Metabolism & Enzymes Quiz

Metabolism & Enzymes

• Metabolism is the sum of all chemical reactions in an organism.
• Metabolism is an emergent property of life, arising from interactions between molecules in the cell.
• A metabolic pathway is a series of chemical reactions, beginning with a specific molecule (the starting molecule) and ending with a product.
• Each step in a metabolic pathway is catalyzed by a specific enzyme.

Catabolic Pathways

• Catabolic pathways release energy by breaking down complex molecules into simpler compounds.
• Catabolic reactions are generally hydrolysis reactions (reactions that use water to break down chemical bonds).
• Cellular respiration (the breakdown of glucose in the presence of oxygen) is an example of a catabolic reaction.

Anabolic Pathways

• Anabolic pathways consume energy to build complex molecules from simpler ones.
• Anabolic reactions are generally dehydration synthesis reactions (reactions that release water to form bonds).
• The synthesis of protein from amino acids is an example of an anabolic reaction.

Concept B: Free Energy Change

• Gibbs free energy (G) measures usable energy in a system.
• The change in Gibbs free energy (ΔG) during a reaction indicates whether the reaction is spontaneous (occurs without an input of energy) or non-spontaneous (requires an input of energy).
• ΔG = G_products - G_reactants
• Negative ΔG indicates a spontaneous (exergonic) reaction.
• Positive ΔG indicates a non-spontaneous (endergonic) reaction.
• ΔG = 0 indicates equilibrium.

Free Energy and Metabolism

• An exergonic reaction releases free energy.
• An endergonic reaction absorbs free energy.

Concept C: ATP

• ATP (adenosine triphosphate) is the cell's energy shuttle.
• ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups.
• The bonds between phosphate groups in ATP can be broken by hydrolysis, releasing energy.
• This energy can be used by organisms for various purposes including active transport and muscle contraction.

Concept D: Enzymes

• Most proteins are enzymes.
• Enzymes act as catalysts, speeding up chemical reactions without being consumed.
• Enzymes are catalytic proteins.
• An enzyme-catalyzed reaction lowers activation energy (the initial energy needed to start the reaction).
• Hydrolysis of sucrose by sucrase is an example of an enzyme-catalyzed reaction.

Activation Energy

• Activation energy (Ea) is the initial energy needed for a reaction to occur.
• The transition state is a high-energy unstable state that occurs when molecules must be bent/contorted to break bonds.
• Enzymes facilitate reactions by lowering the activation energy.

Enzyme Saturation

• The speed of enzyme-catalyzed reactions increases linearly at low substrate concentrations when there are more active sites on the enzyme available to bind the substrate.
• Once the available active sites on the enzymes have been filled with the substrate, the speed of enzyme-catalyzed reactions slows down and plateaus.
• Enzymes reach their maximum speed when all active sites are occupied.

Components of an Enzyme

• Apoenzyme: Protein portion of an enzyme.
• Cofactor: Non-protein component, can be inorganic (metals) or organic (coenzyme).
• Coenzymes are organic co-factors.
• Holoenzyme: Complete active enzyme (apoenzyme + cofactor).

Concept E: Local Conditions Influencing Enzyme Activity

• Enzyme activity can be affected by environmental factors (temperature, pH) and specific chemicals (inhibitors, activators).

Effects of Temperature

• Each enzyme has an optimal temperature where activity is highest.
• Increasing temperature increases the kinetic energy of molecules, leading to higher reaction rates initially but exceeding the peak point, enzyme activity suddenly decreases and plateaus due to denaturation (breaking of bonds in the tertiary enzyme structure)

Effects of pH

• Each enzyme has an optimal pH where activity is highest.
• pH affects the ionic and hydrogen bonds that maintain the enzyme's structure.
• Deviations from the optimal pH lead to denaturation and decreased activity.

Enzyme Inhibitors

• Competitive Inhibitors: bind to the active site, competing with the substrate. Effectiveness of these inhibitors can be overcome by adding more substrate.
• Non-competitive Inhibitors: bind to an allosteric site, causing a change in the enzyme's shape that reduces its effectiveness. Adding more substrate does not reverse the effectiveness of these inhibitors.

Feedback Inhibition

• Feedback inhibition is a metabolic control mechanism where the end product of a metabolic pathway shuts down the pathway.
• The end product usually binds to an allosteric site on an enzyme early in the pathway, reducing its activity and preventing further production of the product. This prevents the cell from wasting resources.