Module 1: Section 1

Question 1

3 Domains

Answer 1

1. Archaea
2. Bacteria
3. Eukaryota

Question 2

Microbes

Answer 2

Microscopic living organisms; can be single-celled or multicellular

Question 3

Bacteria

Answer 3

• Single-celled prokaryotes
• Characterized by cell walls with peptidoglycan

Question 4

Archaea

Answer 4

• Single-celled prokaryotes
• Lack peptidoglycan in their cell walls

Question 5

Eukaryota

Answer 5

Organisms with cells that have a nucleus and membrane-bound organelles

Question 6

Endosymbiont Hypothesis

Answer 6

• Eukaryotes evolved from prokaryotes via symbiosis
• Mitochondria & chloroplasts came from bacteria
• Evidence: they have their own DNA + distinct translation system
• α-proteobacteria is the ancestor of mitochondria

Question 7

Archezoan Scenario - Endosymbiont Hypothesis

Answer 7

• primitive eukaryote (without mitochondria) engulfed α-proteobacterium and became mitochondrion
• Hypothesis now out of favour due to phylogenetic errors with early protist placement

Question 8

Symbiogenesis Scenario - Endosymbiont Hypothesis

Answer 8

• mitochondrial symbiosis happened first, then nucleus/complexity evolved
• α-proteobacterium engulfed by archaeal cell and mitochondria formed first
• Later: nucleus + compartmentalization came

Question 9

Phylogeny

Answer 9

The evolutionary history of a group of organisms

Question 10

Phylogenetic Tree of Life (Carl Woese, 1987)

Answer 10

• Built using rRNA sequence comparisons
• Shows 3 domains: Bacteria, Archaea, Eukaryota
• Major discovery: Archaea are more closely related to Eukaryotes than to Bacteria

Question 11

Bacteria Characteristics

Answer 11

• No nucleus
• RNA polymerase: 3–4 subunits
• Ribosomes: 70S
• Cell wall: murein (peptidoglycan)

Question 12

Archaea Characteristics

Answer 12

• No nucleus
• RNA polymerase: 8–12 subunits
• Ribosomes: 70S
• Cell wall: no murein

Question 13

Eukaryota Characteristics

Answer 13

• Has nucleus
• RNA polymerase: 12–14 subunits
• Ribosomes: 80S
• Cell wall: no murein

Question 14

Phylogenomic Tree of Life (2016)

Answer 14

• Based on entire genome comparisons, not just rRNA
• More accurate than older phylogenetic trees because it uses much larger data sets
• Shows especially wide diversity within Bacteria

Question 15

Horizontal gene transfer

Answer 15

Movement of genetic material between organisms other than via vertical transmission

Question 16

Web of life

Answer 16

• Shows networks of connections between domains, not just branches
• emphasizes a community of common ancestral organisms rather than a single prototype

Question 17

Obligate intercellular parasites

Answer 17

Parasite that cannot reproduce outside of a host cell

Question 18

What are viruses?

Answer 18

small infectious agents that require a host cell to replicate

Question 19

What is a virion?

Answer 19

a complete virus particle outside the host

Question 20

Parts of a virion

Answer 20

• Genetic material (DNA or RNA)
• capsid (protein coat)
• sometimes lipid envelope

Question 21

Virus-first theory

Answer 21

• Viruses came before cells
• They evolved from macromolecules
• Viruses existed as self-replicating units in a pre-cellular world

Question 22

Escape theory

Answer 22

• Cells came before viruses
• Viruses are derived from bits of cellular DNA/RNA that leaked from cells
• When these fragments acquire a protein coat they can become independent entities

Question 23

Reduction theory

Answer 23

• Cells came before viruses
• Viruses come from primitive cells that lost cellular elements over the course of evolution

Question 24

Viral genome integration

Answer 24

• Viruses can insert their genome into the host’s DNA
• allows viruses to pick up host genes, transfer them to other cells, and even between species