Evolution: Lecture 8

Question 1

What are the three domains of life?

Answer 1

The three domains are:

Bacteria - prokaryotes
Archaea - prokaryotes
Eukarya - eukaryotes

Question 2

Bacteria, Archaea and most eukaryotic groups are?

Answer 2

• Bacteria, Archaea & most eukaryote
  groups are microbial life-forms (see ‘protists’ later)
• Bacteria and Archaea are two very different kinds of ‘prokaryotic’ cells

Question 3

Prokaryotic cells are?

Answer 3

Simple cells with few internal organelles. Single cell organisms, very small but could be larger.

Question 4

Importance of prokaryotes?

Answer 4

They were the first living organisms on earth, are and always have been important parts of the earth’s biosphere.

Question 5

What do prokaryotes do?

Answer 5

• On Earth for ~3.5 billion years
• Responsible for most of biological activity in many ecosystems (e.g. Ocean; Soil)
• Most of the biomass in the ocean is composed of microbes. Most of the oxygen is also generated by microbes.
• More prokaryotes than human cells in body
• Cause many major diseases & infections
• Biotechnology

Question 6

What do bacteria do?

Answer 6

They cause a lot of disease in animals, none are really caused by archaea.

Question 7

Bacteria?

Answer 7

Includes almost all well-known prokaryotes.

• all known disease causing species/

Question 8

Outer cell organization?

Answer 8

Each of the domains of life have their own biologically unique characteristic way that the outer part is organized.

Question 9

Bacterial cell envelope?

Answer 9

• Usually* two bounding membranes:
  Plasma membrane and outer membrane
• Peptidoglycan wall between the membranes (complex polymer of sugars and amino acids)
• two membranes with a cell wall between.
• Gram-positive bacteria lack the outer membrane

Question 10

Important types of bacteria?

Answer 10

• Spirochetes
• Gram-positive bacteria
• cyanobacteria (photoautotrophs)
• proteobacteria

Question 11

Spriochetes?

Answer 11

Spiral shape, corkscrew their way through fluid very rapidly. Some cause disease.

Example: Treponema causes Syphilis and Lyme Disease

Question 12

Gram-Positive Bacteria?

Answer 12

No outer membrane. Do really well in many environments, but especially well in environments that dry out, like soil. Layers of peptidoglycan.

Example: lockjaw causes

Question 13

Cyanobacteria (photoautotrophs)?

Answer 13

Blue-green algae prominent in oceans. Photosynthesis in the ocean is caused by them. They make oxygen with photosynthesis - oxygenic photosynthesis.

Question 14

Proteobacteria?

Answer 14

Very diverse bacteria.

Example: E. coli

Question 15

Archaea?

Answer 15

The only prokaryotes that don’t cause disease.

• Many are extremophiles, they are hard to cultivate and grow under weird conditions. Found at the bottom of the ocean in really hot water.
• Many are methanogens, producing methane as a waste product of energy metabolism. Methane is a greenhouse gas and have been rising substantially. A lot of methane is released from the biosphere (living organisms). Example: cows don’t release methane, the microbes in their bodies do.

Question 16

Archaea - cell envelope?

Answer 16

No ‘outer membrane’; no peptidoglycan. Cell membrane lipids are chemically different from those of Bacteria and eukaryotes. Archaeal membrane lipids have branched hydrocarbons.

Question 17

Archaea are closely related to?

Answer 17

Archaea are more closely related
to Eukaryotes than to Bacteria

Question 18

Bacterial origins of mitochondria
and plastids (chloroplasts)?

Answer 18

Idea that eukaryotes may have evolved from archaea.

Endosymbiosis: bacterial cell incorporated into eukaryotic and eventually integrated enough to call it an organelle of the eukaryotic cell.

Happened twice: chloroplasts and mitochondria

Question 19

The origin of eukaryotic cells?

Answer 19

1. Endomembrane system, including
   nuclear envelope evolves conventionally (not by symbiosis)
2. Endosymbiotic alphaproteobacterium becomes mitochondrion
3. Endosymbiotic cyanobacterium
   becomes plastid

Question 20

Prokaryotic cell features of mitochondria and plastids?

Answer 20

• Divide by binary fission
• Have (prokaryotic-like) ribosomes
• Have their own genomes:
  *Encode some RNAs, and proteins that are translated on the organelle ribosomes

Question 21

Eukaryotic diversity?

Answer 21

All lineages except those in red circles are groups of ‘Protists’ (note that this makes protists a paraphyletic group)

Question 22

Protists?

Answer 22

• Make up most of eukaryote diversity
• Abundant in most ecosystems
  *Important photosynthesisers: ‘algae’
• The major predators of prokaryotes
• Parasitic protists cause some major
  diseases (e.g. malaria)

Question 23

Origins of animals and fungi?

Answer 23

• Phylogenies of molecular sequences show that animals and fungi are quite closely related

…but independently evolved from single-celled protistan ancestors

Question 24

Plants evolved from?

Answer 24

Plants evolved from photosynthetic
‘green algal’ protists

Question 25

Are we still finding more microbes?

Answer 25

Scientists are still identifying many new 'kingdom-level groups’ of microbes