effect of pH and temperature on enzymes

what is the optimum pH of pepsin?

1-2 pH (stomach)

what is the optimum pH of amylase?

6.8 pH (in mouth)

what is the optimum pH of trypsin?

7.8 pH (intestine)

what happens if there is an excess of H+ ions?

H+ ions are attracted to negatively charged ions. H+ ions will interfere with the hydrogen bonds and ionic forces (which hold the tertiary structure of the active site together) causing them to break. this causes the active site to change shape, denaturing the enzyme

how do the H+ ions affect the active site?

H+ ions will alter the charges on the active site as more protons (H+) cluster around the negatively charged R-groups. H+ ions replace the hydrogen bonds as the H+ ions are attracted to the negative charges in the alpha helix

what is the symbol of temperature coefficient?

Q10

what is the equation for temperature coefficient (Q10)?

Q10 = rate of reaction (T+10) degrees/ rate of reaction T degrees

explain the graph for rate of reaction vs temperature when temperature has reached 37 degrees

as it continues to rise above 37 degrees, the rate of reaction falls rapidly as thermal energy denatures the enzymes causing the hydrogen bonds/ ionic forces holding the tertiary structure of the active site together to break, this irreversibly changes the active site shape and therefore enzyme/ substrate complexes are less likely to be formed as the active site is no longer complementary to the substrate

describe the graph for rate of reaction vs temperature

as temperature increases, the rate of reaction gradually increases until it reaches optimum at 37 degrees and then as temperature continues to increase, the rate of reaction rapidly decreases

what happens if renaturation cannot occur?

at extremes, renaturation cannot happen and the enzyme is denatured

explain the graph for rate of reaction vs temperature when temperature is rising

enzyme activity gradually increases with temperature up to optimum at 37 degrees because there is increasingly more thermal and kinetic energy, therefore more frequent collisions forming enzyme/ substrate complexes

what happens if pH changes?

enzymes have a very narrow pH range so very small changes either side of the optimum pH will slow the reaction rate, this is due to slight alteration in the active site shape so collisions do not occur as easily

how are enzymes adapted for colder environments?

enzymes will have a more flexible structure particularly at the active site, smaller temperature changes will have a large effect and denature them as they are less stable than enzymes that work at higher temperatures

what happens during renaturation?

if pH returns to optimum, the enzyme is able to repair the broken hydrogen bonds returning the active site to the correct shape

what are acids broken into?

in the body, acids dissociate (break down) into protons and negatively charged ions e.g HCl —> H+ + Cl- (carbonic acid) H2CO3 —> H+ + HCO3-

what is the temperature coefficient in enzyme controlled reactions in a test tube?

it is 2 which means as the temperature goes up by 10 degrees, the rate of reaction doubles

what is pH?

it is a measure of hydrogen (H+) ions or hydroxide (OH-) ions in a solution 0-6 = acid 7 = neutral 8-14 = alkali

how is optimum temperature relevant to living organisms?

optimum temperatures are usually where an organism lives as they are adapted to their conditions e.g plants are adapted to withstand temperature changes but if temperature goes far above normal, plants would die due to water loss and the potential denaturation of enzymes

why are optimum temperatures different for different organisms?

organisms are adapted to live in certain environments so their optimum temperature will differ

what is the equation for rate of reaction?

rate of reaction = 1/ time taken to reach end point measured in s^-1

what does it mean when an enzyme is denatured?

the shape of the enzymes active site is permanently damaged due to irreversible changes

what is optimum temperature?

the temperature at which the enzyme has the highest rate of reaction

how are enzymes adapted for hot environments?

thermophile enzymes are more stable due to an increase in the amount of bonds, namely disulphides bonds making their tertiary structures more heat stable. they are more resistant to heat changes (aren't affected as easily)

what are buffers? e.g BIDDA

they resist change in pH e.g in a red blood cell, the enzyme carbonic anhydrase speeds up the formation of carbonic acid. carbonic acid breaks down to H+ and HCO3- ions and the ions diffuse out of red blood cell to be carried by the plasma back to the lungs, leaving H+ ions inside the blood cell to prevent denaturing carbonic anhydrase in the red blood cell, H+ ions react with haemoglobin to form haemoglobonic acid which acts as a buffer to maintain the correct pH in the red blood cell

how can you improve the method when carrying a pH enzyme experiment?

use more specific pH values that are closer in range (i.e instead of using pH 4,5,6,7 and 8, use pH's of 6.1, 6.2, 6.3 etc)