Chapter 18 Questions Flashcards
If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then
the amino acid acts as a corepressor
Muscle cells differ from nerve cells mainly because they
express different genes
The functioning of enhancers is an example of
transcriptional control of gene expression
Cell differentiation always involves
the production of tissue-specific proteins, such as muscle actin
Which of the following is an example of post-transcriptional control of gene expression?
the removal of introns and alternative splicing of exons
What would occur if the repressor of an inducible operon were mutated so it could not bind the operator?
continuous transcription of the operon’s genes
Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene
normally leads to formation of head structures
Which of the following statements about the DNA in one of your brain cells is true?
it is the same as the DNA in one of your heart cells
Within a cell, the amount of protein made using a given mRNA molecule depends partly on
the rate at which the mRNA is degraded
Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cels?
proto-oncogenes normally help regulate cell division.
Which of the following would be most likely to lead to cancer?
amplification of a proto-oncogene and inactivation of a tumor-suppressor gene
-Excess copies of the proto-oncogene could stimulate cell division abnormally, and the inactivation of a tumor-suppressor gene would eliminate a brake on cell division.
All your cells contain proto-oncogenes, which can change into cancer-causing genes. Why do cells possess such potential time bombs?
Proto-oncogenes are necessary for the normal control of cell growth and division.
-Proto-oncogenes can become oncogenes when a mutation or other genetic change increases the activity of the encoded protein.
Which of these are carcinogens?
cigarette smoke
fat
testosterone
UV light
(all of these substances can cause cancer)
_____ is a carcinogen that promotes colon cancer.
fat
-A diet high in fat increases the risk of both colon and breast cancer.
A cancer cell _____.
does not respond to the chemical signals that control cell division
-Cancer is a set of diseases in which cells escape from the control mechanisms that normally limit their rate of division.
In the human genome, oncogenes _____.
stimulate cell division
-Oncogenes are cancer-causing genes; repair of DNA damage would help prevent cancer.
Most human cancers are _____.
caused by the accumulation of somatic mutations
What gene has been called the “guardian angel of the genome?”
the p53 gene
-The p53 gene can activate several genes involved in DNA repair, halting of the cell cycle, or initiation of apoptosis.
What two genes are often mutated in colon cancer?
ras and p53
-ras, an oncogene, and p53, a tumor-suppressor gene, are often found to be mutated in colon cancers.
Why is cancer more prevalent in older people?
Cancer involves an accumulation of mutations, and older people have had more time to accumulate mutations in their DNA.
-Older people have simply had more cell divisions, more exposure to environmental carcinogens, and so on. Chance dictates that they have had more opportunities for mutations to occur.
In what way can cancer be hereditary?
One or two of several mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer.
-Because most cancers involve several mutations, a person who inherits one or more of these mutations will be more susceptible to cancer, but will not necessarily develop it,
The BRCA1 and BRCA2 genes are thought to be what type of genes?
tumor-suppressor genes
Which of the following accurately characterizes our current understanding of cancer development?
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.
-Although it is understood that p53 plays a critical role in the regulation of normal cells and suppressing tumor development, the precise ways that it carries out this role is not fully understood.
The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because _____.
in a multicellular eukaryote, different cells are specialized for different functions
The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because _____.
in a multicellular eukaryote, different cells are specialized for different functions
In some cases DNA methylation and histone deacetylation combine to _____.
silence certain genes