Molecular Biology of the Cell

Bruce Alberts, Alexander Johnson, Julian Lewis

Chapter 23

Pathogens and Infection - all with Video Answers

Educators

NS

Chapter Questions

Problem 1

Which statements are true? Explain why or why not.Our adult bodies harbor about 10 times more microbial cells than human cells.

Lara Gossage

Lara Gossage

Numerade Educator

Problem 2

Which statements are true? Explain why or why not.The microbiomes from healthy humans are all very similar.

Lara Gossage

Numerade Educator

Problem 3

Which statements are true? Explain why or why not.Pathogens must enter host cells to cause disease.

Lara Gossage

Numerade Educator

Problem 4

Which statements are true? Explain why or why not. Viruses replicate their genomes in the nucleus of the host cell.

Lara Gossage

Numerade Educator

Problem 5

Which statements are true? Explain why or why not. You should not take antibiotics for diseases caused by viruses.

Lara Gossage

Numerade Educator

Problem 6

In order to survive and multiply, a successful pathogen must accomplish five tasks. Name them.

Lara Gossage

Numerade Educator

Problem 7

Clostridium difficile infection is the leading cause of hospital-associated gastrointestinal illness. It is typically treated with a course of antibiotics, but the infection recurs in about $20 \%$ of cases. $C .$ difficile infections are difficult to eradicate because the bacteria exist in two forms: a replicating, toxin-producing form and a spore form that is resistant to antibiotics. Fecal microbiota transplantation-the transfer of normal gut microbiota from a healthy individual-can resolve $>90 \%$ of recurrent infections, a much better cure rate than further antibiotic treatment alone. Why do you suppose microbiota transplantation is so effective?

NS

Nathan Sosna

Numerade Educator

Problem 8

What are the three general mechanisms for horizontal gene transfer?

Lara Gossage

Numerade Educator

Problem 9

The Gram-negative bacterium Yersinia pestis, the causative agent of the plague, is extremely virulent. Upon infection, $Y$. pestis injects a set of effector proteins into macrophages that suppresses their phagocytic behavior and also interferes with their innate immune responses. One of the effector proteins, YopJ, acetylates serines and threonines on various MAP kinases, including the MAP kinase kinase kinase TAK1, which controls a key signaling step in the innate immune response pathway. To determine how YopJ interferes with TAK1, you transfect human cells with active YopJ (YopJ $^{\mathrm{WT}}$ ) or inactive YopJ (Yop] $^{\mathrm{CA}}$ ) and with FLAG-tagged active TAKI (TAK1WT) or inactive $TAKI (TAK1$ $^{K 63 W}$ ), and assay for total TAKI and for phosphorylated TAK1, using antibodies against the FLAG tag or against phosphorylated TAK1 (Figure $Q 23-1$ ). How does YopJ block the TAK1 signaling pathway? How do you suppose the serine/threonine acetylase activity of YopJ might interfere with TAK1 activation?

Niamat Khuda

Numerade Educator

Problem 10

The intracellular bacterial pathogen Salmonella typhimurium, which causes gastroenteritis, injects effect or proteins to promote its invasion into nonphagocytic host cells by the trigger mechanism. S. typhimurium first stimulates membrane ruffling to promote invasion, and then suppresses membrane ruffling once invasion is complete. This behavior is mediated in part by injection of two effect or proteins: SopE, which promotes membrane ruffling and invasion, and SptP, which blocks the effects of SopE. Both effector proteins target the monomeric GTPase, Rac, which in its active form promotes membrane ruffling. How do you suppose SopE and SptP affect Rac activity? How do you suppose the effects of SopE and SptP are staggered in time if they are injected simultaneously?

Lara Gossage

Numerade Educator

Problem 11

John Snow is widely regarded as the father of modern epidemiology. Most famously, he investigated an outbreak of cholera in London in 1854 that killed more than 600 victims before it was finished. Snow recorded where the victims lived, and plotted the data on a map, along with the locations of the water pumps that served as the source of water for the public (Figure $Q 23-2$ ). He concluded that the disease was most likely spread in the water, although he could find nothing suspicious-looking in it. His conclusion ran counter to the then-current belief that cholera was from "miasmas" in bad air. Very few believed his theory during the next 50 years, with the "bad air" theory persisting until at least $1901 .$ What do you suppose Snow saw in the data that led him to his conclusion? Why do you think most scientists remained skeptical for so long?

Lara Gossage

Numerade Educator

Problem 12

Influenza epidemics account for 250,000 to 500,000 deaths globally each year. These epidemics are markedly seasonal, occurring in temperate climates in the northern and southern hemispheres during their respective winters. By contrast, in the tropics, there is significant influenza activity year round, with a peak in the rainy season (Figure $Q 23-3$ ). Can you suggest some possible explanations for the patterns of influenza epidemics in temperate zones and the tropics?

Lara Gossage

Numerade Educator

Problem 13

Several negative-strand viruses carry their genome as a set of discrete RNA segments. Examples include influenza virus (eight segments), Rift Valley fever virus (three segments), Hantavirus (three segments), and Lassa virus (two segments), to name a few. Why does segmentation of the genome provide a strong evolutionary advantage for these viruses?

Lara Gossage

Numerade Educator

Problem 14

Avian influenza viruses readily infect birds, but are transmitted to humans very rarely. Similarly, human influenza viruses spread readily to other humans, but have never been detected in birds. The key to this specificity lies in the viral capsid protein, hemagglutinin, which binds to sialic acid residues on cell-surface glycoproteins, triggering virus entry into the cell (Movie 23.8 ). Hemagglutinin on human viruses recognizes sialic acid in a $2-6$ linkage with galactose, whereas avian hemagglutinin recognizes sialic acid in a $2-3$ linkage with galactose. Humans make carbohydrate chains that have only the $2-6$ linkage between sialic acid and galactose; birds make only the $2-3$ linkage; but pigs make carbohydrate chains with both linkages. How does this situation make pigs ideal hosts for generating new strains of human influenza viruses?

Lara Gossage

Numerade Educator

Problem 15

The majority of antibiotics used in the clinic are made as natural products by bacteria. Why do you suppose bacteria make the very agents we use to kill them?

Lara Gossage

Numerade Educator

Problem 16

In the early days of penicillin research, it was discovered that bacteria in the air could destroy the penicillin, a big problem for large-scale production of the drug. How do you suppose this occurs?

Lara Gossage

Numerade Educator

Problem 17

When the Oxford team of Ernst Chain and Norman Heatley had laboriously collected their first two grams of penicillin (probably no more than $2 \%$ pure!), Chain injected two normal mice with 1 geach of this preparation, and waited to see what would happen. The mice survived with no apparent ill effects. Their boss, Howard Florey, was furious at what he saw as a waste of good antibiotic. Why was this experiment important?

Lara Gossage

Numerade Educator