Chlamydomonas: a model system The chlamydomonas: First: chlamydomonas reinhardtii - Eukaryoric Green Alga (algae) It has an eyespot We can use it as a model system because: easy to grow, haploid Haploid is an advantage from an experimental point of view because: They have a single copy of the genome Unable to mask mutations It enjoys a moderate light and temperature for growth (24-28 C) Two distinct types of life cycles Chlamy are mostly haploids when it comes to mitosis and growth When conditons are unfavorable, it develops mating types (similar to male and female) Haploid gametes subsequently fuse to form diploid zygotes Growth media In lab we will grow Chlamy in a liquid media called TAP. Two types: macronutrients are essential for cell function, micronutrients Example of macronutrient: NH4Cl -> NH4 + Cl- Ammonium is required because it yields Nitrogen, which is desired because it builds protein It's the backbone of DNA. Chlamy cannot grow without source of nitrogen In the case of FeSO4, Fe is required to produce hemoglobin. Conspicuous absence of carbon , water , sugar , etc. Growth curve When grown in the lab, Chlamy cells follow a distinct "growth curve" common to most microbes Flasks of growth media get darker and darker as concentration increases. Growth curve characterized by shallow slope first, then steep slope, then shallow slope . a.k.a. lag phase, exponential phase, stationary phase Generation time/doubling time is amount of time for a cell to divide Growth rate: change in cell number over time Growth rate eases/stops because of lack of macronutrients Growth = cell division Chlamydomonas phylogeny: Chlamy (and all algae) are photosynthetic eukaryotes but they are not plants. Chlamy and plants once had a common ancestor a billion years ago Chlamy and humans share flagella- it is identical flagella. Using Chlamy to investigate ciliopathies Sensory cilia detect light, other things, threats, etc. Defects cause various disorders and issues Flagella: homology vs homoplasy Eukaryotic flagella is made up of microtubules, 500 proteins, etc. Prokaryotic flagella is completely different, less complex Both however have same function, are analogous Both a result of convergent evolution Homolog: traits (or proteins, genes) that share a common ancestry Analysis of 7,476 Chlamydomonas proteins How many of these proteins have homologs in humans, in plants?