Polymers of Life 6: Enzymes Flashcards
Definition of enzyme
- proteins that are folded into complex shapes that allow smaller molecules to fit into them
Definition of active site
The place where a substrate molecule fits into an enzyme
What is an enzymes function
To act as a biological catalyst
Definition of catalyst
- Substance that increases the rate of a chemical reaction but is unchanged at the end
- lowers amount of activation energy required by providing an alternative pathway/ route
Know how to show effect of enzymes on a enthalpy profile diagram & maxwekl Boltzmann distribution curves
Look at sheet in ozone story
- be able to draw both
Describe enzyme structure
- have a precise 3D shape ( tertiary protein )
- cleft ( active site ) in surface formed by the way the protein chain folds
- within cleft = chemical groups = R groups from amino acid residue that bind molecules and possibly react with them
Describe the shape of the active site of an enzyme
- shape of active site is tailored for the substrate molecules to fit into
- Substrate binds to a small part of the enzyme active site
= complementary shape fit
How does an enzyme catalyse a particular reaction in terms of substrate complex
Steps of catalysis ( 5 )
- Substrate approaches enzyme
( E + S ) - Substrate enters and bonds temporarily to form an enzyme substrate complex ( ES )
- Enzyme catalyses the reaction & forms a product = enzyme product complex ( EP )
- Products leaves the active site ( E + P )
- Leaving active site ready for another substrate
How does a substrate bind to an active site
4 different kinds of bonding
- substrate forms hydrogen bonds with R groups
OR
- ionic bonding ( depending on R groups present ) because of zwitterions = zwiterions + substrate = ionic bonding
- instantaneous induced - instantaneous dipole reactions = non polar R groups
- disulphide bridges = permanent = covalent bonds ( very few because nerd enzyme to be empty of substrates once finished or can. It act as a catalyst) = sistine prison
What factors effect the rate of enzyme controlled reactions
- concentration of enzyme
- concentration of substrate
- specificity
- temperature
- pH
- presence of inhibitors
Why can enzymes only catalyse specific reactions
- Enzymes are specific for one substrate
- only one stereoisomer ( optical isomer = chiral carbons ) fits and the other doesn’t
Describe how temperature affects rate of enzyme reaction
- Initially rate increases due to increasing kinetic energy = increasing the frequency of collisions between substrate and the active site
- However if keep increasing temperature = rate decreases due to breaking of a weak bonds that maintain tertiary 3D structure = the substrate can no longer bind to active site
( weak bonds e.g. hydrogen ionic bonds that maintain the test restructure are broken at high temperatures so the enzyme unravels and loses its 3-D shape ( no covalent bonds or disulphide bonds are broken) )
Why can enzymes lose their 3D shape ( be deactivated )
Enzymes = globular proteins = not very stable = deactivated
Why are some enzymes more stable
Tertiary structure may be maintained by more covalent strong disulphide bonds
Definition of pH
- Measure of hydrogen ion ( H+ ) concentration
- pH = -log[H+]
- Low pH ( acidic ) has a high hydrogen ion concentration
- High pH ( alkaline ) has a low hydrogen ion concentration
Definition of optimum
Most efficient catalysis happening
Explain how an increase in pH affects enzyme reaction
- as H+ is increased in concentration = +ve charges attracted to -ve charges on the alpha helix = replace the hydrogen bonds that maintain the tertiary restructure of the enzyme
- enzymes become denatured at extremes of pH as many weak bonds are broken
How else do H+ ions affect an enzyme
H + ions may also associate with certain amino acid R groups at the active site = altering the charge distribution and interfering with the substrate binding = fewer enzyme-substrate complexes form = decrease rate
Why does the activity of the enzyme forward to 0 extremes of pH
Enzyme becomes inactive it needs to expand = states to get denatured
describe Overall effect of pH on enzyme ( 6 )
- at pH away from optimum
- H+ disrupts the hydrogen and ionic bonds that maintain the tertiary structure of the enzyme
- Enzyme changes shape of the active site changes shape so it is no longer complimentary to the substrate
- May also alter the charge distribution at the active site to prevent substrate binding
- Fewer enzyme substrate complexes form
- at extremes of pH the enzyme may = denatured
Definition of inhibitors
- Molecules that fit into the active site but cannot be catalysed
- compete with the substrate = competitive inhibitors
- if inhibitor wins = temporary enzyme-inhibitor complex instead of enzyme-substrate complex
How can you make sure the rate of reaction is not affected when inhibitors are present
Increase the concentration of the substrate as inhibition depends upon relative concentration of inhibitor and substrate
Describe non-competitive inhibition
- inhibitor binds to the enzyme away from the active site
- binding causes a change in the active site shape = Substrate cannot fit complementary into the active site
= not form enzyme-substrate complex
