Introduction to Biology

• Biology is the scientific study of life, encompassing a wide range of topics from the molecular mechanisms within cells to the interactions between organisms in ecosystems.
• It seeks to understand the origin, evolution, structure, function, growth, reproduction, and behavior of living organisms.
• It is a broad and diverse field, often divided into specialized disciplines that focus on specific aspects of life.

Subdisciplines of Biology

• Biochemistry examines the chemical processes within and relating to living organisms.
• Molecular biology studies the structure and function of macromolecules, including DNA, RNA, and proteins, which are essential for life processes.
• Cell biology focuses on the structure, function, and behavior of cells, the fundamental units of life.
• Genetics explores heredity and the variation of inherited characteristics.
• Evolutionary biology investigates the processes that have led to the diversity of life on Earth.
• Ecology studies the interactions between organisms and their environment.
• Physiology examines the functions and mechanisms that operate within living organisms.
• Anatomy studies the structure of living organisms.

Characteristics of Life

• Organization: Living things exhibit a complex organization, from atoms to molecules to cells to tissues to organs to organ systems to organisms.
• Metabolism: The sum of all chemical reactions that occur within an organism, including energy transfer and the synthesis and breakdown of molecules.
• Growth: Increase in size or cell number.
• Reproduction: The ability to produce offspring, either sexually or asexually.
• Response to stimuli: Ability to react to changes in the environment.
• Adaptation: The process by which organisms evolve to become better suited to their environment over time.
• Homeostasis: The maintenance of a stable internal environment despite external changes.

Cell Biology

• Cell biology is the study of cells, the basic units of life.
• It explores their physiological properties, structure, organelles, interactions with their environment, life cycle, division, and death.
• It investigates cells at both the microscopic and molecular level.

Cell Theory

• The cell theory is a foundational principle in biology, stating:
  • 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 Types

• Prokaryotic cells: Lack a nucleus and other membrane-bound organelles; include bacteria and archaea.
• Eukaryotic cells: Possess a nucleus and other membrane-bound organelles; include protists, fungi, plants, and animals.

Cell Structures and Functions

• Plasma Membrane: The outer boundary of the cell, a selectively permeable barrier that regulates the passage of substances in and out of the cell.
• Cytoplasm: The region between the plasma membrane and the nucleus, consisting of the cytosol (fluid) and organelles.

Organelles in Eukaryotic Cells

• Nucleus: Contains the cell's genetic material (DNA) and controls the cell's activities.
• Nuclear envelope: A double membrane that surrounds the nucleus.
• Nucleolus: Site of ribosome synthesis.
• Ribosomes: Synthesize proteins.
• Free ribosomes: Suspended in the cytosol.
• Bound ribosomes: Attached to the endoplasmic reticulum or nuclear envelope.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis.
• Rough ER: Studded with ribosomes; involved in protein synthesis and modification.
• Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
• Lysosomes: Contain enzymes that digest cellular waste and debris.
• Mitochondria: Site of cellular respiration, generating ATP (energy).
• Has a double membrane structure: inner and outer membranes.
• Chloroplasts (in plant cells): Site of photosynthesis, converting light energy into chemical energy.
• Vacuoles: Storage compartments for water, nutrients, and waste.
• Cytoskeleton: A network of protein fibers that provides structural support and facilitates cell movement.
• Microtubules: Involved in cell division, intracellular transport, and cell shape.
• Intermediate filaments: Provide structural support and stability.
• Microfilaments: Involved in cell movement, muscle contraction, and cell shape.

Cell Membrane

• Phospholipid Bilayer: The basic structure of the cell membrane, consisting of two layers of phospholipid molecules.
• Hydrophilic heads: The phosphate-containing region of the phospholipid molecule, which faces outward towards the aqueous environment.
• Hydrophobic tails: The fatty acid region of the phospholipid molecule, which faces inward away from the aqueous environment.
• Membrane Proteins: Embedded within the phospholipid bilayer, performing various functions.
• Transport proteins: Facilitate the movement of substances across the membrane.
• Receptor proteins: Bind to signaling molecules and initiate cellular responses.
• Enzymes: Catalyze chemical reactions at the cell surface.
• Anchors: Connect the cell membrane with other cells

Membrane Transport

• Passive Transport: Movement of substances across the membrane without the use of energy.
• Diffusion: Movement of molecules from an area of high concentration to an area of low concentration.
• Osmosis: Diffusion of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.
• Facilitated diffusion: Movement of molecules across the membrane with the assistance of transport proteins.
• Active Transport: Movement of substances across the membrane with the use of energy (ATP).
• Requires transport proteins to move substances against their concentration gradients.

Cell Communication

• Cells communicate with each other through chemical signals.
• These signals can be local or long-distance.
• Types of cell signaling:
• Direct contact: Communication through cell junctions.
• Paracrine signaling: Local signaling where cells release signals that affect nearby cells.
• Endocrine signaling: Long-distance signaling where hormones are released into the bloodstream and travel to target cells throughout the body.
• Signal transduction: The process by which a cell converts an extracellular signal into an intracellular response.
• Reception: The binding of a signaling molecule to a receptor protein on the cell surface or inside the cell.
• Transduction: A series of steps that convert the signal into a form that can bring about a cellular response.
• Response: A specific cellular activity that is triggered by the signal.

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA (replication) to produce two daughter cells.
• Consists of two major phases:
• Interphase: The period of cell growth and DNA replication, divided into G1, S, and G2 phases.
• G1 phase: Cell growth and preparation for DNA replication.
• S phase: DNA replication.
• G2 phase: Further cell growth and preparation for cell division.
• Mitotic phase (M phase): The period of cell division, consisting of mitosis and cytokinesis.
• Mitosis: Division of the nucleus, resulting in two identical daughter nuclei.
• Cytokinesis: Division of the cytoplasm, resulting in two separate daughter cells.

Cell Division

• Mitosis: Produces two genetically identical daughter cells; used for growth, repair, and asexual reproduction.
• Meiosis: Produces four genetically different daughter cells; used for sexual reproduction.
• Stages of Mitosis:
• Prophase: Chromosomes condense and become visible; the nuclear envelope breaks down; the mitotic spindle forms.
• Metaphase: Chromosomes line up along the metaphase plate.
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: Chromosomes arrive at opposite poles; the nuclear envelope reforms; chromosomes decondense.

Cancer

• Cancer is a disease characterized by uncontrolled cell growth and division.
• It can result from mutations in genes that regulate the cell cycle.
• Cancer cells can metastasize, spreading to other parts of the body and forming new tumors.