Molecular Genetics Test 3

. One of the termination codons is 5'-UGA-3'. Its corresponding anticodon in normal tRNA is:

. none of the above, there are no "normal" tRNAs that recognize stop codons

mRNA is read in the _______ direction, which corresponds to the _______ of the protein being synthesized.

5' to 3'/N terminus to C terminus

During translation, chain elongation continues until what happens?

A stop codon is encountered.

What is a ribozyme?

An enzyme made up of RNA

All of the following are directly involved in translation except

DNA

The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except

DNA was the first genetic material.

_________ is the correct designation of consensus sequence for the following sequences: AATGCA GGTGTA TAGGCG CGTATA

NRTGYA

Which of the following is/are true?

RNAP III promoters usually contain positions that lie downstream of the startpoint

Which of the following is/are true of snRNPs (snurps)?

a. They are made up of both protein(s) and RNA.

Prokaryotic translation initiation may be regulated by all of the following except?

attenuation

How would one describe the bond that holds the inverted methylguanosine cap on the 5' end of a mature eukaryotic mRNA?

d. 5'-5' triphosphate bridge

Termination (termination and ribosome recycling) of translation involves all of the following except

d. peptide bond formation

Which molecular component of the spliceosome is involved in catalysis of the splicing reactions?

d. snRNA

A gene with 11 exons ________ introns

has 10

An extraterrestrial life form is discovered. It has a genetic code much like that of organisms on Earth except that there are five different DNA bases instead of four and the base sequences are translated as doublets instead of triplets. What is a maximum number of different amino acids that could be accommodated by this genetic code assuming that at least one codon is nonsense (stop)?

24

A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be

3' AAA-GAA-TAA-CAA 5'.

How would one describe the bond that holds the inverted methylguanosine cap on the 5' end of a mature mRNA?

5'-5' triphosphate bridge

Why must RNA splicing be absolutely precise?

A single base error at a splice junction will change the reading frame and result in mRNA mistranslation.

Why must RNA splicing be absolutely precise?

A single base error at a splice junction within an OFR will change the reading frame and result in mRNA mistranslation.

. Which of the following most accurately describes Ala-tRNA Cys?

A tRNA for Cys charged with Ala

Which of the following most accurately describes Ala-tRNA Cys?

A tRNA for Cys charged with Ala

Which of the following events can occur co-transcriptionally in eukaryotes? (select all correct answers)

Capping / Splicing

Which of the following events can occur co-transcriptionally in eukaryotes?

Capping and splicing

Which of the fallowing is false about heat shock or heat shock proteins in E. coli?

Core RNA polymerase is very stable and remains active even above 70 degrees.

Which of the following is most likely to interact with a Met-tRNAmet?

EF-Tu-GTP

Which of the following are not transcribed from DNA? Select all that apply (if more than 1).

G-caps / Poly A tails

What is the major difference between intron removal of group I and group II introns?

Group II introns are released as "lariats" but group I introns are released in a linear form.

Which of the following is most likely to interact with a charged bacterial initiator tRNA?

IF-2-GTP

Many of the RNA polymerase II promoters are TATA-less but they are still recognized by the same specific GTF (general transcription factor) in a sequence specific manner. These promoters must contain ______ plus DPE or DCE that are all recognized by a _______ subunit of ________.

Inr/TAF/TFIID

Which of the following does NOT represent a function of TFIIH?

It has a phosphatase activity necessary for transcript modification

Which of the following is true about the genetic code?

It is read in nonoverlapping triplets of nucleotides (bases) from a fixed point

The enzyme peptidyl transferase, which catalyzes the transfer of the polypeptide chain attached to the tRNA in the ____________ site to the aminoacyl-tRNA in the ____________ site, is a(an) ____________.

P; A; rRNA of the large ribosomal subunit

The enzyme peptidyl transferase, which catalyzes the transfer of the polypeptide chain attached to the tRNA in the _____site to the aminoacyl-tRNA in the ____site, is a (an) _____.

P; A; rRNA of the large ribosomal subunit

The RBS or S-D sequence is a consensus sequence found upstream of the start site in mRNAs transcribed from what type of genes?

Phage and bacterial

Which of the following does not contribute to accuracy of translation in prokaryotes?

Proofreading by the peptidyl transferase enzyme

Which of the following statements best describes the "termination" of transcription in eukaryotes by RNA Pol II?

RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase, which continues to synthesize more "nonfunctional" RNA

Which of the following statements best describes the termination of transcription in prokaryotes?

RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript.

Alternative sigma factors are used as a means to regulate gene expression in bacteria. A replacement of one sigma factor for another on bacterial core RNA polymerase will enable __________ .

RNA polymerases to initiate transcription using a new (different) set of promoters

Many of the RNAP II promoters contain ____, an element generally present at a "fixed" distance upstream from startpoint. When present, this element is bound by ____ via its subunit called ____.

