Prokaryotes Eukaryotes small, simple cells large, complex cells cell wall of peptidoglycan cell wall absent (animals)

1. ProkaryotesEukaryotes small, simple cells large, complex cells cell wall of peptidoglycan cell wall absent (animals) or made of cellulose (plants) circular chromosome nucleus containing many straight-line chromosomes no membrane-bound organelles membrane-bound organelles (nucleus, plastids, Golgi) aerobic or anaerobic mostly aerobic (need O2) conjugation through a sexual reproduction via pilus meiosis + fertilization

2. Domain Eukaryota vs. Kingdom “Protista” “Protist” is now a slang term for a diverse group of Eukaryotes, including many unrelated lineages that are structurally simple Metabolically diverse (autotrophic, heterotrophic, both) Many are single celled organisms, but with more complex cells than prokaryotes Others are multi-cellular, but have morphologically simple bodies that lack true tissues - some algae (such as giant kelp) resemble plants, but they lack true leaves, stems or roots

3. PROTISTS Plants Fungi Animals The name “Protists” has no phylogenetic validity It is not a monophyletic group...

4. 8 major lineages of Protists Freeman 2005

5. Mitochondrion – organelle responsible for aerobic respiration - Enclosed within a double membrane 

6. Mitochondrion – organelle responsible for aerobic respiration - Enclosed within a double membrane Extracts maximum energy from organic compounds by using O2 as the final acceptor for electrons Aerobic Respiration (heterotrophy) CH2O + O2  CO2 + H2O sugar

7. Chloroplast – organelle responsible for photosynthesis Series of stacked membranes called thylakoids, which contain the pigment chlorophyll Traps the energy of light, uses it to energize electrons and rip them off of H2O Drives carbon fixation...

8. Lynn Margulis championed the Endosymbiotic Hypothesis, which held that eukaryotic mitochondria and chloroplasts were originally prokaryotes - first presented this idea in 1981; no one believed her Suggested: (a) mitochondria were descended from an anaerobic bacterium (b) chloroplasts from a phytosynthetic cyanobacterium

9. Primary Endosymbiosis Ancient, anaerobic eukaryote engulfed an aerobic bacterium Aerobic respiration yields more ATP (= cellular energy) than less efficient anaerobic respiration Instead of eating this engulfed cell, they struck up a partnership, or symbiosis - bacteria got safe place to live, steady supply of carbon compounds from its host cell - eukaryote got a more efficient form of metabolism

10. Evidence for Endosymbiosis - mitochondria and plastids have their own circular chromosomes encoding genes needed to replicate their DNA - reproduce by binary fission, like bacteria (splitting in 2, cloning) - same size as bacteria - have their own ribosomes for protein synthesis, which are very similar to bacterial ribosomes - each is surrounded by a double membrane, consistent with proposed engulfing mechanism (end up with membrane of originalbacterium, plus 1 layer of the host’s membrane)

11. Molecular Evidence for Endosymbiosis Freeman 2005 Confirmation came a decade later, when DNA sequence analysis showed that DNA in mitochondria is closely related to a-proteobacteria, while chloroplast DNA is closely related to cyanobacteria

12. Plant Cell: a combination of 3 distinct genomes nucleus (eukaryotic ancestor) light, H2O chloroplast (cyanobacteria ancestor) O2, sugar ATP sugar, O2 mitochondrion (proteobacteria ancestor)

13. Cyanobacterium Primary Endosymbiosis - one eukaryotic cell engulfs a prokaryote, which becomes its chloroplast Heterotroph 1 Alga 1 (red)

14. Primary Endosymbiosis Secondary Endosymbiosis - one eukaryotic cell engulfs another eukaryote - the mitochondria & nucleus of the engulfed cell are eventually lost; all that remains is its original chloroplast Alga 1 (red) Heterotroph 2 Alga 2 (brown)

15. Study Question: - how many membranes would you expect there to be around the plastid of a brown alga? Why? Alga 1 (red) Heterotroph 2 Alga 2 (brown)

16. Secondary Endosymbiosis - multiple origins 2 3 1 Primary endosymbiosis occurred here Secondary endosymbiosis occurred 3 different times A red alga was engulfed by the ancestor of: 1) Euglenoids 2) Dinoflagellates 3) Diatoms + Brown algae (kelp)

17. Nuclear division in Eukaryotes Mitosis:copies nucleus & preserves chromosome number (2N or N, whichever it started as) - cloning: produces 2 daughter cells identical to the mother cell Meiosis:halves chromosome number (2NN), producing haploid (N) daughter cells - how animals produce sperm and eggs - putting 2 haploid cells together to form a diploid zygote is called syngamy diploidhaploid

18. Chromosomes: DNA in eukaryotic nuclei, wound around proteins 46 human chromosomes, arranged in 23 pairs of homologous chromosomes – diploid (2N) state In animals, only gametes (sperm + eggs) are haploid – all other cells are diploid Fig. 13.3, Campbell & Reece 2005

19. Mitosis preserves chromosome # Meiosis halves chromosome # Diploid (2N) Diploid (2N) Diploid (2N) Haploid (N) Fig. 13.9, Campbell & Reece 2005

20. Sex in Eukaryotes Chromosome number is cut in half by meiosis, at some point 2N  N Diploid  Haploid adult cell gametogenesis sperm egg

21. Babies, made diploid Chromosome number later doubles during syngamy (fertilization) N  2N Haploid  Diploid syngamy + sperm egg

22. Sex, made boring Chromosome number is cut in half by meiosis, at some point 2N  N Diploid  Haploid adult cell Most important thing to know: during meiosis, through a process called crossing over, sections of homologous chromosomes get swapped - you end up with new combinations of alleles, together on one chromosome for the first time generates diversity

23. Life Cycles Life cycles depict the various stages in an organism’s life - different stages can look exactly the same, or totally different (like caterpillars and butterflies) Sexual reproduction occurs via meiosis & syngamy; haploid (N) and diploid (2N) states alternate N  2N  N  2N  N  2N … Asexual reproductionoccurs via mitosis, makes exact duplicates