Cycle 6 - Evolution of the Eukaryotic Cell Flashcards
Identify the complexity vs time paradox
Given enough time and selective pressure, organisms should get more complex (adaptation through mutation)
However, this is not seen in prokaryotes
- Prokaryotes do not have organelles, so the efficiency in providing a supply and demand of energy and nutrients (in the specific ways that eukaryotes do) is lacking compared to eukaryotes. Becoming larger and forming complex organisms would be impossible in prokaryotes because they would never be able to provide the organism with nutrients and energy it will need.
Define metabolic virtuosity
Metabolic virtuosity: ability to grow in extreme environments
- Seen in prokaryotes, but doesn’t require much complexity, just an enzyme pathway
What is meant by morphological/functional complexity?
- Morphological complexity: structural complicatedness (ex., eyes)
- Complex traits include DNA recombination, introns/exons, nucleus, cytoskeleton, endomembrane system, intercellular signalling, endocytosis
- Eukaryotes have all of these traits, bacteria and archaea have some of them but not all
State the factors driving development of aerobic cells
- The earliest bacteria were anaerobic
- 2.2 billion years ago, cyanobacteria evolved, provided oxygen in atmosphere, introduced oxygenic photosynthesis
- Bacteria began to undergo aerobic respiration; developed ETC and oxidative phosphorylation on plasma membrane
State the relationship between surface area and volume as cells get larger. Why is this impactful?
- As size of cell increases, volume increases much faster than surface area
- This is a problem because more oxidative phosphorylation units are needed on the plasma membrane to support the large volume, but the surface area of the membrane limits this
- This placed constraints on the size of bacteria cells but not on eukaryotic cells because oxidative phosphorylation takes place in mitochondria (can fill up large volume)
Describe the basis of the Proton Motive Force (PMF)
- Requires a gradient of both concentration and charge
- Generation of ATP converts millivolts to Watts, which is needed for cellular function
State the genome size relationships between E. coli, Epulopisculium and Eukaryotes
- E. coli: 9.2 Mb needed to support oxphos
- Epulopiscium: 760 000 Mb needed to support oxphos
- Actually has a smaller genome than E. coli but is very large so copies its genome almost 200,000 times
- Eukaryotes: 3200 Mb of mitochondrial DNA needed to support oxphos
- So eukaryotes can support oxphos using much less DNA
Relationship between genomes and power output.
- Prokaryotes have one genome so to support oxphos, the entire genome needs to be replicated at once - power per gene is small
- Eukaryotes have a large nuclear genome and a small mitochondrial genome (genome asymmetry), so to support oxphos only a small genome needs to be replicated at once - power per gene is large
Describe the rationale for why prokaryotes need to keep genomes as small as possible
- It takes a lot of energy to replicate a genome once, and prokaryotes make very little ATP
- Thus, keeping genomes as small as possible is best for efficiency
State the link between genome size and development of complexity between proks and euks
- Prokaryotes don’t seem to evolve (become more complex) because of their small genome size - they can’t generate enough ATP to support large genomes
- Eukaryotes can support a lot more junk DNA, which are the centres for mutation → novel structure and function → higher complexity
What is endosymbiosis?
Endosymbiosis: the theory that prokaryotic ancestors of modern mitochondria and chloroplasts were engulfed by larger prokaryotic cells, forming a mutually advantageous relationship called a symbiosis. Slowly, over time, the host cell and the engulfed cell became inseparable parts of the same single-celled organism
State the 6 lines of evidence supporting endosymbiosis
- Morphology: the shape and size of both mitochondria and chloroplasts are similar to those of prokaryotic cells
- Reproduction: a cell does not synthesize a mitochondrion of chloroplast; just like prokaryotic cells, mitochondria and chloroplasts are derived from the division of pre-existing organelles via binary fission.
- Genetic information: both mitochondria and chloroplasts contain their own DNA which contains protein-coding and non-coding genes that are essential for organelle function (circular)
- Both chloroplasts and mitochondria contain complete transcription and translational machinery
- Similar to free-living prokaryotic cells, both mitochondria and chloroplasts have ETS and ATP synthase (found on plasma membrane)
- Sequence analysis: the sequence of chloroplast rRNA most closely matches that of cyanobacteria, and the sequence of mitochondrial rRNA is most similar to that of heterotrophic bacteria.
State the origin of the endomembrane system
- Organelles of the endomembrane system include: nuclear membrane, endoplasmic reticulum, Golgi, plasma membrane
- Endomembrane system: infolding plasma membrane system led to the nuclear envelope and ER. This is very distinct compared to how chloroplast and mitochondria evolved.
Explain this graphic
Lateral gene transfer: movement of genetic material from the chloroplast/mitochondria to the nucleus, making it less autonomous.
- The genes that stay are involved in repair
- DNA hybridization is used to detect lateral gene transfer (labelled species specifically binds to a DNA that matches it)
- Species A: Gene is in the mitochondria
- Species B: It has already undergone lateral gene transfer
- Species C: Less concentration in mtDNA and in nDNA; it is caught in the act before it has degraded its mtDNA
- The genes in the mtDNA are copied and a copy is transferred into the nDNA and then the original mtDNA is degraded
Not all eukaryotes have mitochondria (ex., Giardia). How did cpn60 show that Giardia ancestors once had a mitochondria but it was lost?
- CPN60 is required for mitochondria to work, it is found in the nucleus (due to lateral gene transfer)
- It is a chaperone that helps imported proteins fold correctly when they enter the mitochondria
- This is found in Giardia, which is evidence for the idea that it did have a mitochondria, but it was lost
