Question 1

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, such as cyclins that are no longer needed after a specific phase of the cell cycle.

Question 2

At the beginning of this century there was a general announcement regarding the sequencing of the human genome and the genomes of many other multicellular eukaryotes. There was surprise expressed by many that the number of protein-coding sequences is much smaller than they had expected. Which of the following accounts for most of the rest?

Accepted Answer

Non-protein coding DNA that is transcribed into several kinds of small RNAs with biological function accounts for most of the rest of the genome. This includes miRNAs, siRNAs, and other types of small regulatory RNAs that play important roles in gene expression and other biological processes.

Question 3

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

Accepted Answer

The ability to clone plants from somatic cells means that differentiated cells still retain all the genes present in the zygote. This is because cloning involves reprogramming somatic cells to return to an embryonic-like state, where they are able to give rise to an entire plant with all the genetic material needed for development.

Question 4

Which of the following best describes siRNA?

Accepted Answer

siRNA stands for small interfering RNA, which is a short double-stranded RNA that can complement and inactivate a sequence of mRNA through a process known as RNA interference (RNAi). This happens when the siRNA strands are incorporated into the RNA-induced silencing complex (RISC) and guide the complex to the specific mRNA target for degradation or translational inhibition.

Question 5

Differentiation of cells is not easily reversible because it involves

Accepted Answer

The answer of Differentiation of cells is not easily reversible...

Question 6

The researcher in question measures the amount of new polypeptide production in embryos from 2-8 hours following fertilization and the results show a steady and significant rise in polypeptide concentration over that time. The researcher concludes that

Accepted Answer

The rise in polypeptide concentration following fertilization is likely due to the translation of maternal mRNAs, which were present in the egg prior to fertilization. This is a common process in early development, as the zygote relies on maternal gene products before its own genes are activated. The other choices are unlikely explanations given the available information.

Question 7

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 described phenomenon is known as RNA interference or RNAi, in which double-stranded RNA molecules lead to the degradation of complementary RNA molecules in the cell. The other options are not accurate in describing this process.

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

The higher affinity of embryonic and fetal hemoglobin for oxygen is due to the production of different versions of globins during development, which is controlled by nonidentical genes. This allows for oxygen to be efficiently transported from the mother to the developing fetus.

Question 9

A cell that remains entirely flexible in its developmental possibilities is said to be

Accepted Answer

A totipotent cell is one that has the potential to develop into any type of cell, including embryonic and extra-embryonic cells, and thus has not committed to any particular developmental pathway. Differentiated cells, on the other hand, have already undergone specialization and are no longer capable of developing into other cell types. Determined cells have made a commitment to a particular developmental path but are not fully differentiated yet. Genomically equivalent cells have the same genetic information but may differ in their epigenetic modifications or gene expression patterns. Epigenetic cells have undergone changes in gene expression due to modifications to their DNA or histones, but this does not necessarily mean they have lost developmental flexibility.

Question 10

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 11

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 next-generation sequencing and our ability to determine how much of the DNA is expressed have allowed scientists to better understand the function of small RNAs. This was not possible in the past and has led to continued discoveries and explanations about their function.

Question 12

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 13

One of the hopes for use of recent knowledge gained about non-coding RNAs lies with the possibilities for their use in medicine. Of the following scenarios for future research, which would you expect to gain most from RNAs?

Accepted Answer

siRNAs can be used to specifically target and silence the expression of alleles associated with autosomal dominant diseases, where a single copy of a mutant allele can cause disease.

Question 14

The researcher measures the concentration of the polypeptides from different regions in the early embryo and finds the following pattern (darker shading = greater concentration): 
Which of the following would be his most logical assumption?

Accepted Answer

The pattern of increasing concentration suggests that the polypeptide is being produced in region 1 and then diffusing towards region 5. If the substance had entered from the environment near region 1 (option E), the concentration would not decrease towards region 5. Options A, B, and C are unlikely because they do not fit the observed pattern of concentration.

Question 15

In animals, embryonic stem cells differ from adult stem cells in that

Accepted Answer

Embryonic stem cells are totipotent, meaning they can give rise to any cell type in the organism, while adult stem cells are generally only pluripotent, meaning they can differentiate into multiple, but not all, cell types.

Question 16

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

Accepted Answer

Dicer is an enzyme that trims small double-stranded RNAs into molecules known as microRNAs (miRNAs) or small interfering RNAs (siRNAs). These small RNA molecules can then block translation by binding to specific mRNAs, leading to their degradation or inhibition of protein synthesis. Dicer plays a critical role in RNA interference (RNAi), a process that regulates gene expression and defends against invading viruses.

Question 17

In a series of experiments, the enzyme Dicer has been inactivated in cells from various vertebrates, and the centromere is abnormally formed from chromatin. Which of the following is most likely to occur?

Accepted Answer

Dicer is involved in the processing of small RNAs that guide the formation of heterochromatin. Without Dicer, centromeres may become euchromatic, disrupting their function and leading to cell death.

Question 18

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 because the cap protects the mRNA from degradation in the cytoplasm. Without the cap, the mRNA is more susceptible to degradation. Enzymatic shortening of the poly(A) tail may also hasten mRNA degradation, but it is not the most likely option as the poly(A) tail protects the mRNA from degradation. Methylation of C nucleotides, demethylation of histones, and removal of one or more exons are not directly involved in mRNA degradation.

Question 19

The researcher continues to study the reactions of the embryo to these new proteins and you hypothesize that he is most likely to see which of the following (while embryonic genes are still not being expressed)?

Accepted Answer

The determination of spatial axes is one of the earliest embryonic events and occurs before the onset of gene expression. Therefore, studying the reactions of the embryo to new proteins before gene expression occurs is likely to show the spatial axes being determined.

Question 20

The process of cellular differentiation is a direct result of

Accepted Answer

Cellular differentiation refers to the process by which a less specialized cell matures into a more distinct cell type with specialized functions. This process is tightly regulated by differential gene expression, where different sets of genes are turned on or off in different cell types, leading to the expression of unique gene products that define cell identity and function. Morphogenesis, cell division, and apoptosis can all play important roles in shaping and maintaining complex tissues and organs, but they are not the direct drivers of cellular differentiation. Differences in cellular genomes can contribute to cellular diversity, but they do not fully explain the specific changes in gene expression that underlie differentiation.

Quiz 18: Control of Gene Expression