Block A Lecture 1: Microbial Diversity

Question 1

Who discovered the 3 domains of life in the 1970s and what are they?

Answer 1

Carl Woese discovered them and they are; Bacteria, Archaea and Eucarya
(Slide 6)

Question 2

What is phylogenetics?

Answer 2

The science of examining evolutionary relationships of a group of organisms
(Slide 8)

Question 3

How does phylogenetics work?

Answer 3

Sequences of genes can be used to infer the relationship between species we can then align the sequences and look for differences
(Slide 8)

Question 4

What 4 requirements should a gene being used as a phylogenetic marker have?

Answer 4

Orthologous
Present in all species you are interested in
Should be conserved but have observable differences
Should evolve at a slow and steady rate
(Slide 10)

Question 5

What does orthologous mean?

Answer 5

Descended from the same ancestral sequence and separated by a speciation event (vertical descent)
(Slide 10)

Question 6

What do marker genes in phylogenetics provide?

Answer 6

Provides a reliable molecular clock for studying phylogeny
(Slide 11)

Question 7

What are 4 reasons which the 16 S ribosome component gene is used for phylogenetic study?

Answer 7

It’s highly conserved
Slow rate of evolution
RNA component of the 30S subunit
It recognises the Shine-Dalgano sequences of promoter
(Slide 11)

Question 8

What is the two-domain hypothesis?

Answer 8

It directly competes with the three-domain hypothesis with eukaryotes being believed to belong to the same branch as Archaea
(Slide 14)

Question 9

How was the 2 domain hypothesis made?

Answer 9

Authors used ribosomal protein genes and concatenated (linked) these with the 16S rRNA gene and found that these were similar to that of Archaea
(Slide 14)

Question 10

What does LUCA stand for?

Answer 10

The Last Universal Common Ancestor
(Slide 15)

Question 11

How old is the earth?

Answer 11

4.6 billion years old
(Slide 17)

Question 12

When does evidence suggest that cellular life first appeared on earth?

Answer 12

3.8-3.9 billion years ago
ignore the PowerPoint it’s wrong
(Slide 17)

Question 13

What life was present for the first ~1.5 billion years of earth’s life before cellular life appeared?

Answer 13

Microbial life
(Slide 17)

Question 14

Why did all microbial life before cellular life use anoxic metabolism?

Answer 14

As the atmosphere had no oxygen and was mainly comprised of nitrogen and carbon dioxide
(Slide 17)

Question 15

When did anoxic phototrophs and oxygenic phototrophic cyanobacteria evolve?

Answer 15

Anoxic phototrophs evolved around and 3.5 billion years ago and from these oxygenic phototrophic cyanobacteria evolved around 2.5 billion years ago
(Slide 17)

Question 16

What did oxygenic phototrophic cyanobacteria evolving allow?

Answer 16

Development of oxygen-dependent metabolisms and eventual development of multicellular life forms
(Slide 17)

Question 17

Why are viruses not on the tree of life?

Answer 17

As they are ancient and are not enclosed in “LUCA” - suggesting LUCA is cellular instead of common
(Slide 19)

Question 18

What are the 2 main hypothesis describing the emergence of viruses?

Answer 18

Genome reduction to the point of obligate intracellular parasite
Genome escape - aggregations of genes that somehow escaped cellular regulation
(Slide 19)

Question 19

What does evidence from bacteriophage genome suggest about viruses?

Answer 19

That viral genome structure is ancient and from before bacterial and archaea split
(Slide 19)

Question 20

What structure do viral genomes have and what does this mean?

Answer 20

They have a mosaic structure - modules recombine and exchange information
(Slide 19)

Question 21

What percentage of total biological diversity on earth is estimated to be microbial?

Answer 21

99.99%
(Slide 21)

Question 22

What do bacterial and archaeal genomes often exhibit?

Answer 22

Plasticity - ability to adapt to their environment quickly
(Slide 24)

Question 23

What is a genome?

Answer 23

The full complement of genes for an organism
(Slide 25)

Question 24

What are genomes of bacteria and archaea usually?

Answer 24

One single circular DNA molecule with sometimes plasmid being present
(Slide 26)

Question 25

Are bacterial genomes usually diploid or haploid?

Answer 25

Haploid
(Slide 26)

Question 26

What does a genome encode?

Answer 26

All the genes required for the assembly of the organism
(Slide 26)

Question 27

Do bacteria and archaea have introns?

Answer 27

No
(Slide 26)

Question 28

What is Lichen?

Answer 28

An association between cyanobacteria and fungi