A1258150009hXwLq

1
For those of you who are interested in
systematics
http//www.ohiou.edu/phylocode/
2
Introduction to the History of Life
Chapter 26
3
(No Transcript)
4
Prokaryotes Eubacteria Archaea. Lack membrane
around nucleus. Oldest fossils 3.5 billion years
old Stromatolites.
5
Photosynthesis 2.7 billion years
ago cyanobacteria liberated O2
6
Eukaryotes Membrane around nucleus and
organelles 2.1 billion years ago
7
Multicellular Eukaryotes 1.2 billion years ago
8
Animals evolved in the late Precambrian 550-600
mya Multicellular, heterotrophic, no cell walls
9
Precambrian animals
Cambrian explosion
10
Cambrian explosion hypotheses

• ecology predation
• geology oxygen
• genetic Hox genes

11
colonisation of land
12
Colonisation of land hurdles to overcome

• dessication
• waterproofing (waxes and chitinous cuticles)
• gravity
• structural support (wood, animal skeletons)
• water for reproduction
• plants waterproof pollen
• animals internal fertilisation, shell to protect
  eggs, live births

13
Origin of Life

• abiotic synthesis of organic molecules
• joining of molecules into polymers
• replication
• packaging

14
Synthesis of organic molecules

• Oparin Haldanes hypothesis
• reducing atmosphere
• energy

15
Stanley Miller and Harold Urey 1953
16
Miller-Urey experiment points to consider

• Atmosphere?
• Amino acids produced
• -racemic mix
• Ribose, phosphates cytosine

17
Joining of molecules into polymers

• No cells to do this, no enzymes
• hot mineral surfaces?
• problems
• bonding to minerals
• instability of nucleotides at high temp

18
Replication

• RNA as the first genetic material
• acts as an enzyme
• survival of the most stable?

19
Packaging

• protobionts
• liposomes
• internal chemical environment
• selection favouring RNA surrounded by a membrane

20
The universal ancestor

• LUCA (Last universal common ancestor)
• not necessarily the first cell
• Approach to the search for LUCA
• what features are common to all cellular life?
• how do the three domains differ?
• what is the minimal genome

chapter 28
21
The minimal genome

• minimum number to make a cell
• sequence of Mycoplasma genitalium Haemophilus
  influenzae
• 256 genes
• no biosynthetic machinery for making the building
  blocks of DNA (?!)

22
Problems with the minimal genome approach

• ecology affects the list of essential genes
• gene losses (it was in LUCA but hasnt survived
  in 3 extant domains)
• lateral gene transfer

23
Lateral transmission of genes
LUCA
24
Lateral transmission of genes
lateral transfer
LUCA
25
Lateral transfer of genes

• Since diverging from Salmonella 100 million years
  ago 10 of the genome of E. coli has been
  acquired from lateral transfer
• further back you go, more likely that there was
  lateral transfer
• seriously hinders phylogenetic tree
  reconstruction for deep divergences

26
The Endosymbiont Theory
chapter 28
proto-eukaryotic cell
aerobic bacteria
cyanobacteria
plants, some protists
animals, fungi, some protists
27
Endosymbiont Theory

• First suggested by Lynn Margulis in 1960s
• prediction mitochondria would have own DNA
• prediction supported in 1980s

28
chapter 28
29
chapter 28
30
A very rapid overview of Earths biotic diversity
Campbell and Reece Chapters 27-34
http//www.ucmp.berkeley.edu/exhibit/phylogeny.htm
l
excellent site for all things phylogenetic
31
Prokaryotes

• lack a membrane-bound nucleus
• bacteria and archaea

Chapter 27
32
Archaean plesiomorphies and synapomorphies
cell wall and membrane chemically distinct
DNA in chromosomes
DNA in a loop, smaller plasmids
tRNA is more similar to that of Eukaryotes than
to that of Bacteria
33
Go here for a look at the differences between
archaean cell membranes and the cell membranes of
all other organisms
http//www.ucmp.berkeley.edu/archaea/archaeamm.htm
l