changes in the tree of life concept
- Universal phylogenetic tree based on nucleotide changes within the rRNAsequence present in the small subunit of ribosomes
- Aristotle’s ‘ladder of life’
- Whittaker’s ‘five kingdoms’based on morphology
- Woese’s ‘universal tree of life’ based on rRNAsequences (1990-)
Why is an understanding of the diversity of life important?
- A sense of ‘our place in the scheme of things’…“Where do we come from? What are we? Where are we going?”
- The wonder of our natural environment
- Human subsistence – e.g. crop production
- Human health
- Management of our environment – e.g. ecology, conservation, species invasions, pollution…
What would we like you to be able to do by the end of this course?
- – Genetic mutation
- – Environmental heterogeneity and change (e.g. climate, plate tectonics)
- – Development of more complex structures within organisms (e.g. nuclear membrane, multicellularity, vascular system)
- – Colonisation of novel habitats (e.g. land surfaces)
- – Organism effects on environment (e.g. O2in the atmosphere)
- – Interactions among organisms (e.g. symbioses, pathogenesis, competition for limiting resources)
- – Development of more complex reproductive systems (e.g. diploidy, alternation of generations, sexual reproduction)
What are the characteristics of living organisms?
- Microspheres: simple aggregations of proteins; grow; bud-off; could form sheets (membranes) that enclose organic-rich media
- Organisms can: 1) Grow (and survive?)2) Reproduce3) Pass on characteristics to next generation (heredity)
- All organisms achieve these traits through:
- • Organization based on cells bounded by semi-permeable membranes
- • ATP-based energy currency
- • Chemical machinery for the synthesis and degradation of essential molecules
- • Heredity via nucleic acids
- Millar’s expt suggestingpotential for amino acid, sugar and nucleic acid generation on early earth
- Primitive heterotrophs began to compete for limited resources
- Autotrophs (Gk auto “self” and trophos “feeder”) Evolved after heterotrophs Photosynthesis:
- •requires specialized pigments
- •changed the Earth’s atmosphere (ozone, O2)
- •influenced the evolution of life
Differing concepts of ‘Species’
- Biological species – Reproductive isolation: A group of natural populations whose members can interbreed with one another but cannot interbreed with other such groups
- Morphological species – identified based on differences in shape or structure
- Genetic species – identified based on differences in nucleic acid sequence
- Prokaryotic ‘species’??– Strains that share a common set of stable properties
Systematics – the study of biological diversity
- Taxonomics – theory and practice of classifying organisms
- A stable system for naming and identifying organisms
- – Framework for classifying ancestral relationships
- – Assessment and management of biodiversity
- Phylogenetics – theory and practice of discovering the evolutionary interrelationships among organisms.
- Ultimate goal is to discover the evolutionary relationships between all the branches of the tree of life
The Father of Taxonomy: Carl Linnaeus (1707 – 1778)
- 1753 – ‘Species Plantarum’ (“The Kinds of Plants”)
- Polynomial – up to 12 words– e.g. Catnip: Nepeta floribus interruptespicatus pedunculatis
- Binomial – 2 word shorthand version
- = a genome that replicates itself within a host cell by directing the machinery of the host cell to synthesize viral nucleic acids and proteins
- Are viruses organisms?
- 1) Lack fundamental cellular features – e.g. plasma membranes, cytoplasm, ribosomes, or any enzymes for protein synthesis or energy production
- 2) Do not grow by increasing in size or dividing
- 3) Do not respond to external stimulii
- 4) Cannot carry on independent metabolism
- Viruses infect almost every kind of organism.
- Human viruses: influenza, chicken pox, hepatitis, AIDS, West Nile, SARS, Avian flu, Ebola
- Many viruses of other animals. E.g. rabies, mad cow disease
- Plant viruses > 2000 known. E.g. tobacco mosaic viru
Origin of Viruses
- No fossil record
- • Renegade segments of host genomic material that became partially independent– “Infectious nucleic acids”– Replicate independently in another cell– Acquired protein to protect nucleic acid
- • Extremely rapid evolution
- • Have evolved independently many times
- Very small (~1/100ththe size of a bacterium)
- • DNA (mainly animal viruses) or RNA (mainly plant viruses) single or double stranded and surrounded by protein coating
- • Identifying the protein is often the key to medical treatment
- • Some have an outer lipid envelope
- • Protein coating – helical; spherical; sometimes with a tail
- Viruses vary greatly in size and morphology
- Bodily fluids (e.g. herpes virus)
- Animal vectors (e.g. Human Avian influenza H5N1)
- Hand contact
Development of virus treatment strategies
- Vaccus (latin for cow)
- • Smallpox often fatal (10-40% of victims died); survivors disfigured and blinded
- • Local English peasants noticed that those who had contracted cowpox were immune to smallpox
- • Edward Jenner in 1796 extracted contents of a pustule from the arm of a milkmaid with cowpox symptoms, and injected it into a young boy.
- • Boy experienced mild symptoms
- • Jenner then inoculated the boy with smallpox…the boy did not develop any symptoms
- • ….smallpox eradication one of the greatest public health achievements ever
- Vaccine: a preparation of a weakened pathogen or some of its components that primes the organism’s defense mechanisms against the virulent strain.
- • Antiviral drugs: Inhibit reverse transcriptase as it attempts to synthesise DNA from the original viral RNA (e.g. AZT vs. AIDS); Protease inhibitors that block virion protein capsule assembly
Diversity within the Influenza virus
- Influenza A, B and C groups (linear RNA).
- • A (most common) has subtypes based on antigens of the hemaglutinin (H) and neuraminidase (N) proteins on the outer envelope…H2N1 …H10N7…etc.
- Virus-contaminated secretions enter respiratory system as aerosols or via ingestion.
- Neuraminidase hydrolyses epithelial mucus, and then hemaglutinin tail attaches to host blood cells to begin infection.
- Infect most animals especially chickens – major reservoir for human infection is from chickens via pigs.
- Small mutations in the RNAbased sequences for the H and N proteins in a single strain occur each year. Variation largest in Infl. A and moderate in Infl. B.
- Flu jab is a vaccine developed each year based on epidemiological predictions of the specific antigen structures of the prevalent Influenza A virus strains.
- Major genetic reassortment when two strains (from humans and/or other animals) infect the same cell and become incorporated into a single new capsid…leading to novel genome and H N combination
- • A major societal health concern (epidemic risk) E.g. Spanish flu (H1N1) of 1918 killed 40 million peopl