Cell Biology Overview

The Cell: Basic Unit of Life

• A cell is the fundamental building block of all living organisms.
• It's a self-contained unit with a membrane-bound cytoplasm and many essential biomolecules.
• Cells are categorized as either prokaryotic (lacking a nucleus) or eukaryotic (possessing a nucleus).
• The study of cells is known as cell biology.

History of Cell Research

• In 1595, Zacharias Jensen invented the first compound microscope.
• Robert Hooke, in 1655, using a compound microscope, observed cells in cork and living plant tissue, coining the term "cell" from the Latin "cella," meaning "small room."
• In 1656, Antonie van Leeuwenhoek, a self-taught lens maker, crafted microscopes and drew protozoa from rainwater and bacteria from his own mouth.
• Theodor Schwann and Matthias Schleiden, in 1839, determined that plants and animals are composed of cells, laying the foundation for the cell theory. This concept established the cell as the fundamental unit of structure and development in all living organisms.
• Rudolf Virchow, in 1855, articulated the principle that new cells arise from pre-existing cells through division, summarized as "omnis cellula ex cellula."
• In 1859, Louis Pasteur refuted the idea of spontaneous generation, demonstrating that life only emerges from existing life.
• In 1931, Ernst Ruska constructed the first transmission electron microscope (TEM) at the University of Berlin. By 1935, he had developed an EM with twice the resolution of a light microscope, enabling the visualization of previously unobserved cell organelles.
• The double helix structure of DNA was unveiled by Watson and Crick in 1953.
• Lynn Margulis, in 1981, published "Symbiosis in Cell Evolution," outlining the endosymbiotic theory explaining the origin of eukaryotic organelles like mitochondria and chloroplasts.

Cell Theory: Key Principles

• All living organisms are composed of one or more cells.
• The cell is the fundamental unit of structure and organization in organisms.
• Cells originate from pre-existing cells.
• Energy flow occurs within cells.
• Hereditary information (DNA) is transmitted from cell to cell.
• All cells share a basic chemical composition.

Chemical Composition of Cells

• Out of 90 naturally occurring elements on Earth, only 12 are found in living organisms in significant amounts (greater than 0.01%).
• The four most abundant elements in the human body are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), which constitute 96.3% of its weight.
• Carbon is the backbone of organic molecules found in living organisms.
• Carbon atoms can form up to four covalent bonds, enabling them to create diverse molecular structures like straight chains, branches, or rings.
• Organic chemistry focuses on the study of carbon and its compounds.

Macromolecules: Building Blocks of Life

• Macromolecules are large molecules formed by linking together smaller, repeating subunits called monomers.
• The four primary classes of macromolecules in cells are carbohydrates, nucleic acids, proteins, and lipids.
• Carbohydrates, nucleic acids, and proteins are polymers, while lipids are not.

Carbohydrates: Energy Source and Structure

• Carbohydrates are composed of carbon, hydrogen, and oxygen in a 1:2:1 molar ratio.
• They contain numerous carbon-hydrogen bonds, which release energy upon oxidation, making carbohydrates suitable for energy storage.
• Monosaccharides are the simplest carbohydrates and serve as building blocks for larger molecules.
• Disaccharides, formed by linking two monosaccharides, play roles in sugar transport in plants and nutrition in animals.

Nucleic Acids: The Blueprint of Life

• Nucleic acids carry genetic information.
• The two primary types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• DNA stores genetic information and is responsible for transmitting hereditary traits.
• RNA plays a role in protein synthesis.

Proteins: Diverse Functions

• Proteins are complex molecules composed of amino acid chains.
• They perform a wide range of functions, including structural support, catalysis, transport, signaling, and defense.

Lipids: Diverse Roles

• Lipids are a diverse group of molecules characterized by their insolubility in water.
• They include fats, oils, waxes, and steroids.
• Lipids serve important functions, including energy storage, insulation, membrane structure, and hormone synthesis.

Prokaryotic Cells: Simple Yet Diverse

• Prokaryotes are single-celled organisms lacking a nucleus and other membrane-bound organelles.
• They are typically smaller than eukaryotic cells.
• Prokaryotic cells have a cell wall, a plasma membrane, DNA, and ribosomes.
• They are divided into two domains: Bacteria and Archaea.

Bacteria: Ancient and Abundant

• Bacteria are ubiquitous and play crucial roles in ecosystems.
• They are diverse in morphology (shapes), metabolism, and habitat.
• Some bacteria are beneficial, while others are pathogenic, causing disease.

Archaea: Extremotolerant and Evolutionarily Distinct

• Archaea are single-celled prokaryotes initially classified as bacteria.
• However, they possess distinct genetic and metabolic characteristics, more closely related to eukaryotes.
• Archaea thrive in extreme environments, such as hot springs, salt lakes, and deep-sea vents.

Medically Important Prokaryotes: Pathogenic Bacteria

• Pathogenic bacteria are capable of causing infection.
• Examples of medically important bacteria include:
  • Mycobacterium tuberculosis: Causes tuberculosis, a respiratory disease.
  • Staphylococcus aureus: A common cause of skin infections, respiratory infections, and food poisoning.
  • Streptococcus pneumoniae: A major cause of pneumonia.
  • Salmonella sp.: Causes typhoid fever, paratyphoid fever, and food poisoning.
  • Clostridium tetani: Produces tetanospasmin, the toxin responsible for tetanus.
  • Treponema pallidum: The bacterium responsible for syphilis.

Treatment of Bacterial Infections

• Antibiotics are used to treat bacterial infections.
• Antibiotics can be bacteriocidal (kill bacteria) or bacteriostatic (inhibit bacterial growth).
• Penicillin, discovered by Alexander Fleming in 1928, was the first antibiotic.
• Overuse of antibiotics has led to widespread antibiotic resistance in bacteria.
• Antibiotics are ineffective against viral infections.

Symbiotic Bacteria in the Gut: The Microbiome

• The human gut harbors a vast population of bacteria, collectively known as the gut microbiome.
• Gut bacteria play essential roles in vitamin synthesis, metabolism of dietary components, and protection against pathogens.
• Dysregulation of the gut microbiome is associated with various inflammatory and autoimmune conditions.

Key Symbiotic Gut Bacteria:

• Escherichia coli: A beneficial bacterium that produces vitamin K, natural antibiotics, and assists in food decomposition. It's also a widely used model organism in research.
• Lactobacillus: A bacterium that converts lactose and other sugars into lactic acid.

Explore the fundamental concepts of cell biology, including the basic unit of life and the historical milestones in cell research. Learn about prokaryotic and eukaryotic cells, as well as key figures like Robert Hooke and Antonie van Leeuwenhoek. This quiz will enhance your understanding of the cell's significance in biology.