Polymers of Life 6: Enzymes

Question 1

Definition of enzyme

Answer 1

• proteins that are folded into complex shapes that allow smaller molecules to fit into them

Question 2

Definition of active site

Answer 2

The place where a substrate molecule fits into an enzyme

Question 3

What is an enzymes function

Answer 3

To act as a biological catalyst

Question 4

Definition of catalyst

Answer 4

• 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

Question 5

Know how to show effect of enzymes on a enthalpy profile diagram & maxwekl Boltzmann distribution curves

Answer 5

Look at sheet in ozone story

- be able to draw both

Question 6

Describe enzyme structure

Answer 6

• 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

Question 7

Describe the shape of the active site of an enzyme

Answer 7

• 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

Question 8

How does an enzyme catalyse a particular reaction in terms of substrate complex

Steps of catalysis ( 5 )

Answer 8

1. Substrate approaches enzyme
   ( E + S )
2. Substrate enters and bonds temporarily to form an enzyme substrate complex ( ES )
3. Enzyme catalyses the reaction & forms a product = enzyme product complex ( EP )
4. Products leaves the active site ( E + P )
5. Leaving active site ready for another substrate

Question 9

How does a substrate bind to an active site

4 different kinds of bonding

Answer 9

• 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

Question 10

What factors effect the rate of enzyme controlled reactions

Answer 10

• concentration of enzyme
• concentration of substrate
• specificity
• temperature
• pH
• presence of inhibitors

Question 11

Why can enzymes only catalyse specific reactions

Answer 11

• Enzymes are specific for one substrate

- only one stereoisomer ( optical isomer = chiral carbons ) fits and the other doesn’t

Question 12

Describe how temperature affects rate of enzyme reaction

Answer 12

• 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) )

Question 13

Why can enzymes lose their 3D shape ( be deactivated )

Answer 13

Enzymes = globular proteins = not very stable = deactivated

Question 14

Why are some enzymes more stable

Answer 14

Tertiary structure may be maintained by more covalent strong disulphide bonds

Question 15

Definition of pH

Answer 15

• 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

Question 16

Definition of optimum

Answer 16

Most efficient catalysis happening

Question 17

Explain how an increase in pH affects enzyme reaction

Answer 17

• 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

Question 18

How else do H+ ions affect an enzyme

Answer 18

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

Question 19

Why does the activity of the enzyme forward to 0 extremes of pH

Answer 19

Enzyme becomes inactive it needs to expand = states to get denatured

Question 20

describe Overall effect of pH on enzyme ( 6 )

Answer 20

1. at pH away from optimum
2. H+ disrupts the hydrogen and ionic bonds that maintain the tertiary structure of the enzyme
3. Enzyme changes shape of the active site changes shape so it is no longer complimentary to the substrate
4. May also alter the charge distribution at the active site to prevent substrate binding
5. Fewer enzyme substrate complexes form
6. at extremes of pH the enzyme may = denatured

Question 21

Definition of inhibitors

Answer 21

• 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

Question 22

How can you make sure the rate of reaction is not affected when inhibitors are present

Answer 22

Increase the concentration of the substrate as inhibition depends upon relative concentration of inhibitor and substrate

Question 23

Describe non-competitive inhibition

Answer 23

• 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