- a continuous sampling technique can monitor the progress of the reaction
method for the investigation into the effect of pH on enzyme reaction rates
- wear goggles and gloves - enzymes may cause allergic reactions when in contact with skin
- place drops of iodine on the tile
- label a test tube with the pH to be tested
- use the syringe to place 2cm3 of amylase in the test tube
- add 1cm3 of buffer solution to test tube
- use another test tube to add 2cm3 of starch solution to the solution and start the stopwatch whilst mixing
- use pipette to place a drop of solution onto iodine (should turn blue-black in the presence of starch)
- place another drop of solution onto iodine and repeat every 10 seconds (until solution is orange-brown - no presence of starch)
- repeat experiment at different pH values
control variables in the enzyme reaction rates practical
equal volumes and concentrations of enzyme used
equal volumes and concentrations of substrate used
what does it mean when the solution no longer turns blue-black?
no starch present
amylase has broken down starch so there is nothing left to react with iodine
conclusion to be made from enzyme reaction rate experiment
the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
limitations and solutions of the enzyme reaction rate experiment
- adapted to control temperature using a water bath - allows the solution to reach the same temp of 35oC before being used
- colourimeter can be used to measure the progress of the reaction more accurately - takes into account the absorbance/ transmission of light
how does enzyme concentration affect enzyme activity?
the higher the enzyme concentration, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation
what will happen to rate of reaction if there is sufficient substrate available during enzyme activity?
as long as there is sufficient substrate available the initial rate of reaction increases with enzyme concentration
what will happen to rate of reaction if the substrate is limited during enzyme activity?
If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor
how does substrate concentration affect enzyme activity?
the greater the substrate concentration, the higher the rate of reaction
- no of substrate molecules increase, likelihood of enzyme-substrate complex formation increases
- if fixed enzyme concentration but amount of substrate increases - all available active sites eventually become saturated and increase reaction rate
- when active sites are full, additional substrate molecules have nowhere to bind to form an enzyme-substrate complex
describe a graph of substrate concentration against rate of reaction
linear increase in reaction rate as substrate is added
then plateaus when all active sites become occupied
cofactors
some enzymes require inorganic ions to function properly
may help to stabilise the structure of the enzyme or may take part in the reaction at the active site
example of a cofactor
chloride ions act as a cofactor for amylase
in order for amylase to digest starch into maltose, chloride ions must be present
inorganic cofactors
inorganic ions that an enzyme requires in order to function
coenzymes
larger organic cofactors
some are permanently bound to the enzyme they assist - in or near the active site
some bind temporarily during the reaction
they link different reactions into a sequence during metabolic processes e.g. photosynthesis and respiration
examples of coenzymes: vitamins
pantothenic acid
nicotinic acid
vitamin b1
examples of coenzymes: vitamins - pantothenic acid
- pantothenic acid
- key component of coenzyme A
- required for the oxidation of pyruvate during the link reaction
e.g. glycolysis and Krebs cycle
examples of coenzymes: vitamins - nicotinic acid
- nicotinic acid
- used to produce coenzymes NAD and NADP
- required in metabolic reactions
e.g. photosynthesis and respiration
examples of coenzymes: vitamins - riboflavin
- vitamin B1
- used to produce coenzyme FAD
- required in the Krebs cycle
prosthetic groups
cofactors that are a permanent part of the structure of the enzyme they assist
essential to the enzyme functioning properly as they help to form the final shape of the enzyme
example of prosthetic groups
zinc ion acts as the prosthetic group for carbonic anhydrase - an enzyme found in red blood cells that convert CO2 and H20 into H2CO3
competitive inhibitors
it has a similar shape to the substrate, competes with the substrate to bind to the active site
it occupies the active site without causing a reaction
how to reduce inhibition?
greater concentration of substrate molecules –> the substrate will outcompete the inhibitor for the active site which increases the rate of reaction
non-competitive inhibitors
do not bind to the active site
change the shape of the active site
increasing substrate concentration has no effect
reversible inhibitors
form weak bonds with the enzymes
typically form hydrogen or ionic bonds with their enzymes
irreversible reactions
form strong bonds with the enzymes
typically form covalent bonds with their enzymes
how does penicillin function as enzyme inhibitors
inhibits the enzyme that helps proteins form in bacterial cell walls
antibiotic that inhibits transpeptidase in the bacterial cell walls which weakens it and causes the bacteria to rupture
how do antiviral drugs function as enzyme inhibitors?
inhibit the replication of viral DNA - used to treat viral infections
inhibit the enzyme reverse transcriptase - necessary for the virus to replicate its DNA
as a result the virus can no longer replicate inside the host
how can metabolic poisons inhibit enzymes
inhibit enzymes and disrupt metabolic reactions which damages our cells and can be fatal
examples of toxic poisons which inhibit cellular respiration
cyanide - irreversibly inhibits cytochrome c oxidase
arsenic - inhibits pyruvate dehydrogenase
malonate - inhibits succinate dehydrogenase
end product inhibitors
many enzymes can partake in a large metabolic pathway
end product inhibition is when the final product inhibits an enzyme involved in the inital reactions
end product inhibitors are typically reversible inhibitors
