BIOLOGY 1

• Cell first observed


  1665
• Cell


  Individual compartments observed by Robert Hooke in a cork slice using a primitive compound microscope
• Robert Hooke, an English scientist, discovered a honeycomb-like structure in a cork slice using a primitive compound microscope
• Hooke only saw the cell wall as this was dead tissue
• Hooke coined the term "cell" for these individual compartments he saw
• 1670 - First living cells seen

  Anton van Leeuwenhoek, a Dutch biologist, looks at pond water with a microscope he made lenses for
• 1683 - Miniature animals

  
  

  Anton van Leeuwenhoek made several more discoveries on a microscopic level, eventually publishing a letter to the Royal Society in which he included detailed drawings of what he saw. Among these were the first protozoa and bacteria discovered.
• 1833 - The center of the cell seen

  
  

  Robert Brown, an English botanist, discovered the nucleus in plant cells.
• 1838 - Basic building blocks

  Matthias Jakob Schleiden, a German botanist, proposes that all plant tissues are composed of cells, and that cells are the basic building blocks of all plants. This statement was the first generalized statement about cells.
• 1839 - Cell theory

  Theodor Schwann, a German botanist, reached the conclusion that not only plants, but animal tissue as well is composed of cells. This ended debates that plants and animals were fundamentally different in structure.
• Schwann also pulled together and organized previous statement on cells into one theory, which states:

  1. Cells are organisms and all organisms consist of one or more cells
  2. The cell is the basic unit of structure for all organisms.
• 1840 - Albrecht von Roelliker discovers that sperm and eggs are also cells
• 1845 - Carl Heinrich Braun reworks the cell theory, calling cells the basic unit of life.
• 1855 - Rudolf Virchow, a German physiologist, physician, pathologist, added the 3rd part to the cell theory. The original Greek, and states "Omnis cellula e cellula" which translates that all cells develop only from existing cells. Virchow was also the first to propose that diseased cells come from healthy cells.
• Cells are the basic unit of structure and function of all living things. There are two major divisions into which all cells fall: the prokaryotic and eukaryotic.
• Prokaryotic cells are cells that lack a nucleus and membrane-bound organelles. Bacteria and related microorganisms are prokaryotes.
• Eukaryotic cells are cells that contain a nucleus and membrane-bound organelles. Organisms such as plants, animals, fungi, and protist are all eukaryotes.
• Cell wall - protection, structural support and maintenance of cell shape
• Plasma Membrane - Separates cell from external environment, controls passage of organic molecules, ions, water, oxygen, and wastes into and out of the cell
• Cytoplasm - Provides structure to the cell; site of many metabolic reactions; medium in which organelles are found
• Nucleoid - location of DNA
• Ribosomes - protein synthesis
• Cytoskeleton - Maintains cell's shape, secures organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently.
• Flagella/pili - cellular locomotion (some)
• For bacterial and archaeal species, the cell membrane encloses a single compartment - meaning the cell has few or no subdivisions delimited by internal membranes. The cell membrane is also called the plasma membrane, which consist of phospholipid bilayers and membrane proteins. Virtually, all bacteria and archaea also have cell wall that surrounds the cell membrane.
• Gram-positive bacteria

  • cell wall consist of several layers of peptidoglycan
  • retain the purple crystal violet dye when subjected to the Gram-staining procedure
• Gram-negative bacteria

  • cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane
  • do not retain the crystal violet dye
• Chromosomes are structures that consist DNA complexed with specific proteins. Prokaryotic chromosomes are found in a localized area of the cell but are not separated from the rest of the cytoplasm by a membrane. By far, the most extensive internal membranes observed in prokaryotes are found in photosynthetic species.
• Nucleoid - circular, double-stranded piece of DNA, not surrounded by a nuclear membrane

  Plasmid - small circular, independent double-stranded DNA molecule. Plasmid can frequently be transmitted from one bacterium to another.
• Plasmid DNA

  • a small, circular double-stranded DNA molecule that is distinct from a cell's chromosomal DNA
  • not considered as genomic DNA as it is a form of extra chromosomal DNA
  • naturally occurs only in prokaryotes
  • can be 1-200 kilo base pairs
  • circular
  • number of a particular type of DNA vary from 1 to thousand per cell
• Chromosomal DNA

  • a molecule that carries the genetic information in all cellular forms of life
  • a type of genomic DNA
  • occurs in both eukaryotic and prokaryotic cells
  • typically larger than plasmid DNA
  • circular
  • number of copies of a particular chromosome per cell is determined based on the species
• Eukaryotic cells range from 10 to 100um in diameter while prokaryotic cells vary from about 1 to approximately 10um in diameter. A second point is that eukaryotic cells contain numerous internal membranes. The membrane-bound compartments found in eukaryotic cells are called organelle. In effect, eukaryotic cells are compartmentalized.
• Why is it important?

  • Compartmentalization allows incompatible chemical reactions to be separated.
  • Groups of enzymes that work together can be clustered on internal membranes instead of floating free in cytoplasm.
  • Because organelles are membrane-bound containers, they are able to maintain high concentrations of molecules that are needed for specific chemical reactions. As a result, the reactions proceed efficiently
  • Compartmentalization makes large size possible.
• Nucleolus

  • Located inside nucleus and disappears when cell divides
  • Makes ribosomes that makes proteins
• Nuclear envelope - double membrane surrounding nucleus and contains nuclear pore
• Nuclear pore - Where materials enter and leave the nucleus
• Chromatin - DNA is spread out and appears as Chromatin in non-dividing cells
• Rough Endoplasmic Reticulum (RER)

  • Has ribosomes on its surface
  • Proteins are made by ribosomes on ER surface
  • They are then threaded into the interior of the Rough ER to be modified and transported
• Smooth Endoplasmic Reticulum (SER)

  • makes membrane lipids (steroids)
  • regulates calcium (muscle cells)
  • destroys toxic substances (liver)
• Ribosomes

  • made of proteins and ribosomal ribonucleic acid (rRNA)
  • "protein factories" for cell
  • join amino acids to make proteins through protein synthesis