Enzymes

Question 1

Define ‘Enzyme’ ?

Answer 1

Enzyme - A biological catalyst that increases the rate of a reaction by lowering the activation energy required without being used up/ permanently changed itself

Question 2

Explain main features of enzymes ?

Answer 2

• Enzymes are globular proteins with complex tertiary structures
• Some a formed from a single polypeptide, while some are made up from multiple polypeptides and have a quaternary structure

Question 3

What are enzymes so significant ?

Answer 3

Most metabolic reactions that take place in living organisms are catalysed by enzymes

Question 4

Define ‘metabolism’ ?

Answer 4

Metabolism : All the chemcial/ metabolic reactions that occur within a living organism

Question 5

What are anabolic and catabolic reactions ?

Answer 5

• Anabolic reactions : reactions were larger molecules are synthesised/ built from smaller molecules
• Catabolic reactions : reactions were larger molecules are broken down into smaller molecules

Question 6

Define ‘Intrinsic/ intracellular enzyme’ ?

Answer 6

Intrinsic/ intercellular enzyme : An enzyme that catalyses reactions inside the cell which produces it

Question 7

Name an example of an intrinsic/ intracellular enzyme and explain how it functions ?

Answer 7

• Catalase
• It catalyses the break down of hydrogen peroxide into oxygen and water
• Hydrogen peroxide is a toxic product of many metabolic reactions and causes cell damage
• Catalase PREVENTS any damage to cells / tissue

Question 8

Define ‘extrinsic/ extracellular enzyme’ ?

Answer 8

Extrinsic/ Extracellular enzyme : An enzyme that catalyses chemical reactions outside of the cell which produced it after being secrete by the cell

Question 9

Name examples of extrinsic/ extracellular enzymes ?

Answer 9

• Amylase
• Trypsin

Question 10

Explain how amylase functions as an extrinsic/ extracellular enzyme ?

Answer 10

• Amylase catalyses the breakdown of starch into simple sugars / maltose
• They aid in digestion since macromolecules that are being digested are typically too large to enter the cell across the partially permeable membrane

Question 11

Explain how trypsin functions as an extrinsic/ extracellular enzyme ?

Answer 11

• Trypsin catalyses the breakdown of proteins into polypeptides
• Proteases break polypeptides/ peptides into amino acids
• They aid in digestion since macromolecules that are being digested are typically too large to enter the cell across the partially permeable membrane

Question 12

How to enzymes increase the rate of the reaction ?

Answer 12

• Enzymes increase the rate of the reaction by lowering the activation energy required
• This provides an alternative reaction/ energy pathway

Question 13

Explain the mechanism of enzyme action ?

Answer 13

• The active site of an enzyme has a specific shape to fit a specific substrate
• Substrates collide with the enzymes active site and this must happen at the correct orientation and speed in order for a reaction to occur
• This forms an enzyme-substrate complex
• An enzyme-product forms and the product(s) are released

Question 14

Explain the specificity of enzymes ?

Answer 14

• The shape of the active site is determined by the complex tertiary structure of the protein that makes up the enzyme
• Each enzymes active site is specific/ complementary to a specifically shaped substrate molecule

Question 15

What are the two models for enzyme action ?

Answer 15

• The lock-and-key hypothesis
• The induced-fit hypothesis

Question 16

Explain the lock-and-key hypothesis ?

Answer 16

• Enzymes are globular proteins
• These shape of the enzyme, and the enzymes active site, is determined by the complex tertiary structure and is therefore highly specific
• Enzymes and substrates were seen as rigid structures
• The complementary substrate molecule fit/bonded to the enzymes active site exactly, much like a key going into a lock
• An enzyme-subtsrate complex formed, after the reaction occurred a enzyme-product complex formed and products were released

Question 17

Explain the induced-fit hypothesis ?

