questions

Question 1

in euk, which rna polymerase makes rRNA

Answer 1

Rna polymerase 1

Question 2

RNA polymerases

Answer 2

RNA polymerase I= ribosomal rRNA in eukaryotes.

RNA polymerase II =messenger mRNA in eukaryotes.

RNA polymerase III = transfer tRNA in eukaryotes.

Question 3

Which of the following subunits of RNA polymerase is solely required for initiation of transcription?

Answer 3

(sigma)
sigma factor is solely required for the initiation of transcription.
In fact, the sigma subunit will often fall off of the enzyme during the elongation phase of transcription
. Binding of the sigma factor is an important signal for transcription to begin.

The other subunits are crucial to the elongation and termination phases.

Question 4

Which of the following codons is the mRNA start codon that initiates translation?

Answer 4

AUG

Explanation:
The codon AUG initiates translation in both eukaryotes and prokaryotes.
Interaction with this codon by a tRNA molecule allows a methionine residue to enter the ribosome and serve as the starting point for amino acid elongation.

Question 5

Transcription stop codons

Answer 5

UGA, UAA, and UAG
are mRNA stop codons and stop protein synthesis by causing the ribosomal subunits to dissociate and release the polypeptide.

Question 6

Which of the following best describes the key function of helicases during transcription?

Answer 6

Separation of two strands of DNA; “unwinding” gives polymerases access to the strand.
Explanation:
Helicases are required for separating two DNA strands so that the rest of transcription can take place. Polymerases work on single strands of DNA, thus the bonds holding the double strands together must be removed.

Question 7

Transcription factors that are the first to bind DNA in heterochromatin regions, often promote euchromatin formation, and recruit other transcriptional machinery to promote transcription are best known as which of the following?

Answer 7

Pioneer factors
The correct answer is pioneer factors. Pioneer factors are able to bind DNA in condensed regions and promote euchromatin formation by recruitment of histone demethyltransferases and acteyltransfereses to modify proximal histones. Additionally, these pioneer factors recruit other transcription factors and co-factors to promote transcription. DNA polymerases are involved with DNA replication, not transcription. The RNA holoenzyme is a protein complex consisting of RNA polymerase, transcription factors, and regulator proteins that binds promoters and catalyzes transcription.

Question 8

Before RNA polymerase can initiate transcription, this protein must bind to it, creating the RNA polymerase holoenzyme and allowing for the initiation of transcription.

Answer 8

Sigma factor

Question 9

Which of the following is not dependent on the C-terminal domain (CTD) of RNA polymerase II?

Answer 9

Only mRNA transcribed by polymerase II undergo 5’ capping, polyadenylation, and splicing. The C-terminal domain of this polymerase serves as a binding site and docking platform for many of the enzymes that initiate these processes. Moreover, experiments in which the CTD is truncated show that mRNA transcripts are not capped, polyadenylated, and spliced.

Question 10

What is the role of the promoter region in the regulation of gene expression?

Answer 10

Recruit RNA polymerase and transcription factors to DNA
Explanation:
The promoter region is the site of a gene where RNA polymerase and other transcription factors bind to DNA, upstream from the gene locus. A mutation in this region commonly results in a decrease in the amount of gene transcribed.

An enhancer region is a stretch of DNA that alters gene expression by binding transcription factors, while a silencer region is a site on the gene where repressor proteins bind. Introns are intervening non-coding segments of DNA that are not expressed in the final protein. Alternative splicing patterns of introns and exons allows for multiple proteins to be generated from a single gene.

Question 11

Which of the following are methods for termination of transcription in prokaryotes?

Answer 11

The binding of release factors is a common way to terminate translation, not transcription.

Rho-mediated termination and hairpin loop formation are both common ways to terminate prokaryotic transcription. The formation of the hairpin loop disrupts the transcription machinery and the DNA-RNA interactions, which allows termination of transcription. Rho is a protein that is capable of binding single-stranded RNA and terminating transcription.

Question 12

What event is indicative of transcription initiation?

Answer 12

RNA polymerase binds to the promoter

Question 13

Which of the following best describes distant regulatory sequences that influence gene expression?

Answer 13

Enhancers

Question 14

When does alternative splicing occur?

Answer 14

Following pre-mRNA transcription in the nucleus

Question 15

What element(s) do all eukaryotic promoter regions share?

Answer 15

Transcription factors
basal promoter (TATA box)
Enhancers that accept binding agents
Explanation:
Eukaryotic promoters share basic, highly conserved structure. This area does not evolve quickly because it is extremely important in DNA transcription. These promoters (in most cases) include a basic basal promoter like a TATA box, and enhancers that bind to transcription factors.

Question 16

During transcription of a eukaryotic cell, what determines the template strand?

Answer 16

The base sequence of the promoter

Question 17

Which of the following processes is not a type of RNA processing carried out by eukaryotes?

Answer 17

Nucleotide excision repair

Question 18

What are exons?

Answer 18

Genetic information coding for an amino acid sequence that will form a functional protein

Question 19

What are snRNPs (small nuclear ribonucleic particles)?

Answer 19

RNA protein complexes that combine with pre-mRNA and other proteins to form a spliceosome

Question 20

Which of the following is not a type of RNA?

Answer 20

cRNA

Question 21

All of the follwing are types of alternative RNA splicing except __________.

Answer 21

exon reversal

Question 22

Which of the following is not a category of RNA?

Answer 22

Major RNAs

Question 23

What approximate percentage of total RNA content in a cell is messenger RNA (mRNA)?

Answer 23

Only 2-5% of the total RNA content in a cell is mRNA. Approximately 10% is transfer RNA (tRNA), and approximately 85% is ribosomal RNA (rRNA).

