1. The origin of (Eukaryotic) cells

2. Phylogenetic relations between organisms
Five kingdoms of life

3. The Cell: The Basic Unit of Life
The cell theory states that:
Cells are the fundamental units of life.
All organisms are composed of cells.
All cells come from preexisting cells.
If all organisms evolved from an ancient original cell, can we propose the order of events?

4. Phylogenetic relations between organisms
Phylogenetic relationships can be inferred from common characters

5. Mutations drive evolution
Mutation is the molecular basis of change and speciation.
The comparative study of genomic sequences is now used to infer phylogenetic relations.
Genome based analysis confirms many of the traditional classifications of organisms.

6. Phylogenetic relations between organisms
Sequence comparison between plants

7. Phylogenetic relations between organisms
Based on sequence analysis biologists now categorize all life into three domains: Bacteria, Archaea, and Eukarya.
Prokaryotes
~ 3.5 billion
years ago

8. Three Domains All three domains had a single common ancestor.
Present-day Archaea share a more recent common ancestor with eukaryotes than they do with bacteria.
The common ancestor of all three domains was prokaryotic.
Prokaryotes were the only life-forms for billions of years.
The three domains are products of billions of years of natural selection.

9. Comparison between the three domains of life
Prokaryotes Eukaryotes

10. EARLY EARTH AND THE ORIGIN OF LIFE
Life began on a young Earth
Planet Earth formed some 4.6 billion years ago
The early atmosphere probably contained
H2O, CO, CO2, N2, and some CH4
Volcanic activity, lightning, and UV radiation were intense

11. Stanely Miller re-creating his 1953 experiment
Stanley Miller’s experiments showed that organic molecules could have arisen on a lifeless earth

12. Stanely Miller re-creating his 1953 experiment
Simulations of such conditions produced amino acids, sugars, lipids, and the nitrogenous bases found in DNA and RNA
CH4
“Atmosphere”
Water vapor
Electrode
NH3 H2
Condenser
Cold water
Cooled water containing organic
molecules
H2O “Sea”
Sample for chemical analysis

13. The first polymers may have formed on hot rocks or clay
Organic polymers such as proteins and nucleic acids
May have polymerized on hot rocks
High temperatures, electrically charged sites on the clay particle and metal atoms, such as iron and zinc, functioned and catalysts of the polymerization reaction.

14. A hypothesis for the origin of the first genes
Ribozymes G A C U 1 2
Formation of short RNA polymers: simple “genes”
Assembly of a complementary RNA chain, the first step in replication of the original “gene”
Monomers
The RNA world

15. The beginnings of molecular cooperation
Self-replication of RNA
Self-replicating RNA acts as template on which poly- peptide forms.
Polypeptide acts as primitive
enzyme that aids RNA
replication.
RNA
Polypeptide

16. Phospholipids Form a Bilayer

17. Protobionts
Figures\Chapter04\High-Res\life7e-fig jpg

18. Microscopic spheres made of phospholipids
LM 650

19. Cooperation among membrane-enclosed macromolecules
Semi-permeable
Protobiont
Membrane
Polypeptide
RNA
Primitive
metabolism
in a protected
environment

20. The Origin of the Eukaryotic Cell
The evolution of eukaryotic cells included the following components:
The origin of a flexible cell surface
The origin of a cytoskeleton
The origin of a nuclear envelope
The appearance of digestive vesicles
The endosymbiotic acquisition of certain organelles

21. The Origin of the Eukaryotic Cell
The first step toward the eukaryotic condition may have been the loss of the cell wall by an ancestral prokaryotic cell.
A surface that is flexible enough to allow for infolding lets the cell exchange materials with its environment rapidly enough to sustain a larger volume and more rapid metabolism.
A flexible surface also allows endocytosis.
An infolded plasma membrane attached to a chromosome within an ancestral prokaryote may have led to the formation of the nuclear envelope.

22. The Origin of the Eukaryotic Cell
The early steps in the evolution of the eukaryotic cell likely included three advances:
The formation of ribosome-studded internal membranes, some of which surrounded the DNA
The appearance of a cytoskeleton
The evolution of digestive vesicles

23. From Prokaryotic Cell to Eukaryotic Cell (Part 1)

24. Membrane Infolding

25. The Origin of the Eukaryotic Cell
From an intermediate kind of cell, the next advance was likely to have been a motile phagocyte.
The first true eukaryotic cell possessed a cytoskeleton and a nuclear envelope; it also may have had an associated endoplasmic reticulum and Golgi apparatus and perhaps one or more flagella.

26. The Origin of the Eukaryotic Cell
During the early stages of eukaryotic evolution, the O2 levels in the atmosphere were increasing as a result of the photosynthetic activities of the cyanobacteria.
Most living things were unable to tolerate this new aerobic, oxidizing environment, but some prokaryotes and ancient phagocytes were able to survive.
One hypothesis suggests that the key to the survival of the early phagocytes was the ingestion of a prokaryote that became symbiotic and evolved into the peroxisomes of today.

28. From Prokaryotic Cell to Eukaryotic Cell (Part 1)
Dual membrane support endosymbiosis

29. The Origin of the Eukaryotic Cell