Energy and Metabolism

Introduction to Energy in Biological Systems

Energy is a fundamental concept in biology, essential for all cellular processes. Organisms obtain, transform, and utilize energy to maintain life, grow, and reproduce.

• Energy: The capacity to do work or cause change. In biological systems, energy is often stored in chemical bonds.

• Metabolism: The sum of all chemical reactions in an organism, including both anabolic (building up) and catabolic (breaking down) pathways.

• Metabolic Pathways: Series of chemical reactions occurring within a cell, catalyzed by enzymes.

Thermodynamics in Biology

Thermodynamics governs how energy is transferred and transformed in biological systems.

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

• Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

• Application: Cells must manage energy efficiently to maintain order and function.

Types and Forms of Energy

Cells utilize various forms of energy to perform work.

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy, such as in chemical bonds.

• Heat, Mechanical, Chemical Energy: Forms relevant to biological processes.

Free Energy and Spontaneity

Free energy determines whether a reaction can occur spontaneously.

• Gibbs Free Energy (): Indicates the spontaneity of a reaction.

• Equation:

• Exergonic Reaction: Releases energy (), spontaneous.

• Endergonic Reaction: Requires energy input (), non-spontaneous.

ATP: The Energy Currency

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

• Structure: Adenine, ribose, and three phosphate groups.

• Hydrolysis of ATP: Releases energy for cellular work.

• ATP Cycle: ATP is regenerated from ADP and inorganic phosphate.

Enzymes and Activation Energy

Enzymes are biological catalysts that lower activation energy, increasing reaction rates.

• Activation Energy: The energy required to initiate a chemical reaction.

• Enzyme Function: Enzymes bind substrates, stabilize transition states, and speed up reactions.

• Induced Fit Model: Enzyme changes shape to fit substrate.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Autotrophs: Organisms that produce their own food via photosynthesis.

• Heterotrophs: Organisms that obtain food by consuming other organisms.

• Main Pigment: Chlorophyll absorbs light energy.

Light and Dark Reactions

Photosynthesis consists of two main stages: the light-dependent reactions and the Calvin cycle (dark reactions).

• Light Reactions: Occur in the thylakoid membranes, convert light energy to chemical energy (ATP and NADPH).

• Calvin Cycle: Occurs in the stroma, uses ATP and NADPH to fix carbon dioxide into glucose.

• Equation for Photosynthesis:

Electron Transport and Energy Conversion

Photosynthetic electron transport chains transfer energy and produce ATP and NADPH.

• Electron Carriers: NADP+ is reduced to NADPH.

• ATP Synthase: Generates ATP using a proton gradient.

Carbon Fixation and the Calvin Cycle

Carbon fixation incorporates CO2 into organic molecules.

• Rubisco: The enzyme that catalyzes the first step of the Calvin cycle.

• Products: Glucose and other carbohydrates.

Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from organic molecules.

• Aerobic Respiration: Uses oxygen to fully oxidize glucose, producing ATP.

• Anaerobic Respiration: Occurs without oxygen, less efficient.

• Fermentation: Produces ATP without oxygen, yields less energy.

Stages of Cellular Respiration

Cellular respiration occurs in several stages, each with specific inputs and outputs.

• Glycolysis: Glucose is split into two pyruvate molecules, producing ATP and NADH.

• Pyruvate Oxidation: Pyruvate is converted to acetyl-CoA.

• Citric Acid Cycle (Krebs Cycle): Acetyl-CoA is oxidized, producing NADH, FADH2, and ATP.

• Electron Transport Chain: Electrons from NADH and FADH2 are transferred to oxygen, generating ATP.

Redox Reactions and Electron Carriers

Redox reactions transfer electrons and are central to energy production.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Electron Carriers: NAD+, FAD, and others shuttle electrons between reactions.

ATP Generation and Energy Yield

ATP is generated by substrate-level phosphorylation and oxidative phosphorylation.

• Substrate-level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: ATP synthesis driven by electron transport and proton gradient.

• Total ATP Yield: Approximately 30-32 ATP per glucose molecule.

Genetics: Mendelian Inheritance

Introduction to Genetics

Genetics is the study of heredity and variation in organisms. Mendelian genetics explains how traits are inherited from parents to offspring.

• Alleles: Different forms of a gene.

• Genes: Units of heredity, composed of DNA.

• Dominant and Recessive: Dominant alleles mask the effect of recessive alleles.

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

Patterns of Inheritance

Traits can be inherited in various patterns, including complete dominance, incomplete dominance, and codominance.

• Complete Dominance: One allele completely masks the other.

• Incomplete Dominance: Heterozygotes show an intermediate phenotype.

• Codominance: Both alleles are expressed equally (e.g., ABO blood type system).

Examples and Applications

• Purple and white flower color: Used to illustrate Mendelian inheritance.

• ABO Blood Type: Demonstrates codominance.

Additional info:

• Some content inferred from standard General Biology curriculum and context of exam questions.

• Figures referenced (e.g., Figure 8.6, 9.8, 10.5) are typical in biology textbooks and relate to the described processes.