Introduction to Biology

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, and distribution of living organisms

Core Principles of Biology

• Cell theory: All living organisms are composed of cells
• Gene theory: Hereditary information is encoded in genes and passed on to the next generation
• Evolution: Life changes over time through the process of natural selection
• Homeostasis: Living organisms maintain a stable internal environment

Organization of Life

• Atoms: Basic units of matter
• Molecules: Groups of atoms bonded together
• Organelles: Structures within cells that perform specific functions
• Cells: The basic unit of life
• Tissues: Groups of similar cells performing a specific function
• Organs: Structures composed of different tissues working together
• Organ systems: Groups of organs working together
• Organisms: Individual living beings
• Populations: Groups of organisms of the same species living in the same area
• Communities: Populations of different species living in the same area
• Ecosystems: Communities and their physical environment
• Biosphere: All ecosystems on Earth

Characteristics of Life

• Organization: Living things exhibit complex organization
• Metabolism: Living things use energy to power their activities
• Growth: Living things increase in size and/or number
• Reproduction: Living things produce offspring
• Response to stimuli: Living things react to changes in their environment
• Adaptation: Living things evolve over time to better suit their environment

Cell Biology

• Cell biology is the study of cells, their structure, function, and behavior

Cell Structure

• All cells have a plasma membrane, cytoplasm, and genetic material (DNA)
• Eukaryotic cells have membrane-bound organelles, including a nucleus
• Prokaryotic cells lack membrane-bound organelles

Plasma Membrane

• The plasma membrane is a selectively permeable barrier that separates the cell from its external environment
• It is composed of a phospholipid bilayer with embedded proteins
• Functions include:
  • Controlling the movement of substances in and out of the cell
  • Cell signaling
  • Cell adhesion

Cytoplasm

• The cytoplasm is the region of the cell between the plasma membrane and the nucleus
• It contains cytosol, organelles, and the cytoskeleton

Nucleus

• The nucleus is the control center of the cell
• It contains the cell's DNA, organized into chromosomes
• The nucleus is surrounded by a nuclear envelope
• The nucleolus is a region within the nucleus where ribosomes are assembled

Endoplasmic Reticulum (ER)

• The ER is a network of membranes that extends throughout the cytoplasm
• Rough ER: Contains ribosomes and is involved in protein synthesis and modification
• Smooth ER: Lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage

Golgi Apparatus

• The Golgi apparatus is a stack of flattened, membrane-bound sacs
• It modifies, sorts, and packages proteins and lipids

Lysosomes

• Lysosomes are membrane-bound organelles that contain enzymes
• They are involved in intracellular digestion

Mitochondria

• Mitochondria are the powerhouses of the cell
• They generate ATP through cellular respiration
• Mitochondria have a double membrane

Chloroplasts

• Chloroplasts are found in plant cells and algae
• They are the site of photosynthesis
• Chloroplasts have a double membrane and contain chlorophyll

Cytoskeleton

• The cytoskeleton is a network of protein fibers that provides structural support to the cell
• It is involved in cell movement and intracellular transport
• Three main types of fibers:
  • Microfilaments (actin filaments)
  • Intermediate filaments
  • Microtubules

Cell Junctions

• Cell junctions are structures that connect cells together
• Types of cell junctions:
  • Tight junctions: Prevent leakage of extracellular fluid
  • Adherens junctions and Desmosomes: Provide strong adhesion between cells
  • Gap junctions: Allow for communication between cells

Cell Communication

• Cells communicate with each other through chemical signals
• Types of cell signaling:
  • Paracrine signaling: Local signaling
  • Endocrine signaling: Long-distance signaling
  • Autocrine signaling: Cell signals itself
  • Direct contact: Through cell junctions

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication
• Phases of the cell cycle:
  • Interphase: Cell grows and prepares for division (G1, S, G2 phases)
  • Mitotic phase (M phase): Cell divides (mitosis and cytokinesis)

Mitosis

• Mitosis is the process of cell division that produces two identical daughter cells
• Stages of mitosis:
  • Prophase: Chromosomes condense
  • Metaphase: Chromosomes line up in the middle of the cell
  • Anaphase: Sister chromatids separate
  • Telophase: Daughter nuclei form

Meiosis

• Meiosis is the process of cell division that produces four genetically different haploid cells (gametes)
• It involves two rounds of division: meiosis I and meiosis II

Apoptosis

• Apoptosis is programmed cell death
• It is essential for development and tissue homeostasis
• It involves a series of biochemical events that lead to cell dismantling

Cellular Respiration

• Cellular respiration is the process by which cells generate energy (ATP) from glucose and oxygen
• It occurs in the mitochondria
• Stages of cellular respiration:
  • Glycolysis
  • Pyruvate oxidation
  • Citric acid cycle (Krebs cycle)
  • Oxidative phosphorylation (electron transport chain and chemiosmosis)

Photosynthesis

• Photosynthesis is the process by which plants and algae convert light energy into chemical energy (glucose)
• It occurs in chloroplasts
• Stages of photosynthesis:
  • Light-dependent reactions
  • Light-independent reactions (Calvin cycle)

Cell Metabolism

• Metabolism is the sum of all chemical reactions that occur in a cell
• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy
• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy

Cell Transport

• Passive transport: Movement of substances across the cell membrane without the input of energy (e.g., diffusion, osmosis, facilitated diffusion)
• Active transport: Movement of substances across the cell membrane with the input of energy (ATP) (e.g., pumps, endocytosis, exocytosis)

Genetics

• Genes are units of heredity that contain instructions for making proteins
• DNA is the molecule that carries genetic information
• RNA is involved in protein synthesis
• The central dogma of molecular biology: DNA -> RNA -> Protein

Cell Growth and Differentiation

• Cell growth is the increase in cell size and/or number
• Cell differentiation is the process by which cells become specialized
• Stem cells are undifferentiated cells that can differentiate into various cell types

Cell Specialization

• Cell specialization refers to the specific functions that cells perform based on their structure and gene expression patterns
• Different cell types are optimized for specific tasks within an organism

Cell Signaling Pathways

• Cell signaling pathways are networks of interacting proteins and molecules that transmit signals from the cell surface to the interior
• These pathways regulate various cellular processes

Cell Adhesion Molecules (CAMs)

• Cell adhesion molecules are proteins on the cell surface that mediate cell-cell and cell-matrix interactions
• They play crucial roles in tissue development, immune responses, and wound healing.