TATA box/TFIID/TBP

One of the RNA polymerase I ancillary factors, SL1, consists of four proteins. One of its component proteins is also required for the initiation by RNA polymerase II and RNA polymerase III as a part of a "positioning" factor. This protein common to all three "positioning" factors is called _______.

TBP

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.

Which of the following is/are false about miRNAs?

They are derived from dsRNA of viral origin

Which of the following is true of snRNPs (snurps)?

They are made up of both protein(s) and snRNA.

The codon/codons (all written in 5' to 3') that the molecule in the fig. could interact with is/are (select ALL that apply)

UUG / UUA

Which of the following is true

a. IF-1 prevents aa-tRNAs from entering the partial A site on 30S b. IF-2-GTP "places" fMet-tRNAi in the partial P site of 30S c. IF-3 when bound to 30S prevents binding of 50S to it d. eIF2 and eIF3 have very similar functions to IF-2 and IF-3 respectively e. All of the above

Alternative splicing

a. can allow the production of different mature mRNAs from a single gene. b. can allow the production of proteins of different sizes from a single gene. c. can allow the production of proteins with different amino acid sequences from a single gene. d. all of the above

In the process of bacterial protein synthesis ribosomal RNAs (rRNAs) ___________.

a. catalyze peptide bond formation b. interact (by base pairing) with mRNA during initiation c. interact with tRNAs in both the A and P sites d. all of the above

Which of the following may affect the stability of an eukaryotic mRNA?

a. miRNA b. 5' G-cap c. poly A tail d. all of the above

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs (even fewer in some organisms). This is best explained by the fact that

a. some tRNAs have anticodons that recognize two or more different codons. b. the rules for base pairing between the third base of a codon and tRNA are flexible.

Refer to figure above. Which of the codons below (all written in 5' to 3') could be recognized by the anicodon in this tRNA?

b. UUU d. UUC

In the figure above the ESEs are __________

b. cis-acting elements d. sites within RNA

When does translation begin in prokaryotic cells?

b. during transcription

Internal Ribosome Entry Sites (IRES) may be present in the mRNAs of _________ to allow for translation of transcripts lacking G-cap.

b. eukaryotes c. eukaryotic viruses

The RBS or S-D sequence is a consensus sequence found upstream of the start site in mRNAs transcribed from what type of genes? (select all correct answers)

bacterial / phage

Which of the following is the least likely mechanism for the regulation of translation in eukaryotes:

binding of metabolites to riboswitches and affecting availability of RBS for the interaction with the small ribosomal subunit.

Statement A: All prokaryotic mRNAs have a Shine-Dalgarno sequence that is necessary for binding to the small ribosomal subunit via base pairing with a complementary sequence present in rRNA Statement B: Eukaryotic mRNAs do not have Shine-Dalgarno sequences but instead, in order to be translated, they must have either 5'G cap or an IRES.

both A and B are true

Statement A: The active binary complex (elongation factor EF-Tu+ GTP) is required to bring the charged tRNA to the A site of the ribosome Statement B: EF-Ts is required for regeneration of active binary complex (EF-Tu+GDP to EF-Tu+GTP)

both A and B are true

What are ribosomes composed of?

both rRNA and protein

A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA codes for this peptide?

c. 5' TTT-CCC-AAA-GGG-TTT-CCC

Refer to figure above. The portion of the molecule labeled 5:

c. is a peptide or an amino acid

Refer to figure above. The portion of the molecule labeled 1:

c. needs to be unpaired to prevent initiator tRNA from fitting into an A site

In the figure above the SR proteins bound to ESEs function as ____________.

c. splicing activators

Accuracy in the translation of mRNA into the primary structure of a protein depends on specificity in

c. the bonding of the anticodon to the codon. d. the attachment of amino acids to tRNAs.

In the figure below the ESEs are __________ (select ALL that apply)

cis-acting elements / sites within RNA / sites within exons

In bacteria (E.coli) termination codons are recognized byclass I release factors (RF1 or RF2)

class I release factors (RF1 or RF2)

What would most likely happen if SR proteins recruited U1 and U2AF (U2 will bind just upstream of U2AF) to the sites shown in the figure above and no other U1 or U2AF could bind anywhere else within this molecule.

d. The RNA transcript would be spliced, joining exon 1 to exon 3.

