2.1.4 enzymes

Question 1

what is an enzyme?

Answer 1

biological catalyst
globular protein that interacts with the substrate molecules causing them to react at a much faster rate without other environmental conditions

Question 2

what do enzymes do?

Answer 2

they are used in chemical reactions to speed up the rate of reaction
they catalyse reactions

Question 3

what is an anabolic reaction?

Answer 3

builds bonds

Question 4

what is a catabolic reaction?

Answer 4

breaks down bonds

Question 5

why are anabolic reactions needed?

Answer 5

required for growth
catalysed by enzymes

Question 6

why are catabolic reactions needed?

Answer 6

required for energy release from large organic molecules
catalysed by enzymes

Question 7

what is metabolism?

Answer 7

the sum of all the different reactions and reaction pathways happening in the cell
it can only happen as a result of the control and order imposed by enzymes

Question 8

environmental conditions that speed up cellular reactions include:

Answer 8

temperature
pressure
pH

Question 9

what is the Vmax?

Answer 9

maximum initial velocity or rate of the enzyme-catalysed reaction
enzymes can only increase the rates of reaction up to the Vmax

Question 10

what happens when high temperatures and pressures are applied to a reaction?

Answer 10

result in the speed of molecules increasing
meaning the number of successful collisions increase
resulting in an increased rate of reaction

Question 11

what is the specificity of the enzyme?

Answer 11

many different enzymes are produced by living organisms as each enzyme catalyses on biochemical reaction of which there are thousands in any given cell

Question 12

what is activation energy?

Answer 12

energy needed for the reaction to start

Question 13

hypotheses for how enzymes help molecules collide successfully and reduce activation energy

Answer 13

lock and key hypothesis
induced-fit hypothesis

Question 14

explain the lock and key hypothesis

Answer 14

active site within the tertiary structure of the enzyme is an area of the enzyme that has a shape complementary to the shape of the specific substrate molecule that fits into the active site
when the substrate is bound to the active site, an enzyme-substrate complex is formed
they then react to form an enzyme-product complex
products are then released, enzyme is unchanged and able to react in other reactions

Question 15

explain the induced-fit hypothesis

Answer 15

the active site of the enzyme changes shape slightly when the substrate enters
the initial interaction between the enzyme and substrate is weak - these weak interactions rapidly induce changes to the enzymes tertiary structure that strengthen binding, putting strain on the substrate weakening a bond in the substrate
which lowers the activation energy of the reaction

Question 16

what is an intracellular enzyme?

Answer 16

enzymes that are produced and function inside the cell

Question 17

what is an extracellular enzyme?

Answer 17

enzymes that are secreted by cells and catalyse reactions outside cells

Question 18

example of intracellular enzyme and its function

Answer 18

catalase
- hydrogen peroxide is produced as a by-product of many metabolic reactions
- harmful to cells
- catalase converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues

Question 19

example of extracellular enzyme and its function

Answer 19

amylase
- digestion is usually carried out by extracellular enzymes
- because the macromolecules being digested are too large to enter the cell
- amylase hydrolyses starch into simple sugars

Question 20

digestion of starch

Answer 20

-> starch is partially broken down into maltose (disaccharide) by amylase - produced by salivary glands (mouth) and pancreatic juice (pancreas)
-> maltose is broken down into glucose (monosaccharide) by maltase - produced in the small intestine
-> glucose is small enough to be absorbed by the cells lining the digestive system and absorbed into the bloodstream

Question 21

digestion of proteins

Answer 21

-> protein catalysed into peptides by trypsin (by pancreas) in pancreatic juices in the small intestine
-> peptides broken down into amino acids by other proteases
-> amino acids are absorbed by the cells lining the digestive system and absorbed into the bloodstream

Question 22

enzymes have a specific optimum temperature

Answer 22

catalyse reactions at the maximum rate

Question 23

what do lower temperatures in a reaction do?

Answer 23

slow the reaction down
- molecules move slower due to less kinetic energy
- lower frequency of successful collisions between substrate and active sites
- leads to less frequent enzyme-substrate complex formation
- substrates and active sites collide with less energy - less likely for bonds to form or break

Question 24

what does higher temperatures in a reaction do?

Answer 24

speed up the reaction
- molecules move more quickly - more kinetic energy
- results in higher frequency of successful collisions between substrate and active sites
- leads to more frequent enzyme-substrate complex formation
- substrate and active sites collide with more energy - more likely for bonds to be formed or broken

Question 25

what does denature mean?

Answer 25

temperature increases past a certain point, the rate at which an enzyme catalyses a reaction drops sharply

Question 26

what happens when an enzyme is denatured?

Answer 26

• increased kinetic energy and vibration of the enzyme and puts a strain on them
• causes weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break
• causes tertiary structure to change
• active site is permanently damaged
• shape is no longer complementary to the substrate
• substrate can no longer bind to active site due to change of shape

Question 27

temperatures at which rate of reaction is optimum

Answer 27

varies due to habitat and other factors
- humans maintain a body temp of 37oC

Question 28

temperatures at which rate of reaction is denatured

Answer 28

varies due to habitat and other factors
- living organisms denature above 60oC
- human enzymes denature above 50oC
- bacteria can withstand 80oC - thermostable enzymes