Biochemistry: Enzyme Inhibition Quiz

Introduction to Metabolism

• Metabolism encompasses all chemical reactions in an organism.
• These reactions involve energy storage (anabolic processes) and energy release (catabolic processes).
• The energy source on Earth is sunlight.
• Plants use photosynthesis to synthesize sugars using sunlight.
• Living cells act as miniature factories converting energy in many ways.
• An example of this is bioluminescence, in which organisms convert energy to light.
• The sun provides energy for Producers (plants), Consumers (animals) and Decomposers (organisms that break down matter).

Energy Flow

• Energy flows from the sun to producers to consumers to decomposers.

Metabolic Pathways

• A metabolic pathway consists of multiple steps that begin with a specific molecule and end in a product.
• Each step is catalyzed by a specific enzyme.
• Metabolic pathways are regulated according to cellular needs.
• Catabolic pathways break down complex molecules into simpler compounds releasing energy. Cellular respiration is an example of a catabolic pathway. This reaction releases energy for the cell.
• Anabolic pathways build complex molecules from simpler ones consuming energy. Examples are photosynthesis and protein synthesis from amino acids.

Forms of Energy

• Energy is the capacity to cause change.
• Exists in various forms.
• Some forms of energy can do work.
• Life depends on a cell's ability to convert energy from one form to another.
• Thermodynamics is the study of energy conversion.

Kinetic and Potential Energy

• Kinetic energy is associated with motion.
• Heat (thermal energy) is kinetic energy associated with the random motion of atoms or molecules.
• Potential (chemical) energy is stored in the location or structure of matter. It includes chemical energy stored in molecular structure.

Laws of Thermodynamics

• The first law states that energy can be transferred and transformed but not created or destroyed.
• In the cheetah example, the chemical potential energy in the food is converted into the kinetic energy for the cheetah's movement.
• The second law states that every energy transfer or transformation increases the entropy (disorder) of the universe. This is evident in the byproducts of metabolism, which are molecules.

Biological Order

• Living organisms increase the entropy of the universe but decrease the entropy internally by maintaining order through energy consumption.

Free Energy

• Organisms live by consuming free energy.
• Free energy is a living system's energy that can do work under cellular conditions.
• The free-energy change (ΔG) of a reaction predicts spontaneity.

Exergonic and Endergonic Reactions

• Exergonic reactions are spontaneous and release free energy (ΔG < 0).
• Endergonic reactions are non-spontaneous and absorb free energy from their surroundings (ΔG > 0).

Equilibrium and Metabolism

• Reactions in a closed system eventually reach equilibrium (ΔG = 0).
• Cells in our body are open systems with metabolic pathways that experience a constant flow of materials in and out, preventing them from reaching equilibrium.

ATP

• ATP (adenosine triphosphate) is the cell's energy shuttle.
• ATP stores energy in phosphate bonds.
• ATP hydrolysis releases energy (ATP → ADP + Pi).
• ATP synthesis stores energy (ADP + Pi → ATP).
• ATP powers cellular work via energy coupling.
• Cells use ATP to power mechanical, transport, and chemical work.

Enzymes

• Enzymes are catalytic proteins that speed up metabolic reactions by lowering activation energy barriers.
• Enzymes are catalysts, which speed up a reaction without being consumed by it.
• Sucrase is the enzyme that catalyzes sucrose hydrolysis.

Activation Energy

• Activation energy (EA) is the initial amount of energy needed to start a chemical reaction, which de-stabilizes the structure of reactants, allowing for more easy reaction to occur.
• Heat can increase the energy of molecules, allowing them to collide frequently enough to start reactions.

Enzyme Activity and Factors

• Enzymes have an optimal temperature for function. Extreme temperatures can denature enzymes, causing loss of structure and function.
• Optimum pH levels exist for enzymatic activity. Denaturation also occurs outside of optimum pH levels, resulting in loss of function.
• Cofactors such as inorganic metal ions and organic vitamins are required for enzymatic activity.

Enzyme Inhibitors

• Irreversible inhibitors bind to enzymes covalently, permanently inhibiting their function.
• Examples of irreversible inhibitors are some toxins, antibiotics, and poisons.
• Reversible inhibitors bind weakly to enzymes, allowing the enzyme to regain activity.
• Competitive inhibitors compete with substrates for the active site of an enzyme.
• Non-competitive inhibitors bind to a different site on the enzyme, altering its shape and hindering its function.

Regulation of Enzyme Activity

• A cell's metabolic pathways must be regulated to prevent waste of resources.
• Enzyme regulation involves adjusting enzyme production or activity.
• Feedback inhibition prevents pathways from making more of a product than necessary. The end product of a metabolic pathway inhibits the pathway.
• Allosteric regulation is a type of reversible regulation where a regulatory molecule binds to a site different from the active site, affecting enzyme function.
• Homeotropic allosteric regulation means that enzyme subunits are affected by the binding of a substrate and are either activated or inhibited by the substrate.
• Heterotropic allosteric regulation means that an activator or inhibitor is affecting the activity of an enzyme even though it is not a substrate.

Specific Localization of Enzymes

• Enzymes in the same pathway are often located near each other inside the cell, in complexes, in membranes, or in organelles.
• Mitochondria are the sites of cellular respiration, containing many enzymes required for this process.

Test your knowledge on enzyme inhibition mechanisms, including the differences between competitive and non-competitive inhibitors. Explore the characteristics of irreversible inhibitors and their effects on enzymes, as well as the specific enzymes active under varying pH conditions, such as in the stomach.