EXAM 2 BSCI207 STUDY GUIDELecture 12: Origin of Eukaryotes (starts at page 603)I. “Eu” means true, “karvon” mean kernel. “True kernel” referring to the nucleus. Meiosis and the subsequent fusion of haploid derivatives is characteristic of euks. II. Key Features- Nuclear Envelope- Endosymbiotic organelles (mitochondria and chloroplasts)- Spliceosomal introns- Dynamic cytoskeleton (asymmetrical growth, cell shape changes possible)- Sexual reproduction (meiosis and syngamy (fussion)- Linear chromosomes- CLUE TO HOW EUKS CAME FROM PROKARYOTIC ANCESTERSIII. Origin of Nuclear Envelope- Nuclear origins are mysterious…How? Why?- How: ER is topologically connected to the outside of the cell and is associated with nuclear envelope- Leading hypothesis is that it derived from infoldings of plasma membraneIV. Why Have a Nuclear Envelope- Martin and Koonin’s hypothesis: Primordial eukaryotes evolved the nucleus and spliceosome simultaneously to defend themselves againsttransposons (which eventually became introns)- Spliceosome: removes introns to make mature RNA product of a gene- Transposons: segments of DNA that can move to other spots in genome causing mutations- Reasoning Only Eukaryotic genes have large numbers of introns Translation is fast Splicing is slow Nuclear pores exclude ribosomes mRNA export to cytoplasm is highly regulated Benefit: Splicing completed before translation startsV. Origin of Mitochondria and chloroplasts- Endosymbiotic Theory based on size of typical bacteria, they are bounded by two membranes (like engulfed cell), have their own, bacterial-like ribosomes, retain vestigial circular genome with similarity to bacteria- Aerobic Bacteria engulfed by anaerobic eukaryote- Bacteria absorbs high energy molecules from host and oxidizes them to supply host with ATP, while bacterium is protected- Mitochondrial Translation Apparatus??- MtDNA points to bacterial origin of mitochondria, closely related on phylogenetic tree- cpDNA bigger than mtDNA, contains ribosomal protein genes, encodestranscription/translation factors/photosynthesis components- mito/chloro from diff bacterial groups- secondary endosymbiosis of photosynthetic euks: product of symbiosis is then engulfed by another eukaryoteVI. Origins of Eukaryotic Cytoskeleton- Actin:distantly related to bacterial MreB (protein found in bacteria), E.Coli lacking MreB become nearly spherical- Tubulin: similar to FtsZ, localizes to fission zone in bacteria and chloroplastsVII. Origins of Sex- DNA repair hypothesis: diploidy and meiosis allows mutations to be eliminated, crossing over allow more precise replacements, help hold homologous chromosomes together until telophase, when diploidy is dominant phase, deleterious mutations can be tolerated (most are recessive)- Evidence in support: several proteins used in both meiotic crossing over and to repair damage (e.g. yast RAD6, RAD50, RAD52. RAD57)- E.Coli homologs also involved in DNA damage- Many “variation is good” hypotheses: variability is good even without mutations present, Ex. Red Queen hypothesis which says that variability is essential to stay ahead of the parasite which evolve quickly to target dominant genotypeVIII. Linear Chromosomes- DNA polymerase must extend from 3’ to 5’ via 3’ donor- At end of chromosome this is provided by a RNA primer- What provides the primer to replace this primer with DNA? Nothing so DNA gets shorter every replication- The solution is telomeraseLecture 13: Diversity of Unicellular Eukaryotes (pp. 593-623)I. Protist: euks that are not green plants, fungi, or animals.II. Protists are paraphyletic - Do not form monophyletic group of ALL descendants of last common ancestor- Most distantly related protists diverged longer ago than the multicellular groups did (plants/animals/fungi)III. Eukaryotic Evolution- Order goes…origin of nucleusanaerobic, heterotrophic euks, origin of mitochondrionaerobic, heterotrophic euks, origin of plastidsaerobic, photosynthetic euks- Few anaerobic heterotrophs exist in euks today, thought to have descenses from aerobic b/c still have vestigial mitochondrial genes in their nuclear DNA- Aerobic heterotrophs: all euks that lack chloroplasts (fungi, and many protists)- Aerobic photosynthetic autotrophs: plants, unicellular and multicellular aglae, other distantly related protists- Photosynthetic groups don’t seem to be monophyletic, thought to b b/c of secondary endosymbiosisIV. Secondary Endosymbiosis- Predatory protist engulfs photosynthetic protist with chloroplast. Nucleus of photosynthetic protist is lost and we have an organelle with 4 membranes- Cholorplasts transferred from green algae to ancestor or euglenids or chlorarachniophytes- Four-membraned plastid is not only evidence for it: expected early phase of two distinct nuclei, one being in same compartment as plastid. Extant example: Guillarda Theta (Refer to Slides)V. Ecological Roles of Protists Low species diversity but high abundance- Heterotrophic protists: eat primary producers- Autotrophic protists: photosynthetic- Without protists, CO2 levels would be much higher, world much warmer- Phytoplankton take up CO2, eaten by primary consumers which die and are consumed by decomposers or scavengers, or die and sink to bottom of ocean where they can make limestone or other carbon containing rocks, or petroleum. These are long-lived carbon sinks. Iron increases phytoplankton abundance, so may help with global warming. - Key primary producers in aquatic environments along with photosynthetic bacteriaVI. How to Move hen Your So Small- Ameoboid motion via pseudopodia- Swimming via flagella- Swimming via ciliaVII. Sex and the Single Cell- Organism doesn’t need sex organs to have sex- Does not need to be mulitcellular- Needs a diploid phase of life cycle, meiosis, reunions of haploid meiotic products- Gazillion ways to have sex!1. Life cycle dominated by haploid cells2. Life cycle dominated by diploid cells3. Amoebozoan slime: spores- a single cell that develops into an adult organism but not formed by gamete fusion. Occasionally will undergo sexual reproduction when two cells fuse during aggregation which then have haploid offspringLecture 14: Multicellular Life (pp. 664-670, 690-694, 800-802)I. Physiochemical Constraints-Why cant unicellular organisms reach large sizes?- Can get pretty big (Bubble alga can be up to 5 cm in diameter)- As cell diameter increases, surface area/volume ratio
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