Origin of Microbial Life

Question 1

What did prebiotic earth look like?

Answer 1

Inorganic compounds
Very little free oxygen
Lots of water (oceans)
Hot
Lots of ionizing radiation from space (no ozone layer)
Frequent electrical storms due to an unstable atmosphere
Volcanic and thermal vent activity

Question 2

Miller-Urey Experiment

Answer 2

-created the primordial soup
-showed that the mixture of heat, water, lightning, and inorganic gases could produce the first organic compounds on earth
-water turned dark, revealed complex molecules (amino acids)

Question 3

Chemical composition of cells

Answer 3

7% ions and small molecules
23% macromolecules (carbohydrates, proteins, lipids, nucleic acids)
70% H2O

Question 4

What are the major nucleic acids in cells?

Answer 4

DNA and RNA

Question 5

Common building blocks of DNA/RNA

Answer 5

1. sugar (deoxyribose or ribose)
2. phosphorus group
3. nitrogenous base

Question 6

Types of nitrogenous bases

Answer 6

pyrimidines and purines

Question 7

Pyrimidines

Answer 7

one ring
“Y” in their names
Cytosine and Thymine (DNA)/Uracil (RNA)

Question 8

Purines

Answer 8

multiple rings
energy storing molecules (ATP/GTP)
Adenine and Guanine

Question 9

First nucleic acid oligomers and tidal pools

Answer 9

1. High tide to tide goes out: Evaporation/concentration of nucleotides (mineral-rich ocean floor)
2. Low tide to dry tidal pool: polymerization (dehydration synthesis)
3. Tide comes back/high tide (cooling): H bond formation and polymers dissolve
4. Repeat

Question 10

Advantages of RNA over DNA

Answer 10

-self-replicate
-catalytic
-can form ribozymes

Question 11

RNA World Hypothesis

Answer 11

Self-replicating RNA in cell membranes (protocells) were the precursors to modern life by storing genetic information and catalyzing the chemical reactions in these primitive cells

Question 12

Evidence for RNA World

Answer 12

-RNA invovled in ancient, cellular processes (mRNA, rRNA)
-conserved ribosomes from all taxa have catalytic and structural RNAs
-catalytic ribozymes can be self-splicing and self-cleaving
-RNA genomes known in viruses

Question 13

What are the seven major groups of viruses?

Answer 13

1. DNA virus: dsDNA (+/-)
2. DNA virus: ssDNA (+)
3. RNA: dsRNA (+/-)
4. RNA: ssRNA (+)
5. RNA: ssRNA (-)
6. Reverse transcribing virus: ssRNA (+)
7. Reverse transcribing: dsDNA (+/-)

Question 14

dsRNA

Answer 14

rotavirus (inflamed intestine/abdominal pain)

Question 15

ssRNA (+)

Answer 15

SARS-CoV-2

Question 16

ssRNA (-)

Answer 16

Measles

Question 17

RT ssRNA (+)

Answer 17

HIV

Question 18

What are the two possible models for the evolution of viruses and modern cells?

Answer 18

1. virus-first
2. escape

Question 19

Virus-first model

Answer 19

-hypothesis that viruses preceded cellular life
-selfish replicons > viruses > protocell > modern cell

Question 20

Escape model

Answer 20

-modern cells evolved then viruses evolved from escaped transposable elements
-protocell > modern cell > viruses from escaped elements

Question 21

Panspermia Hypothesis

Answer 21

I. An impact on a “donor planet” produced a shock wave which forces a surface rock into space at high speed.
II. Organisms on the surface rock then survived space
III. Organisms on the surface rock survived atmospheric entry and impact

Question 22

Evidence for Panspermia

Answer 22

1. Organic compounds and amino acids in meteorites
2. Bacteria can survive harsh environment of space
3. Over half a ton of Mars lands on Earth every year

Question 23

Microbes are subjected to these conditions in space

Answer 23

-extreme desiccation
-low temperatures
-cosmic UV radiation
-vacuum conditions
-microgravity

Question 24

Thermophilic

Answer 24

optimal growth at 45ºC or greater
ex: sulfolobus solfataricus (archaea) and thermus aquaticus (bacteria)

Question 25

Hyperthermophilic

Answer 25

optimal growth at temperatures above 80ºC

Question 26

Mesophilic

Answer 26

optimal growth from 20-45ºC ex: Salmonella spp. (bacteria)

Question 27

Psychrophilic

Answer 27

optimal growth at temperatures of 15ºC or lower ex: Colwellia psychrerythraea (bacteria) and Chlamydomonas nivalis (eukaryote)

Question 28

Obligate Anaerobe

Answer 28

only grows in environments devoid of oxygen, bottom of tube ex: C. diff

Question 29

Aerotolerant Anaerobe

Answer 29

cannot perform aerobic respiration but can tolerate oxygen, dispersed throughout tube

Question 30

Facultative Anaerobe

Answer 30

can perform aerobic or anaerobic metabolism, clustered at surface of tube and dispersed throughout ex: E. coli

Question 31

Microaerophilic

Answer 31

cannot perform anaerobic metabolism but poisoned by large amounts of oxygen, clustered at top of tube but not on the surface ex: Campylobacter jejuni

Question 32

Obligate Aerobe

Answer 32

can only perform aerobic metabolism, all microbes are clustered at surface ex: Mycobacterium tuberculosis

Question 33

Autotrophic

Answer 33

-Can produce its own food -photosynthesis or chemosynthesis -photoautotroph: Prochlorococcus marinus -chemoautotroph: Nitrososphaera gargensis

Question 34

Heterotrophic

Answer 34

-Derive energy from organic compounds -most bacteria -Staphylococcus aureus

Question 35

Halophilic

Answer 35

-Optimal growth w/ HIGH salt concentrations -are also Alkaliphiles -Haloferax volcanii (archaea in Dead Sea)

Question 36

Acidophilic

Answer 36

-Optimal growth at pH 3 or below -Picrophilus torridus (archaea) in vents for volcanic vapor

Question 37

Alkaliphile

Answer 37

-Optimal growth at pH 9 or above -Natronomonas Pharaonis (archaea) in soda lakes

Question 38

LUCA

Answer 38

Last Universal Common Ancestor

Question 39

Likely characteristics of LUCA

Answer 39

-strict anaerobe -thermophilic -autotroph

Question 40

What are the 3 domains of life?

Answer 40

1. Archaea 2. Eukaryotes 3. Bacteria

Question 41

How did Carl Woese resolve the tree of life (phylogenetic tree)?

Answer 41

Compared the similarity of 16S and 18S rRNA across a number of organisms. 16S and 18S are homologous sequences.