Question 24

Why is the post-transcriptional poly-A tail an important addition to a mRNA molecule?

Answer 24

The tail adds stability to the transcript, controlling the time of degradation.

Question 25

Researchers first identified parts of genes that are spliced out of mRNA and not included in the final protein product by observing that not all of the original gene hybridizes to the cognate mRNA. What are these regions called?

Answer 25

Introns

Question 26

How is splicing regulated at the level of cis-acting RNA sequence elements?

Answer 26

Splicing repressors bind splicing silencers and decrease nearby splice junction activity. Splicing activators bind splicing enhancers and increase likelihood of proximal sites as splice junction.

Question 27

Which of the following is a recognized mode of alternative splicing?

Answer 27

Exon skipping

Alternative donor site

Alternative acceptor site

Mutually exclusive exons

Question 28

To which of the following structures in a typical molecule of tRNA is an amino acid attached?

Answer 28

CCA tail

Question 29

Chloramphenicol prevents protein translation by which of the following mechanisms?

Answer 29

It blocks the peptidyl transferase reaction on ribosomes

Question 30

During translation, which site in the ribosome allows for tRNA moelcules to enter the complex?

Answer 30

A site

Question 31

Which of the following most accurately describes the chronological order of ribosome biogenesis in eukaryotes?

Answer 31

Ribosomal proteins are translated in the cytoplasm and transported to the nucleolus. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA and ribosomal proteins form the 60S and 40S subunits in the nucleolus and are then transported to the cytoplasm for functional ribosome assembly.

Question 32

How many ribosomal binding sites are there and what are their functions?

Answer 32

There are three sites. A site binds aminoacyl-tRNA, P site binds peptidyl-tRNA, E site binds free tRNA before ribosomal exit

Question 33

Which of the following is not a type of modification that can occur after translation?

Answer 33

5’ capping

Question 34

Which of the following ensures that viral gene translation occurs even when host translation is inhibited?

Answer 34

Internal Ribosomal Entry Sites (IRES)

Question 35

Which amino acid is the “start” amino acid in a peptide chain?

Answer 35

Methionine

Question 36

Most translation occurs by a mRNA cap-dependent mechanism, however, translation can occur by cap-independent initiation. One mechanism by which eukaryotic cells can initiate cap-independent translation is by which of the following approaches?

Answer 36

Internal ribosome entry site
The correct answer is the internal ribosome entry site. This site is a specific nucleotide sequence that allows for translation initiation in the middle of a mRNA sequence, rather than at the 5’ end, and does not require the cap-dependent elF4F initiation complex or the 5’cap. The poly(A)-binding protein complexes with the 3’ end of mRNA strands during translation initiation via the cap-dependent mechanism.

Question 37

In prokaryotes what site on the mRNA does the ribosome bind to initiate translation?

Answer 37

The Shine-Dalgarno sequence

Question 38

Which of the following proteins are likely to contain leucine zipper domains?

Answer 38

Transcription factors

Explanation:
Leucine zippers are domains that allow for the binding of DNA. The question is essentially asking, “which of these proteins are capable of binding DNA?”

Proteases cleave proteins, lipases hydrolyze lipids, and transmembrane proteins interact with membranes. Transcription factors are the only given proteins that bind DNA and, therefore, are much more likely to contain leucine zipper domains than the other options.

Question 39

The 5’ cap on eukaryotic mRNA molecules is recognized by which of the following proteins?

Answer 39

eIF4e

Explanation:
The 5’ cap is recognized by the important translation factor eIF4e. Once bound, eIF4e helps transport the mRNA molecule to the ribosome and facilitates bonding to the ribosomal machinery.

The 3’ poly-A tail is recognized by PABP. RNA polymerase is involved in transcription, not translation. The 40s ribosomal subunit is recruited by the initiation complex (including eIF4e, PABP, and various other translation factors).

Question 40

When conducting a stain of chromosomes, certain regions along the chromosome will stain more darkly than the rest. This is due to the fact that these regions are more tightly condensed. What is the functional outcome of having one region more condensed (heterochromatin) than the rest (euchromatin)?

Answer 40

Heterochromatin is typically not transcribed/transcribed at a lower rate because the tight packing limits accessibility to polymerases.

Explanation:
Heterochromatin often contains simple, repetitive sequences, and although it cannot be said that it is completely void of coding sequences, it is not typically transcribed. The tight wrapping prevents polymerase from accessing the strand, and euchromatin typically contains the regions that get transcribed. Thus, heterochromatin is though to contain repressed or inactive genes.

Question 41

Small GTPases are important molecular switches and signaling pathways. What proteins are responsible for promoting the activation of these small GTPases?

Answer 41

Guanine nucleotide exchange factors

Question 42

In which of the following organelles does the initial linkage of a sugar for post-translation modification N-linked glycosylation most commonly occur?

Answer 42

Endoplasmic reticulum

Explanation:
Two of the more common types of glycosylation, N-linked and O-linked, occur at different points and in different places in the cell. N-linked glycosylation takes place in the lumen of the endoplasmic reticulum, while O-linked glycosylation takes place in the Golgi body.

The other options, the mitochondria and the nucleus, are not involved in these post-translational modifications.

Question 43

“The addition of a CH3CO group to the N-terminus of a protein is the most common form of protein modification. This chemical modification is called ________.”

Answer 43

Acetylation

Explanation:
This question requires knowing either that CH3CO is an acetyl group, or that acetylation is the most common protein modification. Each of the other modifications described are biologically occurring modifications, but acetylation was the correct answer for the given statement.