Biology 1020 lecture 6 Cell Structure 1

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  1. Cells
    • Basic structural and functional unit of every organism.
    • First observed by Hooke and Leeuwenhoek in the late 1600s with the first microscopes
  2. Chemical components of cells
    • 70% water
    • 15% Protein
  3. All cells have to...
    • Separated from external enviroment. a.k.a, plasma membrane
    • Undergo chemical reactions in aqueous environment ---> Semi-fluid substance called cytosol
    • Make proteins --> ribosomes
    • Trasmit genetic materials --> chromosomes
    • Acquire nutrients and expel wastes
  4. Plasma Membrane
    Selective barrier: allows passage of some materials (oxygen, nutrients, and waste) and blocks others

    General structure- a double layer of phospholipids

    Hydrophilic region - outside of the cell and inside of the cell.

    Hydrophobic region in between the two hydrophilic regions
  5. Cells exist in a narrow size window
    • Cells: 1 - 100 micrometres
    • Organelles: ~1 micrometre
  6. Cell Size: Why so narrow a size range?
    • Large enough for all things needed for life and reproduction.
    • - Enzymes, DNA, etc.
    • => This sets lower size limit

    • Small enough so that that the plasma membrane area allows for nourishment of needed materials in, and wastes out.
    • => This sets the upper size limit

    Small cell - large surface area relative to volume
  7. Prokaryotic cells
    • 1-5 micrometers.
    • Much smaller than eukaryotic cells
  8. The first cells on earth were prokaryotic
    • Small, did not use oxygen in metabolism
    • 3.5 billion YBP
    • - Layered rock containing fossilized prokaryotes - stromatolites
    • First life - 3.9 billion YBP
  9. What was it like on early Earth?
    Lightning, volcanic activity

    • Atmosphere
    • -water vapor which condensed to form oceans
    • - nitrogen, CO2, methane, NH3, H2 and hydrogen sulfide from volcanic eruptions
  10. Formation of first cells
    Membrane requires organic macromolecules
  11. Hypothesized stages in the formation of the first cells
    • 1. Non- living sythesis of small organic molecules. ex. amino acids, phospholipids
    • 2. Polymerization into macromolecules. Ex. amino acids --> proteins
    • 3. Enclose macromolecules within membranes
    •     * internal chemistry different from surroundings
    • 4. Origin of self replicating molecules --> RNA world
  12. Abiotic sythesis of organic molecules:
    Miller's (1953) experiments
    • Attempt to recreate the "primitive soup"of early Earth
    • Flask with H2, CH4, NH3
    • Electricity, condensation
    • Amino acids formed after a week
  13. Evidence for abiotic membrane formation
    • Phospholipids that make up cell membranes self assemble in aqueous environments
    • - Forms a lipid bi-layer

    • PROTOCELLS - Abiotically created molecules within a membrane; created by adding lipid to water
    • * Swell and shrink, "give birth" to daughters
    • * Simple metabolic reactions ocur within if reactants and enzymes included
  14. Evidence for RNA as the first self replicating molecules: ribozymes
    • Some RNAs (ribozymes) can carry out enzyme like catalytic functions
    • * Can make complimentary segments of RNA if nucleotides are present

    Selection for RNA molecules that were more stable or replicated more quickly
  15. Metabolism of the first cells?
    • Low oxygen levels, oxygen not used in metabolism
    • ATP generated without oxygen - another molecule (ex. sulfate)
  16. Photosythesis by Early Prokaryotes
    • Produced oxygen as a byproduct
    • Oxygen accumalated: Oxygen revolution
    • Extinction of groups that could not tolerate oxygen
  17. Oxygen Revolution
    • Some prokaryotes survived and adapted using cellular respiration (using oxygen) to harvest energy
    • * produces more ATP
  18. Prokaryotic cell structure
    • No membrane-bound organelles within the cell
    • DNA in an unbound region called the nucleoid
    • Move with a flagella
    • They attach to surfaces with fimbriae and/or the capsule
    • Protected against dehydration by the capsule (jelly like outer coating)
    • Rigid cell wall maintains shape and protects cell. Consists of peptidoglycan.
    • Plasma membrane encloses cytoplasm
    • Infoldings of plasma membranes in some
  19. Peptidoglycan
    Polymer of sugars crossed linked by peptides
  20. Prokaryotes exist in communities
  21. Prokaryotes grow quickly
    • Adapt to changing conditions quickly
    • low levels of nutrients
    • beneficial mutations
  22. Eukaryotic Cells
    Unicellular eukaryotes (protists) appeared first after prokaryotes.
  23. Structure of Eukaryotic Cells
    • Internal membranes partition the cell into organells.
    • Cytoplasm: materials inside the cell membrane excluding nucleus (cytosol is the jelly-like portion of the cytoplasm)
  24. Nucleus
    • Contains the genes (DNA) ~5 μm in diameter
    • Enclosed by double membrane - nuclear envelope
    • Shape maintained by a network of proteins of the inside face - nuclear lamia
    • Material (eg. proteins, RNA) enters and leaves through nuclear pores
    • DNA (in chromosomes) is bundled with proteins in a compact form - chromatin
    • Ribosomal RNA, rRNA, and proteins form dense granules adjoining chromatin - Nucleolus/nucleoli
    • Proteins imported into nucleus and added to rRNA to make RIBOSOMES
  25. Some red blood lack a ...
    Nucleus. They can carry more hemoglobin that way.
  26. Ribosomes
    • Free -->
    • - Suspended in the cytosol
    • - Making cytosolic proteins (glycolysis enzymes)

    • Bound -->
    • - Attached to endoplasmic or nuclear envelope
    • - Make proteins for secretion or for membranes
Card Set:
Biology 1020 lecture 6 Cell Structure 1
2013-10-04 05:42:01
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