Module 2.4 Flashcards
enzymes increase the rate of reactions ( make reactions fater ) . MEANING ENZYMES ARE CTALSYSTS .
aS WE FND ENZYMES IN LVIING ORGANSIMS , WE SAY , ENZYMES ARE bioligcal catalsysts .
Check sheet for the equation with hdyrogen perxoide
the enzyme is CATALAE .
-as we find catalase inside cells , catalase is an example of an intracellular enzyme .
-Catalase , binds to the toxic moelcule , hydrogen perxodide and speeds up its breakdown to the harmless molecules wter + oxygen .
Amyalse , is another enzyme , unlike catalase , amyalse is not found isndie cells .
-Check sheet for equation .
…
Amylase is pordued in the pancrease and released into the small intenstine .
JOB of amylas eis to catalsye the breakdowns trarch moelcules into the disa
ccharide maltsoe .
-Maltose is then brokken by other enzymes into glucose .
-Which is abosrbed into the bloodsream .. As we ind amalse outide cells ,w e say that amyalse is an exmaple of an extracellualr enzume .
yeah come one ,
Another example of an enzyme .
-Check sheet for equation .
Trypsin , is another exmpale of an extraceullr enzyme , Trypsin is produced by the pancreas and released into the digestive system .
What is the job of trypsin ?
To catalyse the breakdwon of protein moelcules , into shorter fragments called peptides .
-Again , other enzymes break down peptides into mino acids , which can be abosrbed into blodstreams .
In each of these examples
the enzyme attaches to and breaks down another moelcules .
What is the substrate
(hydorgen peroxide ,s tarch , proteins )
-The moelcule that the enzyme attaches to is called the SUBSTRATE MOELCULE .
What is the product ?
The moelcules porduces (Water + oxyge , maltose and peptides . )
-The vast majority of enzymes are globular proteins .
What are globular proteins again ?
Globular porteins have hydrophillic amino cids on their surface and any hydrophobic amino cids are buried within the center of the prtoein .
-Making Globular porteins osluble in water .
Check sheet for simplfiied strucuture of enzyme molecule
-On the surface of an enzyme moelcule , we find a groove , which scieniststs call the active site .
-The job of the active sitwe is to attach to the substarte moelcule .
-Scienits now call the enzyme substrate complex .
Key ; the tertiary strucutre of the active site is complementary too the strucuture of the susbrate
AL , the susbrtae meolcue fits perfectly inot the ctive site .
BECAUSE O THIS , each enzyme is specific for the substarte it binds to .
-As youc an see , a molecul with a strucuture different to the substarte cannot successfully bind to the active site .
What happens when the substrate bind to ?
Oncd the susbtarte binds , the aminoa cids on the suraface of the active site ,c an form temproary bonds witht he susbtrate moelcule .
-The enzyme then catalsyes the reaction . TO FORM the enzyme product compelx .
-now th PRODUCTS ARE RELSED FROMT HE ACTIVE SITE .
key ; NEED TO UNDERSTAND is that in any reaction , the moelcules must have a certain amount of energy before they can react .
Scienits call this hte ctivationn energy . Anu moelcles , whch don’t hae at leasst the actvation energy CANNOT REACT .
-Enzymes rpodvide a pathway for the ractio with a lower ACTIVATIONE ENEGRY .
iN THE PRESENCE OF AN ENZYME
tHE ACTIATION ENERGY barrier is lwoer than it would be without the enzyme .
-This means that more subsrat emoielcuels , now have enogiuunenergy tocross the activation energybarrier and react .
-SO THE presecne of an enzyme , the reavtion rate increases .
On the surface , the tertiaery strucuture of the enzyme , folds into three dimensional shape called the active site .
The active site is a aprt of the enzyme where the substrate molecule attached to form the enzyme substrat ecomplex .
As we have seen , the tertiary strucutre of the active site is specific to the strucuture of the substrte moelcule .
Explaining hwy enzymes are specfific .
Temporary bonds form between the substrate molecule and the aminoacids on the surface ont he active site .
These temporary bonds , help to the lwoer the activation eneegyr of the reaction . Explaining how enzymes increse the reaction rate l.
When scienists first looked t catalsts , they though the tertiary strucuutre of rhe active site is FIXED and does not chnge shape .
So esentaly ,t he susbtrate mooelcule slots perfectly into the active site .
-Scienitsts call this hte lock nd key hypothesis . / Lock and key theory .
Later , scienitsts saw this model ws not ccurate . As the teriary strucuture of the active sire changes . as the substarte molecule approaches .
As the substarte starts to form bonds with the amino acids in the active sit . The tetriary strucuture of the enzyme , ajusts so that the active site moduls itself tghtly aroun the susbtrate .
-This change in the tertiary sturucutrepof the enzyme , ensures tht the active site perfectly to the sbsrtate .
The bonds that the substarte forms witht he active site , helps to catalyse the reaction .
-Scienitsts call this the induced fit mdoel / induced fit hypothesis .
Moleucles which are not the susbrtate canno formt he correct bonds to the correct bonds to the correct aminoa cids int he active site .
because of this , the tertiary strucuture of the enzyme DOES NOT CHANGE .
-Mening the hsap eof the active site does not adjust to fit the moelcule . Heping to explain why enxymes are specific for the subrate .
check sheet for RECAP on both theories
even though experiments hsow induced fit model is correct .
