Enzymes and Metabolism

Question 1

Characteristics of Enzymes

Answer 1

Enzyme is a globular protein that acts as a biological catalyst

Enzymes are three dimensional with a hydrophilic R group on the outside to ensure solubility

Enzymes speed up a metabolic reaction

Enzymes are made of living things

Enzymes have specific shape and chemical properties to allow binding of specific substrate

Question 2

Active Site

Answer 2

A region on the surface of the enzyme which the substrate binds to and gets catalyzed

Question 3

Substrate

Answer 3

The reactant in enzyme-catalyzed reactions

Question 4

Role of Enzyme in Metabolism

Answer 4

Metabolism is the sum of all chemical reactions, with each chemical reaction being interdependent on one another

They usually form pathways which are organized into chains or cycles

Each chemical reaction in the pathway is unique and is controlled by a specific enzyme, and because of enzyme specificity, living organisms require many different enzymes in order to control metabolism

Question 5

Difference between Anabolism and Catabolism

Answer 5

Anabolism is the synthesis of a complex molecule from simple molecules
Catabolism is the breakdown of a complex molecule into simpler molecules

Anabolism involves condensation reactions where H2O is released
Catabolism involves hydrolysis reactions where H2O is required

Energy is required in Anabolism
Energy is released in Catabolism

Question 6

Benefits of Enzyme Specificity

Answer 6

Allows organisms to control metabolism

Prevents unwanted side reactions at a particular active site

Question 7

Benefits of Increasing Rate of Reaction in Cells

Answer 7

Less time for product formation which enhances metabolism

Can enhance energy production to support various life processes

Question 8

Activation Energy

Answer 8

The minimum amount of energy required in order to start a reaction

The higher the activation energy, the slower the reaction

Enzymes reduce activation energy by distorting the shape of the substrate when it binds to the active site

Question 9

Difference with Endothermic and Exothermic Reaction

Answer 9

Endothermic is Anabolic
Exothermic is Catabolic

Endothermic requires energy
Exothermic releases energy

Energy of products is more than energy of reactants in Endothermic
Energy of products is less than energy of reactants in Exothermic

Question 10

Importance of Random Motion

Answer 10

Catalysis only happens when substrate is in liquid, so it needs random motion

Random motion increases the chances of collision between substrate and active site of enzyme

Question 11

Variation in Molecular Motion of Substrates and Enzymes

Answer 11

Usually, the substrate is smaller than the active site so it moves more than the enzyme

Some substrates are very large and don’t move a lot, therefore enzymes move in relation to substrate

Some enzymes are embedded into the membrane and can’t move, in this case the substrate needs to do all the movement

Question 12

Interaction between Substrate and Active Site

Answer 12

As the substrate grows closer to the active site, the chemical properties of the enzyme attract the substrate towards the active site to bind

The interactions between the substrate and active site cause bond lengths and angles to change, therefore changing both their 3D structures

Question 13

Lock and Key Model

Answer 13

Enzyme can only bind to 1 substrate

The enzyme’s active site has a shape complementary to the substrate’s shape

The substrate binds to the enzyme perfectly forming enzyme-substrate complex

Products are released, while enzyme is unchanged and ready for another reaction

Question 14

Induced Fit Model

Answer 14

Enzyme can bind to multiple substrates

The enzyme’s active site doesn’t have a rigid shape and isn’t complementary to the substrate’s shape either

Active site and substrate change their shape slightly in order to have a perfect fit, forming enzyme-substrate complex

Products are released, while enzyme returns to original shape once the reaction is done

Question 15

Factors Affecting Enzyme-Catalyzed Reactions

Answer 15

Temperature

pH

Substrate Concentration

Question 16

How Temperature Affects Reactions

Answer 16

At low temperatures, the enzyme and substrate molecules have little kinetic energy, this makes them move slowly and collide less frequently leading to lower rate of reaction

As temperature increases, kinetic energy increases and enzyme and substrate collide with each other more often which raises rate of reaction

The temperature at which the enzyme works most rapidly is optimum temperature

Right after optimum temperature, however, the temperature is too high and it changes the tertiary 3D structure of the enzyme, causing the substrate to no longer fit. At this point the enzyme is said to be denatured, and can no longer catalyze reactions

Question 17

How pH Affects Reactions

Answer 17

Each enzyme has an optimum pH

If this pH changes, this can cause a disturbance in their ionic bonds which can lead to a change in tertiary structure, which means the substrate can’t bind, therefore denaturing the enzyme

Question 18

How Substrate Concentration Affects Reactions

Answer 18

As substrate concentration increases, collisions between enzyme and substrate increases, and therefore the faster the rate of reaction

However, at high substrate concentrations, it stops affecting the enzyme as it is saturated with substrate, and therefore no more active sites are available, leading the rate to remain constant

Question 19

Intracellular Enzymes and Extracellular Enzymes

Answer 19

Intracellular Enzymes: Catalyse the reactions in the cells, which are usually synthesized by free ribosomes

Extracellular Enzymes: Catalyse the reactions outside the cell, which are usually synthesized by ribosomes attached to the RER

Question 20

Generation of Heat Energy

Answer 20

Endotherms (Warm-Blooded Animals) use the heat generated by metabolism to keep a stable internal body temperature

Some of the heat released by metabolism is used for cellular activities

Ectotherms (Cold-Blooded Animals) change their body temperature in response to the environment

Question 21

Inhibitor

Answer 21

A substance that slows down the rate at which an enzyme works

Question 22

Features of a Competitive Inhibitor

Answer 22

Has a similar structure to the normal substrate

Binds with the active site, and therefore competes with the substrate for the active site, thus reducing the number of enzyme-substrate complexes

Can be overcome with increasing substrate concentration

Rate will eventually reach maximum

Question 23

Features of a Non-Competitive Inhibitor

Answer 23

Has a different structure to the substrate

Binds to the allosteric site of the enzyme, therefore changing the enzyme shape and preventing substrates from binding to the active site

Increasing substrate concentration won’t help

Rate will never reach maximum

Question 24

End-Product Inhibition

Answer 24

The product of the last reaction of the metabolic pathway inhibits the enzyme that catalyzes the first reaction of the pathway

An example of Negative Feedback Inhibition

Can be reversible once concentration of end product decreases

Question 25

Advantages of End-Product Inhibition

Answer 25

If there is too much of an end product, the whole metabolic pathway stops working and less of the end product is produced

When levels of end product decrease, the inhibitor can release and allow the metabolic pathway to work and create end product again

Question 26

Mechanism-Based Inhibition (MBIs)

Answer 26

MBIs are molecules that irreversibly bind to the active site of the enzyme and make permanent chemical changes, making it never work as a catalyst again

Some living organisms create MBIs in order to kill another organism

Question 27

Penicillin and Transpeptidase

Answer 27

Penicillin kills bacteria by irreversibly binding to the transpeptidase enzyme which is responsible for the cross linking of peptidoglycan during the formation of the cell wall

Without the cell wall, the bacteria is vulnerable to the external environment and dies quickly

Bacteria can also develop mutations to resist penicillin, which can change the active site of the transpeptidase enzyme which increases its resistance against penicillin