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Bio Study Guide Exam 31. How is DNA organized into chromosomes? What are nucleosomes and how are they involved in packaging DNA – what leads to chromosomes being visible during mitosis – why does chromatin need to be decondensed before genes can be transcribed- DNA is packed into nucleosomes attached to histones and condensed- nucleosomes are the full structure of the DNA wrapped around 8 histones that forms when DNA is condensing- the condensation of the DNA leads to the visibility of DNA during mitosis- chromatin needs to be de condensed before genes can be transcribed because to break apart the DNA for replication they cant be wrapped around histones2. what was the scientific evidence that DNA was the cells genetic material – what are Chargaff rules and how did they help Watson and crick come up with the double helix structure for DNA- scientific evidence for DNA as the genetic material was that DNA could get into bacteria and cause it to be radioactive whereas proteins couldn’t and so couldn’t be genetic material – Hershey chase experiment- Chargaff rules are that the percentage of base pairs is always essentially the same – this helped Watson and Crick come up with the structure because they knew that it had to be a symmetrical structure and had to mimic itself and so the double helix was born from x-ray crystallography3. What is meant by the 5’ and 3’ ends of a DNA or RNA strand – how is DNA replicated – why is there a leading and lagging strand – what is meant by the major and minor groove – why does there need to be an origin of replication – what is meant by semiconservative replication and how was this shown to be the way DNA replicates- the 5’ and 3’ end are names that were assigned to the stands to differentiate them from each other - DNA is replicated by transcription, and translation, - The major groove is the bigger space between the spiraling strands of DNA- There needs to be an origin of replication because the DNA is not circular and so has to have a start and a stop- Semiconservative replication means that the parent strand breaks apart to help replicate more strand but doesn’t break apart the actual strand simply moves around making more kid strandso Was shown to be how DNA replicates through making the parent strand heavy and so in a solution would sink to the bottom – since there was still 2 bands after 2 or 3 rounds of replication had to be semiconservative4. why is one DNA strand replicated in a discontinuous fashion – why are RNA primers required to replicate DNA – what are polymerases – what would happen if DNA polymerases didn’t have a repair function - why is it not important for RNA polymerasesto have a repair function- DNA is replicated like this because the DNA polymerase can only work in the 5 – 3 prime direction and so has to do like suicides down the DNA- RNA primers are required to replicate DNA because the polymerase cannot bind and recognize the place to start replication without one - Polymerases are enzymes that pull nucleotide bases from the nearby cytoplasm to base pair the existing DNA strand- If DNA polymerases didn’t have a repair function than our DNA would get very mutated very quick and the human race probably wouldn’t still be around- RNA doesn’t need to be repaired because has a really short lifespan and so a mutation wouldn’t hurt it really5. What is transcription – how does it differ from replication – how do RNA polymerasesknow where to initiate transcription – how do mRNA’s specify a particular protein – howdo mutations in the DNA effect this specification – how does the cellular machinery that makes proteins know where to start – how does it know the correct reading frame- Transcription is the writing of the complementary RNA strand to a DNA strand - It differs from replication because your turning DNA into RNA rather than just matching DNA with DNA- RNA polymerases know where to start transcription because they can recognize the promoter and tata box in an AT rich area- mRNA’s specify a particular protein because during translation they code for the various amino acids that make up the protein- mutations in the DNA effect this because they change the amino acids that code for the protein essentially changing the structure and function of the protein- the machinery knows where to start because it can recognize the cap/poly-a tail that is put on the end of a mRNA- it knows the correct reading frame by going along the mRNA until it comes upon a start sequence – usually AUG which aligns the coding frame6. Will a prokaryotic promoter work in a eukaryotic cell – will an animal promoter work in a plant cell – how would you test this?- 7. What is the difference between general and specific transcription factors – what is the general function of each – how do steroid hormones activate gene expression- transcription factorso General Stretch from the specific factors to the tata box and sets the polymerase to start in the right placeo specific needed for the polymerase to find the strand and anchor to it- steroid hormone receptors activate gene expression by binding to a ligand or otherspecific transcription factor and activates the binding of the kinase, this causes thestat protein to dimerize which stimulates transcription8 what are the different types of RNA’s found in pro and eukaryotic cells – what are theirspecific functions – how/where are they processes – what are the differences in processing RNA’s between pro and eukaryotes (tRNA and rRNA) tRNA – used for protein synthesis rRNA- helps decode mRNA into tRNA mRNA – used for protein synthesis – codes for tRNA’s the differences in processing RNA’s between eukaryotes and prokaryotes are that in prokaryotes they don’t need caps and poly a tails so that it can be immediately translated as its being transcripted9. Where and how do ribosomes initiate, elongate, and terminate translation – how do tRNA function – Why are aminoacyl tRNA synthase so important – how can their be fewer tRNA than codons this happens in the cytoplasm and get on the translation and when they hit a stop codon everything falls off at once tRNA function by being pieces of amino acids that the translating ribosomal subunit pulls into site A and then attaches to the chain of amino acids it is using to make a protein aminoacyl tRNA synthase is important because it is responsible


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UMD BSCI 105 - Bio Study Guide Exam 3

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