10 - Evolution of Eukaryotes

Question 1

endosymbiosis

Answer 1

A symbiotic association in which one symbiont or partner lives inside the other.

Question 2

cyanobacteria

Answer 2

also known as blue-green bacteria, blue-green algae, and Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis.The name “cyanobacteria” comes from the color of the bacteria (Greek: κυανός (kyanós) = blue).

Question 3

lateral gene transfer

Answer 3

the transfer of genetic material between species.

Ex: genes move from the nucleus to the organelles

Question 4

endomembrane system

Answer 4

• A collection of internal membranes that divide the cell onto structural and functional regions.
  
  • include the nuclear envelope, the endoplasmic reticulum, and the Glgi complex.

Question 5

origin of endomembrane system, nuclear membrane, ER etc.

Answer 5

• the most widely held hypothesis is that it is derived from the infolding of the plasma membrane.
• pockets of the plasmma membrane may have extended inward and surrounded the nuclear region.
• Some of these membranes fused around the DNA, forming the nuclear envelope, which defines the nucleus.
• The remaining membranes formed vesicles in the cytoplasm that gave rise to the endoplamic reticulum and the Golgi complex.

Question 6

origin of mitochondria and chloroplasts

Answer 6

• mitochondria and chloropasts are actually descended from free-living prokaryotic cells.
• Mitochondria: descended frome aerobic (with oxygen) bacteria
• Chloroplasts: descended from cyanobacteria
• through endosymbiosis, where prokaryotic ancestors of modern mitochondria and chloroplasts were engulfed by larger prokaryotic cells, forming a mutually advantagous relationship.
• they slowly became unceperable and formed one organism

Question 7

Evidence supporting theory of endosymbiosis for Mitochondria and Chloroplasts

Answer 7

1. Morphology - The form or shape is similar to that of bacteria and archaea
2. Reproduction - A cell cannot synthesize a mitochondrion ar a chloroplast. they are derived only from pre-existing mitochondria and chloroplasts. They didvide by binary fission.
3. Genetic Information - contain their own DNA (circular), which contains protein-coding genes that are essential for organelle function.
4. Transcription and Translation - contain a complete transcription and translational machinery
5. Electron Transport Chains - Both have (ETCs) used to generate chemical energy. Both also have an inner membrane that contains the ETC.
6. Sequence Analysis - Chroloplast ribosomal RNA is most similar to the of cyanobacteria. Mitochondrial ribosomal RNA is most similar to that of proteobacteria

Question 8

Factors driving development of early eukaryotic cells

Answer 8

• Oxygen drove this evolution
• Earliest bacteria were anaerobic. They were simple and could not generate huge amounts of energy (ATP).
• 2.2 bya Cyanobacteria evolved: they undergo oxygenic photosynthesis that relies on the oxidation of water, which produces oxygen.
• with the presence of more oxygen, bacteria that undergo aerobic respiration evolved (mitochondria, chloroplasts). They can generate much greater amounts of ATP from the breaking down of organic molecules that pathways of anaerobic metabolism.

Question 9

Why eukaryotic cells can be larger and more complex than prokaryotic cells

Answer 9

• aerobic bacterium relies on its plasma membrane for many functions, including nutrient and waste transport and energy prodiction
• Contrast, eukaryotic cell contains hundreds of mitochondria, each having a huge internal membrane surface area dedicated to generating ATP.
• With more ATP production, cells could now become larger as now there was enough energy to support a greater volume, more complex.
• this complexity comes about by being able to support a learger genome that codes for a greater number of proteins (protein synthesis, protein diversity, more ribosomes).
• Eukaryotes overcame the energy barrier and now were able to support a veriety of genes that led to eukaryotic-specific traits.

Question 10

• Evidence for lateral gene transfer (horizontal gene transfer (HGT)) from organelles to the nucleus
• Hypotheses for why genes move to the nucleus from organelles (lateral gene transfer)

Answer 10

• the early eukaryotic cell would have contained at least two and perhaps three compartments, each with its own genome. This could not have stayed like this.
• in the modern eukaryotic cell, the function of mitochondria is integrated to the cells metabolism.
• Two major processes led to this:

1. some of the genes would have been reductant, as the nucleus would already have genes that encode proteins with the same function.
2. many of the genes withing the protomitochondria and protochloroplast were relocated to the nucleus (HGT), because of the evolutionary advantage the cell would gain by centralizing crucial genetic information in one place (nucleus).

• Lateral gene transfer is still going on and it has not ended.

Question 11

General idea about how lateral gene transfer is detected (Southern blot)

Answer 11

• the sounthern Blot is useful for ditermening if a genome has a particular gene, or the number of copies of that gene.
• genomic DNA is isolated and run on a gel
• DNA is made so it is single stranded and if it hybridizes with the DNA prob that means that on the membrane you have a sequence that is similar to your prob
• this is how you can identify the presence or lack there of of a particular gene
• Example: mtDNA and nDNA are isolated from three related species of plants A, B, C. For each isolated DNA is run through the gel. We are looking for where the mitochodrial specific gene is located (oxidase3 gene).
  
  • A: still in the mitochondria. LGT has not occured
  • B: only sticks to the nuclear DNA gene has migrated, no hybridization in mtDNA prob
  • C: it is in both genomes. Because in LGT the gene is copied that is sent to the nucleus, and then the original copy is degraded. This was caught before it has been degraded.

Question 12

Possible reasons why certain genes have NOT moved to the nucleus from organelles

Answer 12

• Perhaps gene transfer is not yet complete
• since most of the genes that are retained by the mitochondrion or chloroplast code for proteins involved in electron transport, the tight regulation of these gene, which is difficult to do if the genes are in the nucleus, is essential to maintain optimal rates of energy transformation.
• Could be an import problem. It might be difficult to import proteins back into the organelle after they have been synthesized in the cytosol.
• Some cells have organelles far from the nucleus (like neurons) and so they need local control and local production of proteins to make things go quicker

Question 13

Role of cpn60 in tracing endosymbiotic and lateral gene transfer event in eukaryotes.

Answer 13

• cps60 is a mitochondrial protein and it is absolutely essential for mitochondrion to work
• it is found in the nuclear genome which means that lateral gene transfer has occured
• Giardia has a copy of cpn60 but has no mitochondria
• there was an ancestor very early on that went through symbiosis with mitochondrion and also went through LGT
• giardia had to have mitochondra in its past because it has cpn60 which has no known function in this species
• these mitochondrion-less eukaryotes are not intermediates to symbiosis and LGT, it just means that they found no advantage of keeping the mitochondria and simply got rid of it after symbiosis and LGT occured.