Why is the lac operon said to be an inducible operon?
When allolactose is present, it induces the inactivation of the lac repressor.

The lac repressor keeps the production of lactose-digesting enzymes turned off. When allolactose is present, the lac repressor is inactivated, allowing the expression of lactose-digesting enzymes.

What does an inducer do?
When taken up by a cell, it binds to a repressor so that the repressor no longer binds to the operator.
What is a repressor?
a protein produced by a regulatory gene
Lack of corepressor
Would result in a cell’s inability to “turn off” genes
DNA methylation is a mechanism used by eukaryotes to do what?
inactivate genes

DNA methylation, involving the attachment of methyl groups to certain bases, is a mechanism for the long-term inactivation of genes during development.

In humans, the hormone testosterone enters cells and binds to specific proteins, which in turn bind to specific sites on the cells’ DNA. These proteins probably act to do what?
help RNA polymerase transcribe certain genes

Testosterone stimulates the expression of genes involved in male sexual characteristics; it follows that the proteins that it interacts with and which bind to DNA will promote transcription.

miRNAs can control gene expression by what action?
binding to mRNAs and degrading them or blocking their translation

miRNAs can effectively “silence” genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable to physically interact with the ribosomes to complete translation.

How do master regulatory genes function in cell differentiation?
They produce proteins that act as transcription factors to produce proteins specific to the function of the particular cell type.
They are often capable of changing some fully differentiated cells of different types into their particular cell type.
They may produce proteins that stimulate production of more of the master regulatory gene.
The transcription factors they produce coordinately control related genes.
Which of these is true of the cytoplasm of an unfertilized egg?
It is an unevenly distributed mixture of mRNA, proteins, organelles, and other substances.

Many proteins are found concentrated at one end of the cell or another and provide positional information to the developing embryo.

How do cells become differentiated?
Different genes are expressed so that different proteins are produced.

Cell differentiation results from changes in gene expression.

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.


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