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Purdue BIOL 10200 - Ploidy and Cell Cycle Notes

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Class Overview:There will be an extra credit opportunity in this classYou have to register for PSOs to be able to come. I am registered for Tuesday 5:30-6:20 in LilyG-126, but I can also attend Monday 1:30-2:20 in Stewart Room 320.Each PSO session reviews the previous session, because multiple choice quizzes are over theprevious week’s lab and lectures.Lectures are usually slightly ahead of LabsCourse Overview:● Cell cycle, division, mitosis and meiosis● Genetics (Mendelian and non-Mendelian inheritance)● Gene expression: how info stored in DNA is used to direct production of proteins● Cellular communication● Development● Physiology: circulation and gas exchange, neuronal and muscular function, endocrinesignaling, immunity, waste and water balance, etc.Ploidy and Genetic Info:In Biology, we use n both as a measurement of the amount of information; and the number ofdifferent chromosomes in a setA human sperm has “n” informationA human ovum surrounded by sperm has “n” informationTogether, they make a human zygote with 2nPloidy=number of sets of chromosomes in a cell● 1n = 1 chromosome in a set = haploid● 2n = 2 chromosomes in a set = diploid● 3n = 3 chromosomes in a set = triploid (seen in frogs, for example)● 4n = 4 chromosomes in a set = tetraploid (ex: seen in flowering plants)The number of chromosomes in a set is not the same as the unique types of chromosomes. Forexample, humans have 23 types of chromosomes and they are diploids (two each). This meansthat for humans, they have 23 * 2 = 46 chromosomesPeas, on the other hand, have 7 types of chromosomes. They are also diploids (2n) so theyhave 7 * 2 = 14 chromosomesFor eukaryotes, we will be focusing on sexually reproducing diploid organismsOccasionally mistakes will happen. This is known as Aneuploidy, which means not having theTRUE number of chromosomes● An extra chromosome (Down Syndrome)● Missing a chromosome (Where females have only one X chromosome in Turnersyndrome, for example)_________Cell Division is needed to heal wounds, grow the body, evolve the body and reproduce.Reproduction is a key element of life that requires 3 things:1. Replication of genetic material (Interphase)2. Accurate segregation of genetic material (Cell Division)3. Division of cytoplasm (Cytokinesis)This process needs to be controlled and responsive to environmental conditions.What happens if cell division is uncontrolled? This leads to tumors and cancerous growthsProkaryotes have no organelles or internal compartmentalization, but Eukaryotes do havethose things.Eukaryotes divide by Mitosis (2 daughter cells) or Meiosis (4 daughter cells).It should be mentioned that prokaryotes have a very simple form of asexual cell divsion calledbinary fission, but it is NOT the same thing as Mitosis or Meoisis. It still requires replication andsegregation of genetic material, but the genetic material is highly compacted and twistedbecause there is so much less room, which simplifies the replication and segregation process.For example, E Coli’s chromosome is about 1400 um but the E Coli length is about 2 um. So thegenetic information that is going to be put in that chromosome is super twisted and condensed.Cell Cycle:Binary fission is an asexual reproduction where replication is immediately followed bysegregation. This is very different from eukaryotes, where there is time in-between replicationand segregation● We once thought this was passive, but now we know it is activea. It requires specific proteinsb. Most bacteria and archaea produce FtsZ proteins (see textbook notes forChapter 10)c. Septum (new cell wall) forms at the site of the ring of FtsZ protein to split the cellwall in a process called septationd. FtsZ resembles tubulin (which is normally used to create microtubules ineukaryotes), suggesting an evolutionary link● The chromosome is basically a twisted circle of DNA● Replication starts at the origin and stops at the terminus● The cell elongates at this pointCyanobacteria are photosynthetic bacteria that circulate oxygen in the atmosphere, and weuse them as an example of the regulation of FtsZ proteins.● They actively grow about 19 hours a day. Because of all the runoff from chemicals seenin fertilizers and stuff, they are exposed to lots of nutrients and they grow like fuckingcrazy. When they grow like this, they produce toxins that are damaging to the livers,neurons and kidneys. This is why cell growth needs to be regulated. If they are growingtoo much, it leads to toxinsThree genes (Kai A, Kai B and Kai C) regulate the expression of FtsZ. This means that whenthey are being expressed, they let the cells divide again and again_____The DNA molecule of a bacteria (prokaryote) is usually circularThe DNA molecule of a eukaryotic organism is usually linear, with a point of constriction (thecentromere)What is the Condition of DNA at Each Point in the Eukaryotic Cell Cycle:● The chromosomes start decompressed in Interphase. It’s basically big purple spaghetti.The chromatids have not yet quite come together, so it is pretty much invisible● They start to compress and it looks like one chromosome with one chromatid● Then it replicates and becomes one chromosome with two chromatids● Then it splits and becomes two chromosomes with one chromatid● Rinse and repeatReplication and chromosome separation occur at different times (S phase and mitosis)● Chromatids need to stay together until separation● Release of attachment is irreversibleComponents and Compaction of DNA:Chromatids are one huge, long molecule of DNA that can’t fit into the cell. So it has to be foldeda ton. But how does it compact?DNA (- charge) is complexed with basic histone proteins (+ charge)2 H2A + 2 H2B = tetramer2 H3 + 2 H4 = tetramerTwo tetramers (one of each kind) are connected by Linker DNA to make a histone octamer.DNA spools around the histone octamer, creating nucleosome (which in turn helps createchromatin. Chromatin is 40% DNA and 60% protein and this is why!!!)The nucleosome is the first level of compaction. It is further wrapped into a higher order coilcalled the solenoid (this is a condition of interphase during chromatin)Solenoid is further coiled and radially wrapped around the protein scaffold to make themetaphase chromosomesIf we deconstruct chromosomes, it looks like this: Chromosomes -> rosettes of chromatin loops-> chromatin loops -> solenoids -> nucleosomes -> DNA double helix that we know and loveEnzymes:There are


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