Answer 17

• The substrate does not perfectly fit/ bond to the enzymes active site
• The enzyme and its active site can change shape slightly to accommodate the substrate molecule
• As the substrate molecule binds to the enzymes active site, this induces a change in the enzymes tertiary structure
• This causes the enzymes active site to change shape to accommodate the substrate molecule; conformational change
• THIS PUTS A STRAIN ON BONDS IN SUBSTRATE MOLECULE AND WEAKENS BONDS IN SUBSTRATE MOLECULE
• THIS LOWERS THE ACTIVATION ENERGY

Question 18

What factors affect enzyme activity ?

Answer 18

• pH
• Temperature
• Substrate concentration
• Enzyme concentration
• Inhibitors

Question 19

Explain how pH affects enzyme activity ?

Answer 19

• All enzymes have an optimum pH at which they function optimally
• Enzymes are denatured at extremes of pH

Question 20

Explain how extremes in pH affects enzyme activity ?

Answer 20

• Enzymes are globular proteins with complex tertiary structures
• Hydrogen and ionic bonds hold the tertiary structure of the enzyme together
• At extreme pH, solutions with an excess of H+ ions and OH- ions can cause these bonds to break
• The breaking of bonds alters the shape of the active site, which means enzyme-substrate complexes form less easily
• Eventually, enzyme-substrate complexes can no longer form at all ; complete denaturation of the enzyme has occurred

Question 21

Explain how lower temperatures affect enzyme activity ?

Answer 21

• Lower temperature decrease or prevent enzyme activity
• As temperature decreases, the kinetic energy of moecluels decreases causing them to move/ vibrate less rapidly
• This means enzyme and substrate molecules collide successfully less frequently per time period
• This results in enzyme-substrate complexes forming less frequently per time period causing enzyme activity to decrease

Question 22

Explain how higher temperature effect enzyme activity ?

Answer 22

• Higher temperature cause enzyme activity to increase
• As the temperature increases, the kinetic energy of molecules increases causing them to move/ vibrate more rapidly
• This means enzyme and substrate molecules collide successfully more frequently per time period between
• This results in enzyme-substrate complexes forming more frequently per time period causing enzyme activity to increase

Question 23

Explain how extremely high temperature effects enzyme activity ?

Answer 23

• As the temperature increases, the kinetic energy of molecules increases
• This cause the hydrogen and ionic bonds in the tertiary structure of enzymes to vibrate more, become weaker and eventually break
• This alters the tertiary structure of enzymes causing the active site to permanently change shape; DENATURED
• The substrate molecule is no longer complementary to the enzymes active site and cannot form a enzyme-substrate complex
• The enzyme has become denatured

Question 24

Explain how enzyme concentration effects enzyme activity ?

Answer 24

• As the enzyme concentration increases, the number of active sites available increases
• This means enzyme-substrate complexes form more frequently per time period
• As long as there is sufficient substrate available, the initial rate of reaction increases linearly/ proportionally with enzyme concentration
• If amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate; limiting factor

Question 25

Explain how substrate concentration effects enzyme activity ?

Answer 25

- As the number of substrate molecules increases, the enzyme activity/ rate of reaction increases - As the number of of substrate molecules increases, the substrate and enzyme molecules collide successfully more often per time period - This results in enzyme-substrate complexes forming more frequently - If the enzyme concentration remains fixed, all available active sites eventually become saturated - As the substrate concentration increases, the enzyme activity/ rate of reaction will not increase - There will be no active sites to which the substrate molecules can bind to so no enzyme-substrate complexes can form

Question 26

Define ‘Turnover number’ ?

Answer 26

Turnover number : The number of reactions that an enzyme molecule can catalyse per second

Question 27

What are the two types of inhibitors ?

Answer 27

- Competitive inhibitors - Non-competitive inhibitors

Question 28

Define ‘Competitive inhibitors’ ?

Answer 28

Competitive inhibitors : Inhibitors that have a similar shape to the substrate molecule and compete with the substrate for the active site

Question 29

Explain the effect of competitive inhibitors ?

