Energy & Enzymes

Energy: Definition and Forms

Energy is defined as the capacity to move or change matter. It is essential for all biological processes and exists in various forms.

• Forms of Energy:

  • Chemical

  • Radiant

  • Heat

  • Mechanical

  • Electrical

  • Nuclear

• Energy can be transformed from one form to another.

Laws of Thermodynamics

The laws of thermodynamics govern the flow and transformation of energy in biological systems.

• First Law: Energy cannot be created nor destroyed; it can only be converted from one form to another.

  • The sum of the energy before the conversion is equal to the sum of the energy after the conversion.

• Second Law: Some energy dissipates during transformations and is lost as heat.

  • Usable energy decreases; the amount of usable energy therefore decreases after each transformation.

ATP (Adenosine Triphosphate)

ATP is the primary energy currency of the cell, used to power most cellular reactions.

• Each glucose molecule is used to produce 36 ATP molecules.

• ATP is a nucleotide composed of:

  • Adenine (a nitrogenous base)

  • Ribose (a 5-carbon sugar)

  • Three phosphate groups

ATP Hydrolysis

The breakdown (hydrolysis) of ATP releases energy by removing a phosphate group, forming ADP and inorganic phosphate (Pi).

• ATP hydrolysis equation:

• ATP is regenerated from ADP by cellular processes.

Types of Reactions: Exergonic and Endergonic

Cellular reactions are classified based on energy changes.

• Exergonic Reaction: Releases energy.

• Endergonic Reaction: Requires an input of energy; does not occur spontaneously.

Catabolic and Anabolic Reactions

Metabolic reactions are divided into two main types:

• Anabolic Reactions: Synthesize compounds; energy is required.

• Catabolic Reactions: Break down molecules; energy is released.

• Both types may require activation energy to start.

Photosynthesis and Cellular Respiration

These are the two major energy-transforming processes in cells.

• Photosynthesis: Occurs in the chloroplasts. (Carbon dioxide + Water → Sugar + Oxygen)

• Cellular Respiration: Occurs in the mitochondria. (Glucose + Oxygen → Carbon Dioxide + Water + Energy)

Enzymes

Definition and Function

Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process.

• Organic catalysts are enzymes.

• Enzyme names often end in "-ase" (e.g., dehydrogenase).

Induced-Fit Theory

The induced-fit model describes how enzymes interact with substrates.

• The enzyme's active site binds with the substrate like a key fitting a lock.

• The shape of the enzyme must match the substrate for binding.

• Binding induces a change in the enzyme's conformation to make a closer fit.

• The enzyme does not form a chemical bond with the substrate.

• After the reaction, the enzyme returns to its original shape and can be reused.

Activation Energy

Activation energy is the minimum energy required to start a chemical reaction.

• The amount of activation energy is considerably less when the enzyme is present.

Factors Affecting Enzyme Activity (Rate of Reaction)

Several conditions influence how quickly enzymes catalyze reactions.

1. Substrate Concentration: Higher concentration increases collisions and reaction rate, but levels off at saturation.

2. Enzyme Concentration: Increasing enzyme amount raises reaction rate until saturation.

3. Temperature: Activity increases with temperature up to a point, then declines as enzymes denature.

4. pH: Each enzyme has an optimal pH range for activity.

Regulation of Enzyme Activity

• Competitive Inhibition: A similar-shaped molecule competes with the substrate for the active site.

• Noncompetitive Inhibition: An inhibitor binds to an allosteric site, distorting the active site and reducing enzyme function.

Coenzymes and Cofactors

Many enzymes require additional molecules to function.

• Cofactors: Non-protein helpers, often metal ions (e.g., Mg2+, K+, Ca2+).

• Coenzymes: Organic molecules that assist enzymes.

Electron Carriers in Cellular Respiration

Electron carriers transport electrons during cellular respiration.

• NAD (Nicotinamide Adenine Dinucleotide): Functions by carrying two electrons from one reaction site to another.

Additional info: The notes include diagrams and equations for ATP hydrolysis, photosynthesis, and cellular respiration, which are central to understanding energy flow in cells. The induced-fit model and enzyme regulation mechanisms are foundational concepts in biochemistry and cell biology.