Chemistry of Life

Essential Elements and Chemical Bonds

The chemistry of life is based on a small set of essential elements and the interactions between their atoms. These elements and their chemical bonds form the foundation for all biological molecules and processes.

• Essential elements: Carbon, Hydrogen, Oxygen, and Nitrogen (CHON) make up most living matter.

• Trace elements: Required in small amounts (e.g., iodine, iron) for proper biological function.

• Atomic structure: Atoms bond to fill their outer electron shells, forming ionic, covalent, or hydrogen bonds.

• Polarity: Water's polarity enables hydrogen bonding, making it an excellent solvent and affecting acid-base balance.

Macromolecules and Cellular Structure

Major Biological Molecules

Cells are built from four main types of macromolecules, each with unique structures and functions.

• Carbohydrates, lipids, proteins, nucleic acids: The four major classes of biological macromolecules.

• Protein structure: Proteins have primary, secondary, tertiary, and quaternary structures.

• DNA structure: DNA is composed of base pairs (A-T and G-C) held together by hydrogen bonds.

Cells and Organelles

Cell Types and Key Organelles

Cells are the basic units of life, with prokaryotic and eukaryotic types distinguished by the presence of a nucleus and organelles.

• Prokaryotes: Lack a nucleus; eukaryotes have a nucleus and membrane-bound organelles.

• Key organelles: Nucleus (DNA storage), mitochondria (ATP production), lysosomes (digestion), Golgi apparatus (processing and packaging).

• Cell membrane: Composed of phospholipids and proteins; selectively permeable to regulate transport.

Transport and Homeostasis

Movement Across Membranes

Cells maintain internal balance by controlling the movement of substances across their membranes.

• Diffusion and osmosis: Passive transport processes that move substances down their concentration gradients.

• Active transport: Requires energy to move substances against their concentration gradients.

• Endocytosis and exocytosis: Move large materials across membranes via vesicles.

Energy, Enzymes, and Metabolism

ATP and Metabolic Pathways

Cells use metabolic pathways to extract and use energy, with enzymes catalyzing each step.

• ATP: The main energy currency of the cell; hydrolysis of ATP releases energy for cellular work.

• Catabolic reactions: Break down molecules, releasing energy.

• Anabolic reactions: Build up molecules, requiring energy input.

• Enzymes: Lower activation energy and function best at optimal pH and temperature.

Cellular Respiration

Energy Production in Cells

Cellular respiration is the process by which cells convert glucose into ATP, the usable form of energy.

• Stages: Glycolysis, citric acid cycle (Krebs cycle), and oxidative phosphorylation.

• Location: Occurs in mitochondria; oxygen is required for aerobic respiration.

Photosynthesis

Energy Capture in Plants

Photosynthesis is the process by which plants convert light energy into chemical energy (glucose).

• Location: Occurs in chloroplasts.

• Light reactions: Make ATP and NADPH.

• Calvin Cycle: Uses CO2 to produce sugars.

• Complementary processes: Photosynthesis and respiration are interconnected in energy flow.

Cell Communication

Signaling and Response

Cells communicate using chemical signals to coordinate activities and respond to their environment.

• Hormones: Steroid hormones enter cells; peptide hormones bind to receptors on cell surfaces.

• Apoptosis: Programmed cell death removes damaged or unnecessary cells.

Cell Cycle and Division

Growth and Reproduction

The cell cycle describes the stages a cell goes through to grow and divide.

• Phases: Interphase (G1, S, G2), mitosis (division of the nucleus), and cytokinesis (division of the cytoplasm).

• Mitosis: Produces two identical daughter cells.

• Cancer: Results from loss of cell cycle control and unregulated division.

Meiosis and Heredity

Genetic Variation

Meiosis is a special type of cell division that produces gametes and increases genetic diversity.

• Crossing over: Exchange of genetic material between homologous chromosomes.

• Independent assortment: Random distribution of chromosomes to gametes.

• Separation: Homologous chromosomes separate in meiosis I; sister chromatids separate in meiosis II.

Mendelian Genetics

Inheritance Patterns

Mendelian genetics explains how traits are inherited through dominant and recessive alleles.

• Alleles: Different forms of a gene; dominant alleles mask recessive ones.

• Punnett squares: Used to predict genetic outcomes.

• Linked genes: Genes located close together on a chromosome tend to be inherited together.

• Recombination: Increases genetic diversity by shuffling alleles.

DNA and Molecular Biology

Structure and Replication

DNA is the hereditary material, with a double helix structure and specific base pairing.

• DNA bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).

• Replication: Semi-conservative; key enzymes include DNA polymerase, ligase, and primase.

• Griffith's and Chargaff's experiments: Provided foundational evidence for DNA as the genetic material.

Bioenergetics: Energy and Life

Energy Flow in Ecosystems

Bioenergetics studies how energy flows through living systems, connecting producers and consumers.

• Photosynthesis: Stores energy in glucose; respiration releases it for cellular work.

• Energy flow: Described by food chains and food webs.

Study Tips

• Use diagrams for ATP cycle, mitochondria, chloroplasts, and cell processes.

• Memorize steps of energy cycles, mitosis, respiration, and cellular functions.

• Practice connecting processes (e.g., how photosynthesis supports respiration).