23.1 Eukaryotic Origins

Question 1

Characteristics of Eukaryotes

Answer 1

1) Cells with nuclei surrounded by a nuclear envelope with nuclear pores
2) Mitochondria
3) Cytoskeleton with actin microfilaments and microtubules
4) Flagella & Cilia
5) Chromosomes coiled around alkane histones
6) Mitosis
7) Sex
8) Some major lineages have cell walls.

Eukaryotes cannot do nitrogen fixation

Question 2

Endosymbiotic theory

Answer 2

A host cell engulfs an alpha-proteobacterium

Question 3

Eukaryotic Origins

Answer 3

Cyanobacteria photosynthesis (due to endosymbiotic theory) => produced lots of oxygen => aerobic respiration became more needed.

3.5 - 2.1 bya - rise of oxygen
2.1 bya - first eukayotic cell fossil

Question 4

Evidence for Mitochondria being an endosymbiant

Answer 4

• Shaped like an alpha probacteria
• has 2 membranes that resemble the outersurface of the alpha probacteria
• divide independently due to binary fission (not de novo)
• Owns usually circular DNA, rRNA & tRNA that is similar to prokayotic ones.
• can produce sulfur & iron clusturs that are enzyme cofactors

Question 5

De novo production

Answer 5

when cells create organelles from scratch

Question 6

Mitochondria and the Nucleus

Answer 6

• Uknown if mitochondria comes before or after nucleus
• Gene responsible for repiratory proteins are similar to alpha proteobacterial origin
• sometimes the gene is in the mitochondria BUT sometimes it is present in the nucleus
• this is evidence that mitochondria lost its individuality after engulfment

Question 7

Plastids

Answer 7

• Photosynthesis organelle (chloroplast)
• derived from cyanobacteria through endosymbiosis
  2 different ones
• Archarplastida
• Paulinella

outer membrane layer = from the vacuole host
inner membrane layer = plasma membrane from the symbiont

Question 8

Archarplastida

Answer 8

took on a cyanobacterial endosymbiont
- has 2 membranes known as glaucophytes

Question 9

Paulinella

Answer 9

took on a diffferent cyanobacterial endosymbiont ameboid rhizarian
- Has a thin peptodoglycan layer present betewen inner & outer plastid membranes

Question 10

Primary vs Secondary endosymbiosis

Answer 10

Primary = first prokaryotic engulfment
Secondary = second prokaryote engulfment OR engulfment of a full primary eukaryotic endosymbiont.

Question 11

Example of secondary endosymbiosis

Answer 11

Green alga engulfed cyanobacterium => has 4 membranes