Cell Evolution

Major Cell Type

Eukaryotes - Eukaryotes (have a nucleus and

membrane-bounded organelles)

Archaea - prokaryotes, no nucleus

Bacteria - prokaryotes, no nucleus, most diverse and widespread prokaryotes

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3 major domains - eukarya, archaea, bacteria all derived from a common ancestor

phylogenies show evolutionary relationships

What was needed for the first life to form?

First unicellular organism - 3.5BYA

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Organic (macro)molecules

* nucleic acids
* proteins
* lipids
* Polysaccharides

Self replication

* RNA

Enclosed spaces (protocells)

Approaches to classify organisms

Molecular approaches to define the different types of life

The more related an organism the more similar their DNA

Based on genetics: ribosomal RNA and other genes AND morphology

Prokaryotes

* Mostly single celled (cocci, bacilli, spirilla)
* Size 1-5 micrometre
* Can aggregate to form colonies
* DNA is circular in chromosomes and plasmids
* Can be motile - flagella
* Peptidoglycan in cell wall 
* no nucleaus or membrane bound organelles

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Features

* Binary fission - reproduction
* Fimbriae - attachment
* Capsule - protection, adherence
* Flagella - motility 
* Ubiquitous - everywhere
* If removed by antibiotic treatment, pathogens may fill the empty niche

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* Most bacterial species can’t cause disease 
* Many are beneficial (antibiotics and food production, e.g. Streptomyces, Lactobacillus)
* Free-living soil bacteria and cyanobacteria perform many essential functions in the biosphere, (e.g. Rhizobium and nitrogen fixation)

Bacterial Cell Walls

**Gram positive** 

* Retains violet dye - purple
* Peptidoglycan layer on outside

**Gram negative**

* Dye washes out - pink
* Peptidoglycan layer on inside

DNA transfer in bacteria

Circular DNA free floating forming the nucleoid region

Small genomes

Contain Plasmids: multiple small circular DNA fragments

Plasmids: extra, useful genes, e.g. encoding antibiotic resistance

Archea

* Small size
* Rapid reproduction
* Mutations
* Diverse adaptation
* Rapid evolution

Bacteria Vs Archea

Membrane lipids with branched hydrocarbons

Cell wall - NOT peptidoglycan

Grow at extreme temperatures

Extremophiles

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* High salt 
* Extreme temperatures - hot or cold
* Extreme acidity 
* Methanogens

Eukaryotes

* Nucleus - DNA enclosed in a membrane
* Membrane bound organelles
* Commonly classified into 4 kingdoms: protists, animalia, fungi and plantae
* Single celled or multi celled
* Autotrophic: contain chloroplasts 
* Heterotrophic: no chloroplasts 

Domain Eukarya

**SAR** 

*Stramenopila* 

* Large, extremely diverse lineag
* Grouping based on whole genome sequencing

*Alveolata* 

* Membrane-lined sacs regulate diffusion across plasma membrane 
* Red tides (carotenoids), bioluminescence 
* Parasites

*Rhizaria* 

* Many species are amoebas 
* Move and feed by pseudopodia

*Excavata*

* Diverse, often groove on bodies
* Often modified/reduced mitochondria (dysfunctional)
* Parasitic, predatory and photosynthetic species

Endosymbiosis