What type of mechanism could result in joining of RNA fragments originating from two different transcription units.

d. trans-splicing

Different types of riboswitches are used by prokaryotes to regulate gene expression. The binding of a metabolite specific for a particular riboswitch may cause any of the following except:

d. transcription initiation

Many eukaryotic DNA sequences may code for more than one protein in the following way(s) except:

different proteins may be encoded by the same mRNA by utilizing alternative stop codons

Which of the following does not constitute a difference between intron removal in nuclear pre-mRNAs and group II introns?

e. both b. and d. are not true

During splicing of nuclear pre-mRNAs the splicing apparatus called _______has to be assembled in a specific sequence in order to precisely remove all of the _______ and splice together the ____.

e. spliceosome/introns/exons

Internal Ribosome Entry Sites (IRES) may be present in the mRNAs of _________ to allow for translation of transcripts lacking G-cap. (select all correct answers)

eukaryotic viruses / eukaryotes

A scientist studying a "new" organism isolated RNA molecules that may have represented splicing intermediates, excised intron(s), and determined their structure. All of these molecules were linear and all had a G at 5' end. From what you know about splicing what is the most likely explanation of these results?

group I introns were involved

A gene with 13 exons ________ introns

has 12

Which of the following is/are not the function of Class I Release Factor (RF1 for example)?

interaction with the P site of ribosome

A scientist studying fly development isolates two proteins encoded by the same gene that differ from each other by the length of the C-terminal domain. The protein isolated from the head region is identical to the one from the thorax in the N-terminal region but is shorter by 30 amino acids. Analysis of gene sequence indicates a presence of a single ORF that would lead to the production of the longer peptide, the one produced in the thorax . What is the most likely mechanism responsible for the production of the two different peptides encoded by this gene?

mRNAs in the head region are edited by CDAR generating a premature stop codon.

A scientist studying fly development isolates two proteins encoded by the same gene that differ from each other by the length of the C-terminal domain. The protein isolated from the head region is identical to the one from the thorax in the N-terminal region but is shorter by 30 amino acids. Analysis of gene sequence indicates a presence of a single ORF that would lead to the production of the longer peptide, the one produced in the thorax. What is the most likely mechanism responsible for the production of the two different peptides encoded by this gene? Hint: draw a picture.

mRNAs in the head region are edited by CDAR generating a premature stop codon.

A specific eukaryotic transcription unit that is 5,000 nucleotides long uses only 1,200 nucleotides to make a protein consisting of 400 amino acids. This is best explained by the fact that __________________- (select all correct answers).

many nucleotides may be present within 5' and 3'UTRs / it may contain several introns that are spliced out.

Following peptide bond formation between the amino acid in the A site on the ribosome and the growing polypeptide chain, the tRNA in the A site:

moves to the P site of the ribosome

Many eukaryotic DNA sequences may code for more than one protein in the following ways except

none of the above.

Concerning the promoters recognized by general sigma factor in E. coli, mutations in the -10 region tend to affect the formation of the _______ complexes and the mutations in the -35 region affect the formation of the ______ complexes.

open/closed

Termination (termination and ribosome recycling) of translation involves all of the following except

peptide bond formation

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-GGC 3' (mRNA). The following activated transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. tRNA Anticodon Amino Acid GGC Proline CGU Alanine UGC Threonine CCG Glycine ACG Cysteine CGG Alanine The dipeptide that will form will be

proline-glycine

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine instead of phenylalanine to tRNAs with the AAA anticodon. The consequence of this for the cell will be that

proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of a phenylalanine. The consequence of this for the cell will be that

proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

Which of the following is not an activity of bacterial core RNA polymerase or any of the eukaryotic RNAPs (I, II and III)?

recognition of promoters

Which of the following is false about the E. coli general sigma factor (∂70)?

removal of C-terminus allows sigma (alone) to bind promoters

Which of the following is not a type of cis-acting element?

repressor

Suppose the following DNA sequence (on template strand) was mutated from 3' AGAGAGAGAGAGAGAGAG 5' to 3' AGAAGAGAGATCGAGAGA 5'. What amino acid sequence will be generated based on this mutated DNA?

ser-ser-leu

There are 61 mRNA codons that specify an amino acid, but only at most 45 different tRNAs in a cell. This is best explained by the fact that

some tRNAs have anticodons that recognize two or more different codons.

Which of the following strategies is not used by phages to organize the expression of their genes into regulatory cascades?

successive alternative ribosomes

Organisms produce different proteins at different developmental stages, under different environmental conditions, in different cell types (in multicellular organisms) etc. Gene expression can be regulated at several different levels. Which of the following is the least likely control point for gene expression in eukaryotes?

termination of transcription

Which of the following is false about bacterial RNA polymerase catalyzed reactions (synthesis of RNA)?

these reactions occur at the catalytic site located in the sigma subunit

Which of the following is false about nuclear genes for large rRNAs in higher eukaryotes?

they are translated into r-proteins

Wobble hypothesis accounts for the ability of some tRNAs _______

to recognize more than one codon by unusual pairing with third base of the codon

A scientist studying a "new" organism isolated RNA molecules that may have represented splicing intermediates, excised intron(s), and determined their structure. These molecules looked linear, no loops present, but they were branched and resembled the letter "y". From what you know about splicing/editing what is the most likely explanation of these results?

trans splicing was taking place