Proteins and enzymes

Question 1

describe the general structure for an amino acid

Answer 1

-carbon in the centre
-amine group on the left
-carboxyl group on the right
-hydrogen group at the top
-r group at the bottom

Question 2

explain how two amino acids join together

Answer 2

• condensation reaction
• between carboxyl group of one amino acid with the amine group from another amino acid
• water is removed and a peptide bond is formed

Question 3

what are the 4 organisation levels in a protein

Answer 3

1)primary
2)secondary
3)tertiary
4)quaternary

Question 4

explain the first organisation level in a protein

Answer 4

primary
-order /sequence of amino acids
-determines the positions of the bonds

Question 5

explain the second organisation level in a protein

Answer 5

secondary
-a hydrogen bond forms between the slight positive chare on the H and the slight negative charge on the O
-these two groups form weak hydrogen bonds which are strong cuz of the large numbers
-this causes the polypeptide to coil into alpha helixes or fold into beta pleated sheets

Question 6

explain the third organisation level in a protein

Answer 6

tertiary
-further folding of the secondary structure into a specific, complex 3d shape
-this is held together by bonds between R groups which are maintained by:
-hydrogen bonds which are
weak and broken easily with
increasing temperature
-ionic bonds which are also
weak and broken by changed
in ph
-disulphide bridges which are
covalent bonds that are
extremely strong

Question 7

explain the fourth organisation level in a protein

Answer 7

quaternary
-contains two or more polypeptide chains

Question 8

explain the test for protein

Answer 8

-place a small volume of sample into a test tube
-add an equal volume of biuret solution
-if protein is present it changes from blue to purple

Question 9

active sites have a unique shape which is ________ to only one substrate

Answer 9

complementary

Question 10

explain how an enzyme lowers activation energy

Answer 10

-an enzyme-substrate complex is formed when and active site binds to a substrate
-the substrate is held in the active site by temporary bonds
-these bend and stress the bonds in the substrate which lowers activation energy

Question 11

explain the induced fit model of enzyme action

Answer 11

-the substrate enters the active site and induces a change in the shape of the active site as an enzyme-substrate complex is formed
-this stresses the bonds and lowers the activation energy
-the active site will then return to its previous state

Question 12

how do you calculate rate

Answer 12

divide change in measurement (dy) by the time taken (dx)

Question 13

name 4 factors that affect enzyme action

Answer 13

1)temperature
2)ph
3)substrate concentration
4)enzyme concentration

Question 14

explain how temperature affects enzymes

Answer 14

• -as the temp increases there is more kinetic energy so they move around more and collide more and form enzyme-substrate complexes
• -the temperature rise also causes the hydrogen bonds and the ionic bonds to break. This changes the tertiary structure and the shape of the active site
• -the active site is no longer complementary to the substrate so fewer enzyme-substrate complexes form
  -the enzyme is now denatured

Question 15

explain how ph affects enzymes

Answer 15

-the active site changes shape and is no longer complimentary
-no enzyme-substrate complexes can be formed

Question 16

explain how substrate concentration effects rate of reaction (ror)

Answer 16

when there is a low substrate concentration not all the active sites are saturated so ror is slower

Question 17

explain how enzyme concentration rate of reaction (ror)

Answer 17

when there is a low enzyme concentration the ror is low because all of the enzymes active sites are saturated

Question 18

explain the effect of competitive inhibitors on ror

Answer 18

-they have a similar shape to the substrate and can bind to the active site of an enzyme and block the active site
-this prevents enzyme substrate complexes from forming
-this reduces ror
-they are not permanently bound

Question 19

explain the effect of non-competitive inhibitors on ror

Answer 19

-they bind to the allosteric site on an enzyme
-this changes the shape of the active site so that it is no longer complementary to the substrate
-fewer enzyme-substrate complexes will form and ror decreases