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    Primitive life photos Primitive life photos Presentation Transcript

    • Lecture 6b: ‘Primitive’ Lifeforms
    • By far, most living organisms
      • 4 groups:
        • Viruses
        • Viroids and Prions
        • Prokaryotes
        • Protists
    • Viruses
      • Do not have a cell
      • Obligate intercellular parasites: they can not reproduce outside of a cell
      • Do have DNA/ RNA
      • Tend to be host specific to some degree
        • Only attach to specific cells
    •  
    • Viruses
      • Reproduce by taking over machinery of the host cell and using it to their own ends
      • Some viruses are specific to bacteria, plants, or animals, and reproduce in slightly different ways
        • Sometimes there are periods in which the virus is latent- not reproducing
    • Viruses
      • Retroviruses: have RNA instead of DNA inside, make DNA by integrating with host genome
        • Ex. HIV
    • Viruses
      • Examples of human diseases caused by viruses
        • Flu
        • SARS
        • West Nile
        • HIV/ AIDS
        • Ebola
      • Viruses can travel around the world on an airplane, leading to their quick and easy spread
    • Viroids and Prions
      • Even more weird than viruses!
      • Viroids are just naked strands of DNA
        • Several crop diseases
      • Prions are misshapen proteins, the mechanism of damage is not known
        • Ex: mad cow, Creutzfeldt-Jacob disease, scrapie
    • Prokaryotes
      • Two main groups to discuss: Bacteria and the Archaea
      • Have no membrane- bound organelles
      • Oldest prokaryote fossils are 3.5 billion years old
      • Origin of life?- Endosymbiotic theory
    •  
    • Bacteria
      • Millions of bacteria exist everywhere!
      • We do not know all the different types of bacteria that exist today
      • They are in your intestine and on your skin, on the table, in the soil, etc. etc.
    • Bacteria
      • Come in several shapes, most basic are sphere, rod, and spiral
      • DNA is in single closed circle chromosome, plus sometimes also plasmids
      • Can have flagella to move around
      • Reproduce asexually- called binary fission
        • Not mitosis because no spindle fibers
    •  
    • Bacteria
      • Can not recombine genes using sex, but have different ways of sharing DNA
      • Conjugation - one cell donates DNA to another directly
      • Transformation - one bacterium picks up DNA that is floating around in environment
      • Transduction - bacterial viruses carry DNA from one bacterium to another
    • Bacteria
      • Some bacteria are able to form endospores, in which the chromosome and some cytoplasm dehydrate and are encased in a protective coat
      • Enables them to survive very harsh conditions: extreme heat or dryness, extreme cold, UV radiation
        • Ex. botulism
    • Bacteria
      • Can be autotrophs or heterotrophs
        • Autotrophs- produce own food
          • Photoautotrophs use photosynthesis
          • Chemoautotrophs use a source other than the sun for electrons- S compounds, for example
        • Heterotrophs- eat something else
          • Chemoheterotrophs take in organic nutrients as food, break down large molecules into smaller ones that are absorbable
          • Bacteria in our intestines are this type
    • Bacteria
      • Important to our everyday life:
        • They fix atmospheric N and make it available for plants to use
        • Decompose dead organisms into usable organic materials
        • Can be used to clean polluted areas
        • Used to make cheese, pickles, etc.
        • Can be engineered to make useful molecules, like insulin
    • Bacteria
      • Also cause human diseases
      • Some leave behind toxins when they die-
        • Ex. tetanus toxin prevents relaxation of muscles
      • Some bind to other cells
        • Ex. Shigella dysentaeriae binds to intestinal wall, results in severe diarrhea
      • Some invade organs or cells
        • Ex. Salmonella, may only result in food poisoning, but sometimes can invade the body and cause typhoid
    • Archaea
      • Archaea and eukaryotes probably share a common ancestor, because tRNA, ribosomal proteins, and other characteristics are shared between them but not bacteria
    • Archaea
      • Many found in extreme environments
      • Methanogens- produce methane in the production of their ATP- live in intestines and swamps
      • Halophiles- found in high saline environments, such as Great Salt Lake
      • Thermoacidophiles- found in HOT and acidic environments, such as hot springs, geysers, volcanos
    • Protists
      • Eukaryotic
      • Very diverse
      • Endosymbiotic theory: Eukaryotes arose when bacterial cells lived in close association with a proto-eukaryote that had a nucleus and ER- the bacterial cells became absorbed into the eukaryote and became what we know as mitochondria and chloroplasts
    • Protists
      • So diverse, we don’t have a good classification system yet
      • Book, and therefore we, divide them by modes of nutrition:
        • Algae, protozoans, slime molds and water molds
    • Protists- algae
      • Aquatic photosynthesizers
      • Phytoplankton in oceans provide base of food web
      • Some Oceanic algae form seaweeds
      • Can be symbiotic- corals, lichen
    •  
    • Protists- protozoans
      • Unicellular, but complex
      • Are heterotrophic, many feed by engulfing food particles
      • Usually able to move using cilia, flagella, or pseudopods
    • Protists- protozoans
      • Human diseases caused by protozoans:
        • Amoebic dysentery (Entamoeba)
        • African sleeping sickness (trypanosome)
        • Girardia
        • Malaria (Plasmodium)
        • Toxoplasmosis (carried by cats)
    •  
    •  
    • Protists- slime molds
      • Help decompose dead plant material in forests
        • They are many cells fused together to form a plasmodium with many nuclei
        • Can actually move slowly along
    • Protists- water molds
      • Decomposers, but also are parasites
        • Potato blight
        • Have a cell wall similar to plant cell walls
    • Potato blight- a water mold Slime molds