Cell Bio - Chapter 13 (Book Questions)

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The structure labeled C is a promoter. A promoter is a region of DNA that initiates the transcription of a particular gene. It provides the necessary binding sites for RNA polymerase and other transcription factors to bind and begin the process of gene expression. Promoters are crucial in regulating gene expression and determining when and where a gene is transcribed.

The structure labeled A is DNA. DNA, or deoxyribonucleic acid, is a molecule that contains the genetic instructions for the development and functioning of all living organisms. It is a double-stranded helix structure made up of nucleotides, which consist of a sugar molecule, a phosphate group, and a nitrogenous base. DNA is responsible for storing and transmitting genetic information from one generation to the next.

The structure labeled D is an operator. This means that it is a symbol or function that performs a specific operation on one or more operands to produce a result. Operators are commonly used in programming and mathematics to perform calculations or manipulate data.

The structure labeled B is a regulator gene. A regulator gene is a type of gene that controls the expression of other genes. It acts as a switch, turning genes on or off, and plays a crucial role in regulating various biological processes. In this context, the structure labeled B is likely a gene that regulates the expression of other genes in a specific pathway or system.

The correct answer is "bind with RNA polymerase." In common operon models, the promoter region is responsible for initiating the transcription process by binding with RNA polymerase. This binding allows the RNA polymerase to recognize the start site of the gene and begin transcribing the DNA into RNA. The promoter does not code for the repressor protein, bind to the repressor, or code for the regulator gene.

Translational control of gene expression occurs within the cytoplasm. This is because after transcription, the mRNA molecule is transported from the nucleus to the cytoplasm, where it undergoes translation to produce proteins. The cytoplasm contains the necessary machinery, such as ribosomes and tRNA molecules, for the process of translation to occur. Additionally, various regulatory factors can act on the mRNA molecule in the cytoplasm to control its translation, allowing for precise regulation of gene expression.

Barr bodies are genetically inactive X chromosomes in females. In females, one of the X chromosomes is randomly inactivated in each cell to ensure equal gene expression between males and females. The inactivated X chromosome condenses into a dense structure called a Barr body. This process is known as X chromosome inactivation and is responsible for the genetic dosage compensation in females.

Alternative mRNA splicing is a process in which different combinations of exons are joined together to produce different mRNA molecules from a single gene. This process occurs after transcription, when the pre-mRNA is processed to remove introns and join exons together. Therefore, alternative mRNA splicing is an example of posttranscriptional regulation of gene expression.

All of these options are correct because a cell being cancerous can involve abnormalities in various aspects. A proto-oncogene is a gene that can become an oncogene and promote cell division and tumor growth when mutated. A tumor suppressor gene, on the other hand, normally helps regulate cell growth and prevent tumors, but when mutated or inactivated, it can lead to uncontrolled cell growth. Regulation of the cell cycle is crucial for normal cell division, and abnormalities in this process can contribute to cancer. Lastly, tumor cells themselves are abnormal and can exhibit various characteristics that distinguish them from normal cells. Therefore, all of these factors can be involved in the development and progression of cancer.

When a guanine base is added at the beginning of the DNA codons CAT CAT CAT, it would result in the sequence GCA TCA TCA T. This is because the guanine base pairs with cytosine, so the original sequence is shifted by one base and the guanine is added at the beginning.

This answer is correct because negative control refers to the regulation of gene expression by the binding of a repressor protein to the operator region of a gene. The repressor protein becomes active when bound to a corepressor molecule, and this complex inhibits transcription by preventing RNA polymerase from binding to the promoter region of the gene. This mechanism effectively turns off the expression of the gene.

Alternative mRNA splicing is a mechanism that can create multiple mRNAs from the same gene. This process involves the removal of introns and the joining of exons in different combinations, resulting in the production of different mRNA isoforms. Each mRNA isoform can then be translated into a distinct protein, allowing for the generation of multiple protein variants from a single gene. This mechanism plays a crucial role in increasing the diversity of proteins in eukaryotic organisms.

