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1 What is the significance of the Central Dogma How does this relate to the functioning of cells How has this changed over time How does it relate to the process of gene expression The Central Dogma dictates the flow of all genetic information in cells DNA is the initial source of information it is copied and transcribed into RNA and that transcribed information is then translated to create proteins The proteins made here are needed for the cell to function Over time we started to realize that certain viruses called retro viruses can actually copy information from RNA into DNA instead of the other way around in a process called reverse transcription This relates to gene expression because the genetic material written on DNA is eventually expressed in proteins However the specific way that it is expressed can vary tremendously because of splicing In essence some bits of DNA are called introns and others are called exons and after it is transcribed into RNA the RNA removes some of these introns and keeps the exons to make mature RNA Depending on which introns were removed and which exons were kept several different mature RNAs corresponding to several different proteins and several different gene expressions can come from a single strand of DNA 2 What is the relationship between genes and proteins What did Beadle and Tatum contribute to understanding this Beadle and Tatum took several mutations of Neurospora mold that all had a conversion chain where they converted various substances into one another glutamate precursor ornithine citrulline arginine The different mutations which were all one gene apart only ever lacked the enzyme to make just one of these substances Thus they concluded that one gene one protein Enzymes are proteins Now we know it s more like one gene one polypeptide 3 What is the genetic code How many bases are the minimum needed to specify all amino acids Why The genetic code is the sequence of nucleotide bases A C G and T in DNA A C G and U in RNA These nucleotides appear in segments of 3 called codons We know this because there are 20 amino acids and there needs to be enough nucleotides to produce 20 or more unique combinations 3 is the number we settled on as 4 3 64 which is more than enough 4 How was the code broken What are the general features of this code This code is nearly universal redundant has 1 START codon and 3 STOP codons and has no other punctuation Plus as I mentioned above there are 3 nucleotides corresponding to one codon which corresponds to one amino acid While one amino acid can have multiple codons no codon can have multiple amino acids Without punctuation the code is broken with the STOP codons 5 What are the different kinds of RNA and what are their roles in gene expression What are the stages in gene expression and how do these relate to the different kinds of RNA The two main stages in gene expression are transcription where DNA is converted into the simpler mRNA and translation where mRNA acts as a blueprint for rRNA to put together the amino acids that tRNA brought in mRNA is the direct product of transcription copied from the template antisense strand of DNA to resemble the coding sense strand It is an intermediate form of DNA sent to the cytoplasm providing information for how proteins are constructed rRNA is a necessary component of both the small and large ribosomal units In addition it creates the enzyme peptidyl transferase which is the enzyme that makes the peptide bond between initiator tRNA s carboxyl group in the P site and charged tRNA s amino acid in the A site tRNA interacts with both mRNA and amino acids and is crucial to translation Charged tRNA is a combination of tRNA and a specific amino acid This combination is created by the enzyme aminoacyl tRNA synthetase which has to be specific to both the amino acid and the anticodon on the tRNA Eventually once the charged tRNA gets to the ribosome in the cytoskeleton it arrives at the A site It s anticodon has to match the mRNA s codon so the chain can be assembled Initiator tRNA is paired with either methionine eukaryotes or N formylmethionine prokaryotes and it s presence at the P site initiates translation Specifically it carries the anticodon UAC which corresponds to AUG the START codon snRNA is involved in the modification of primary transcripts into proper mRNA When paired with proteins it creates something called snRNPs These snRNPs are at intron exon splice junctions indicating the end of an intron and they also make up the spliceosome Their presence at the splice junctions tells the spliceosome where to cut during splicing miRNA and siRNA interfere in certain messages in DNA that they don t want expressed Specifically miRNA silences while siRNA cleaves the mRNA 6 What is the basic enzymatic activity of prokaryotic RNA Pol Does it exist in different forms and if so what distinguishes them What are the requirements for the transcription reaction The basic enzymatic activity of RNA POL is the successive addition of amino acids onto each other to form a chain RNA polymerase does not exist in specific forms in prokaryotes After the sigma factor recognizes the promoter on the DNA the basic enzymatic activity happens the core polymerase adds matching nucleotides to whatever code is on the template antisense strand The transcription reaction requires a promoter which the holoenzyme recognizes a start site where core polymerase attaches and begins transcription and a terminator where transcription ends 7 How does transcription in eukaryotes differ from prokaryotes How does the polymerase used for transcription differ Eukaryotic transcription is quite similar with the same basic parts of RNA Polymerase sigma factor core polymerase and the same basic requirements promoter start site terminator However it differs in a few major ways It s transcription and translation are not coupled The 3 end is not the end of transcription Instead a couple hundred A bases are added to make the 3 poly A tail Splicing occurs transforming it into a different final product The biggest change is that there are three different forms of RNA Polymerase creating three different things and all of these forms have their own promoters RNA Polymerase I makes rRNA Polymerase II makes mRNA and Polymerase III makes tRNA Pol II is notable because it cannot detect its own promoter it needs the help of proteins called transcription factors 8 What is RNA processing When and where does it occur Do both prokaryotes

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Purdue BIOL 10200 - Focus Questions #3 (Gene Expression)

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