CHEM

• Cell


  Smallest unit of living things, made up of molecules
• Robert Hooke


  • British scientist
  • Observed mass of tiny cavities from thin slices of cork with his self-made microscope
  • Named these structures "cells" since they reminded him of small rooms in a monastery
• Anton Van Leeuwenhoek


  • Dutch scientist
  • Made pioneering discoveries concerning protozoa, red blood cells, capillary systems, and the life cycles of insects
  • Perfected the construction of the compound microscope
  • Observed a single bacterium but did not know what it was
  • Discovered protozoans - animal like protist (unicellular) called animalcules
• Robert Brown


  • British botanist
  • Observed plant cells with a distinct central part (nucleus)
  • Described the streaming movement of the cytoplasm (Brownian movement)
• Felix Dujardin


  • French biologist
  • Observed that cells were not empty but filled with thick, jelly-like fluids (protoplasm)/cytoplasm
  • Cytoplasm is the medium of biochemical reactions and mode of transportation of cells
• Matthias Schleiden


  • German botanist
  • Concluded that plants are composed of cells and formulated the plant cell theory
• Theodore Schwann


  • German zoologist
  • Concluded that animals are composed of cells and formulated the animal cell theory
• Rudolf Virchow


  • German pathologist
  • Concluded that all cells must come from pre-existing cells
• Max Knoll and Ernst Ruska

  • German engineers
  • Built the first transmission electron microscope
• James Watson and Francis Crick

  • American biochemist and British biophysicist
  • Discovered the structure of DNA that ushered in the era of molecular biology
• Cell theory


  The observations and conclusions of Schleiden, Schwann and Virchow that established the cell theory
• Principles of the cell theory

  • All organisms are composed of cells
  • Cells are the basic unit of life
  • All cells arise from pre-existing cells
• Eukaryotes


  Complex organisms
• Prokaryotes


  Simple organisms
• Smallest cell is a bacterium known as a mycoplasma, 0.0001 mm in diameter
• Largest cells are the nerve cells in an ostrich and the longest cell in a giraffe's neck, 3.0 m in length
• In humans, the variety of cell sizes ranges from red blood cells that measure 0.00076 mm to the largest cells which are found in egg cells
• Smaller cell


  Has more surface area per volume than a large cell
• Cell shape


  • Long for contraction (muscle cell)
  • Protoplasmic processes for conduction of impulses (nerve cell)
  • Concave disc for distribution of oxygen (blood cell)
  • Ideal shape of an isolated cell is spherical
• Factors affecting variations in cell shape

  • Elasticity or rigidity of the membrane
  • Surface tension
  • Viscosity of the cytoplasm
  • Pressure exerted by neighboring cells
  • Functional adaptation
• Common features of all cells

  • Nucleus (a membrane bound compartment which stores the DNA)
  • Cytoplasm (includes everything except the plasma membrane and nucleus)
  • Plasma membrane (serves as the boundary between cell and the environment)
• Prokaryotic cells


  Cells without a true nucleus, characteristic of bacteria with a size ranging from 1 to 10 µm, outer boundary is composed of cell wall and plasma membrane, cytoplasm contains ribosome, thylakoids and innumerable enzymes, nucleoid contains single chromosome (DNA only)
• Eukaryotic cells


  Cells with true nucleus, characteristic of protists (unicellular), fungi, plants, and animals (multicellular), consists of plasma membrane, cytoplasm, and a distinct nucleus, outer membrane is composed of plasma membrane made up of phospholipid bilayer with embedded proteins, nucleus is a membrane-bounded containing multiple chromatin, cytoplasm contains compartmentalized organelles
• Levels of structural organization

  • Chemical level - tiny building blocks of matter, combine to form molecules
  • Cellular level - smallest units of living things, are made up of molecules
  • Tissue level - tissues consist of similar types of cells that have common function
  • Organ level - organs are made up of different types of tissues that perform specific function for the body
  • Organ system level - organ systems consist of different organs that work together closely to accomplish a common purpose
  • Organismal level - human organisms are made up of many organ systems, the sum total of all structural levels working together to keep us alive

