Intro to Biology: Principles and Branches

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, and distribution of living organisms
• Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species

Core Principles of Biology

• Cell theory: All living organisms are composed of cells
• Gene theory: Hereditary information is encoded in DNA and genes
• Evolution: The diversity of life is the product of descent with modification by natural selection
• Homeostasis: Living organisms maintain a stable internal environment
• Thermodynamics: Life depends on the flow of energy and matter

Branches of Biology

• Biochemistry: Study of the chemical processes within and relating to living organisms
• Botany: Scientific study of plants
• Cell biology: Study of cell structure and function
• Ecology: Study of the interactions of organisms with one another and with their environment
• Evolutionary biology: Study of the evolutionary processes that produced the diversity of life on Earth
• Genetics: Study of genes, heredity, and variation in living organisms
• Microbiology: Study of microorganisms, such as bacteria, viruses, and fungi
• Molecular biology: Study of the molecular basis of biological activity
• Physiology: Study of the normal functions of living organisms and their parts
• Zoology: Study of animals

Cell Biology

• Cell biology is a branch of biology that studies the structure, function, and behavior of cells

Cell Theory

• The cell theory states that all living organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells

Cell Structure

• Cells are typically composed of:
  • Plasma membrane: an outer covering that separates the cell's interior from its surroundings
  • Cytoplasm: a gel-like substance inside the cell that contains organelles
  • DNA: the genetic material of the cell
  • Ribosomes: where protein synthesis occurs

Types of Cells

• There are two main types of cells:
  • Prokaryotic cells: Lack a nucleus and other membrane-bound organelles
  • Eukaryotic cells: Have a nucleus and other membrane-bound organelles

Prokaryotic Cells

• Prokaryotic cells are generally smaller and simpler than eukaryotic cells
• They are found in bacteria and archaea
• The DNA of a prokaryotic cell is located in the cytoplasm, in a region called the nucleoid
• Prokaryotic cells have a cell wall that provides support and protection

Eukaryotic Cells

• Eukaryotic cells are found in plants, animals, fungi, and protists
• They contain a variety of organelles, each with a specific function:
  • Nucleus: Contains the cell's DNA and controls the cell's activities
  • Endoplasmic reticulum (ER): Involved in protein and lipid synthesis
  • Golgi apparatus: Modifies, sorts, and packages proteins and lipids
  • Mitochondria: Produce energy for the cell through cellular respiration
  • Lysosomes: Contain enzymes that break down cellular waste and debris
  • Chloroplasts (in plant cells): Carry out photosynthesis

Plasma Membrane

• The plasma membrane is a selective barrier that regulates the passage of substances into and out of the cell
• It is composed of a phospholipid bilayer with embedded proteins
• The phospholipid bilayer is made up of two layers of phospholipid molecules, with their hydrophobic tails facing inward and their hydrophilic heads facing outward
• Proteins in the plasma membrane can act as channels, carriers, or receptors

Cell Communication

• Cells communicate with each other through a variety of signaling molecules
• These signaling molecules can bind to receptors on the surface of the cell or inside the cell
• Cell communication is essential for coordinating cell activities and maintaining homeostasis

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication
• It consists of two main phases:
  • Interphase: the cell grows and prepares for division
  • Mitotic phase: the cell divides into two daughter cells
• Interphase is further divided into three phases:
  • G1 phase: the cell grows and synthesizes proteins
  • S phase: the cell replicates its DNA
  • G2 phase: the cell prepares for mitosis
• The mitotic phase consists of two processes:
  • Mitosis: the division of the nucleus
  • Cytokinesis: the division of the cytoplasm

Cell Division

• Cell division is the process by which a cell divides into two or more daughter cells
• There are two types of cell division:
  • Mitosis: produces two identical daughter cells and is used for growth, repair, and asexual reproduction
  • Meiosis: produces four genetically different daughter cells and is used for sexual reproduction

Mitosis

• Mitosis is divided into four phases:
  • Prophase: the chromosomes condense and become visible, and the nuclear envelope breaks down
  • Metaphase: the chromosomes line up along the middle of the cell
  • Anaphase: the sister chromatids separate and move to opposite poles of the cell
  • Telophase: the chromosomes arrive at the poles of the cell, and the nuclear envelope reforms
• Cytokinesis typically occurs during telophase, resulting in two separate daughter cells

Meiosis

• Meiosis is a type of cell division that produces four genetically different daughter cells
• It consists of two rounds of cell division:
  • Meiosis I: homologous chromosomes separate
  • Meiosis II: sister chromatids separate
• Meiosis is essential for sexual reproduction because it reduces the number of chromosomes in the gametes (sperm and egg cells)

Cell Metabolism

• Metabolism is the sum of all chemical reactions that occur in a cell
• It includes:
  • Catabolism: the breakdown of complex molecules into simpler ones, releasing energy
  • Anabolism: the synthesis of complex molecules from simpler ones, requiring energy
• ATP (adenosine triphosphate) is the main energy currency of the cell
• Enzymes are biological catalysts that speed up chemical reactions in the cell

Cellular Respiration

• Cellular respiration is the process by which cells break down glucose to produce energy in the form of ATP
• It occurs in the mitochondria of eukaryotic cells
• Cellular respiration involves four main stages:
  • Glycolysis: glucose is broken down into pyruvate
  • Pyruvate oxidation: pyruvate is converted to acetyl CoA
  • Citric acid cycle (Krebs cycle): acetyl CoA is oxidized to carbon dioxide
  • Oxidative phosphorylation: electrons are transferred from electron carriers to oxygen, producing ATP

Photosynthesis

• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose
• It occurs in the chloroplasts of plant cells
• Photosynthesis involves two main stages:
  • Light-dependent reactions: light energy is used to split water and generate ATP and NADPH
  • Light-independent reactions (Calvin cycle): carbon dioxide is fixed and used to produce glucose

Cell Growth and Differentiation

• Cell growth is the increase in cell size and mass
• Cell differentiation is the process by which cells become specialized in structure and function
• Cell growth and differentiation are regulated by a variety of factors, including:
  • Growth factors: signaling molecules that stimulate cell growth and division
  • Hormones: signaling molecules that regulate cell differentiation
  • Cell-cell interactions: interactions between cells that regulate cell behavior

Cell Death

• Cell death is a normal part of development and tissue homeostasis
• There are two main types of cell death:
  • Apoptosis: programmed cell death, which is a highly regulated process
  • Necrosis: uncontrolled cell death, which is caused by injury or infection
• Apoptosis is essential for removing damaged or unwanted cells