Unit 3

• Cell


  • The fundamental unit of life
  • The basic unit of any living organism
  • Exhibits the basic characteristics of life
  • Obtain food to produce energy for metabolism
  • Grow and reproduce
  • Respond to stimuli
  • Can mutate as a result of accidental changes in genetic material (DNA)
• Etymology of cell


  • Latin word 'cella' meaning small chamber
  • Greek word 'kytos' meaning vessel
  • Coined by its discoverer Robert Hooke in 1665
• Cytology


  The study of the structure and function of cells
• Cell theory


  All living things are composed of cell and all cells come from other cells
• Rene Dutrochet (1776-1847) proposed that the cell is the fundamental element in the structure of living bodies, forming both animals and plants
• Matthias Jakob Schleiden (1804-1881) proposed that plants are made up of cells
• Theodor Schwann (1821-1902) proposed that animals are made up of cells
• Rudolf Virchow (1821-1902), the father of Pathology, proposed that every cell comes from a pre-existing cell
• Robert Remak (1815-1865) first published the idea that all cells come from other cells in 1852, which Virchow later popularized
• Historical developments


  • Ancient Greeks proposed miasma theory
  • Fracastoro (1546) began early version of germ theory
  • Robert Hooke (1665) observed cork cells under microscope
  • Anton van Leeuwenhoek (1674) observed single celled microorganisms
  • Semmelweiss (1847) demonstrated that hand washing reduces puerperal infections
  • Snow (1854) demonstrated that cholera bacteria were transmitted in contaminated drinking water
  • Louis Pasteur (1856) discovered microbial fermentation
  • Louis Pasteur (1862) disproved spontaneous generation
  • Lister (1867) began using carbolic acid as a disinfectant during surgery
  • Koch (1876-1906) determined causative agents for many bacterial infections
• Germ theory


  • Specific microorganisms are the cause of specific diseases
  • Revolutionized the theory and practice of medicine and the understanding of disease
  • Focused on the reduction of diseases to simple interaction between microorganism and host
• Eukaryotic cell


  • With TRUE nucleus (membrane-bound)
  • DNA is enclosed by a nuclear membrane
  • About 10 times larger than a prokaryotic cell
• Endosymbiotic theory


  • Organelles in eukaryotic organisms were once prokaryotes that survived within them and developed a symbiotic relationship
  • Proposed by Lynn Margulis in 1967
• Endosymbiotic theory


  1. Infoldings in the plasma membrane of an ancestral cell gave rise to endomembrane components, including a nucleus and endoplasmic reticulum

  2. In the first endosymbiotic event, the ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria

  3. In a second endosymbiotic event, the early eukaryote consumed photosynthetic bacteria that evolved into chloroplasts
• Major components of the eukaryotic cell

  • Plasma membrane
  • Cytoplasm
  • Nucleus
• Plasma membrane


  • Membrane at the boundary of every cell
  • Acts as a selective barrier
  • Regulates the cell's chemical composition
  • Fluid-Mosaic Model composed of phospholipids and Proteins with hydrophilic, hydrophobic, and amphiphilic regions
  • Movement of materials could be via diffusion, osmosis, endocytosis and exocytosis
• Membrane transport mechanisms


  • Diffusion (passive and facilitated)
  • Active transport
  • Endocytosis (phagocytosis, pinocytosis, receptor-mediated)
  • Exocytosis
• Diffusion


  Passive movement of molecules from higher concentration to lower concentration following the concentration gradient
• Facilitated diffusion


  Movement of molecules and other large materials across the membrane with the help of carriers or channels
• Active transport


  Movement of molecules across the cell membrane against the concentration gradient, requires Adenosine Triphosphate (ATP)
• Endocytosis


  Uptake of matter through plasma membrane invagination and vacuole/vesicle formation (phagocytosis, pinocytosis, receptor-mediated)
• Exocytosis


  Process by which secretory vesicles empty or release their contents to the cell's exterior
• Cytoplasm


  Semi-fluid or gelatinous substance of a cell containing the cytoplasmic components, external to the nuclear membrane and internal to the cell membrane, site of many cell activities
• Nucleus


  Chromosome-containing organelle, involved in information processing and administration of the cell, contains the nucleolus, serves an essential role in reproduction and heredity, bound by the nuclear membrane/envelope with pores, its shape is determined by the nuclear lamina
• Karyokinesis


  Nuclear division, part of the M phase of the cell cycle
• Eukaryotic cell cycle


  An ordered and regulated series of events involving cell growth, replication, and division
• Cellular organelles


  • Ribosome
  • Golgi apparatus
  • Endoplasmic reticulum
  • Mitochondrion
  • Lysosome
  • Peroxisome
  • Cytoskeleton
  • Cell wall
  • Chloroplast
  • Vacuole
• Ribosome


  Responsible for protein synthesis, composed of large and small subunits with RNA template, involved in translation, can be organelle-associated or non-organelle-associated
• Golgi apparatus


  Modifies proteins and lipids built in the ER and prepares them for export or transport, produces glycolipids, glycoproteins or proteoglycans, has cis (receiving) and trans (outgoing) faces
• Endoplasmic reticulum


  Network of flattened sacs and branching tubules that extends throughout the cytoplasm, pipeline between the nucleus and cytoplasm, manufactures, processes, and transports biochemical compounds, consists of smooth ER (without ribosomes) and rough ER (with ribosomes)
• Mitochondrion


  Rod-shaped organelle, powerhouse of the cell, converts oxygen and nutrients into ATP
• Lysosome


  Serves as digestion compartments for materials through autophagy, breaks down cellular waste products, fats, carbohydrates and proteins
• Peroxisome


  Membrane-bound organelle not part of the endomembrane system, produces hydrogen peroxide and the enzyme catalase, plays a role in lipid biosynthesis
• Cytoskeleton


  Made up of microfilaments, intermediate filaments and microtubules, primarily structural in function, an important component of the cytoskeleton, generate forces used in cellular contraction and basic cell movements
• Cell wall


  Distinguishing feature of plant cells, rigid and renders plants sedentary, composed mainly of cellulose
• Chloroplast


  Carry out photosynthesis, ellipsoid-shaped, enclosed in a double membrane with an intermembrane space
• Vacuole


  Membrane-bound sacs within the cytoplasm that store water and other materials
• Prokaryotic cell


  Lacks nucleus (membrane-bound), generally has a single, circular chromosome in the nucleoid, covers organisms under the domains bacteria and archaea
• Prokaryotic cell morphology


  • Cellular shape or form
  • Individual cells of a particular prokaryotic organism are typically similar in morphology or shape
• Cell wall


  Protects the prokaryotic cell from osmotic pressure