Microbial Genetics Questions and Answers

Answer: A

Correct answer: proteins

Bacteriocins are proteins produced by one strain that kill closely related strains, usually by forming pores or degrading nucleic acid. They are typically plasmid-encoded, and the producing cell carries an immunity protein to protect itself - which is what makes the weapon usable.

Answer: C

Correct answer: E. coli has acquired many genes via horizontal transfer

Comparison of the two genomes shows a substantial fraction of the E. coli chromosome differing in base composition and codon usage from the rest, which marks it as foreign in origin. Several hundred kilobases appear to have arrived by horizontal transfer since the two lineages separated, and much of what distinguishes the two species lies in that acquired material.

Answer: C

Correct answer: Mitochondria have evolved from endosymbiotic bacteria

Rickettsia prowazekii is an obligate intracellular parasite whose genome is small and whose retained genes for aerobic energy generation resemble those of mitochondria more closely than any other bacterium’s. That similarity is strong evidence that mitochondria descend from an alpha-proteobacterial endosymbiont.

Answer: A

Correct answer: structural genomics

Structural genomics is concerned with the physical organisation of the genome - sequencing it, mapping it, and determining the structures of what it encodes. Functional genomics asks what the genes do, and comparative genomics what the differences between genomes signify.

Answer: B

Correct answer: M. tuberculosis

About 250 of the roughly 4,000 genes of M. tuberculosis are devoted to lipid metabolism, an extraordinary proportion. It reflects the organism’s unusual cell envelope of mycolic acids and complex lipids, which gives it its acid-fast staining, its impermeability to drugs and much of its ability to survive inside macrophages.

Answer: C

Correct answer: Because it lacks the genes needed for TCA cycle and oxidative phosphorylation

The genome of Treponema pallidum shows it cannot make its own amino acids, nucleotides or fatty acids, and lacks a complete respiratory chain, so it depends on the host for compounds no ordinary medium supplies. The sequence explained a difficulty that had defeated bacteriologists for a century.

Answer: B

Correct answer: 250-350 genes

Comparisons of the smallest genomes, together with experiments knocking genes out one at a time, put the minimum for an independently replicating cell at around 250 to 350. The figure is not fixed, since what is essential depends on how rich the environment is, but it is far below the few thousand a free-living bacterium carries.

Answer: C

Correct answer: DNA through RNA to proteins

This is the central dogma: DNA is transcribed to RNA and RNA translated to protein. Retroviruses reverse the first step with reverse transcriptase, but no mechanism translates protein back into nucleic acid, and it is that last impossibility which gives the dogma its force.

Answer: B

Correct answer: Annotation

Sequencing yields a string of bases; annotation identifies what is in it - the open reading frames, their boundaries, the regulatory regions, and the likely function of each product by comparison with known genes. Without it the sequence is data rather than information.

Answer: D

Correct answer: the study of the entire collection of proteins expressed by an organism

The proteome is what the genome actually produces, and it differs between cells, conditions and moments in a way the genome does not. It also reflects processing and modification that the sequence cannot predict, which is why proteomics is a separate study rather than a corollary of genomics.