Lecture 2. Evolution And Diversity

Question 1

What was the surface origin hypothesis?

Answer 1

‘Warm little pond’
Primordial soup (evidence that organic molecules can form spontaneously)
Unlikely due to hostile conditions on surface (high UV, meteor strikes, volcanic activity)

Question 2

What was the subsurface hypothesis?

Answer 2

Hydrothermal vents at ocean floor
More stable conditions
Constant source of energy (reduced inorganic compounds)

Question 3

What were the key features allowing cellular life to develop from prebiotic chemistry?

Answer 3

Self replicating RNA (RNA world, ribozymes)
Enzymatic proteins
DNA - genetic code
Evolution of biochemical pathways
Divergence of lipid biosynthesis
Divergence of cell walls

Question 4

What was early life probably dependent on?

Answer 4

H₂ and CO₂ (bacteria making acetate and archaea making methane)

Question 5

What did phototrophy originally use as an electron donor and what photosystem did it evolve into?

Answer 5

Initially used H₂S, evolved into oxygenic photosystem using H₂O

Question 6

What do phylogenetic methods allow?

Answer 6

Determine how related organisms are to each other (how Archaea were identified)

Question 7

What makes a molecular sequence useful in phylogenetic studies?

Answer 7

Must be universal
Contain variable and conserved regions
Not be subject to horizontal gene transfer
Must be truly homologous

Question 8

Why are ribosomal RNA genes universal molecular markers?

Answer 8

They are present in all forms of life (including LUCA)

Question 9

What defines the phylogenetic tree of life?

Answer 9

Comparative ribosomal RNA sequencing

Question 10

When did eukaryotic cell arise?

Answer 10

~2 billion years ago

Question 11

What is the endosymbiont theory?

Answer 11

Mitochondria: Incorporation of aerobic chemo-organotrophic bacteria into a host (bacterial) cell

Question 12

What is the hydrogen hypothesis?

Answer 12

Association of an archaeal host using H₂ as energy source with an aerobic bacterium that produced hydrogen as a ‘waste’ product

Question 13

What is Aquifex aeolicus?

Answer 13

Isolated from a hot spring
Hyperthermophilic (grows up to 95°C)
One of the deepest branching bacterial phyla
Chemolithoautotroph: oxidises H₂ to water using O₂ as e⁻ acceptor
Autotrophic: C-fixation

Question 14

What is Deinococcus?

Answer 14

Extremely radiation resistant
Isolated from canned meat sterilised by gamma irradiation
Very rapidly reassembles radiation damaged DNA
Interest in using organism for bioremediation as it remaining viable in radiation contaminated sites

Question 15

What is Clamydia?

Answer 15

Obligate intracellular parasites
Distinct life cycle
Important human pathogens
C. trachomatis cause sexually transmitted disease, can lead to infertility
Also can infect the eye

Question 16

What are Spirochaetes?

Answer 16

Helically shaped, motile, gram negative
Unusual flagellum inside the cell
Heterotrophs
Contains free living, symbiotic and parasitic species
Human pathogens Borellia (Lyme disease) Treponema (Syphillis)

Question 17

What are methanogens?

Answer 17

Produce methane as a waste product
Are at the very bottom of the food chain
Degrade the degradation products of other organisms (Hydrogen and CO₂, acetate, methylated compounds)
Release vast amounts of methane to the atmosphere

Question 18

What are halophilic archaea?

Answer 18

Organisms that can grow in a saturate salt solution
20 times saltier than seawater
Salt lakes and ponds and salt crystals in subsurface
Can take very strange shapes and colours