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Transcription (RNA Synthesis)

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This quiz is based on the process of Transcription (RNA synthesis).

1. The process by which messenger RNA is synthesized by complementary base pairing of ribonucleotides with deoxyribonucleotides to match a section of DNA (a gene) is called :
• Translation
• Replication
• Transcription
• I have no idea ! !
Answer: Transcription
The correct answer is Transcription. Transcription is the process of copying DNA to mRNA and is the first step of protein biosynthesis.


2. The sequence of bases located prior to the gene (along the DNA strand), to which a complex of RNA polymerase and sigma factors attaches itself to initiate transcription is called :
• terminator
• exon
• promotor
• telomere
Answer: promotor
A promotor may be described as a sequence of bases at which RNA polymerase begins transcription. Once the RNA polymerase - sigma factor complex recognizes the promoter sequence, the sigma factor dissociates from RNA polymerase which unwinds the DNA helix thus exposing a template for transcription.


3. A segment of DNA that includes regions preceding and following the coding DNA ( introns as well as exons ) is called :
• cistron
• retroposon
• operon
• transposon
Answer: cistron
The correct answer is cistron. Note that the terms cistron and gene are approximately the same. A gene could have several cistrons but this is unusual.



4. Genes that are expressed at all times and under all conditions of growth are called :
• constitutive genes
• regulatable genes
• antibody genes
• chimeric genes
Answer: constitutive genes
Constitutive genes are expressed under all circumstances by a cell or organism, regardless of environmental influences.


5. Proteins that bind between the promotor region and the section of the gene which is transcribed thus blocking transcription (preventing gene expression) are called :
• Activators
• inducer
• Operator
• Repressors
Answer: Repressors
Repressor proteins bind to DNA in such a way that they interfere with RNA Polymerase action and prevent gene expression. This is a form of negative control on protein synthesis. Hence, the activity of specific proteins within cells is regulated through either blocks or enhancement of RNA polymerase action at the level of transcription. Also, genes whose expression can be controlled by external factors are called regulatable genes.


6. A G-C-rich stretch of nucleotides, followed by an A-T-rich stretch of nucleotides is the signal for :
• Rho independent termination
• Initiation
• transcription
• Rho dependent termination
Answer: Rho dependent termination
For rho-independent termination, there is a G-C-rich stretch of nucleotides, followed by an A-T-rich stretch of nucleotides. When this stretch is transcribed into RNA, the sequence of the nucleotides is such that the RNA molecule forms a short double-stranded region called a hairpin which significantly slows down RNA polymerase causing it to pause in the A-T-rich region. Because the A-T rich region is relatively unstable, the transcription complex falls apart, ending transcription.


7. The bacterial promotor sequence usually found at the -10 position (ten base pairs upstream of the transcription start site) is :
• TTGACA
• TAGACA
• TATTAT
• TATAAT
Answer: TATAAT
Bacterial promoters usually contain two important DNA sequences that are involved in the regulation of transcription :
1) TATAAT at the -10 position.
2) TTGACA at the -35 position.
Both sequences are upstream of the actual gene...The –10 sequence is also known as the Pribnow box, in honor of its discoverer.


8. Sections of DNA within a gene that do not encode part of the protein that the gene produces are called :
• Exons
• Transposons
• Introns
• intein
Answer: Introns
Introns are sections of DNA within a gene that do not encode part of the protein that the gene produces. They are spliced out of the mRNA that is transcribed from the gene before it is exported from the cell nucleus. The regions of a gene that remain in the spliced mRNA are called Exons. Introns allow for alternative splicing of a gene, so that several different proteins that share some common DNA sections can be produced from a single gene.


9. An RNA molecule that can catalyze either its own cleavage (self-splicing) or the cleavage of other RNA molecules is :
• A ribozyme
• A spliceosome
• A chaperone enzyme.
• An inducer
Answer: A ribozyme
RNA with enzymatic activity, (for example - self-splicing RNA) are called ribozymes. Note that the functional part of the ribosome (the protein translator), is a ribozyme.


10. Due to the presence of Introns and Exons, in Eukaryotes the splicing process of pre-mRNA can lead to different ripe mRNA molecules and therefore to different proteins. This phenomenon is called :
• exonic splicing
• alternative splicing
• intronic splicing
• gene splicing
Answer: alternative splicing
The transcribed mRNA includes several introns and exons. But what is an intron and what is an exon is not decided yet. This decision is made during the splicing process. The result of alternative splicing is that information can be stored much more economically. Several proteins can be encoded in a DNA sequence whose length would only be enough for two proteins. The regulation of the splicing process is still widely unknown...