During a reaction , if we plot the amount of product formed at different types we get a graph like this
…
Check the graph one - star one
Rapid inital rate ,a s you can see , at the start , the line is STEEP .
-This means that a large amount of product is produced in a short time .
-So the rate of the reaction is rapid initially .
Check graph one - star two
However , as the reaction continues , the line becomes less steep .
-Although , we are making product , the amount of product being formed in a given time is LESS then at the start .
-This tells us , that at this point , the rate of reaction has decreases (AKA - slows down ) .
Check graph - star three
At the end , the line is horizontal . Meaning no more product has been formed . So the reaction ha stopped .
Instead of measuring the amount of product being formed , we can measure the amount of substrate remaining .
Check the graph .
Checking graph two .
Again , we can see a rapid initial rate .
-Followed by the reaction slowing down .
-Then finally stopping
We can measure the rate of the reaction at any point , by drawing a tangent .
-Tangent is used to measure the rate of reaction at five seconds ( for example ) .
-Workout the gradient of the tangent by making a triangle .
(vertical side long – > 27 mg so y has a value of 17 mg ) .
-Measure the length of x = 1.5-8s —>: so x has the value of 6.5 s .
-Calculate the gradient = y/x =n 17/6.5 = 2.62mg/s (3sf)
EXAM - explain the shape of the graph
KEY ; rate of the enzyme controlled reaction , depends on the frequency of successful collisions between the substrate and the active site .
~frequency “ means the number of successful collisions .
Star one of graph three
At the start of the reaction , we have a large amount of substrate molecules . Meaning , there is a high frequency of successful collisions between the substrate and the active site .
-Giving a rapid rate of initial reaction .
Star two of graph three
As the reaction takes place , some of the substage is converted to product . Meaning the amount of substrate molecules falls .
-So the chances of a Subrata molecule colliding with he active site decreases .
-making reactions lowdown .
star three of graph three
Finally , at a certain point , all of the substrate molecules have been converted to product .
-There are no more substrate molecules left to collide with he active site .
-At this point k the reaction stops .
-We can calculate the rate of an enzyme controlled reaction , by plotting the amount of product formed against the time .
-We can then draw a tangent at the point of the reaction we are interested in .
-Select an enzyme to calculate the amount of product formed with time .
-We then , repeat this , using a range of temperatures . Then , we draw tangents to measure the rate of reactions at each temperature .
KEY ; - important that we draw the tangents at the same point for each reaction .
check graph for sample results
-each of these graphs represent the SAME enzyme controlled reaction .
-Just changed temperature for each reaction .
-As we increase the temperature , up to 40 degrees , we increase the rate of reaction .
-HOWEVER , if we increase the temperature to 50 degrees , we get a different reaction .
-At 50 degrees , the reaction is much slower . At higher temperatures than this , the enzyme may not function at all.
key ; when an enzyme denatures , due to high temperatures , it cannot renature if we cool it back down , why ?
As it’s tertiary structure has changed so much that it cannot be renatured .
What is the temperature coefficient , check sheet for the equation .
check sheet for the equation
1. Measure the rate of the reaction , at a certain temperature (20 degrees ) .
2.We then measure the rate again , at a temperature ten degrees higher . (30 degrees ) .
What do we find when working out the temperature coefficient ?
Generally , what we find is that if we increase the temperature by ten degrees , the rate of an enzyme controlled reaction DOUBLES .
-Meaning the value of Q10 is usually has a value of 2 .
-HOWEVER - this does not apply for enzymes that are above the optimum temperature , as at that point the enzymes denature .
The pH of a solution depends on the concentration of hydrogen ions , Which are also called h+ ions .
-Solution with a low pH , (pH 2 ) , has a high concentration of hydorgen ions .
-Higher pH –> low concentration of hydrogen ions .
check the graph , that measures the rate of an enzyme at different pH .
-each enzyme works the fastest at an optimum PH .
(for this enzyme = 7 ) —> this could be an enzyme in salivary glands .
-if the optimum ph. is 2 then the enzyme may work in an acidic environment like the stomach .
-If the pH change as away from the optimum ph. , then the rate of reaction decreases .
pH depends on the concentration of hydrogen ions present .
what can hydrogen ions bond with in an enzyme ?
-Hydrogen ions can bond with the R groups of amino acids in he protein .
-This includes amino acids within the active site , which form temporary bonds to the substrate .
-As this can prevent the R groups from bonding with the substrate , this can reduce how frequently the substrate binds to the active site –> reducing the rate of reaction .
Hydrogen ions also bond with the R groups of amino acid in the rest of the enzyme molecule .
The effect of this , can be to break the bonds, holding the tertiary structure of the enzyme in place .
example shown .
-check sheet , shows ionic bond between two amino acids on different parts of the enzyme molecule .
REMEMBER ; ionic bonds form between two charged R groups .
-f Ph falls the concentration of hydrogen ions increases . and the bond breaks (shown in the picture )
check sheet , what happens if the ph rises?
this causes the concentration of hydrogen ions to decrease and the bonds break .
-So as you can see , changing the pH can break the bonds which are essential for the enzyme’s tertiary structure
-This can change the shape o f the active site , making it less likely for the substrate to attach succesfully .
What might happen if the ph. changes significantly ?
The active site may change shape so much that it is no longer complementary to the substrate and therefore the enzyme has now denatured .
