A major difference between eukaryotes and prokaryotes is that eukaryotes have a nucleus, whereas prokaryotes do not. Discuss the impact of having a nucleus on the creation of mature mRNA.
More complex when transcription and translation are separated.
A coworker in your lab discovered a strain of E. coli that has a nonfunctional RNA polymerase. He felt sorry for the suffering E. coli and decided to add an RNA polymerase enzyme and gene from Drosophila to this mutant E. coli to allow the mutant strain to survive. You think that this is a foolish idea that will not work. Put together an argument as to why the addition of a Drosophila RNA polymerase could not possibly allow this mutant E. coli to survive.
E.Coli is a prokaryote and Drosophila is a eukaryote. Eukaryotes have a nucleus and separate transcription and translation.
What happens to a chromosome that loses its centromere?
The chromosome is no longer able to attach to a spindle fiber. Since this is the case, they are usually lost when the cell splits.
What are the three classes of "functional" RNAs? Briefly describe the role of each class of functional RNA.
-Messenger: contains blueprint for protein synthesis
-Transfer: brings correct amino acid to the ribosome
-Ribosomal: makes ribosomes
How many primase molecules are needed on the leading strand? The lagging strand?
One for the leading strand, many for the lagging strand
This form of DNA replication was eliminated during the Meselson-Stahl experiment because the original double-helix did not appear to be preserved during cell division.
This new strand of DNA has its 3' end oriented in the opposite direction as that in which the replication fork travels.
MC: RNA differs from DNA in that it:
-U rather than T
-Usually single stranded
-Ribose sugars instead of deoxy
RNA polymerase must bind to a region of DNA called a(n) ____________ in order to begin transcription.
MC: In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?
DNA contains phosphorous
MC: Which of the following best describes the addition of nucleotides to a growing DNA chain?
A nucleoside triphosphate is added to the 3' end of the DNA, releasing a molecule of pyrophosphate
MC: Two eukaryotic proteins were found to be very similar except for one domain that was very different. Which of the following processes is most likely to have contributed to this phenomenon?
MC: Which of the following statements best describes the messenger RNA?
mRNA is the only type of RNA that carries DNA's protein building instructions
MC: After the peptide bond forms, what will happen?
tRNA B will be carrying the polypeptide and it will shift to the P site.
A number of scientists have become interested in telomerase as a drug target. Why would they be interested in telomerase? How might cancer drug therapies that target telomerase work?
Telomerase is an enzyme that prevents the telomeres of a chromosome from shortening. When the telomeres shorten, the cell eventually dies. In cancer cells, telomerase is constantly working so the cells never die.
What three general characteristics must the genetic material possess?
Contain complex information, replicate faithfully, encode the phenotype.
This term describes the sequence of nucleotides which direct the formation of a new nucleic acid strand.
MC: Splicing of eukaryotic pre-mRNA involves ___ reactions and occurs in the ___ .
Write the anticodon, with correct polarity, of all tRNAs that will bind to the mRNA codon 5' UCG 3', considering wobble-base pairing rules.
This enzyme links two separate lengths of nucleic acid by creating a phosphodiester bond between them.
MC: The poly(A) tails found in the 3' end of an mRNA are important for all the processes listed below except for ___ and ___.
Intron splicing and protein stability
MC: A bacterial protein is encoded by the following mRNA sequence: AUGGUGCUCAUGCCCTAA.... The second methionine codon (AUG) in this mRNA sequence will
MC: Which statement is true regarding negative supercoiled DNA?
That negative supercoiled DNA is underrotated allows for easier strand separation during replication and transcription
MC: DNA consists of repeating units of nucleotides. Which is NOT a component of a nucleotide?
a ribose sugar
MC: Before DNA was known to be the genetic material, scientists knew that genetic material must do or be all of the following, EXCEPT that
genetic material must be composed of many different units to account for the variability seen in nature.
MC: The role of tRNA is:
to act as transporters bringing amino acids to the site of protein synthesis
MC: All of the following are general purpose translation components and could be used in the translation of any gene, except for one. Which one?
MC: In DNA replication, the lagging strand is
the strand which must be replicated in a direction away from the replication fork.
MC: A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is
MC: Which of the following statements about the genetic code are TRUE?
Most amino acids are encoded by more than one codon
Why do eukaryotic chromosomes have multiple origins of replication, whereas prokaryotic chromosomes typically have only one origin?
Eukaryotes have a very large genome and it would take to long if there was only one origin. Prokaryotes have a smaller genome and can have only one.
Briefly discuss the evidence for the semi-conservative replication of DNA
Experiments by Matthew Meselson and Frank Stahl allowed E. coli to be labeled with 15N and 14N and then followed the density of the daughter cells using cesium chloride gradient centrifugation. They predicted that parental DNA molecules of one density which were allowed to replicate in another medium of a different density will show daughter DNA molecules of intermediate density because half will be old DNA and the other half will be new DNA. Their results proved that indeed half was old and other half was new indicating DNA of intermediate density.
