Proteins + Enzymes

Question 1

Draw the structure of an amino acid.

Answer 1

• amino group on left of central C
• carboxyl group on right of central C
• H beneath central C
• R (variable group) above central C

Question 2

Describe how dipeptides form.

Answer 2

• 2 AA join together by a condensation reaction forming a peptide bond + releases water
• involves OH of the 1st AA carboxyl group + the H of the 2nd AA amino group

Question 3

What are the 4 levels of protein structure?

Answer 3

• primary
• secondary
• tertiary
• quaternary

Question 4

What is the primary structure of a protein?

Answer 4

• the order/sequence of AA in a polypeptide chain

Question 5

What is the secondary structure of a protein?

Answer 5

• sequence of AA causes hydrogen bonds to form between AAs in the chain making it coil into an α-helix or fold into a β-pleated sheet

Question 6

What is the tertiary structure of a protein?

Answer 6

• further folded + coiled to form a unique 3D shape
• held in place by **hydrogen, ionic + disulphide bonds [between AA cysteine] **

Question 7

What is the quaternary structure of a protein?

Answer 7

• 3D structure resulting from more than 1 polypeptide chain chemically bonded together
• e.g. haemoglobin + collagen

Question 8

Describe the biochemical test for proteins.

Answer 8

• add sample to a test tube
• add Biuret reagent to the sample (sodium hydroxide + dilute copper (II) sulphate)
• turns purple/lilac in the presence of proteins

Question 9

What are enzymes?

Answer 9

• tertiary structure globular proteins which lower activation energy of the reactions they catalyse

Question 10

How do enzymes lower the activation energy?

Answer 10

by forming an enzyme-substrate complex bc:
- holds substrates molecules close together, reducing any repulsion between the molecules so can bond more easily
- catalyse breakdown by putting a strain on bonds in the substrate, so breaks up more easily

Question 11

What is activation energy?

Answer 11

• the minimum amount of energy needed to activate the reaction

Question 12

What is the lock + key model?

Answer 12

• suggested that the rigid shape of the active site of the enzyme was a precise fit for the specific shape of the substrate

Question 13

What is the induced fit model?

Answer 13

• prior to binding, substrate + active site are not completely complementary in shape
• when substrate binds the active site alters shape + moulds around substrate

Question 14

What factors affect enzyme activity?

Answer 14

• T°C
• pH
• enzyme conc
• substrate conc
• inhibitors

Question 15

How does T°C affect enzyme activity?

Answer 15

• higher T°Cs inc KE so molecules move faster
• so enzymes more likely to collide w substrate + form enzyme-substrate complexes
• inc ROR until optimum T°C, then the vibration can break bonds + denature the enzyme

Question 16

How does pH affect enzyme activity?

Answer 16

• if pH is too high/low, bonds holding tertiary structure in place break changing shape of the active site (denatures
• substrate can no longer fit reducing formation of enzyme-substrate complexes

Question 17

How does enzyme conc affect enzyme activity?

Answer 17

• lower enzyme conc means enzyme active sites become saturated w substrate quicker so unable to work any faster

Question 18

How does substrate conc affect enzyme activity?

Answer 18

• lower substrate conc = slower reaction bc fewer collisions between enzyme + substrate

Question 19

What are the 2 types of enzyme inhibitors?

Answer 19

• competitive inhibitors
• non-competitive inhibitors

Question 20

How do competitive inhibitors affect enzyme activity?

Answer 20

• similar shape as substrate so binds to active site preventing enzyme-substrate complexes

Question 21

How do non-competitive inhibitors affect enzyme activity?

Answer 21

• binds to allosteric site causing active site to change shape so no enzyme-substrate complexes form as substrate can no longer bind