EXAM 3 Flashcards
Draw the structure of deoxycytidine monophosphate (dCMP). Be sure to indicate all charges that exist at physiological pH.
Draw a linear diagram of a typical, protein-coding, eukaryotic gene. Assume this gene contains one intron. Indicate important regions of the gene and briefly describe their function.
Choose one classical experiment that led to the discovery that DNA was the genetic material, and explain it. Be sure to include the experimenters, their experiment approach, their results, and their conclusions.
Henry and Chase used two kinds of markers on bacteriophages, S34 on the protein part of the bacteriophages and P32 (a radioactive marker) on the DNA part of the bacteriophages. They allowed the bacteriophages to mix/infect e. coli and then centrifuged this until the E. coli was at the bottom and was separated from the bacteriophages. They only found P32 markers in the E. coli and this proved DNA to be the genetic material.
Suppose you isolate genomic DNA from a newly discovered organism and find that 20% of its bases are adenine. What percent of nucleotides in the genome of this organism are cytosine?
30% cytosine
Suppose an error occurs during splicing of an intron and one extra nucleotide is left attached to the junction between the two exons. Describe the effect, if any, this would have on the protein made by ribosomes that read the mRNA.
If one extra nucleotide was left all the following codon would be read incorrectly (shifted over one letter). This would cause the wrong amino acids to be made because its reading the shifted codons
Would you expect mRNA in mitochondria of eukaryotic cells to have a 7-methyl G cap at their 5’ end? Why or why not?
No, in eukaryotic cells mRNA’s are capped with a 5’ m7G cap that promotes their translation and stability
Briefly describe how eukaryotic ribosomes translate a messenger mRNA. Be sure to include steps involved in initiation, elongation, and termination.
A. The very end of linear chromosomes cannot be replicated by the standard mechanism used to replicate the bulk of the DNA. Why not?
B. Briefly describe how typical eukaryotic cells get around this problem of replicating the ends of chromosomes.
A. the lagging strand, synthesized in short fragments called Okazaki fragments, experiences a challenge when it comes to the end. The removal of the RNA primer at the end of the lagging strand leaves a single-stranded overhang known as the “telomere,” and conventional DNA replication mechanisms cannot fully replicate this region.
B. They get around this problem two ways, first they have telomeres at their ends which are non repetitive non coding sequences, because they are noncoding it doesn’t matter if some get left off. Second, telomeres attract telomerase, this carries RNA fragments that match the long noncoding sequences of telomeres and they come and fill in the ends.
Describe the function of the following proteins, complexes, or enzymatic activities
Histone -
Primase -
Ligase -
Ubiquitin -
3’ to 5’ Exonuclease activity of DNA polymerase -
Histone - used to form histone octamers that will be wrapped around by DNA to compress it
Primase - used for DNA polymerase to be able to bind to DNA to begin replication (its an RNA)
Ligase - joins Okazaki fragments together
Ubiquitin - entry ticket to proteosome where proteins are recycled
3’ to 5’ Exonuclease activity of DNA polymerase - does the proof reading , checks for “typos”
Suppose a mutation in the gene encoding the tryptophan repressor prevented the repressor protein from binding tryptophan. What effect would this mutation have on expression of the trp operon?
This mutation would cause an excess of tryptophan because there will be nothing to prevent the creation of more.
Describe how E. coli uses both positive regulation and negative regulation to ensure that the lactose operon is expressed at the appropriate times.
