There are four main groups of primitive lifeforms: viruses, viroids and prions, prokaryotes, and protists. Viruses are obligate parasites that reproduce by taking over a host cell's machinery. Prokaryotes include bacteria and archaea, which were some of the earliest lifeforms and lack membrane-bound organelles. Protists are a diverse group of eukaryotic organisms that include algae, protozoans, slime molds, and water molds.

1. Lecture 6b: ‘Primitive’ Lifeforms

2. By far, most living organisms 4 groups: Viruses Viroids and Prions Prokaryotes Protists

3. 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

5. 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

6. Viruses Retroviruses: have RNA instead of DNA inside, make DNA by integrating with host genome Ex. HIV

7. 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

8. 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

9. 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

11. 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.

12. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. Archaea Archaea and eukaryotes probably share a common ancestor, because tRNA, ribosomal proteins, and other characteristics are shared between them but not bacteria

20. 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

21. 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

22. 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

23. Protists- algae Aquatic photosynthesizers Phytoplankton in oceans provide base of food web Some Oceanic algae form seaweeds Can be symbiotic- corals, lichen

25. Protists- protozoans Unicellular, but complex Are heterotrophic, many feed by engulfing food particles Usually able to move using cilia, flagella, or pseudopods

26. Protists- protozoans Human diseases caused by protozoans: Amoebic dysentery (Entamoeba) African sleeping sickness (trypanosome) Girardia Malaria (Plasmodium) Toxoplasmosis (carried by cats)

29. 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

30. Protists- water molds Decomposers, but also are parasites Potato blight Have a cell wall similar to plant cell walls

31. Potato blight- a water mold Slime molds