Chapter 18 Biology Review Questions
You have inserted the gene for human growth factor into the E. coli lactose operon, replacing the structural genes with the gene for human growth factor. What substance must you add to your culture of bacteria to cause them to produce human growth factor for you? (Concept 18.1)
Allolactose (Allolactose will bind to the repressor protein, inactivating it and allowing transcription of the genes in the operon, including human growth factor.)
Which of the following best depicts coordinate control of genes in eukaryotes? (Concept 18.2)
Although a group of genes involved in a related metabolic process are typically scattered over different chromosomes, their co-activation is achieved by every gene of the group sharing a specific combination of control elements and activator molecules that bind to them. Although a group of genes involved in a related metabolic process are typically scattered over different chromosomes, coordinated expression of this group is enhanced by the congregation of loops from different chromosomes in a specific site of the nucleus to form a transcription factory.
Why is cancer more prevalent in older people? (Concept 18.5)
Cancer involves an accumulation of mutations, and older people have had more time to accumulate mutations in their DNA.
Which of the following is/are involved in controlling eukaryotic gene expression? (Concept 18.2)
DNA packing Transcriptional regulation Methylation of DNA mRNA processing
Which of the following best describes the current understanding of the makeup of the human genome? (Concept 18.3)
Genes for noncoding RNA make up the majority of meaningful genetic information in the human genome.
Which of the following accurately characterizes our current understanding of cancer development? (Concept 18.5)
In order for a cell to become fully cancerous, it typically must have at least one active oncogene and the mutation or loss of several tumor-suppressor genes.
What is the evolutionary significance of alternative RNA splicing? (Concept 18.2)
It expands the number of proteins that can be coded for by one gene, increasing an organism's ability to produce novel proteins.
In the case of E. coli, the bacterium may need to synthesize tryptophan, or its host, a human, may supply all the tryptophan it needs. Why do both bacteria and humans need tryptophan? (Concept 18.1)
It is one of the 20 amino acids used by all organisms to synthesize proteins.
What determines how long a particular mRNA molecule will persist in a eukaryotic cell? (Concept 18.2)
Nucleotide sequences in the 3′ untranslated region of the mRNA
In what way can cancer be hereditary? (Concept 18.5)
One or two of several mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer.
MicroRNAs and small interfering RNAs both function similarly in "silencing" genes. What are two ways in which they may act? (Concept 18.3)
Promote the degradation of mRNA and bind to complementary mRNA sequences to prevent translation
What gene has been called the "guardian angel of the genome"? (Concept 18.5)
The p53 gene
What is the role of proteasomes? (Concept 18.2)
They are giant protein complexes that recognize ubiquitin and degrade the tagged proteins.
The BRCA1 and BRCA2 genes are thought to be what type of genes? (Concept 18.5)
Tumor-suppressor genes
It is hypothesized that an increase in the number and diversity of noncoding RNA (ncRNA) in the genomes of species has driven the evolution of morphological complexity by way of their influence on gene regulation. Which of the following accurately represents our current understanding of the role that ncRNA is thought to play in gene regulation? (Concept 18.3)
Whereas some ncRNA block the transcription and translation of some genes, others have been observed to activate gene expression. Some ncRNA can promote the formation of heterochromatin, thereby blocking the expression of genes in the tightly coiled region. ncRNAs can fine-tune translation by binding with mRNA via complementary base pairing and promote the degradation of the mRNA strand or block its translation. ncRNAs can re-establish proper patterns of DNA methylation in the genome during gamete formation.
Instead of developing a head and a tail, an abnormal Drosophila embryo develops two tails. This is most likely due to __________. (Concept 18.4)
a mutation in a maternal effect gene
Although the number of genes in the human genome is surprisingly low compared to less complex organisms, the number of possible products from those genes is greatly amplified by __________. (Concept 18.2)
alternate arrangements of exons from a primary transcript
In prokaryotic genomes, groups of functionally related genes along with their promoters and operators are found together in __________. (Concept 18.1)
an operon
Cytoplasmic determinants __________. (Concept 18.4)
are coded for by maternal genes.
