Lecture 2: Early Life

Question 1

What are the 3 domains of life?

Answer 1

1. Bacteria
2. Archaea
3. Eukarya

Question 2

Microbes are small and _____.

Answer 2

ubiquitous

Question 3

Describe the bacterial cell structure.

Answer 3

Question 4

What are the 7 bacterial cell shapes?

Answer 4

1. Coccus
2. Bacillus
3. Coccobacillus
4. Fusiform bacillus
5. Vibrio
6. Spirillum
7. Spirochete

Question 5

How do we categorize microbes?

Answer 5

• Metabolic lifestyle
• Genetic characterization
• Pigmentation

Question 6

List different pigments.

Answer 6

• Carotenoids
• Melanin
• Chlorophylls
• Violacein
• Fucoxanthin
• Perinidin
• Pyocyanin

Question 7

What are the 3 metabolic classifications of life?

Answer 7

1. Carbon source
2. Energy source
3. Source of reducing power

Question 8

How do we classify organisms by carbon source?

Answer 8

• Inorganic (autotroph)
• Organic (heterotroph)
• both (mixotroph)

Question 9

How do we classify organisms by energy source?

Answer 9

• Phototroph (energy from light)
• Chemotroph (energy from chemicals)

Question 10

How do we classify organisms by source of reducing power?

Answer 10

• Organotroph (reducing equivalents obtained from organic compounds)
• Lithotroph (reducing equivalents obtained from inorganic compounds)

Question 11

What does the genome tell us?

Answer 11

• Pure culture vs. environment
• Lateral gene transfer can make this hard too

Question 12

What were the hostile conditions on early Earth?

Answer 12

• Early bombardment by meteors
• Twice as much ocean as today
• Much higher temps
• No free oxygen
• High UV radiation
• High CO₂, CH₄, N₂, NH₃, H₂O
• Traces of H₂, H₂S, FeS

Question 13

How long have microbes been on Earth?

Answer 13

At least 3.8 billion years

Question 14

Explain the chemical evolution model for the origin of life.

Answer 14

“Life arose from non-life”
- Oparin and Haldane (1920s): early conditions on Earth resulted in formation of organic compounds (need concentrated pools of prebiotic soup for evolution of life)
- Miller-Urey (1950s): experiments demonstrated that complex fatty acids and amino acids could form under these conditions
- They were wrong about conditions and there is no bridge between soup and life

Question 15

What is the thermophilic origin of life based on?

Answer 15

The occurrence of thermophiles at root of tree of life

Question 16

What is the evidence of the origin of life?

Answer 16

• Stable isotopic evidence of microbial life
• Fossil evidence

Question 17

What is a microbial mat?

Answer 17

Multi-layered sheet of microbes

Question 18

How were microbial mats involved in early fossilization?

Answer 18

Good at capturing corpses of other organisms
- Delaying decay
- Form impressions and replicas of vertebrates and invertebrates

Question 19

Explain the RNA world hypothesis.

Answer 19

rRNA
1. Universally conserved
2. Functionally homologous
3. Alignable
4. Slowly evolving if looking at ancient divergence - multiple hits problem

Question 20

Compare and contrast bacteria, archaea, and eukarya.

Answer 20

Question 21

How did huge diversity arise?

Answer 21

• Long time periods
• Short generation time = fast evolutionary rate
• Prokaryotes have evolved into many different niches
• Huge metabolic/functional diversity allow organisms that coexist in the environment to differentiate themselves

Question 22

What is the sequence of metabolic innovation?

Answer 22

Question 23

What is Riftia and what is its symbiont?

Answer 23

• Riftia = giant tube worm, bottom or ocean near hydrothermal vents, no digestive system
• Symbiont: chemolithotrophic sulfur oxidizing gamma Proteobacteria

Question 24

What are fossil stromatolites?

Answer 24

Ancient microbial mat communities