Chapter 4 - Enzymes

Question 1

Enzymes

Answer 1

➜ biological catalysts
➜ globular proteins - complex tertiary structures
➜ Metabolic pathways
➜ All enzymes are proteins that are produced via the process of protein synthesis inside cells
➼ intracellular and extracellular

Question 2

Intracellular enzymes

Answer 2

➜ reactions inside cell
➜ could be part of a metabolic pathway (involve a series of small steps, each step involves a chemical change)
➜ e.g catalase

Question 3

Catalase

Answer 3

➼ intracellular example
➼ hydrogen peroxide is the toxic by-product of several cellular reactions

➼ if left to build up, it can kill cells
➼ works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen and water

Question 4

Extracellular enzymes

Answer 4

➜ reactions outside the cell
➜ where enzymes have been secreted outside cell
➜ amylase, trypsin

Question 5

Amylase

Answer 5

➼ extracellular example - digestion
➼ work outside cells in digestive system

➼ macromolecules being digested are too large to enter cell
➼ amylase is found in saliva - secreted in the mouth by cells in the salivary glands - hydrolyses starch into simple sugar
-catalyses the hydrolysis of starch into maltose in the mouth
-produced by cells in pancreas and salivary glands and used for digestion of starch in mouth and small intestine

Question 6

Trypsin

Answer 6

➼ extracellular example - digestion
➼ work outside cells in digestive system

➼ trypsin catalyses the hydrolysis of peptide bonds - turning proteins into peptides and amino acids
- secreted by the pancreas and enters the small intestine

Question 7

Anabolic pathways

Answer 7

➜ energy is used to synthesise larger molecules from smaller ones

Question 8

Catabolic pathways

Answer 8

➜ metabolites are broken down to smaller molecules and energy is released

Question 9

Cofactors

Answer 9

some enzymes need a small non protein molecule to attach to them so that they can catalyse certain reactions
➼inorganic Ions
➼help to stabilise the structure of the enzyme or may actually take part in the reaction at the active site
➼ are not used up or changed in any way (don’t directly participate)
➼ CI- are cofactors for amylase

Question 10

Coenzyme (carbon containing)

Answer 10

➜ organic non-protein cofactors
➜ some coenzymes are permanently bound to the enzyme and some coenzymes only bind temporarily during the reaction to assist in catalysing reaction
➜ vitamins = important source of coenzymes
➜ e.g pantothenic acid - key component for coenzyme A, Nicotinic acid, NAD & NADP, FAD

Question 11

Cosubstrate

Answer 11

cofactor that works with the substrate to form the correct shape to bind to the active site

Question 12

Prosthetic group
- non protein compound

Answer 12

➜ type of cofactor that is permanently covalently bonded to an enzymes active site
➜ essential to the enzyme functioning properly, as they help to form the final 3D shape
➼eg. Zn2+ are a prosthetic group for carbonic anhydrase

Question 13

Competitive Inhibitor

Answer 13

➜ have similar shape to substrate
➜ fit into active site forming enzyme inhibitor complex - no reaction takes place
➜ no substrate molecules can fit in

Samiras part i dont understand a word:
➼ high conc of the inhibitor, it will take up nearly all the active sites and hardly any of the substrate will get to the enzyme
➼ higher conc of substrate, substrate chance of getting to active site before the inhibitor will increase

Question 14

Non-competitive Inhibitor

Answer 14

➜ bind to enzyme away from active site
↳ this area is called the allosteric site
➜ causes active site shape to change
➜ substrate can no longer fit
➜ increasing conc of substrate makes no difference as non comp inhibitors don’t compete with substrate

Question 15

Factors affecting enzyme activity

Answer 15

➼ temp
➼ pH
➼ substrate conc
➼ enzyme conc

Question 16

Substrate Concentration

Answer 16

➜ ↑ substrate conc, then ROR ↑ so MORE collisions and more active sites used
➜ more enzyme-substrate complexes are formed.
➜ substrate conc = limiting factor = saturation point where active sites are full
➜ certain point, rate of reaction plateaus

Question 17

Enzyme Concentration

Answer 17

➜ higher the conc = greater number of active sites so higher chance of enzyme-substrate complex formed
➜ sufficient substrate available = initial rate of reaction increases linearly with enzyme concentration
➜ if substrate limited then = limiting factor

