Enzymes

Question 1

Why are enzymes important

Answer 1

Many reactions demand very high temperatures and pressures which are not possible in living cells as they would damage cell components and instead these reactions are catalysed by enzymes.

Question 2

What is an enzyme

Answer 2

Biological catalysts that are globular proteins and they interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions.

Question 3

What is the mechanism of enzyme action

Answer 3

• molecules in a solution move and collide randomly.
• for a reaction to happen, molecules need to collide in the right orientation
• when high temperatures and pressures are applied the speed of the molecules will increase due to greater kinetic energy
• the number of successful collisions will increase and so will the overall rate of reaction

Question 4

what is activation energy

Answer 4

the energy that needs to be supplied for a reaction to start

Question 5

what is the active site

Answer 5

an area within the tertiary structure of the enzyme that has a shape that is complementary to the same of the specific substrate molecule

Question 6

what is the lock and key hypothesis

Answer 6

the idea that in the same way that only the right key will fit into a lock, only a specific substrate will fit the active site of an enzyme. the substrate is complementary to the shape of the active site

Question 7

describe the lock and key hypothesis

Answer 7

• substrate is complementary to the shape of the active site
• the substrate bounds to the active site to form an enzyme-substrate complex
• the substrate reacts and the products are formed in an enzyme-product complex
• the products are then released, leaving the enzyme unchanged

Question 8

describe the interaction between the substrate and the active site

Answer 8

the substrate is held in such a way by the enyme that the right atom groups are close enough to react. The R groups within the active site will also interact with the substrate, forming temporary bonds which puts strain on the bonds within the substrate which also helps the reaction along

Question 9

describe the induced fit hypothesis

Answer 9

most recent evidence suggests the active site of the enzyme actually changes shape slightly as the substrate enters.

Question 10

describe the interaction in the induced fit model

Answer 10

the initial interaction is relatively weak but these weak interactions rapidly induce changes in the enzymes tertiary structure that strengthen binding, putting strain on the substrate molecule which can weaken particular bonds in the substrate and therefore lowering the AE

Question 11

what is an intracellular enzyme

Answer 11

enzymes that act within the cell that they are produced in

Question 12

give an example of an intracellular enzyme

Answer 12

hydrogen peroxide is a toxic product of many metabolic pathways. the enzyme catalase ensures hydrogen peroxide is broken down to oxygen and water therefore preventing accumulation

Question 13

what is an extracellular enzyme

Answer 13

enzymes that work outside the cell that made them.

Question 14

give an example of an extracellular enzyme

Answer 14

nutrients are often in the form of polymers such as proteins and polysaccharides which cannot enter cells directly through the cell surface membrane and need to broken down into smaller components first. enzymes are released from cells to break down these large nutrient molecules into smaller molecules in the process of digestion.

example: fungi

Question 15

describe the digestion of starch

Answer 15

• begins in the mouth and continues in the small intestine
• digested in two steps involving two different enzymes because each enzyme only catalyses one specific reaction
• starch polymers are partially broken down into maltose, which is a disaccharide. the enzyme is amylase which is produced by the salivary glands and the pancreas and released in saliva into the mouth and in pancreatic juice into the small intestine
• maltose is then broken down into glucose which is a monosaccharide. the enzyme involved here is maltase which is present in the small intestine.

glucose can then be absorbed by the cells lining the digestive system and subsequently absorbed into the bloodstream

Question 16

describe the digestion of proteins

Answer 16

trypsin is a protease which is a type of enzyme that catalyses the digestion of proteins into smaller peptides which can then be broken down further into amino acids by other proteases.
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 17

how does temperature affect enzyme activity

Answer 17

increased temperature
increased kinetic energy
particles move faster
particles collide more and with greater force
more frequent successful collisions between the substrate and the enzyme
increased rate of reaction

Question 18

how does denaturation from temperature occur

Answer 18

as enzymes are proteins their structure is affected by temperature
at higher temperatures the bonds that hold 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 site and the enzyme will no longer function as a catalyst

Question 19

what is meant by optimum temp

Answer 19

the temperature at which the enzyme has the highest rate of activity.
human - around 37-40
thermophilic bacteria - 70
psychrophilic organisms - below 5
once the enzymes have denatured above the optimum the decrease in the RoR is rapid.

Question 20

what is an example of an extremely code environment

Answer 20

deep oceans
high altitudes
polar regions

Question 21

how are enzymes adapted to cold environments

Answer 21

more flexible structures especially at the active site making them less stable than enzymes that work at higher temperature so smaller temperature changes will denature them

Question 22

examples of hot environments

Answer 22

hot spring
deep sea hydrothermal vents

Question 23

how are enzymes adapted to hot environments

Answer 23

more stable due to the increased number of bonds particularly hydrogen bonds and sulphur bridges in their tertiary structures. the shapes of these enzymes and their active sites are more resistant to change as the temperature rises.

Question 24

ph

Answer 24

proteins are affected by changes in ph. hydrogen bonds and ionic bonds between amino acid R groups hold proteins in their precise 3D shape. these bonds result from interactions between the polar and charged R groups present on the amino acid forming the primary structure. a change in the ph refers to a change in the hydrogen ion concentration. more hydrogen ions are present in low ph (acidic) environments and fewer hydrogen ions are present in high ph (alkaline) environments

Question 25

how does ph affect enzyme activity

Answer 25

the active site will only be in the right shape at a certain hydrogen ion concentration which is the optimum ph for any enzyme.