11. A base sequence that is part of the DNA of an organism and appears to have once coded a gene product, such as a protein or transcription factor but no longer does so is called :
• A selfish gene
• A jumping gene
• A pseudogene
• An Oncogene
Answer: A pseudogene
Pseudogenes are inactive sequences of genomic DNA which have a similar sequence to known functional genes and are considered to be evolutionary relatives to normally functioning genes.


12. A guanine triphosphate nucleotide that binds to the 5' end of the mRNA thus increasing the stability of the synthesized RNA and enhancing translation efficiency is called a :
• poly-A-tail
• leader
• trailer
• Cap
Answer: Cap
Most mRNAs have their starting end blocked by the addition of a cap (7-methylguanosine) which has no free phosphates. As a result it is protected from attack by phosphatases, or nucleases. It also helps ribosomes attach for translation.


13. The series of three consecutive mRNA bases coding for one specific amino acid in a protein is called a :
• intron
• exon
• transposon
• codon
Answer: codon
A codon is a three nucleotide sequence which codes for the insertion of a unique amino acid during translation. As an example, UCU specifies the amino acid serine.


14. A series of 20 to 200 Adenine ribonucleotides that is added to the 3' end of the transcribed RNA molecule (pre-mRNA) that helps in the transportation of mRNA out of the nucleus is called :
• trailer
• cap
• a Shine-Dalgarno sequence
• the poly-A-tail
Answer: the poly-A-tail
The poly A tail which is usually 20 to 200 nucleotides is not encoded by the gene but is added post-transcriptionally. It is is thought to confer stability to the mRNA. The addition of the poly-A-tail is called RNA polyadenylation.


15. A collection of genes including one which acts as a switch that governs the expression of the structural genes in the collection is called :
• An Operon
• lac operon
• A regulon
• Does everything have to have a name ? ? ! !
Answer: An Operon
An Operon is a collection of multiple structural genes so that they are transcribed as a single mRNA. Operons found primarily in prokaryotes and nematodes were first described by Francois Jacob and Jacques Monod in 1961. They allow cells to respond to their environment.


16. The switch of an operon is turned on if specific substance is not bound to the operator. This substance is called :
• a repressor
• a promoter
• an operon
• an activator
Answer: a repressor
A DNA-binding protein in prokaryotes that prevents the transcription of a gene by binding to the operator region is called a Repressor. For example : The lac repressor protein prevents the expression of the lac Operon which governs the production of enzymes for metabolizing lactose.


17. The lac repressor protein binds to the operator region...
• in the absence of lactose
• in the presence of lactose
• in the presence of cAMP
• in the absence of glucose
Answer: in the absence of lactose
The lac repressor stops the metabolism of lactose in bacteria as long as glucose is available. However, when lactose is plentiful and glucose is scarce, the lac repressor becomes inactive. This allows the conversion of lactose to glucose.


18. A RNA transcript (whose base sequence is complementary to that of the mRNA of a gene) that can inhibit the expression of a gene by forming a duplex with the mRNA strand is called :
• antisense RNA
• tRNA
• dsRNA
• rRNA
Answer: antisense RNA
A RNA sequence that is complementary to the mRNA of a particular gene will prevent the translation of that gene into a protein by binding to the mRNA of that gene. This may be a defense mechanism against viruses which can use double-stranded mRNA as an intermediate.


19. A gene that encodes RNA that functions without being translated into a protein is called :
• An RNA gene
• AN Oncogene
• A quiet gene
• A pseudogene
Answer: An RNA gene
A Gene that is transcribed into RNA which in turn is not translated into a protein is called an RNA gene or non-coding RNA (ncRNA) or functional RNA (fRNA). Examples are : Transfer RNA (tRNA) and Ribosomal RNA (rRNA), both of which are involved in the process of translation.


20. The base sequence of the RNA strand transcribed from a DNA strand of the sequence T-G-C-A-G-C-A-C-A is :
• A-C-G-U-C-G-U-G-U
• A-C-G-U-C-G-U-G-U
• U-G-C-A-G-C-A-C-A
• G-U-A-C-U-A-C-A-C
Answer: A-C-G-U-C-G-U-G-U
For the transcribed RNA sequence, base pairs are : A - U and G - C.



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