In the regulation of the trp operon, when tryptophan is present, the repressor is able to bind to the operator. This means that the repressor protein, which is normally inactive, becomes active and attaches to the operator region of the operon. This binding prevents RNA polymerase from transcribing the structural genes, effectively shutting down the production of tryptophan. Therefore, the presence of tryptophan triggers the binding of the repressor to the operator, inhibiting transcription of the operon.

Exposure of the cell to radiation, certain chemicals, viral infection, and pollutants can all cause a proto-oncogene to become an oncogene. Radiation and certain chemicals can damage the DNA, leading to mutations in the proto-oncogene that can activate its oncogenic potential. Viral infection can introduce viral genes into the cell, which can disrupt the normal regulation of the proto-oncogene and cause it to become an oncogene. Exposure to pollutants can also lead to DNA damage and mutations in the proto-oncogene, promoting its transformation into an oncogene. Therefore, all of these factors can contribute to the development of oncogenes.

A tumor suppressor gene is a gene that regulates cell division and prevents the formation of cancer. It acts by opposing the activity of oncogenes, which promote uncontrolled cell growth. Tumor suppressor genes can be mutated, leading to a loss of their normal function and allowing cancer development. Therefore, all of the statements provided - inhibiting cell division, opposing oncogenes, preventing cancer, and being subject to mutations - are correct in relation to tumor suppressor genes.

Euchromatin is the correct answer because it is the less condensed and more transcriptionally active form of chromatin. It contains genes that are actively being transcribed into RNA, which is why it is more likely to show the label for radioactive uridine (label for RNA). Heterochromatin, on the other hand, is highly condensed and transcriptionally inactive, so it is less likely to show the label. The histones and DNA are not directly related to the labeling of RNA in this context.

Cancer is characterized by mutations in certain types of genes. These mutations can lead to uncontrolled cell growth and division, which is a hallmark of cancer. These gene mutations can be inherited or acquired throughout a person's lifetime, and they can be caused by various factors such as exposure to carcinogens or errors in DNA replication. Understanding these specific gene mutations is crucial for diagnosing and treating different types of cancer.

A point mutation refers to a mutation in a DNA molecule where there is a replacement of one nucleotide base pair with another. This type of mutation can occur due to various factors such as errors during DNA replication or exposure to mutagens. Point mutations can have different effects depending on the specific nucleotide change and its location within the gene. They can lead to changes in the amino acid sequence of a protein, potentially altering its structure and function.

When lactose is present and glucose is absent, the repressor is unable to bind to the operator. This allows for transcription of structural genes to occur. Therefore, both statement b (the repressor is unable to bind to the operator) and statement c (transcription of structural genes occurs) are correct.

Both transcriptional control and posttranscriptional control regulate gene expression in the eukaryotic nucleus. Transcriptional control refers to the regulation of gene expression at the level of transcription, where the DNA is converted into RNA. This can involve the activation or repression of specific genes through the binding of transcription factors to DNA. Posttranscriptional control, on the other hand, refers to the regulation of gene expression after transcription has occurred. This can involve processes such as RNA splicing, RNA editing, and mRNA stability, all of which can affect the final protein product.

Operons are a group of genes that are transcribed together as a single mRNA molecule. The regulator gene, which codes for a protein that controls the expression of the structural genes, is transcribed with the structural genes. However, the structural genes are not always transcribed. The transcription of the structural genes is regulated by the protein product of the regulator gene. Therefore, not all genes are always transcribed. The regulator gene has its own promoter, which is responsible for initiating the transcription of the regulator gene. This allows for the regulation of the operon by controlling the expression of the structural genes.

The occurrence of mutations is not evidence that eukaryotes control transcription. Mutations can happen randomly and are not directly controlled by eukaryotic cells. The other options, such as euchromatin/heterochromatin, existence of transcription factors, and lampbrush chromosomes, are all related to the control of transcription in eukaryotes.