Lecture 12

In prokaryotic genomes, groups of functionally related genes along with their promoters and operators are found together in __________.

• a regulatory gene

• Transcription factor

• an operon

• an enhancer

Answer explanation

Putting these related sequences together helps prokaryotes keep related genes under coordinate control

An operon is the entire stretch of DNA that includes the operator, promoter, and the genes that they control.

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?

• human growth factor

• allolactose

• operator protein

• repressor protein

Answer explanation

Allolactose will bind to the repressor protein, inactivating it, and allowing transcription of the genes in the operon, including human growth factor.

Both repressible and inducible operons control gene expression at the level of __________.

• post-transcriptional processing

• translation

• post-translational processing

• transcription

Answer explanation

The repressors that attach to operators act to block transcription.

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 __________.

• causing tighter packing of the chromatin at the target gene, thereby inhibiting translation

• causing looser packing of the chromatin at the target gene, thereby enhancing transcription

• causing looser packing of the chromatin at the target gene, thereby inhibiting transcription

• causing tighter packing of the chromatin at the target gene, thereby enhancing transcription

Answer explanation

Acetylation promotes a more open chromatin structure, making DNA more accessible for transcription.

What is the evolutionary significance of alternative RNA splicing?

• It expands the number of proteins that can be coded for by one gene, increasing an organism's ability to produce novel proteins.

• It acts as a defense against viral RNA, helping organisms avoid infection, particularly by cancer-causing viruses

• The introns that are spliced out can become miRNAs and can recognize and degrade mRNA transcripts.

• It can silence genes, giving cells another way of controlling gene expression.

Answer explanation

Some genes could produce thousands of different proteins from a primary transcript. In most cases, only a few of the possibilities are actually produced. However, different splicing could give rise to novel proteins, some of which could be advantageous.

MicroRNAs and small interfering RNAs both function similarly in "silencing" genes. What are two ways in which they may act?

• promote the degradation of mRNA and inhibit RNA splicing

• inhibit RNA splicing and bind to complementary DNA sequences to prevent transcription

• promote the degradation of mRNA and bind to complementary mRNA sequences to prevent translation

• cut up mRNAs using the Dicer enzyme and bind to complementary mRNA sequences to prevent translation

Answer explanation

miRNAs and siRNAs act in both of these ways to prevent a transcribed gene from being translated into protein. In addition to their normal roles in cells, researchers see these RNAs as useful tools in studying the function of genes by being able to silence them.

In what way can cancer be hereditary?

• Proto-oncogenes can be inherited, giving the person a predisposition to developing cancer.

• A person can inherit cancer cells from one of his/her parents.

• Tumor-suppressor genes can be inherited, giving the person a predisposition to developing cancer.

• One or two of several mutations necessary for full cancer development can be inherited, giving a person a predisposition to developing cancer.

Answer explanation

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.