Energy and Metabolism

Forms and Types of Energy

Energy is the capacity to do work and is essential for all living organisms. It exists in various forms and can be transferred or transformed between systems.

• Kinetic Energy: Energy of motion (e.g., movement of molecules).

• Potential Energy: Stored energy (e.g., chemical bonds, gradients).

• Common forms: Mechanical, heat, sound, electric current, light, radioactivity.

Heat is the most convenient way of measuring energy. The calorie is a unit of energy, defined as the amount required to raise 1 gram of water by 1°C.

• 1 calorie (cal): Energy required to raise 1g water by 1°C.

Origin and Flow of Energy

Most energy in living systems originates from the sun. Energy flows through biological systems via chemical reactions, often involving oxidation-reduction (redox) processes.

• Oxidation: Atom or molecule loses an electron.

• Reduction: Atom or molecule gains an electron.

• Redox reactions transfer energy and are always paired.

Laws of Thermodynamics

The laws of thermodynamics govern energy transformations in biological systems.

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Disorder (entropy) in the universe increases; energy transformations are never 100% efficient.

Free Energy and Chemical Reactions

Gibbs Free Energy ()

Free energy determines whether a reaction is spontaneous or requires energy input.

• Positive : Products have more free energy than reactants; non-spontaneous, requires energy input.

• Negative : Products have less free energy than reactants; spontaneous (may not be instantaneous).

• Exergonic: Releases energy ( negative).

• Endergonic: Requires energy input ( positive).

Activation Energy

Activation energy is the extra energy required to destabilize existing bonds and initiate a chemical reaction.

• Enzymes lower activation energy, increasing reaction rates.

• Increasing temperature or using catalysts can lower activation energy.

Enzymes and Catalysis

Definition and Function of Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy. Most enzymes are proteins, but some are RNA molecules.

• Enzymes are not changed or consumed in reactions.

• Enzymes are highly specific for their substrates.

• Enzyme activity can be regulated by various factors.

Structure and Mechanism of Enzyme Action

• Active Site: Region where substrate binds; highly specific shape and chemical properties.

• Induced Fit Model: Enzyme changes shape to fit substrate more tightly, enhancing specificity and catalysis.

• Denaturation: Loss of enzyme structure (due to temperature, pH, chemicals) leads to loss of function.

Enzyme Specificity and Regulation

• Allosteric Sites: Additional binding sites for regulators (activators/inhibitors) that change enzyme activity.

• Coenzymes: Organic molecules (e.g., vitamins) required for enzyme function.

• Cofactors: Inorganic ions (e.g., metal ions) that assist enzyme activity.

Environmental Effects on Enzyme Activity

• Temperature: Enzymes have optimal temperature; too high or low can denature enzyme.

• pH: Enzymes have optimal pH range; extremes can disrupt structure and function.

Enzyme Inhibition

• Competitive Inhibition: Inhibitor binds to active site, blocking substrate.

• Noncompetitive Inhibition: Inhibitor binds to allosteric site, changing enzyme shape and reducing activity.

Michaelis-Menten Parameters:

• : Maximum velocity of enzyme-catalyzed reaction.

• : Substrate concentration at which reaction rate is half of .

ATP: The Energy Currency of the Cell

Structure and Function of ATP

Adenosine triphosphate (ATP) is the primary energy carrier in cells.

• Composed of ribose (5-carbon sugar), adenine (nitrogenous base), and three phosphate groups.

• Energy is stored in the high-energy phosphate bonds.

• ATP is used for cellular work, including biosynthesis, transport, and movement.

Metabolism: Catabolism and Anabolism

Overview of Metabolic Pathways

Metabolism includes all chemical reactions in an organism, divided into two main types:

• Anabolism: Synthesis of complex molecules from simpler ones; requires energy.

• Catabolism: Breakdown of complex molecules into simpler ones; releases energy.

Cellular Respiration

Types of Organisms

• Autotrophs: Produce their own food (e.g., plants).

• Heterotrophs: Obtain energy from consuming other organisms.

Overview of Cellular Respiration

Cellular respiration is the process by which cells harvest energy from organic molecules, primarily glucose.

• Involves glycolysis, pyruvate oxidation, Krebs cycle, and electron transport chain.

• Electron carriers (NAD+, FAD) play key roles in transferring electrons.

Glycolysis

• Glucose is broken into 2 molecules of pyruvate.

• Net production of 2 ATP.

• Occurs in the cytoplasm.

Pyruvate Oxidation

• Occurs in mitochondria.

• Produces CO2, NADH, and Acetyl-CoA.

Krebs Cycle (Citric Acid Cycle)

• Produces CO2, NADH, FADH2, and ATP.

Electron Transport Chain (ETC)

• Uses electrons from NADH and FADH2 to create a proton gradient.

• ATP is produced via chemiosmosis.

ATP Production

• Substrate-level phosphorylation and oxidative phosphorylation are two ways ATP is generated.

Fermentation

• Occurs when oxygen is not available.

• Produces less ATP than aerobic respiration.

Photosynthesis

Overview and Equation

Photosynthesis is the process by which autotrophs convert light energy into chemical energy.

• General equation:

Light-Dependent and Light-Independent Reactions

• Light-dependent reactions: Occur in thylakoid membranes; produce ATP and NADPH.

• Light-independent reactions (Calvin Cycle): Occur in stroma; use ATP and NADPH to fix CO2 into glucose.

Photosynthetic Pigments

• Chlorophyll a: Main pigment in photosynthesis.

• Chlorophyll b, carotenoids: Accessory pigments that absorb different wavelengths.

Calvin Cycle

• Consists of three phases: Carbon fixation, reduction, regeneration.

• Multiple turns required to produce one molecule of glucose.

Types of Photosynthesis

• C3 Photosynthesis: Most common; Calvin Cycle directly fixes CO2.

• C4 Photosynthesis: Adapted to hot, dry environments; separates initial CO2 fixation and Calvin Cycle.

• CAM Photosynthesis: Adapted to arid conditions; CO2 fixation occurs at night.

Stomata and Storage

• Stomata: Pores on leaf surfaces that regulate gas exchange.

• Complex sugars (starch): Produced for energy storage.

Relationship Between Chloroplasts and Mitochondria

• Both organelles share products and have roles in energy metabolism.

Additional info: These notes expand on the study guide by providing definitions, examples, and context for key concepts in energy, metabolism, enzymes, cellular respiration, and photosynthesis, suitable for General Biology college students.