Enzymes

Question 1

explain that enzymes are
globular proteins that
catalyse metabolic
reactions

(Definition of metabolism,
anabolism and catabolism
required)

Answer 1

Enzymes are indeed globular proteins that catalyze metabolic reactions within living organisms. To understand this statement fully, let’s break it down:

Enzymes as Globular Proteins:

Enzymes are biological catalysts made up of proteins.
Proteins are large, complex molecules made up of amino acid chains folded into specific three-dimensional structures.
Enzymes typically have a globular shape, which means they are compact and roughly spherical in form.
This globular structure allows enzymes to have a specific active site where substrates (reactant molecules) bind and undergo chemical reactions.
Catalysis of Metabolic Reactions:

Metabolism refers to the sum total of all biochemical reactions that occur within an organism.
Metabolic reactions can be broadly categorized into two main types: anabolism and catabolism.
Anabolism and Catabolism:

Anabolism refers to the metabolic processes that build complex molecules from simpler ones. These processes typically require energy input and include reactions such as protein synthesis, DNA replication, and photosynthesis in plants.
Catabolism, on the other hand, refers to the metabolic processes that break down complex molecules into simpler ones. These processes often release energy and include reactions such as cellular respiration, digestion, and the breakdown of glycogen into glucose.
Enzymes and Metabolic Reactions:

Enzymes play a crucial role in both anabolic and catabolic reactions by lowering the activation energy required for these reactions to occur.
In anabolic reactions, enzymes facilitate the synthesis of complex molecules by bringing together substrates and promoting the formation of chemical bonds.
In catabolic reactions, enzymes facilitate the breakdown of complex molecules by catalyzing the cleavage of bonds, allowing the release of energy and the production of simpler molecules.
Enzymes are highly specific, meaning that each enzyme typically catalyzes a specific reaction or a group of closely related reactions

Question 2

explain the mode of
action of enzymes in
terms of an active site,
enzyme and/or substrate
complex, lowering of
activation energy and
enzyme specificity

(Properties of enzymes.
Lock and key hypothesis,
and Induced-fit hypothesis.)

Answer 2

Active Site:

The active site of an enzyme is a specific region where the substrate(s) bind(s) and undergoes a chemical reaction.
The active site has a unique three-dimensional shape complementary to that of the substrate, allowing for precise binding.
The amino acid residues within the active site play crucial roles in substrate binding and catalysis.
Enzyme-Substrate Complex:

Enzymes catalyze reactions by forming temporary complexes with their substrates, known as the enzyme-substrate complex.
The formation of the enzyme-substrate complex brings the substrates into close proximity and orients them in a way that facilitates the catalytic reaction.
This complex is transient and dissociates into the enzyme and products after the reaction is complete.
Lowering of Activation Energy:

Enzymes catalyze reactions by lowering the activation energy required for the reaction to occur.
Activation energy is the energy barrier that must be overcome for a reaction to proceed.
By stabilizing the transition state of the reaction, enzymes reduce the amount of energy required for the reaction to reach its transition state, thus accelerating the reaction rate.
Enzyme Specificity:

Enzymes exhibit specificity for their substrates, meaning that they catalyze specific reactions with specific substrates.
Enzyme specificity arises from the precise complementary fit between the active site and the substrate, as well as from specific interactions between amino acid residues and substrate molecules.
This specificity ensures that enzymes catalyze specific reactions without interfering with other biochemical processes.
Lock and Key Hypothesis:

The lock and key hypothesis proposes that the active site of an enzyme has a rigid structure that precisely fits the shape of the substrate, similar to a lock and key.
According to this hypothesis, the enzyme and substrate are complementary in shape from the outset, and no significant conformational changes occur upon binding.
Induced-Fit Hypothesis:

The induced-fit hypothesis suggests that the active site of an enzyme is flexible and can undergo conformational changes upon substrate binding.
When the substrate binds to the enzyme, the active site undergoes a conformational change to better accommodate and bind the substrate.
This induced fit optimizes the interactions between the enzyme and substrate, enhancing catalytic activity and specificity.

Question 3

explain the effects of pH,
temperature, enzyme
concentration, and
substrate concentration
on enzyme action

(Construction and
interpretation of graphs.)

Answer 3

pH:

pH affects enzyme activity by altering the charge properties of amino acid residues within the enzyme’s active site.
Each enzyme has an optimal pH range at which it exhibits maximum activity.
Deviations from the optimal pH can disrupt the enzyme’s structure and its interactions with substrates, leading to reduced enzyme activity.
Extreme pH levels can denature enzymes, rendering them inactive.
Temperature:

Temperature affects enzyme activity by altering the kinetic energy of molecules, including enzymes and substrates.
Generally, enzyme activity increases with temperature, as higher temperatures provide more kinetic energy, leading to more frequent collisions between enzymes and substrates.
However, enzymes have an optimal temperature range at which they exhibit maximum activity. Beyond this range, high temperatures can denature enzymes, disrupting their structure and reducing their activity.
Low temperatures decrease enzyme activity as molecular motion slows down, reducing the frequency of enzyme-substrate collisions.
Enzyme Concentration:

Enzyme concentration directly influences the rate of enzyme-catalyzed reactions.
At low enzyme concentrations, the rate of reaction is limited by the availability of enzyme molecules. Increasing enzyme concentration leads to an increase in the rate of reaction, as more enzyme molecules are available to catalyze substrate molecules.
However, at higher enzyme concentrations, the rate of reaction may reach a plateau, as all available substrate molecules become saturated with enzyme molecules.
Substrate Concentration:

Substrate concentration directly affects the rate of enzyme-catalyzed reactions.
Initially, as substrate concentration increases, the rate of reaction also increases proportionally, as more substrate molecules are available for enzyme binding.
However, at higher substrate concentrations, the rate of reaction may plateau, as all enzyme active sites become saturated with substrate molecules.
At this point, further increases in substrate concentration do not significantly increase the rate of reaction, as the enzymes are working at their maximum capacity.

Question 4

discuss the effects of
competitive and noncompetitive inhibitors on enzyme activity.

(Use of succinic dehydrogenase, antabuse and organophosphates as
examples of enzyme
inhibitors)