Enzymes (enzyme action, factors affecting activity, inhibitors, cofactors/coenzymes/prosthetic groups)

Question 1

What are enzymes important?

Answer 1

Most of the processes necessary for life involve chemical reactions, which need to happen quickly. In a lab or industry, these reactions would occur via high temperatures and pressures - this is not suitable for living cells, so instead, they’re catalysed by enzymes (biological catalysts)
*They interact with substrate molecules causing them to react at much faster rates

Question 2

What structure do enzymes have?

Answer 2

Globular proteins, tertiary structure

Question 3

The chemical reactions required for growth are anabolic reactions that are catalysed by enzymes. What is anabolism?

Answer 3

Reactions of metabolism that construct molecules from smaller units. These reactions require energy from the hydrolysis of ATP
*Building up

Question 4

Energy is released from large organic molecules, like glucose, in metabolic pathways consisting of many catabolic reactions. Catabolic reactions are all catalysed by enzymes. What is catabolism?

Answer 4

Reactions of metabolism that break molecules own into smaller units. These reactions release energy
*Breaking down

Question 5

Give an example of a bodily function that is catalysed by enzymes

Answer 5

Digestion

Question 6

What factors may affect the rate of the chemical reactions/enzymes?

Answer 6

Temperature, pressure and pH

Question 7

What is the Vmax of an enzyme?

Answer 7

Maximum initial velocity or rate of an enzyme-catalysed reaction

Question 8

What is the ‘specificity’ of an enzyme?

Answer 8

Many different enzymes are produced by living organisms, as each enzyme catalyses one biochemical reaction, of which there ae thousands in any given cell. This is termed the ‘specificity’ of the enzyme

Question 9

What is activation energy?

Answer 9

The energy required to initiate a reaction

Question 10

What is the lock and key hypothesis?

Answer 10

• An area within the tertiary structure of the enzyme has a shape that is complementary to the shape of a specific substrate molecule - this is the active site
• When a substrate is bound to the active site (right atom-groups react; R-groups within the active site interact with the substrate, forming temporary bonds) an enzyme-substrate complex is formed. The substrate/s then react within the complex to form product/s, which are then released
• After the product leaves, the enzyme remains unchanged and this allows it take part in subsequent reactions

Question 11

What is the induced fit hypothesis?

Answer 11

• Evidence from scientific research suggests that the active site of an enzyme changes shape slightly as the substrate enters - this is modified version of the lock and key hypothesis
• The initial reaction between the enzyme and substrate is relatively weak, however these weak interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding, putting strain on the substrate molecule
• This can weaken a particular bond or bonds in the substrate, therefore lowering the activation energy for the reaction

Question 12

What are intracellular enzymes? Example of a role?

Answer 12

• Enzymes which react within a cell

- The synthesis of polymers from monomers, for example making polysaccharides from glucose, requires enzymes

Question 13

What enzyme breaks down toxic hydrogen peroxide?

Answer 13

Catalase (breaks it down to oxygen and water)

Question 14

What are extracellular enzymes?

Answer 14

These are enzymes that are released from cells, whose job is to break down the nutrients (too large; often in the form of polymers such as proteins or polysaccharides) into smaller molecules in the process of digestion
*Nutrients supply the raw materials/substrates, which need to be constantly supplied to keep up with demands/metabolism

Question 15

In which organisms do extracellular organisms work outside the body?

Answer 15

Fungi

Question 16

How do single-celled organisms, such as yeast and bacteria, rely on extracellular enzymes to make use of polymers for nutrition?

Answer 16

They release enzymes into their immediate environment, which break down larger molecules, such as proteins, and the smaller molecules produced, such as amino acids and glucose, are then absorbed by the cells

Question 17

How do multicellular organisms rely on extracellular enzymes to make use of polymers for nutrition?

Answer 17

• Many multicellular organisms eat food to gain nutrients
• Although the nutrients are taken into the digestive system the large molecules still have to be digested so smaller molecules can be absorbed into the bloodstream. From there they are transported around the body to be used as substrates in cellular reactions
• Examples of extracellular enzymes involved in digestion in humans are amylase and trypsin

Question 18

Digestion of starch

Answer 18

• It begins in the mouth and continues in the small intestine
  1. Star polymers are partially broken down into maltose, which is a disaccharide. The enzyme involved in this stage is called amylase. Amylase is produced by the salivary glands and the pancreas. It is released in saliva into the mouth, and in pancreatic juice into the small intestine
  2. Maltose is then broken down into glucose, which is a monosaccharide. The enzyme involved in this stage is called maltase. Maltase is present in the small intestine
• Glucose is small enough to be absorbed by the cells lining the digestive system and subsequently absorbed into the bloodstream

Question 19

Digestion of proteins

Answer 19

• Trypsin is a protease
• Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins
• The amino acids that are produced by the action of proteases are absorbed by the cells lining the digestive system and then absorbed into the bloodstream

Question 20

What is a protease?

Answer 20

A type of enzyme that catalyses the digestion of proteins into smaller peptides, which can then be broken own further into amino acids by other proteases

Question 21

How does temperature affect enzyme activity?

Answer 21

Increasing the temperature of a reaction environment increases the kinetic energy of the particles. As temperature increases, the particles move faster and collide more frequently. In an enzyme-controlled reaction an increase in temperature will result in more frequent successful collisions between substrate and enzyme. This leads to an increase in the rate of reaction

Question 22

What is the temperature coefficient, Q₁₀, of a reaction?

Answer 22

• A measure of how much the rate of a reaction increases with a 10°C rise in temperature
• For enzyme-controlled reactions this is usually taken as two, which means that the rate of reaction doubles with a 10°C temperature increase

Question 23

What does it mean if an enzyme has become denatured?

Answer 23

• As enzymes are proteins, their structure is affected by temperature. At higher temperatures the bonds holding the protein together vibrate more. As the temperature increases the vibrations increase until the bonds strain and then break. The breaking of these bonds results in a change in the precise tertiary structure of the protein, The enzyme has changed shape and is said to have been denatured
• When an enzyme is denatured the active site changes shape and is no longer complementary to the substrate. The substrate can no longer fit into the active sites and the enzyme will no longer function as a catalyst