Question 1

Of the following scenarios for future research,from which would you expect to gain most medical benefit from noncoding RNAs?

Accepted Answer

Targeting siRNAs to disable the expression of an allele associated with autosomal dominant disease could provide significant medical benefits, as it could potentially silence the harmful allele and prevent the expression of the disease phenotype.

Question 2

You are given an experimental problem involving control of a gene's expression in the embryo of a particular species.One of your first questions is whether the gene's expression is controlled at the level of transcription or translation.Which of the following might best give you an answer?

Accepted Answer

The answer of You are given an experimental problem involving...

Question 3

Among the newly discovered small noncoding RNAs,one type re-establishes methylation patterns during gamete formation and blocks expression of some transposons.This type is known as

Accepted Answer

The type of small noncoding RNAs that re-establishes methylation patterns during gamete formation and blocks expression of some transposons is known as piRNA (PIWI-interacting RNA). miRNAs (microRNAs) are involved in post-transcriptional gene regulation, snRNAs (small nuclear RNAs) are involved in splicing of pre-mRNA, siRNAs (small interfering RNAs) are involved in RNA interference, and RNAi (RNA interference) is a process involving the degradation of mRNA by a complex of small RNAs and proteins.

Question 4

The fact that plants can be cloned from somatic cells demonstrates that

Accepted Answer

The ability to clone plants from somatic cells shows that differentiated cells still have all the genes of the original zygote, meaning they have not lost any genetic information during differentiation. This is in contrast to the idea that genes are lost during differentiation, which is not supported by the ability to clone plants from differentiated cells.

Question 5

In eukaryotes,general transcription factors

Accepted Answer

General transcription factors bind to other proteins or to a sequence element within the promoter called the TATA box.

Question 6

Which of the following describes the function of an enzyme known as Dicer?

Accepted Answer

Dicer is an enzyme involved in RNA interference. It trims double-stranded RNAs into small interfering RNAs (siRNAs) that can block translation or help degrade mRNA. Thus, it plays a crucial role in regulating gene expression.

Question 7

Since Watson and Crick described DNA in 1953,which of the following might best explain why the function of small RNAs is still being explained?

Accepted Answer

Changes in technology, such as RNA sequencing, and our ability to determine how much of the DNA is expressed have allowed for a better understanding of the function of small RNAs. While new functions may have evolved since Watson and Crick described DNA, this does not necessarily explain why the function of small RNAs is still being explained. While Watson and Crick did not initially predict a function for RNA, this does not explain why its function is still being explained. The sequencing of the human genome was completed in 2003, and although it was a major milestone, it does not explain why the function of small RNAs is still being explained. Ethical considerations may have limited the study of certain aspects of human genetics in the past, but this does not specifically explain why the function of small RNAs is still being explained.

Question 8

In humans,the embryonic and fetal forms of hemoglobin have a higher affinity for oxygen than that of adults.This is due to

Accepted Answer

Embryonic and fetal hemoglobin have a higher affinity for oxygen due to nonidentical genes that produce different versions of globins during development. These nonidentical genes result in different amino acid sequences, which affect the oxygen-binding properties of the hemoglobin molecules. Adult hemoglobin is produced from a different gene that has a slightly different amino acid sequence, resulting in a lower affinity for oxygen.

Question 9

Which of the following seems to account for most of the non-protein-coding DNA?

Accepted Answer

Non-protein-coding DNA that is transcribed into several kinds of small RNAs with biological function seems to account for most of the non-protein-coding DNA. This includes microRNAs, siRNAs, and piRNAs, which play important roles in gene regulation, chromosome structure, and genome defense. Therefore, this DNA is not just "junk" but has an important function in the cell.

Question 10

Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding.In general,which of the following would you expect many of them to be able to bind?

Accepted Answer

Transcription factors often interact with and regulate the activity of other transcription factors, so it would be expected that many of them have domains that can bind to other transcription factors. While some transcription factors also interact with repressors or hormone receptors, these interactions are not universal and not necessarily applicable to all transcription factors, making choices A and C less likely. ATP and tRNA are not typically involved in transcription, so choice B and E can be eliminated.

