Upload
kwiley0019
View
634
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Citation preview
Lecture 6b: ‘Primitive’ Lifeforms
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
VirusesReproduce 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
BacteriaCan 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
BacteriaCan 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
BacteriaImportant 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
BacteriaAlso 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
ArchaeaMany 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
ProtistsEukaryotic
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- protozoansHuman 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