Telomeres regulate the replication of the ends of chromosomes in eukaryotes. Why is this structure implicated in human aging?
Telomeres shorten as cells age and cells die when the telomeres are no longer present. When tested on mice, symptoms of aging were observed telomerase was not present. People with diseases of premature aging such as Werner syndrome and dyskeratosis congenital have shorter telomeres than healthy people.
Here is a list of eukaryotic RNA polymerases. Match them with what they transcribe. RNA Pol I; RNA Pol II; RNA Pol III.
Pol I: rRNA. Pol II: snRNA. Pol III: tRNA.
Two double-stranded fragments of DNA are exactly the same length. At 89°C, fragment A has completely denatured, which means that the two strands have separated. At that temperature, fragment B is still double-stranded. How might these fragments differ, to result in different denaturation temperatures?
The fragments may have a different composition of nucleotides. GC have three hydrogen bonds while AT have two hydrogen bonds.
What is the spliceosome?
The spliceosome is the RNA-protein complex that is responsible for intron-exon splicing in eukaryotes.
While actually a form of RNA polymerase, this enzyme lays down the initial nucleotides to set up a condition where DNA polymerase can then take over for replication.
Whereas the nucleotide strand used for transcription is termed the____________ the nontranscribed strand is called the _____________ .
template, non-template strand
This method of replication preserves the covalent links on one strand of DNA but allows permanent separation of the "parental" double helix to form two templates.
MC: Which of the following are role(s) of the 5' cap?
The cap plays a role in the removal of introns.
The cap protects the RNA from degradation.
The cap acts as a binding site for the ribosome.
MC: The 5' cap on an mRNA is important for all the processes listed below except for the ___ of an mRNA molecule.
The cap acts as a binding site for the ribosome, The cap plays a role in the removal of introns
MC: The TATA-binding protein (TBP) binds to the TATA box sequence in eukaryotic promoters. What is its function in transcriptional initiation?
It bends and partly unwinds DNA at a promoter.
MC: As a ribosome translocates along an mRNA molecule by one codon, which of the following occurs?
The tRNA that was in the A site moves into the P site.
MC: Which is true of the secondary structure of DNA?
Bases on complementary strands are held together by hydrogen bonds.
MC: What would Avery, Macleod, and McCarty have concluded if their results had been that only RNAse treatment of the heat-killed bacteria prevented transformation of genetic virulence?
that protein was the genetic material
What is semiconservative replication?
Each of the original nucleotide strands remains intact even though they are not combined in the same molecule.
Genetic material must replicate faithfully. Describe how the double-stranded structure of DNA gives it this property.
The double-stranded structure can be used as a template. Each strand is replicated so that the information is passed down correctly.
Explain at least two reasons why the following definition of a gene is inadequate: "A gene consists of DNA sequences that are transcribed into a single RNA molecule that encodes a single polypeptide."
This does not include all of the components of a gene such as transposable elements. This definition says what a gene does but not what a gene is.
Are Okazaki fragments formed on the leading strand during DNA replication? Explain your answer.
No they are formed on the lagging strand.
In the Meselson-Stahl experiment, what hypothetical form of DNA replication results in the same DNA density distribution as the semiconservative method after the first cell division, but was not supported upon the second cell division?
Identify Purine or Pyrimidine: Adenine, uracil, guanine, thymine, cytosine.
Purines: A, G
Pyrimidines: T, C, U
MC: Which of the following statements is not true concerning RNA and DNA?
RNA is more stable than DNA
MC: What secondary structures are formed when single-stranded DNA or RNA is inverted and complementary?
MC: Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes
excision of introns
Kornberg used the phage PhiX174 to demonstrate DNA pol I was able to produce biologically active DNA in vitro. Describe the experimental methodology that he used to draw the conclusions that DNA pol I could produce biologically active DNA.
Name the three major modifications of mRNA of eukaryotes before it is transported to the cytoplasm. In addition, tell why each of the modifications is necessary.
MC: The 3' untranslated region affects the ___ of mRNA and the ___ of the mRNA protein-coding sequence.
Short "bursts" of DNA synthesis that establish the lagging strand are called these.
MC: In each round of the elongation cycle of protein synthesis, a new _______ binds to the codon in the _______ site, then the peptide is transferred from the tRNA in the _______ site to the new aminoacyl-tRNA, and finally the entire _______ moves along the mRNA in a 5' to 3' direction.
MC: If a DNA molecule of 50 base pairs contains 15 cytosine bases (C), how many thymine bases will it have?
MC: When codons that code for the same amino acid differ in their ________, a single tRNA might bind both of them through wobble base pairing.
MC: Heterochromatin is characterized by all of the following, EXCEPT that it
contains genes that require high levels of transcription.
MC: The chemical differences between DNA and RNA make RNA __________ stable than DNA and allow it to exist __________ in the life of most cells.