Question 11

During DNA replication

Accepted Answer

Methylation of the DNA is maintained because maintenance methylation enzymes such as DNA methyltransferase act at DNA sites where one strand is already methylated, and correctly methylate daughter strands after replication. This ensures that the epigenetic information is passed on to the next generation of cells.

Question 12

Which of the following is most likely to have a small protein called ubiquitin attached to it?

Accepted Answer

Ubiquitin is often attached to proteins that need to be degraded by the proteasome. Cyclins are regulatory proteins that are only needed during specific stages of the cell cycle. Once their function is complete, they are targeted for degradation by ubiquitination and subsequent proteasomal degradation.

Answer: B
 Proteins that are destined for secretion or for the cell membrane are often modified with ubiquitin as part of the quality control process during their transport from the ER to their final destination.

Answer: D
 Ubiquitination can also be used to regulate protein activity or localization within the cell. In this case, a regulatory protein that requires sugar residues to be attached may be modified with ubiquitin as part of its regulation.

The other choices are unlikely to have ubiquitin attached to them, as mRNA does not typically undergo ubiquitination, and post-translation modifications usually target certain residues, not the entire protein.

Question 13

In prophase I of meiosis in female Drosophila,studies have shown that there is phosphorylation of an amino acid in the tails of histones of gametes.A mutation in flies that interferes with this process results in sterility.Which of the following is the most likely hypothesis?

Accepted Answer

Histone tail phosphorylation is necessary for chromosome condensation during meiosis. Without it, the chromosomes may not properly separate during meiosis, leading to sterility. The other choices are not supported by the information given.

Question 14

What is the following phenomena called? RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA.

Accepted Answer

This phenomenon is called RNA interference (RNAi), where the introduction of double-stranded RNA triggers the destruction of complementary RNA molecules in the cell. This process plays a role in regulating gene expression and defending against viral infections.

Question 15

Two potential devices that eukaryotic cells use to regulate transcription are

Accepted Answer

Eukaryotic cells primarily use DNA methylation and histone modification to regulate transcription. DNA methylation involves the addition of a methyl group to a cytosine in DNA, which can cause repression of transcription. Histone modification refers to the addition or removal of chemical groups (such as acetyl or methyl groups) to the histone proteins that DNA wraps around. This can also affect transcription by altering the accessibility of DNA to transcription factors. The other answer choices either do not accurately describe mechanisms for transcriptional regulation in eukaryotic cells or combine mechanisms that do not commonly occur together.

Question 16

Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?

Accepted Answer

The answer of Gene expression might be altered at the...

Question 17

Steroid hormones produce their effects in cells by

Accepted Answer

Steroid hormones enter cells and bind to intracellular receptors, forming a hormone-receptor complex that promotes the transcription of specific genes, leading to changes in protein expression and ultimately producing the hormone's effects.

Question 18

Which of the following best describes siRNA?

Accepted Answer

siRNA (short interfering RNA) is a short double-stranded RNA molecule that can complement and inactivate a specific sequence of mRNA. This process is known as RNA interference (RNAi) and plays a crucial role in regulating gene expression. Once siRNA binds to mRNA, it recruits complexes that cause degradation of the mRNA, preventing translation and leading to gene silencing.

Question 19

The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA is called

Accepted Answer

The phenomenon described is RNA interference (RNAi), also known as post-transcriptional gene silencing (PTGS). It is a cellular mechanism that controls gene expression by destroying RNA molecules that have a sequence complementary to an introduced double-stranded RNA molecule. This process can be triggered by endogenous small noncoding RNAs or introduced synthetic RNAs, and it has become a powerful tool in genetic research and therapeutic development.

Question 20

Which of the following experimental procedures is most likely to hasten mRNA degradation in a eukaryotic cell?

Accepted Answer

Removal of the 5' cap is likely to hasten mRNA degradation in a eukaryotic cell because the cap is important for protecting the mRNA from degradation by exonucleases. Without the cap, the mRNA is more vulnerable to degradation. Enzymatic shortening of the poly-A tail can also lead to degradation, but removal of the 5' cap is likely to have a more immediate effect. Methylation of C nucleotides and histones are not directly involved in mRNA degradation, and removal of exons may affect the protein product but not necessarily the stability of the mRNA itself.

Quiz 18: Regulation of Gene Expression