Question 1

If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then

Accepted Answer

The trp operon is a repressible operon that regulates the production of the amino acid tryptophan. In the absence of tryptophan, the repressor protein is inactive, allowing transcription to occur. However, when tryptophan levels are high, it acts as a corepressor, binding to the repressor protein and causing it to bind to the operator, preventing transcription. If an operon encoding enzymes for making an essential amino acid is regulated like the trp operon, then it is likely that the amino acid would act as a corepressor to inhibit transcription when levels are high.

Question 2

Why are BRCA1 and BRCA2 considered to be tumor-suppressor genes?

Accepted Answer

BRCA1 and BRCA2 are considered to be tumor-suppressor genes because their normal products participate in repair of DNA damage. Mutations in these genes can result in a loss of DNA repair function, leading to an increased risk of developing certain cancers, particularly breast and ovarian cancers.

Question 3

Forms of the Ras protein found in tumors usually cause which of the following events to occur?

Accepted Answer

The forms of the Ras protein found in tumors usually cause excessive cell division, which can contribute to the formation and growth of tumors.

Question 4

Which of the following functions does the product of the p53 gene carry out?

Accepted Answer

The p53 gene carries out the function of inhibiting the cell cycle in response to DNA damage or other stressors. This prevents the cell from replicating its DNA and potentially passing on mutations to daughter cells. Choices B, C, and D are incorrect because they do not accurately describe the function of the p53 gene.

Question 5

The bicoid gene product is normally localized to the anterior end of the embryo. If large amounts of the product were injected into the posterior end as well, which of the following developmental events would occur?

Accepted Answer

The bicoid gene product is a morphogen that determines the anterior-posterior axis in Drosophila embryos. Injecting it into the posterior end would cause anterior structures to form at both ends.

Question 6

Which of the following are maternal effect genes that control the orientation of the egg and thus the Drosophila embryo?

Accepted Answer

The maternal effect genes that control the orientation of the egg and thus the Drosophila embryo are known as egg-polarity genes. These genes are critical for establishing the anterior-posterior and dorsal-ventral axes of the embryo, setting up the body plan for development. Homeotic genes and segmentation genes are not involved in this process, and morphogens may contribute to cell differentiation but are not specifically related to egg orientation.

Question 7

When the Bicoid protein is expressed in Drosophila, divisions between cells in the embryo are not yet fully developed. This information helps to explain which observation by Nüsslein-Volhard and Wieschaus?

Accepted Answer

Nüsslein-Volhard and Wieschaus observed that the concentration gradient of the Bicoid protein, which diffuses from the anterior end of the embryo, determines the development of the anterior-posterior axis of the embryo. The fact that the cell divisions are not fully developed yet when Bicoid protein is expressed helps to explain how the protein can establish this gradient.

Question 8

What would be the result of a mutation in a maternal effect gene in a female Drosophila?

Accepted Answer

Maternal effect genes are expressed in the mother and their products are deposited in the egg, affecting the phenotype of the offspring regardless of the offspring's genotype.

Question 9

What essential information does the product of the bicoid gene in Drosophila provide during development?

Accepted Answer

The bicoid gene in Drosophila provides essential information for the orientation of the anterior-posterior axis during development. It is responsible for defining the head and thorax of the fly.

Question 10

Cell differentiation always involves

Accepted Answer

Cell differentiation involves the production of tissue-specific proteins, which allow cells to develop specialized structures and functions. Transcription of the myoD gene is specifically related to differentiation of muscle cells, and the selective loss of certain genes from the genome can occur, but these are not always involved in cell differentiation. The movement of cells is not a necessary component of differentiation, although it may occur during certain developmental processes.

Question 11

Which axis in the embryo does the protein product of the bicoid gene in Drosophila determine?

Accepted Answer

The protein product of the bicoid gene in Drosophila determines the anterior-posterior axis in the embryo. This protein is responsible for forming the head and thorax regions at the anterior end of the embryo.

Question 12

A genetic test to detect predisposition to cancer would likely examine the APC gene for involvement in which type(s) of cancer?

Accepted Answer

The APC gene is associated with the development of colorectal cancer.

Question 13

Mutations in which of the following genes lead to transformations in the identity of entire body parts?

Accepted Answer

Homeotic genes, also known as Hox genes, specify the identity of body parts during development. Mutations in these genes can result in the transformation of one body part into another, such as a fly leg developing in place of an antenna. Segmentation genes and egg-polarity genes play important roles in early development and do not typically result in whole-body part transformations. Inducers refer to signaling molecules that can influence gene expression but are not genes themselves.

Question 14

The functioning of enhancers is an example of

Accepted Answer

Enhancers are specific DNA sequences that can bind transcription factors and other regulatory proteins to activate or enhance transcription of nearby genes. This is an example of transcriptional control of gene expression, as it regulates the rate of RNA synthesis from DNA. Option A is incorrect because enhancers are not the equivalent of prokaryotic promoters, although they serve similar functions in regulating gene expression. Option C is incorrect because enhancers do not directly stimulate translation, but rather affect transcription. Option D is incorrect because enhancers regulate transcription, but not post-translational modifications.

Question 15

Muscle cells differ from nerve cells mainly because they

Accepted Answer

Muscle cells and nerve cells have different functions and therefore express different genes to carry out those functions.

Question 16

Which of the following types of mutation would convert a proto-oncogene into an oncogene?

Accepted Answer

A mutation that greatly increases the amount of the proto-oncogene protein can lead to its conversion into an oncogene. Proto-oncogenes normally promote cell growth and division, but when they are overexpressed due to mutation, they can become permanently activated and contribute to the uncontrolled cell growth seen in cancer. Blocking transcription or deleting the coding sequence would likely inactivate the proto-oncogene altogether, while creating an unstable mRNA would not necessarily increase protein levels.

Question 17

Which of the following processes do normal proto-oncogenes typically exhibit?

Accepted Answer

Normal proto-oncogenes typically stimulate normal cell growth and division. They are involved in regulating cell growth and proliferation to maintain tissue homeostasis. However, mutations or alterations in proto-oncogenes can lead to their conversion into oncogenes, which promote cancer growth.

Question 18

In colorectal cancer, several genes must be mutated for a cell to develop into a cancer cell. Which of the following kinds of genes would you expect to be mutated?

Accepted Answer

Genes involved in control of the cell cycle are responsible for regulating normal cell growth and division. Mutations in these genes can result in uncontrolled cell growth and division, leading to the development of cancer.

Question 19

Which of the following statements correctly describes a characteristic of tumor-suppressor gene?

Accepted Answer

Tumor-suppressor genes encode proteins that help prevent uncontrolled cell growth. They regulate the cell cycle and inhibit the formation of tumors. Mutations in these genes can lead to uncontrolled cell growth and the development of cancer.

Question 20

Which of the following statements describes a cell that is considered to be differentiated?

Accepted Answer

A differentiated cell is a specialized cell that performs a specific function in the body. One way that a cell becomes differentiated is by producing specific proteins necessary for its specific function. Choices A and B are incorrect because they do not necessarily indicate differentiation. Choice D is also incorrect because simply appearing different from surrounding cells does not necessarily mean that the cell is differentiated.

Quiz 18: Regulation of Gene Expression