Introduction to Biology

• Biology is the study of life and living organisms, encompassing their structure, function, growth, origin, evolution, distribution, and taxonomy.
• It is a broad field containing many subdisciplines and topics.

Core Principles of Biology

• Cell theory: All living organisms are composed of cells, and all cells arise from pre-existing cells.
• Gene theory: Hereditary information is encoded in DNA and genes.
• Evolution: Life evolves over time through processes of natural selection and genetic drift.
• Homeostasis: Living organisms maintain a stable internal environment.
• Thermodynamics: Life requires energy and is subject to the laws of thermodynamics.

Subdisciplines of Biology

• Biochemistry: The study of the chemical processes within and relating to living organisms.
• Molecular biology: The study of the structure and function of biological macromolecules.
• Cell biology: The study of cells, their structure, function, and behavior.
• Genetics: The study of heredity and variation in organisms.
• Evolutionary biology: The study of the evolutionary processes that have produced the diversity of life.
• Ecology: The study of the interactions of organisms with each other and their environment.
• Physiology: The study of the normal functions of living organisms and their parts.
• Anatomy: The study of the structure of living organisms.
• Microbiology: The study of microorganisms, such as bacteria, viruses, and fungi.
• Botany: The scientific study of plants.
• Zoology: The scientific study of animals.

Cell Biology

• Cell biology is a branch of biology that studies the structure, function, and behavior of cells.
• It encompasses the study of cell organelles, cell signaling, cell division, and cell death.

Cell Structure

• Cells are the basic structural and functional units of all known living organisms.
• There are two main types of cells: prokaryotic and eukaryotic.
• Prokaryotic cells lack a nucleus and other membrane-bound organelles.
• Eukaryotic cells have a nucleus and other membrane-bound organelles.

Key Cell Structures

• Plasma membrane: The outer boundary of the cell that controls the movement of substances in and out of the cell.
• Cytoplasm: The gel-like substance within the cell that contains the organelles.
• Nucleus: The control center of the cell, containing the DNA.
• Ribosomes: Sites of protein synthesis.
• Endoplasmic reticulum (ER): Involved in protein and lipid synthesis.
  • Rough ER: Contains ribosomes and is involved in protein synthesis and modification.
  • Smooth ER: Involved in lipid synthesis and detoxification.
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.
• Lysosomes: Contain enzymes that digest cellular waste and debris.
• Mitochondria: Powerhouses of the cell, producing ATP through cellular respiration.
• Chloroplasts: Found in plant cells, where photosynthesis occurs.
• Cytoskeleton: Network of protein fibers that provides structural support and facilitates cell movement.

Cell Membrane

• The cell membrane, also known as the plasma membrane, is a biological membrane that separates the interior of a cell from the outside environment.
• It is composed of a lipid bilayer with embedded proteins.
• The lipid bilayer is primarily made up of phospholipids with hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
• The cell membrane is selectively permeable, meaning it allows some substances to pass through while blocking others.
• Membrane proteins perform various functions, including transport, signaling, and cell adhesion.

Cell Signaling

• Cell signaling is the process by which cells communicate with each other and their environment.
• Signaling pathways involve a series of molecular events that lead to a cellular response.
• Cells use various signaling molecules, such as hormones, neurotransmitters, and growth factors.
• Receptors on the cell surface or within the cell bind to signaling molecules and initiate the signaling cascade.
• Common signaling pathways include G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), and ion channels.

Cell Division

• Cell division is the process by which a cell divides into two or more daughter cells.
• There are two main types of cell division: mitosis and meiosis.
• Mitosis is the process of cell division that results in two identical daughter cells.
• Meiosis is the process of cell division that results in four daughter cells with half the number of chromosomes as the parent cell.
• Mitosis is involved in growth, repair, and asexual reproduction.
• Meiosis is involved in sexual reproduction.
• The cell cycle is a series of events that lead to cell growth and division, including interphase, mitosis, and cytokinesis.

Cell Cycle

• The cell cycle is a repeating series of growth, DNA replication, and division, resulting in the production of new cells
• It consists of two major phases: interphase and the mitotic (M) phase
• Interphase is further divided into G1, S, and G2 phases
• G1 phase: The cell grows and synthesizes proteins and organelles
• S phase: DNA replication occurs, resulting in the duplication of chromosomes
• G2 phase: The cell continues to grow and prepares for cell division
• M phase includes mitosis (nuclear division) and cytokinesis (cytoplasmic division)

Mitosis

• Mitosis is the process of nuclear division in eukaryotic cells.
• It consists of four main phases: prophase, metaphase, anaphase, and telophase.
• Prophase: Chromosomes condense, and the nuclear envelope breaks down.
• Metaphase: Chromosomes line up at the metaphase plate.
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: Chromosomes arrive at the poles, and the nuclear envelope reforms.
• Cytokinesis is the division of the cytoplasm, resulting in two separate daughter cells.

Meiosis

• Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells.
• It is required to produce egg and sperm cells for sexual reproduction.
• Meiosis involves two rounds of division: meiosis I and meiosis II.
• Meiosis I separates homologous chromosomes, while meiosis II separates sister chromatids.
• Prophase I includes pairing of homologous chromosomes and crossing over, which increases genetic diversity.

Cell Death

• Cell death is a normal and essential process in multicellular organisms.
• There are two main types of cell death: apoptosis and necrosis.
• Apoptosis is programmed cell death, which is a highly regulated process that eliminates unwanted or damaged cells.
• Necrosis is accidental cell death, which is caused by injury or infection.
• Apoptosis plays a crucial role in development, tissue homeostasis, and immune function.
• Dysregulation of apoptosis can contribute to cancer and other diseases.

Key Techniques in Cell Biology

• Microscopy: Used to visualize cells and their structures.
  • Light microscopy: Uses visible light to create magnified images.
  • Electron microscopy: Uses beams of electrons to create highly magnified images with greater resolution.
• Cell culture: Growing cells in a controlled environment outside of their natural context.
• Electrophoresis: Separating molecules based on size and charge.
• Centrifugation: Separating cell organelles and molecules based on density.
• Flow cytometry: Analyzing cell populations based on their characteristics.
• Immunofluorescence: Using antibodies to detect specific proteins in cells.
• Molecular cloning: Isolating and amplifying specific genes or DNA sequences.
• Gene editing (CRISPR): Modifying genes within cells.