Describe operons in your own words, as if you were explaining what an operon is to someone who knew about DNA and cells etc but did not know what an operon was. Here are some things you can discuss: Are operons controlling transcription or translation? Which organisms are they found in? What do the genes in an operon have in common with each other?

Figure 16.5 In E. coli, the tip operon is on by default, while the lac operon is off. Why do you think that this is the case?

Antibiotics and Protein Synthesis Antibiotics are molecules produced by microorganisms as defense mechanisms. The most effective antibiotics work by interfering with essential biochemical or reproductive processes. Many antibiotics block or disrupt one or more stages in protein synthesis. Some of these are mentioned here. Tetracyclines are a family of chemically related compounds used to treat several types of bacterial infections. Tetracyclines interfere with the initiation of translation. The tetracycline molecule attaches to the small ribosomal subunit and prevents binding of the tRNA anticodon during initiation. Both eukaryotic and prokaryotic ribosomes are sensitive to the action of tetracycline, but this antibiotic cannot pass through the plasma membrane of eukaryotic cells. Because tetracycline can enter bacterial cells to inhibit protein synthesis, it will stop bacterial growth, helping the immune system fight the infection. Streptomycin is used in hospitals to treat serious bacterial infections. It binds to the small ribosomal subunit but does not prevent initiation or elongation; however, it does affect the efficiency of protein synthesis. Binding of streptomycin changes the way mRNA codons interact with the tRNA. As a result, incorrect amino acids are incorporated into the growing polypeptide chain, producing nonfunctional proteins. In addition, streptomycin causes the ribosome to randomly fall off the mRNA, preventing the synthesis of complete proteins. Puromycin is not used clinically but has played an important role in studying the mechanism of protein synthesis in the research laboratory. The puromycin molecule is the same size and shape as a tRNA/amino acid complex. When puromycin enters the ribosome, it can be incorporated into a growing polypeptide chain, stopping further synthesis because no peptide bond can be formed between puromycin and an amino acid, causing the shortened polypeptide to fall off the ribosome. Chloramphenicol was one of the first broadspectrum antibiotics introduced. Eukaryotic cells are resistant to its actions, and it was widely used to treat bacterial infections. However, its use is limited to external applications and serious infections. Chloramphenicol destroys cells in the bone marrow, the source of all blood cells. In bacteria, this antibiotic binds to the large ribosomal subunit and inhibits the formation of peptide bonds. Another antibiotic, erythromycin, also binds to the large ribosomal subunit and inhibits the movement of ribosomes along the mRNA. Almost every step of protein synthesis can be inhibited by one antibiotic or another. Work on designing new synthetic antibiotics to fight infections is based on our knowledge of how the nucleotide sequence of mRNA is converted into the amino acid sequence of a protein. Questions Why is targeting protein synthesis an effective strategy for preventing infection?

Binding of _______ to _______ in DNA can increase the rate of transcription of specific genes. a. activators; repressors c. repressors; operators b. activators; enhancers d. repressors; enhancers

Eukaryotic mRNA: usessnRNPs to cut out introns and seal together translatableexons. uses a spliceosome mechanism made of DNA to recognizeconsensus sequences to cut and splice. has a guanine cap on its 39 end and a poly(A) tail on its 59 end. is composed of adenine, thymine, guanine, and cytosine. codes the guanine cap and poly(A) tail from the DNAtemplate.

IS. Alternative splicing has been estimated to occur in more than 95% of multi-exon genes. Which of the following is not an evolutionary advantage of alternative splicing? Alternative splicing increases diversity without increasing genome size Different gene isoforms can be expressed in different tissues Alternative splicing creates shorter mRNA transcripts Different gene isoforms can be expressed during different stages of development.

Binding or ___ to ___ in DNA can increase the rate of transcription of specific genes. a. activators; repressors b. activators; enhancers c. repressors: operators d. repressors: enhancers

In the gene-coding sequence shown here, which of the following events will produce a frameshift after the last mutational site? a. insertion of an A after the first codon b. deletion of the second codon (AAA) c. insertion of TA after the second codon and deletion of CG in the fourth codon d. deletion of AC in the third codon

Which of the following is an example of positive control? (a) transcription occurs when a repressor binds to an inducer (b) transcription cannot occur when a repressor binds to a corepressor (c) transcription is stimulated when an activator protein binds to DNA (d) a and b (e) a and c

The prospect of using gene therapy to alleviate genetic conditions is still a vision of the future. Gene therapy for adenosine deaminase deficiency has proved to be quite promising, but many obstacles remain to be overcome. Currently, the correction of human genetic defects is done using retroviruses as vectors. For this purpose, viral genes are removed from the retroviral genome, creating a vector capable of transferring human structural genes into sites on human chromosomes within target-tissue cells. Do you see any potential problems with inserting pieces of a retroviral genome into humans? If so, are there ways to combat or prevent these problems?