Most human cancers are __________. (Concept 18.5)
caused by the accumulation of somatic mutations
A scientist clones a regulatory gene that is involved in controlling the expression of other genes and discovers that the regulatory gene encodes an enzyme that acetylates histones. It is likely that this enzyme regulates gene expression by __________. (Concept 18.2)
causing looser packing of the chromatin at the target gene, thereby enhancing transcription
A bacterium can make the amino acid glycine or absorb it from its surroundings. A biochemist finds that glycine binds to a repressor protein and causes the repressor to bind to the bacterial chromosome, turning off an operon. If it is like other similar operons, the presence of glycine will result in the __________. (Concept 18.1)
cessation of the synthesis of glycine
In eukaryotes, DNA packing seems to affect gene expression primarily by __________. (Concept 18.2)
controlling access to DNA
Gene expression in bacteria is regulated primarily by __________. (Concept 18.1)
controlling the transcription of genes into mRNA.
A cancer cell __________. (Concept 18.5)
does not respond to the chemical signals that control cell division
In a eukaryote, transcription factors called activators may stimulate gene expression by binding to DNA sites called __________. (Concept 18.2)
enhancers (Enhancers are sites within the DNA where activators bind, increasing the rate of transcription.)
The expression of a gene located in a tightly coiled region of DNA can be promoted by __________. (Concept 18.2)
histone acetylation
The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because __________. (Concept 18.2)
in a multicellular eukaryote, different cells are specialized for different functions
Cells can influence each other's development by a process known as __________. (Concept 18.4)
induction
Cell differentiation is first observable when __________. (Concept 18.4)
mRNAs for tissue-specific proteins appear in a cell
Enhancers __________. (Concept 18.2)
may be located upstream or downstream from the genes they regulate may be located thousands of base pairs away from the promoter increase the rate of transcription are found in eukaryotic genomes
Post-transcriptional controls of gene expression __________. (Concept 18.2)
may involve changes to the rate at which an mRNA is translated can include changes to mRNA stability may involve regulation of mRNA splicing can include translational controls
Specific cells that appear undifferentiated under the microscope but are already fated to become muscle cells are called __________. (Concept 18.4)
myoblasts
What two genes are often mutated in colon cancer? (Concept 18.5)
ras and p53
In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway (such as the trp operon) are __________, and those encoding the enzymes of a catabolic pathway (such as the lac operon) are __________. (Concept 18.1)
repressible; inducible
In some cases, DNA methylation and removal of acetyl groups from histones (i.e., deacetylation) combine to __________. (Concept 18.2)
silence certain genes
A high rate of gene transcription in eukaryotic cells is usually dependent on __________. (Concept 18.2)
specific binding of activator molecules to enhancers protein-protein interactions that are promoted by the activation domains of activator proteins
Dioxin, produced as a by-product of various industrial chemical processes, is suspected of causing cancer and birth defects in animals and humans. It apparently acts by entering cells and binding to specific proteins, which then enter the nucleus and alter the pattern of gene expression. Therefore, dioxin acts by mimicking the action of __________. (Concept 18.2)
steroid hormones
In the human genome, oncogenes __________. (Concept 18.5)
stimulate cell division
In an inducible operon, the inducer is often the __________ in the pathway being regulated; the inducer binds to the __________, which then becomes __________. (Concept 18.1)
substrate; repressor; inactive (The presence of the substrate turns the operon on by binding to the repressor and inactivating it.)
The discovery of many noncoding RNAs is causing scientists to revise the long-held view that __________. (Concept 18.3)
there are only three types of RNA—tRNA, rRNA, and mRNA only DNA that codes for protein, tRNA, and rRNA is transcribed the vast majority of the human genome consists of "junk" DNA all genes code for proteins
Both repressible and inducible operons control gene expression at the level of __________. (Concept 18.1)
transcription
MyoD promotes muscle cell development by __________. (Concept 18.4)
turning on the expression of multiple muscle-related genes.
