B4 - Enzymes

Question 1

What are enzymes

Answer 1

• globular proteins
• biological catalysts

Question 2

Why is important that enzymes are globular proteins

Answer 2

• this means the shape of their active site is determined by their complex tertiary structure
• therefore the shape of the enzyme is high specific

Question 3

What are catalysts

Answer 3

Catalysts are something that speed up the rate of chemical reactions without being used up or changed.

Question 4

Intracellular enzymes

Answer 4

• work inside cells
• catalase is an example that breaks down hydrogen peroxide
• hydrogen peroxide = water + oxygen

Question 5

Extracellular enzymes

Answer 5

• extracellular enzymes work outside cells
• amylase and trypsin are both enzymes that work outside cells in the human digestive system
• amylase catalyses the hydrolysis of starch into maltose in the mouth
• trypsin catalyses the hydrolysis of peptide bonds in the small intestine

Question 6

Anabolic reactions

Answer 6

• anabolic reactions build larger molecules from smaller molecules and ATP energy

Question 7

Catabolic reactions

Answer 7

• catabolic reactions break down larger molecules into smaller molecules and ATP energy

Question 8

Enzymes specificity

Answer 8

• enzymes have an active site where specific substrates bind forming an enzyme-substrate complex
• the active site of an enzyme is complimentary to the shape of the substrate.
• extreme heat or pH can denature the shape of the enzyme, making it unusable .

Question 9

Enzyme-substrate complex

Answer 9

• an enzyme-substrate complex forms when an enzyme and its substrate join together.
• the enzyme-substrate complex is only formed temporarily before the enzyme catalyses and the reaction and the products are released.

Question 10

Lock and key hypothesis

Answer 10

• emil Fischer suggested that both the enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock

Question 11

Induced-fit hypothesis

Answer 11

• the enzyme and its active site can change shape slightly as the substrate molecule enters the enzyme
• these changes in shape are known as conformational changes.
• the conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved.
• this maximises the ability of the enzyme to catalyse the reaction.

Question 12

How do enzymes speed up the rate of reaction

Answer 12

• enzymes lower the activation energy of a reaction
• this happens because they form an enzyme-substrate complex
• also because of the weakening of the bonds in the substrate.