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