Enzyme action (a,b,c)

Question 1

What are enzymes?

Answer 1

• biological catalysts
• globular proteins
• interact with substrate molecules to facilitate chemical reactions

Question 2

Anabolic reactions

Answer 2

• building up

- enzymes catalyse reaction that are required from growth

Question 3

Catabolic reactions

Answer 3

• breaking down

- energy is released from many catabolic reactions

Question 4

What is metabolism?

Answer 4

The sum of all the different reactions and reaction pathways happening in a cell or an organism + can only happen as a result of the control and order imposed by enzymes

Question 5

Role of enzymes

Answer 5

• catalyse at a cellular level e.g. respiration
• catalyse at whole organism level e.g. digestion
• can affect structures and function in an organism

Question 6

Intracellular reactions and example of enzyme

Answer 6

• enzymes acting within cells
• e.g. hydrogen peroxide, H₂O₂, is the toxic by-product of several cellular reactions and if left to build up it can kill cells. Catalase works inside cells to catalyse the breakdown of H₂O₂ into O₂ and H₂O. found in plants and animals

Question 7

Extracellular reactions

Answer 7

• enzymes that work outside of the cell that made them

- break down large molecules that cannot directly enter cells through the cell-surface membrane.

Question 8

Examples of extracellular enzymes

Answer 8

• amylase: digests starch into maltose. produced by salivary glands + pancreas and is released in saliva and pancreatic juice in the small intestine
• trypsin: a protease - catalyses the digestion of proteins into smaller peptides. produced in the pancreas + released with pancreatic juice

Question 9

Mechanism of enzyme action

Answer 9

• each enzyme catalyses one biochemical reaction - specificity
• enzymes help molecules collide successfully - reducing activation energy required

Question 10

What is the active site?

Answer 10

The area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind to a substrate. determined by the tertiary structure of the protein.

Question 11

Lock and key hypothesis

Answer 11

• only the correct key will fit into a lock = the substrate into the active site of an enzyme
• enzyme-substrate complex formed when the substrate binds to the active site
• substrate(s) react and the products are formed in an enzyme-product complex
• products are then released, leaving the enzyme unchanged + able to take part in subsequent reactions
• R-groups in an enzymes active site will interact with the substrate, forming temporary bonds - which strain the bonds within a substrate, helping the reaction along

Question 12

Induced-fit hypothesis

Answer 12

• evidence suggests the active site of the enzyme changes shape slightly as the substrate enters
• initial interaction between enzyme + substrate is relatively weak, but these interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding, putting strain on the substrate molecule
• this can weaken bonds in the substrate - lowering the activation energy for the reaction