CH 9

Viruses reproduce inside a host cell because ___________ A) viruses package DNA from the host-cell genome into the virus particle. B) viruses need host-cell reverse transcriptase to convert its RNA into DNA. C) viruses use host-cell ribosomes to produce viral coat proteins. D) all viruses must insert their genomes into the host-cell genome in order to be replicated

D) all viruses must insert their genomes into the host-cell genome in order to be replicated

T/F: Most mutations and genome alterations have neutral consequences. Explain.

T

HIV is a human retrovirus that integrates into the host cell's genome and will eventually replicate, produce viral proteins, and ultimately escape from the host cell. Which of the following proteins is not encoded in the HIV genome? A) Reverse transcriptase. B) Envelope protein. C) RNA polymerase. D) Capsid protein.

C) RNA polymerase.

Viral genomes _____ A) can be made of DNA. B) can be made of RNA. C) can be either double-stranded or single-stranded. D) All (A-C) are true.

D) All (A-C) are true.

Which of the following is true of a retrovirus, but NOT of the Alu retrotransposon? A) It requires cellular enzymes to make copies. B) It can be inserted into the genome. C) It can be excised and moved to a new location in the genome. D) All (A-C) are true.

D) All (A-C) are true.

Which of the following statements about mobile genetic elements is true? A) Mobile genetic elements can sometimes rearrange the DNA sequences of the genome in which they are embedded by accidentally excising neighboring chromosomal regions and reinserting these sequences into different places within the genome. B) DNA-only transposons do not code for proteins but instead rely on transposases found in cells that are infected by viruses. C) The two major families of transposable sequences found in the human genome are DNA-only transposons that move by replicative transposition. D) During replicative transposition, the donor DNA will no longer have the mobile genetic element embedded in its sequence when transposition is complete.

D) During replicative transposition, the donor DNA will no longer have the mobile genetic element embedded in its sequence when transposition is complete.

The human genome has ~3 × 10__________ nucleotide pairs that make up the sequence of __________ sets of chromosomes. This sequence encodes approximately 1.9 × 10 __________ protein-coding genes and about 5 × 10__________ non-protein-coding genes, which include structural catalytic, and regulatory RNAs. Approximately __________% of the human genome is made up of high-copy repetitive elements, while the percentage of DNA sequence in protein-coding exons is __________%. 0.5 1.5 3 4 9 23 30 50 75

*** 9 23 4 ? 50 1.5

Compare the movement of DNA-only transposons and retrotransposons

*** Transposons move by means of a DNA intermediate, whereas retrotransposons move by means of an RNA intermediate.

Explain how mobile genetic elements can alter the activity of regulation of a gene or promote gene duplication and exon shuffling

***Specialized DNA sequences moving from one chromosomal location to another

In humans and in chimpanzees, 99% of the Alu retrotransposons are in corresponding positions. Which of the following statements below is the most likely explanation for this similarity? A) The Alu retrotransposon is not capable of transposition in humans. B) Most of the Alu sequences in the chimpanzee genome underwent duplication and divergence before humans and chimpanzees diverged. C) The Alu retrotransposons are in the most beneficial position in the genome for primates. D) The Alu retrotransposons must also be in the same position in flies.

B) Most of the Alu sequences in the chimpanzee genome underwent duplication and divergence before humans and chimpanzees diverged.

Which of the following statements about retroviruses is false? A) Retroviruses are packaged with a few molecules of reverse transcriptase in each virus particle. B) Retroviruses use the host-genome integrase enzyme to create the provirus. C) The production of viral RNAs can occur long after the initial infection of the host cell by the retrovirus. D) Viral RNAs are translated by host-cell ribosomes to produce the proteins required for the production of viral particles.

B) Retroviruses use the host-genome integrase enzyme to create the provirus.

Which of the following DNA sequences is NOT commonly carried on a DNA-only transposon? A) Transposase gene. B) Reverse transcriptase gene. C ) Recognition site for transposase

B) Reverse transcriptase gene.

Some retrotransposons and retroviruses integrate preferentially into regions of the chromosome that are packaged in euchromatin and are also located outside the coding regions of genes that contain information for making a protein. Why might these mobile genetic elements have evolved this strategy?

The most evolutionarily successful mobile genetic elements are those that are best at reproducing themselves. To increase the number of copies of a particular element, the element must meet two criteria: (1) it must not kill its host, and (2) it must maximize its ability to continue reproducing. If an element inserts into the coding region of a gene, it might disable the gene and thereby confer a selective disadvantage in the reproduction or survival of its host. Thus, elements that devised a way to avoid insertion into coding regions were probably better able to increase their copy number throughout the human population. If an element inserts into a heterochromatic region of a chromosome, its genes may not be expressed and therefore it may become immobile. Elements that devised a way to direct insertion into euchromatin would be more likely to maintain mobility and thereby increase their copy number over time.

T/F: Proteins required for growth, metabolism, and cell division are more highly conserved than those involved in development and in response to the environment. Explain

True. All organisms need to perform a similar basic set of fundamental functions, such as those for metabolism, protein synthesis, and DNA replication. Proteins involved in these functions are shared by descent, and their evolution is constrained. Different species and cells are likely to require different developmental paths and to encounter different environmental challenges, so the proteins involved in these processes will tend to be more variable. For example, bacteria do not undergo elaborate developmental programs and so lack many of the regulators of development found in eukaryotes.