Lecture 18

Question 1

What are the categories of classification?

Answer 1

Kingdom Phylum(=division) Class Order Family Genus species often intermediate taxa like subclass, subgenus… -order is of use anything above not much use

Question 2

What does the phylogenic tree look like?

Answer 2

-based on genetic evidence!

Question 3

What do we know about the origin of the Eukaryotic cell?

Answer 3

• 1.3 - 2 billion years before the present • mechanism of evolution is not known – nucleus and endomembrane system? – cytoskeleton? – complex cell division? – complex sexual reproduction? • There is good evidence for the origin of mitochondria and chloroplasts from primary endosymbiosis -not much known about their origin

Question 4

What were the first eukaryotic cells to evolve?

Answer 4

The Protists - the first Eukaryotic cells to evolve were protists and they are an extremely diverse group of organisms.

Question 5

When do eukaryotic cells first appear in the fossil record?

Answer 5

Precambrian acritarch fossils are the first known of eukaryotic cells –– about 1.3 –– 2 billion years old. -larger, some internal structure, looks like pollen grains

Question 6

When did the first multicellular (filamentous), eukaryotic organisms appear?

Answer 6

1.4 billion years ago -maybe Grypannia= possibly a fossil alga

Question 7

Are there any fossils of eukaryotes from pre-cambrian times?

Answer 7

-yes, recently described in phosphate mines in china

Question 8

When can we see early seaweed fossils from?

Answer 8

-365 million years ago

Question 9

How did eukaryotic cells evolve?

Answer 9

-primary endosymbiosis, ata a purple bacteria= mitichiondria

nucleus= invagination of membrane

Question 10

How did nucleus and membrane bound organelles form?

Answer 10

There is no real evidence to explain the origin of the nucleus, but it probably arose by the aggregation of flattened membrane spheres around a nucleoid containing DNA and RNA. The nuclear pores remain to allow communication between the nucleus and cytoplasm (for example, to allow for the passage of RNA out of the nucleus to the cytoplasm). The membrane probably came from invaginations of the cell membrane.
What about other membrane bound organelles, specifically the mitochondria and chloroplasts? The eukaryotic cell may actually be a chimera of other cells. Double membrane bound organelles (mitochondrion & chloroplast) are probably prokaryotes living permanently inside a eukaryotic cell.
Evidence for an endosymbiotic origin of organelles is interesting, and is still accumulating in the scientific literature.

Question 11

What isthe key evidence for endosymbiosis and the origin of mitochondria and chloroplasts?

Answer 11

1. Mitochondria and chloroplasts are semi-autonomous, retaining their own genome (DNA, RNA). Their genomes resemble those of prokaryotes (I.e., purple bacteria, cyanobacteria)
2. They also retain their own machinery for synthesizing proteins, including ribosomes.
3. Their metabolism is like existing prokaryotic organisms (e.g., a cyanobacteria for chloroplast).
4. ftsZ protein involved in division of prokaryotes and organelles
5. Some chloroplasts still have the bacterial peptidoglycan wall between the inner and outer membranes.

Question 12

What is secondary endosymbiosis?

Answer 12

There are organisms today that appear to be in the process of obtaining organelles, particularly chloroplasts, from other organisms. If a eukaryotic cell devours another eukaryotic cell and obtains a chloroplast from it, the process is referred to as secondary or eukaryotic endosymbiosis. An example is a cryptomonad cell, a classic protistan pirate. Other examples are the Euglenids and Chlorarachniophytes, which will be mentioned briefly.

Question 13

Why are cyanobacteria the most interesting organisms on earth?

Answer 13

Cyanobacteria are classified within the Super Kingdom Bacteria.
1. They gave rise to an oxygenated atmosphere.
2. All chloroplasts are derived from Cyanobacteria via
endosymbiosis, a key
process in the evolution of Eukaryotic cells

Question 14

What is panspermia?

Answer 14

-the theory that life evolved somewhere else and then came to Earth via a meteorite

Question 15

What characteristics do cyanobacteria share with chloroplasts?

Answer 15

1. Theirphotosyntheticthylakoids contain chlorophyll A, as do all chloroplasts.
2. Theiraccessorypigments, phycocyanin and phycoerythrin, are found in the chloroplasts of several protists.
3. Chloroplastgenomesshowthey are related to Cyanobacteria

typically blue/green can make them look different in a lab

Question 16

Describe the origin of chloroplast from cyanobacteria?

Answer 16

the food vacuole breaks down eventually so only 2 membranes

Question 17

How many genomes do protist with primary and secondary endosymbiosis have?

Answer 17

Protists with primary chloroplasts have 3 genomes, while all protists with secondary chloroplasts have
either 3 or 4 genomes.

Question 18

How many times did primary endosymbiosis occur during the origin of chloroplasts?

Answer 18

• Up until 3 years ago, molecular evidence suggested all chloroplasts arose from a single endosymbiotic event.
• There is now a second example where primary endosymbiosis has given rise to a photosynthetic protist.
• In both cases, the endosymbiont was a cyanobacteria.
• The origin of the mitochondrion is less clear?

Question 19

What is the second example of primary endosymbiosis resulting in photosynthetic organelle (discovered recently)?

Answer 19

Paulinella chromatophora - An amoeba with a chloroplast (called a chromatophore)

Question 20

How many organisms have Primary chloroplasts? (i.e., are surrounded by 2 membranes)?

Answer 20

Question 21

What is secondary endosymbiosis?

Answer 21

• The engulfed endosymbiont is a eukaryotic cell.
• Has occurred many times.

• Has resulted in enormous diversity - the
“protistan pirates”.

• Occasionally the host cell retains more than just
the symbiont’s chloroplast (e.g., a remnant nucleus, or nucleomorph, is retained by cryptomonads and some other protists).

• Many of the worlds most important primary producers are protistan pirates (e.g., brown seaweeds and diatoms)

difference= eukaryote eats eukaryote and pirates its chloroplast(not cyanobacteria like primary endosymbiosis)= this happens all the time

Question 22

How many membranes and genomes do protistan pirates have?

Answer 22

protistan pirates! always 3 or 4 membranes- cell membrane food vacuole maybe
4 genomes-host cell, mitochondria, chloroplast and the remainder of nucelus of the eaten cell= still active

Question 23

What is a nucleomorph?

Answer 23

the almost dead nucleus of eaten cell= only in some pirates and then not true pirates

Question 24

Which species had primary endosymbiosis?

Answer 24

primary: glaucophytes, red algae, green algae, land plants

primary (another source): Paulinella

Question 25

Which species have secondary endosymbiosis?

Answer 25

• cryptomonads, chrysophytes, phaeophytes, haptophytes, diatoms, oomycetes
• dinoflagellates, apicomplexans
• euglenois
• cerchozoans

Question 26

Which primary endosymbiots provided the chlorpolast for secondary endosymbiosis?

Answer 26

Only the red algae and green algae provided chloroplasts for secondary endosymbiosis
Paulinella & Glaucophytes NOT involved in secondary endosymbiosis

Question 27

What pigments does red alga have?

Answer 27

Chl A + C plus phycoerythrin and phycocyanin

Question 28

Give an example of a protistan pirate with chloroplast form red alga.

Answer 28

Cryptomonad flagellates (pigments:Chl A + C plus phycoerythrin and phycocyanin= from red alga)

Question 29

Give an example of a protistan pirate with chloroplast form green alga.

Answer 29

Chlorarachniophytes - amoeboid protistan pirates with green algal chloroplasts (Chl A + B) that contain a nucleomorph each.

-Euglenids (photosynthetic and non-photosynthetic species exist)