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Example Questions
Example Question #1 : Understanding Prokaryotic Genes
Which of the following is true of Rho-dependent transcription termination in prokaryotes?
None of the other answers
Rho unwinds the DNA-RNA helix at the transcription bubble
Rho uses GTP as a source of energy
Rho is a nuclease that terminates transcription by cutting template DNA
Rho attaches to a Rho recognition site on the DNA template
Rho unwinds the DNA-RNA helix at the transcription bubble
Rho attaches to a Rho recognition site on the mRNA strand and uses ATP to move along the mRNA strand towards RNA polymerase. When RNA polymerase pauses at the terminator, Rho unwinds the DNA-RNA hybrid. RNA polymerase, Rho, and the newly synthesized mRNA are released.
Example Question #1 : Understanding Prokaryotic Genes
Prokaryotic genes are often grouped together based on function. What are these groups of genes called?
Clusters
Promoter sequences
Operator sequences
Linked genes
Operons
Operons
Bacteria organize some of their genes into operons. Operons contain genes of a similar function grouped together, and these genes are all transcribed together. For example, the lac operon involves the three genes required for breaking down lactose. There is no point in only transcribing one or two of the three genes since they are all required to break down lactose. Thus, they are under the control of a single operator and are all transcribed when the operator is active.
Example Question #11 : Genes And Dna
Bacterial plasmids can __________.
be present in multiple copies
carry antibiotic resistance genes
transfer between bacterial cells
All of these
integrate into the bacterial genome
All of these
Plasmids are small pieces of DNA that are not part of a bacteria's genome. The genes contained on plasmids are not necessary for proper function of the bacteria. However, bacterial plasmids can carry genes to confer antibiotic resistance, and commonly do. Plasmids can be transferred between bacteria via conjugation, and can be integrated into their genomic DNA.. Plasmids are usually present in more than one copy per cell.
Example Question #2 : Understanding Prokaryotic Genes
Which of the following technological advances allows for the creation of a “recombinant plasmid”?
Restriction endonucleases
Viral vectors
Sanger sequencing
cDNA libraries
Watson-Crick base pairing
Restriction endonucleases
Restriction Endonucleases, or otherwise known as restriction enzymes, allows biologist to “cut and paste” different DNA sequences together. The use of restriction endonucleases is critical for the creation of recombinant plasmids. Viral vectors is incorrect, as viral vectors are useful in the application of recombinant DNA plasmids, delivery to host cell, but not in forming.
Example Question #1 : Understanding Prokaryotic Genes
A mutation in the bacterial cell escherichia coli makes it unable to break down the sugar lactose. Which of the following is not a potential mutation that could result in this phenotype?
A point mutation in the LacZ gene that abolishes enzyme activity
A mutation in the region DNA polymerase binds to in the promoter
A frameshift mutation in the LacZ coding region
A mutation in the operator that blocks the activator from binding
A mutation in the region DNA polymerase binds to in the promoter
DNA polymerase is not involved in the process of transcription. The incorrect answer could be corrected if it was rewritten as "a mutation in the promoter region where the RNA polymerase binds to."
Example Question #2 : Understanding Prokaryotic Genes
When a repressor binds to the __________, the LacZ gene does not get expressed.
promoter
terminator
operator
gene
operator
The region of a gene where activator/repressors bind in prokaryotic organisms is called an operator. The protein that's bound to the operon strongly influences the level of gene expression.
Example Question #11 : Transcription
What is an important distinction between the process of translation in prokaryotes versus eukaryotes?
Prokaryotes produce a different set of amino acids from translation than eukaryotes
Only eukaryotes perform translation
Translation may occur at the same time as transcription in prokaryotes; they always occur separately in eukaryotes
Eukaryotes perform translation before transcription, while prokaryotes perform transcription first
Prokaryotes do not use RNA; eukaryotes do
Translation may occur at the same time as transcription in prokaryotes; they always occur separately in eukaryotes
The lack of a nuclear membrane in prokaryotes has the advantage of allowing the cell to translate RNA as it is transcribed from DNA. This means that even before the full RNA is produced, the protein coded by that RNA can start being made. Eukaryotes produce RNA inside the nucleus, so it must first be fully transcribed and undergo modifications before it can be moved to the cytoplasm, where translation occurs.
Example Question #11 : Understand Regulation Of Transcription
Hydrogen bonds form between RNA nucleotide residues and DNA nucleotide residues, forming a temporary DNA-RNA hybrid. This process is a part of which phase of prokaryotic transcription?
Template recognition
Initiation
Elongation
Termination
Elongation
Prokaryotic transcription has three essential steps: initiation, elongation, and termination. The initiation process involves the binding of RNA polymerase to the correct region of DNA, and is characterized by the binding of the sigma factor to the RNA polymerase. Elongation occurs as the RNA strand is synthesized from the DNA template. Termination occurs when the RNA polymerase enzyme encounters a rho factor or particular DNA structure that causes it to release the DNA strand and cease RNA synthesis.
It is during the elongation process that RNA nucleotides are matched to the DNA template. The temporary DNA-RNA hybrid exists only briefly at the point of transcription before phosphodiester bonds form between adjacent ribonucleotides.
Example Question #12 : Understand Regulation Of Transcription
Which of these does not contribute to the termination of RNA transcription in bacteria?
Rho factor
Disruption of uracil-adenine RNA-DNA hybrid
Reattachment of the sigma factor
Hairpin loops
Reattachment of the sigma factor
The sigma factor is an important part of initiation for prokaryotic transcription. Once transcription has been initiated, however, the sigma factor is released during elongation. RNA polymerase synthesizes the RNA product until it is interrupted in one of two ways. In rho-dependent termination, a rho factor protein interferes with RNA polymerase binding and causes it to release the DNA strand. In rho-independent termination, structural features of the DNA cause RNA polymerase to become detached. The structures include hairpin loops, which generate steric hindrance, and adenine-rich sequences, which lead to weak binding of the RNA product to the DNA template.
Example Question #13 : Understand Regulation Of Transcription
In prokaryotic transcription, which of the following is recruited to facilitate the binding of the synthesis enzyme to the DNA template?
A promoter sequence
The sigma factor
RNA polymerase
Messenger RNA
The sigma factor
Inactive RNA polymerase must bind to a specific sigma factor in order to become active in gene transcription. Sigma factors are specialized transcription factors involved in recruiting and activating RNA polymerase. Only once RNA polymerase has bound the sigma factor can it identify promoter sequences and initiate transcription.
mRNA is the product of transcription and is not involved in prokaryotic RNA polymerase recruitment. An RNA primer is essential to recruiting DNA polymerase for DNA replication.
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