Answer 29

- Inhibitors that have a similar shape to the substrate molecule - They compete with the substrate molecule to bind with the enzymes active site - Competitive inhibitor TEMPORARILY binds to the enzymes active site - This prevents the substrate molecule from binding with the enzymes active site

Question 30

Define ‘Non-competitive inhibitors’ ?

Answer 30

Non-competitive inhibitors : Inhibitors that bind to enzyme's allosteric site, which alters the shape of the active site and therefore prevents the substrate from binding to it

Question 31

Explain the effect of reversible inhibitors ?

Answer 31

- They slow down/ prevent enzyme activity which decrease the rate of the reaction - As you increase the concentration of the reversible inhibitor, the rate of the reaction decreases - If this continues, the reaction stop completely

Question 32

Explain how increasing the substrate concentration affects reversible competitive inhibitors ?

Answer 32

- As substrate concentration increases, enzyme activity increases and the rate for the reaction increases - This means that substrate and enzyme molecules will collide successfully more frequently per time period - This means more enzyme-substrate complexes will form per time period

Question 33

Explain how increasing the substrate concentration affects reversible non-competitive inhibitors ?

Answer 33

- As the substrate concentration increases, the enzyme activity/ rate of the reaction does not increase - The shape of the enzymes active site remains permanently changed and the substrate molecule is no longer complementary - Enzyme-substrate complexes can no longer form

Question 34

What is the Vmax ?

Answer 34

Vmax is the maximum rate of a reaction when all active sites have been occupied and enzyme activity has reached its maximum

Question 35

What is the symbol of the temperature coefficient ?

Answer 35

Qv10

Question 36

What is the temperature coefficient ?

Answer 36

The measure of how much the rate of reaction increases with a 10oC rise in temperature

Question 37

What is the temperature coefficient of enzyme-controlled reactions ?

Answer 37

- As the temperature increases by 10oC, the rate of the reaction double - Qv10 is around two for enzyme-controlled reactions

Question 38

Define ‘End-product inhibition’ ?

Answer 38

End-product Inhibitor : When the product of a reaction acts as an inhibitor to the enzyme that produces it

Question 39

Why is end-product inhibition important ?

Answer 39

- They serve as negative feedback/ a control mechanism - Excess products aren't made and resources aren't wasted

Question 40

What are irreversible inhibitors ?

Answer 40

Inhibitors that form covalent bonds with the enzyme, inhibiting them permanently

Question 41

Define ‘Cofactors’ ?

Answer 41

Cofactors : Non-protein substances that enzymes require in order to function properly

Question 42

Name examples of cofactors ?

Answer 42

- Chloride ions (Cl-) for amylase

Question 43

Define ‘coenzymes’ ?

Answer 43

Coenzymes : Organic non-protein cofactors

Question 44

How do coenzymes function ?

Answer 44

They accept or donate hydrogen ions or chemical groups/ phosphate groups

Question 45

What is the role of coenzymes and cofactors ?

Answer 45

- They assist/ help enzymes carry out their function properly - They are NOT permanently bound to the enzyme - They lower the activation energy required for the reaction to take place, involved in substrate molecule binding to active site, allow substrate molecule to bind more easily, they allow more enemy complexes to form etc..

Question 46

Define ‘prosthetic group’ ?

Answer 46

Prosthetic group : cofactors that are tightly/ permanently bound to the enzyme and are essential for the enzyme’s function

Question 47

Name an example of a prosthetic group ?

Answer 47

- Zn2+ prosthetic group in carbonic anhydrase : plays a crucial role in the rapid conversion of carbon dioxide and water into carbonic acid - Fe2+ ions / haem groups in globular protein haemoglobin

Question 48

Where are cofactors and coenzymes obtained ?

Answer 48

- Cofactors are obtained from minerals in the diet - Coenzymes are obtained from vitamins in the diet