जीव विज्ञान का परिचय

• Biology is the scientific study of life and living organisms.
• It explores the structure, function, growth, origin, evolution, and distribution of living things.
• 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 origin and extinction of species.
• Living organisms are open systems that survive by transforming energy and decreasing their local entropy.

Subdisciplines of Biology

• Biochemistry examines the fundamental chemistry of life.
• Botany studies plants.
• Cell biology studies the cell, the fundamental building block of life.
• Ecology examines how organisms interact with their environment.
• Evolutionary biology studies the origins and changes of life over time.
• Genetics studies heredity and variation in organisms.
• Microbiology studies microorganisms.
• Molecular biology studies biological molecules and their interactions.
• Physiology studies the functions of organisms and their parts.
• Zoology studies animals.

Cell Biology

• Cell biology is the branch of biology that studies the structure, function, and behavior of cells.
• It encompasses the physiological properties, metabolic processes, signaling pathways, life cycle, chemical composition, and interactions of cells with their environment.
• Cell biology studies both prokaryotic and eukaryotic cells.
• Research in cell biology is closely related to genetics, biochemistry, molecular biology, and developmental biology.

Cell Theory

• The cell theory, developed in the mid-19th century, is a foundational principle of biology.
• All living organisms are composed of one or more cells.
• The cell is the basic unit of structure and function in organisms.
• All cells arise from pre-existing cells.

Cell Structure

• Cells are broadly classified as prokaryotic or eukaryotic.
• Prokaryotic cells lack a nucleus and other membrane-bound organelles, examples include bacteria and archaea.
• Eukaryotic cells possess a nucleus and other membrane-bound organelles, examples include animal cells, plant cells, fungi, and protists.

Key components of eukaryotic cells

• Nucleus: Contains the cell's genetic material (DNA) organized as chromosomes.
• Nuclear envelope: A double membrane surrounding the nucleus, regulating transport in and out.
• Nucleolus: Site of ribosome synthesis within the nucleus.
• Endoplasmic reticulum (ER): A network of membranes involved in protein and lipid synthesis; rough ER contains ribosomes, smooth ER does not.
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
• Mitochondria: The "powerhouses" of the cell, responsible for ATP production through cellular respiration.
• Lysosomes: Contain enzymes for degrading cellular waste and debris.
• Peroxisomes: Involved in detoxification and lipid metabolism.
• Cytoskeleton: A network of protein filaments (microtubules, actin filaments, intermediate filaments) that provides structural support, facilitates cell movement, and enables intracellular transport.
• Plasma membrane: The outer boundary of the cell, composed of a lipid bilayer with embedded proteins, controlling the movement of substances in and out of the cell.

Cell Membrane

• The cell membrane, also called the plasma membrane, separates the interior of the cell from the outside environment.
• It consists of a lipid bilayer composed of phospholipids, cholesterol, and proteins.
• The lipid bilayer is selectively permeable, allowing some molecules to pass through while restricting others.
• Membrane proteins perform various functions, including transport, signaling, and cell adhesion.

Cell Transport

• Cells transport materials across the membrane through different mechanisms.
• Passive transport: Does not require energy input, includes diffusion, osmosis, and facilitated diffusion.
• Active transport: Requires energy input (ATP) to move molecules against their concentration gradients via protein pumps.
• Endocytosis: The process by which cells engulf extracellular material by invaginating the cell membrane to form vesicles.
• Exocytosis: The process by which cells release intracellular material by fusing vesicles with the cell membrane.

Cell Communication

• Cells communicate with each other through various signaling pathways.
• Signaling molecules, such as hormones and neurotransmitters, bind to receptors on the cell surface or inside the cell.
• Receptor activation triggers a cascade of intracellular events, leading to a cellular response.
• Types of cell signaling include: endocrine, paracrine, autocrine, and direct contact.

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 and mitosis (or meiosis).
• Interphase: The cell grows, replicates its DNA, and prepares for division - G1 phase (growth), S phase (DNA replication), G2 phase (preparation for mitosis).
• Mitosis: Nuclear division resulting in two identical daughter cells - prophase, metaphase, anaphase, telophase.
• Meiosis: Nuclear division resulting in four genetically distinct daughter cells (gametes).
• Cytokinesis: The division of the cytoplasm, resulting in two separate cells.
• The cell cycle is tightly regulated by checkpoints to ensure proper DNA replication and chromosome segregation.
• Dysregulation of the cell cycle can lead to uncontrolled cell growth and cancer.

Cell Metabolism

• Cell metabolism encompasses all the chemical reactions that occur within a cell.
• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy, for example, cellular respiration.
• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy, for example, protein synthesis.
• Enzymes: Biological catalysts that speed up chemical reactions.
• ATP: Adenosine triphosphate, the main energy currency of the cell.

Cell Growth and Development

• Cell growth is the increase in cell size and mass.
• Cell differentiation is the process by which cells become specialized in structure and function.
• Development is the process by which a multicellular organism arises from a single cell.
• Apoptosis: Programmed cell death, is a crucial process in development and tissue homeostasis.
• Cell signaling plays a critical role in regulating cell growth, differentiation, and development.