Chapter 13 Homework

Mutations Place the correct word into each sentence to describe the different types and causes of mutations.

A gene mutation is a change in the sequence of bases of DNA. These changes in bases can affect protein production, protein activity, or have no effect on protein production or activity at all. Germline mutations are those that occur in sex cells and can be passed on to future generations. Somatic mutations occur in body cells of an individual. Some mutations are spontaneous and happen for no apparent reason. Other mutations are called induced mutations and are the result of exposure to toxins or radiation.

Genetic mutations Use your knowledge of genetic mutations to complete the following statements. Responses can be used more than once.

A genetic mutation is a change in the sequence of bases in DNA. This can have negative effects on the organism because a change in DNA bases can change the resulting protein. Mutations that occur in body cells are called somatic mutations, and those that oocur in sex cells are called germline mutations. There are several different types of mutations. Those that involve a change in a single base are called point mutations. Those that insert or delete one or more bases are called frameshift mutations. An example of a disorder caused by a point mutation is sickle-cell disease. An example of a disorder caused by a frameshift mutation is cystic fibrosis.

Translational control Complete the following paragraph to describe translational and posttranslational gene regulation.

Translational control of gene expression involves the activity of mRNA at the ribosome where translation takes place. The presence of a 5' cap and a 3' poly-A tail allow translation to take place. Once they are degraded, translation stops. Posttranslational control of gene expression involves the activity of proteins after they have been synthesized. They cannot be activated until they have been folded into their active form. Enzymes called proteases are contained within structures called proteosomes where proteins are broken down when necessary.

Activators, which are a set of transcription factors,

are located apart from the promoter, bound to a DNA region called the enhancer.

In the absence of tryptophan, the trp repressor is

inactive and cannot bind to the operator.

Efficient binding of RNA polymerase

increases the rate of transcription initiation.

RNA polymerase binds to the

promoter.

When present, tryptophan binds to the

trp repressor.

Mutations and cancer Complete each statement to explain how mutations may cause cancer.

Although somatic mutations are not passed on to future generations, they can lead to the development of cancer. Many mutagens, which cause induced mutations, are carcinogens, or cancer-causing mutagens. The organic chemicals in tobacco smoke as well as several forms of radiation are examples of such mutagens. The development of cancer involves the accumulation of mutations; mutation of proto-oncogenes leads to unregulated stimulation of cell division. When tumor suppressor genes are inactive and oncogenes are active, cells divide uncontrollably. Tumor suppressor genes and proto-oncogenes often code for transcription factors or proteins that control transcription factors. Thus, when mutated, normal control of transcription, and thus gene expression, is disrupted.

In the presence of tryptophan, the trp operon is turned "on".

FALSE

The passage of an mRNA transcript out of the nucleus is a passive, nonspecific process.

FALSE

Mutations 2 Use the images below to complete the discussion on mutations and their effects. Figure 1 shows no mutation. Responses can be used more than once.

Figure 1 depicts a point mutation, in which a single DNA nucleotide has been changed. These changes have effects on a single codon within the sequence, and therefore a single amino acid. Figure 2 is an example of a frameshift mutation, in which a single DNA nucleotide has been inserted. These changes have effects on all following codons within the sequence, and therefore many amino acids. Figure 3 depicts a frameshift mutation, in which a single DNA nucleotide has been deleted. These changes have effects on all following codons within the sequence, and therefore many amino acids.

Regulation of gene expression Place a single word into each sentence to accurately describe the levels of control regulating gene expression.

Gene expression in eukaryotes can be regulated in both the nucleus and the cytoplasm. In one control mechanism, chromatin packing is used as a way to keep genes turned off by preventing access to the DNA for transcription. Transcriptional control is used to determine the degree to which a gene is transcribed into mRNA. How fast the mRNA leaves the nucleus is the basis for posttranscriptional control. Translational control regulates when translation begins in the cytoplasm. Posttranslational control occurs after translation is complete, ensuring a functional protein.

Operons Complete the following statement to describe the structure and function of an operon. Choices may be used more than once.

Prokaryotes contain genes that are arranged in a(n) operon and undergo transcription at the same time. These genes typically include a(n) regulator gene located upstream of the operon that codes for a(n) repressor protein. This repressor protein controls whether transcription occurs or not. When the repressor protein is bound to the operator, RNA polymerase cannot bind to the promoter region, so transcription cannot occur and the genes are not expressed. When the repressor protein is not bound to the operator, transcription occurs and the genes are expressed becauseRNA polymerase can bind to the promoter region.

Transcription is carried out by the enzyme

RNA polymerase

Point mutations Place the correct word into each sentence for more information on the different types of mutations.

Point mutations include changes in one base of a segment of DNA. A point mutation can result in no change in protein synthesis, or in a different protein being made, like in the example of hemoglobin above. Sometimes a point mutation can lead to an improper stop codon, resulting in the termination of synthesis before the protein is completely made.

An operon is a group of genes that are all transcribed together, which is under the control of single operator site.

TRUE

Gene expression can be controlled by altering intron removal and the splicing of exons because this produces different mRNA products. Group startsTrue or False

TRUE

Which of the following statements about transcription factors is TRUE?

They form a complex that interacts with RNA polymerase and they function to pull double-stranded DNA apart and position RNA polymerase at the promoter.

Transcriptional control Complete the following paragraph to describe transcriptional control of gene expression.

Transcriptional control involves transcription factors, or proteins that help RNA polymerase bind to the promotor region of a DNA strand. Proteins called transcription activators bind to DNA regions called enhancers. These proteins form hairpin loops, which connect the enhancer region to the transcription factor complex, thus increasing transcription. These proteins typically require activation, usually in the form of phosphorylation by kinase enzymes, before they can function.