  
• Typical animal cell components

  • Cell membrane
  • Nucleus
  • Endoplasmic reticulum with ribosomes attached
  • Lysosome
  • Mitochondrion
  • Ribosomes
  • Golgi apparatus
• Typical plant cell components

  • Chloroplast
  • Endoplasmic reticulum
  • Cell wall
  • Cell membrane
  • Vacuole
  • Mitochondrion
  • Ribosomes
  • Golgi apparatus
• Prokaryotic cell components


  • DNA
  • Ribosomes
  • Plasma membrane
  • Cell wall
• Organelle functions


  • Nucleus - Location of main genome; site of most DNA and RNA synthesis
  • Mitochondrion - Site of energy-yielding oxidation reactions; has its own DNA
  • Chloroplast - Site of photosynthesis in green plants and algae; has its own DNA
  • Endoplasmic reticulum - Continuous membrane throughout the cell; rough part studded with ribosomes (the site of protein synthesis)
  • Golgi apparatus - Series of flattened membranes; involved in secretion of proteins from cells and in reactions that link sugars to other cellular components
  • Lysosomes - Membrane-enclosed sacs containing hydrolytic enzymes
  • Peroxisomes - Sacs that contain enzymes involved in the metabolism of hydrogen peroxide
  • Cell membrane - Separates the cell contents from the outside world; contents include organelles (held in place by the cytoskeleton) and the cytosol
  • Cell wall - Rigid exterior layer of plant cells
  • Central vacuole - Membrane-enclosed sac (plant cells)
• Water


  The biological medium on Earth, all living organisms require water more than any other substance, most cells are surrounded by water, and cells themselves are about 70-95% water
• Polar covalent bonds in water molecules

  Result in hydrogen bonding, the water molecule is a polar molecule with the two hydrogens having a slightly positive charge and the oxygen having a slightly negative charge

  
• Forces in the universe

  • Repulsive force
  • Attractive force
• Intermolecular forces


  • Covalent bond - involves the sharing of electrons, which can be either equal or unequal due to differences or similarities in electronegativity
  • Polar covalent bond - occurs when there's a significant electronegativity difference between the atoms involved
  • Metallic bond - is like a "sea of electrons" surrounding metal atoms
  • Ionic bond - formed through electron transfer, resulting in one atom donating electrons (positively charged) and the other receiving electrons (negatively charged), leading to electrostatic attraction
• Intramolecular forces


  • Dipole-dipole interaction - the attraction between polar molecules' positive and negative poles
  • Hydrogen bonding - a special case of dipole-dipole interaction, occurs when hydrogen is covalently bonded to highly electronegative atoms like nitrogen (N), oxygen (O), or fluorine (F)
  • London dispersion - the weakest intramolecular forces, involve the temporary creation of dipole-dipole interactions due to momentary fluctuations in electron distribution
  • Ion-dipole interaction - occurs between ionic compounds and polar molecules, where the charged ions are attracted to the polar molecules' dipoles
• Polarity of water molecules

  Oxygen side is slightly negative (2.1) because it is more electronegative than hydrogen, hydrogen side is slightly positive (3.5), this polarity allows water molecules to form hydrogen bonds with each other

  
• Properties of water that contribute to Earth's suitability for life

  • Cohesive behavior: Stickiness!
  • Moderates temperature: Water has a strong resistance to change in temperature
  • Expansion upon freezing: Frozen water floats
  • Water is a common solvent for life
• Cohesion


  The attraction between molecules of the same substance, hydrogen bonds hold water molecules together by cohesion

  
• Adhesion


  An attraction between different substances, for example, between water and tiny tubes (xylem) located in tree trunk
• Surface tension


  A measure of how hard it is to break the surface of a liquid, water has a high surface tension due to the hydrogen bonding between water molecules
• Heat and temperature


  Heat is the amount of kinetic energy associated with the movement of the atoms and molecules in a body of matter, temperature measures the intensity of heat due to the average kinetic energy of molecules
• Water can absorb and store large amounts of heat while only changing a few degrees in temperature