Question 18

Temperature

Answer 18

• ↑ temp, up to optium, then rate of reaction ↑
  ↳ ↑ kinetic energy
  ➼ more successful collisions between the substrate and active site
  ➼ more successful collisions = more enzyme-substrate complex
• ↑ temp above optimum, then rate of reaction ↓ sharply
  ➼ vibration breaks some of the bonds (hydrogen and ionic bonds)
  ➼ active site shape changes permanently (as tertiary structure changes)
  ➼ enzyme denatures - substrate can no longer bind
• rate of reaction = 0 = when all enzymes denatured

Question 19

Temperature coefficient

Answer 19

Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)

Question 20

Enzyme Substrate Complex

Answer 20

If a substrate successfully collides with enzyme
➼ formation of this enzyme substrate complex lowers activation energy
⤥ ↬ if the enzyme is catalysing a breakdown reaction, fitting into active site puts a strain on bonds in the substrate
↬ substrate molecule breaks up more easily

Question 21

pH

Answer 21

• pH above or below optimum then rate of reaction ↓
• the H⁺ and OH⁻ ions found in acids and alkalis mess up ionic bonds and H bonds that hold the tertiary structure in place
  ↳ Enzymes denature and active site changes shape due to breaking of bonds
• complementary substrate can no longer bind to active site

Question 22

Buffer solutions

Answer 22

➼ each have specific pH
➜ maintain specific pH even when reaction is taking place (reactions can change pH)
➜ a measured vol of buffer solution is added to reaction mixture
➜ same vol (of each buffer) should be added for each pH val being investigated

Question 23

Conc of Inhibitors

Answer 23

Competitive:
• ↑ substrate conc, then ↓ effect of inhibitor
• ↑ inhibitor conc, then ↓ effect of substrate
Non competitive:
• ↑ substrate conc has no effect on rate of reaction as there is a permanent change to active site
- and also inhibitor doesn’t bind to active site

Question 24

Competitive inhibitors (reversible)

Answer 24

➜ a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site

Question 25

Non-competitive inhibitors (irreversible)

Answer 25

➜ bind to the enzyme at the allosteric site, which alters the shape of the active site and therefore prevents the substrate from binding to it

Question 26

End product inhibition

Answer 26

➜ reversible inhibitors act as regulators in metabolic pathways
➜ metabolic reactions must be tightly controlled and balanced
➜ enzyme converts substrate to product so reaction slowed down as end product of reaction binds to an allosteric site on original shape
➜ this changes shape of active site = prevents formation of enzyme substrate complex
➜ end product detaches from enzyme and active site reforms so enzyme returns to active state
➜ this means as product levels fall, enzyme begins catalysing reactions again in a feedback loop

Question 27

Non-reversible inhibitors

Answer 27

➜ some inhibitors form covalent bonds with enzymes, inhibiting them permanently
- known as non-reversible or irreversible inhibitors
➜ if occurs in a living cell or organism it will result in the complete inactivation of the enzyme
- dangerous: cause the biological reaction enzyme is catalysing will be stopped
➜ some non-reversible inhibitors are considered to be metabolic poisons
e.g cyanides, lead, mercury
➜ some inhibitors are beneficial in medical context like penicillin, aspirin

Question 28

Enzyme Product Complex

Answer 28

substrate molecules are broken down or built up into the product

Question 29

Lock and Key Hypothesis

Answer 29

➜ substrate only fit a specific enzyme
1890’s the first model of enzyme activity was described by Emil Fischer: suggested that both enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock
* enzyme + substrate enter active site
* form enzyme substrate complex
* form enzyme product complex
* enzyme + product leave active site

Question 30

Enzymes lowering Ae

Answer 30

➜ activation energy = minimum amount of energy needed for substrate to become unstable enough for reaction to occur
➜ enzymes speed up reactions = reduce stability of bonds in reactants = making it more reactive

Question 31

Induced

Answer 31

➜ substrate can induce a change in the active site’s shape
* substrate entering active site of enzyme
* enzyme changes shape slightly as substrate binds (known as conformational changes) - ensures an ideal binding arrangement
* change in shape of active site weakens the bond in substrate
* form enzyme substrate complex
* form enzyme product complex
* products leave active site of enzyme