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Lecture 4

Biology 1001A Lecture Notes - Lecture 4: Deuterostome, Global Catastrophic Risk, Protostome


Department
Biology
Course Code
BIOL 1001A
Professor
Beth Mac Dougall- Shackleton
Lecture
4

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Biology Lecture 4 - BioDiversity
Independent Study Outcomes
1. The approximate times by which the first cells, and the first eukaryotic
cells, had appeared.
- the first organisms may have been single-celled methane-producing bacteria that existed 3.5
billion years ago
- the first eukaryotic cells are said to have appeared about 2.5-2.8 billion years ago
2. The two-kingdom, five-kingdom and three-kingdom (three domain) sys-
tems for classifying living things.
-Two Kingdom - Plantae and Animalia
- assignment to one kingdom or the other was based on structure and function, type of
metabolism (plants use photosynthesis), movement (animals can move from place to
place)
-Two Domain - Prokaryotes (single celled) and Eukaryotes (multicellular)
- differences -
- prokaryotes do not contain nuclear membranes, organelles or cytoskeletons
- prokaryotes reproduce by binary fission and eukaryotes by mitotic cell division
- prokaryotes lack: endoplasmic reticulum associated with ribosomes in protein
synthesis, golgi apparatus, and a mitochondria for energy production
- membrane closed compartments allow eukaryotic cells to isolate enzymes for specific
reactions(translation of DNA into RNA to cytoplasm)
- the evolution of compartmentalization was a major series of steps in the origin and di-
versification of eukaryotes
-Two Became Five - prokaryotes, eukaryotes => (protists, fungi, plants, and
animals)
- prokaryotic and eukaryotic domains reflect the two types of cellular organizations but
they are not monophyletic, they are polyphyletic
-Five Became Three - eubacteria, archaea, and eukarya
- rRNA sequences from an archaebacterium (prokaryote) were found to be different from
those of other prokaryotes, therefore new domain (ARCHAEA) was formed
-Eubacteria - includes major forms of bacteria and the cyanobacteria, the latter being
the earliest organisms known as fossils
-Archaea - unicells with cell walls made of different molecules than those found in Eu-
bacteria. Often live under more rigorous environmental conditions
-Eukarya - includes some unicellular organisms and the three groups of multicellular
organisms (fungi, plants, animals)

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Biology Lecture 4 - BioDiversity
3. Main characteristics distinguishing members of the Eubacteria, Archaea,
Eukaryota domains of life.
-Eubacteria - includes major forms of bacteria and the cyanobacteria, the latter being the ear-
liest organisms known as fossils
-Archaea - unicells with cell walls made of different molecules than those found in Eubacte-
ria. Often live under more rigorous environmental conditions
-Eukarya - includes some unicellular organisms and the three groups of multicellular organ-
isms (fungi, plants, animals)
4. Meaning of horizontal gene transfer and why this makes it challenging to
recreate the universal tree of life.
- horizontal gene transfer is the transfer and incorporation of one organism’s or species DNA into
the DNA of a different organism or species
- HGT contrasts dramatically with the vertical transmission of genes from generation to
generation
- advances in sequencing technology and the availability of entire organismal genomes have pro-
duced a flood of molecular info
- it is a challenge to recreate the universal tree of life because of HGT
- HGT scrambles the info on which biologist rely to reconstruct the phylogeny (the his-
tory of organismal lineages as they change through time)
- HGT also poses challenges because early branches of the tree of life spanned long time
intervals and involved large number of organisms, many low HGT events occurred
5. Monophyletic vs. polyphyletic groupings of organisms.
- monophyletic - term that is used for a lineage of organisms that share a single common ancestor
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