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Many dangerous microbes co-opt their host’s own molecular structures.

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Manager
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Joined: 15 Feb 2012
Posts: 115

Kudos [?]: 143 [0], given: 216

Concentration: Marketing, Strategy
GPA: 3.6
WE: Engineering (Computer Software)
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Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 19 Jul 2015, 12:31
Question 1
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A
B
C
D
E

Question Stats:

75% (01:30) correct 25% (01:16) wrong based on 179

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Question 2
00:00
A
B
C
D
E

Question Stats:

51% (00:42) correct 49% (00:45) wrong based on 179

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Question 3
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A
B
C
D
E

Question Stats:

20% (01:10) correct 80% (00:46) wrong based on 177

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Many dangerous microbes co-opt their host’s own molecular structures. For example, Shigella flexneri is a rod-shaped bacterium that causes severe intestinal discomfort in humans. Shigella contains a gene called IcsA that allows it to appropriate actin filaments inside the host’s infected cell. Actin is normally used to provide structure and form to the cell, but the microbe forms the fibers into a propulsive tail that moves it freely from cell to cell. To appropriate the actin, Shigella sticks to the epithelial cells of the intestinal lining. Once there,it signals the epithelial cell to alter its own shape and pulls the microbe inside.Once Shigella is ensconced within the cytoplasm, it begins replicating. The replicants can then make use of the IcsA gene and create their own tails from the cell’s actin, spreading the infection to other cells. Thus, the bacterium bypasses the blood and lymph systems entirely, which allows it to avoid alerting the body’s immune system.

Researchers tested the IcsA hypothesis by transferring the gene into E. coli bacteria and then placing the bacteria inside host cells. The organisms formed actin tails and began behaving much as the Shigella bacteria did. Such microbes as Listeria monocytogenes also co-opt host actin,though a different gene is involved in the process.


1. It can be inferred from the passage that which of the following is true of the blood and lymph systems?
The blood and lymph systems are in some way linked to the immune system.
The blood and lymph systems are not able to overcome most bacterial infections.
The blood and lymph systems are used by IcsA genes to obtain actin for the creation of propulsion tails.
The blood and lymph systems signal noninfected epithelial cells to deny actin filaments to intrusive microbes.
The blood and lymph systems will be alerted to the presence of a Shigella flexneri infection when a microbe infects a white blood cell.

[Reveal] Spoiler:
A

2. According to the author, what happens after a Shigella flexneri microbe enters a host cell?
The microbe depletes the nutrients in the cytoplasm and creates a replica of the original cell.
The microbe duplicates itself, and the duplicates form actin tails and spread to other cells.
After using the IcsA gene to signal to the invaded cell, the microbe spreads through the cellular lining.
By avoiding the immune system, the microbe spreads quickly through the blood stream.
The microbe first develops a propulsive tail out of actin, then co-opts the host's molecular form.

[Reveal] Spoiler:
B

3. According to the passage, the IcsA gene is believed to control the development of actin tails for which of the following reasons?
I. The formation of actin tails cannot be attributed to any other cellular structure associated with Shigella flexneri.
II. Experiments have shown that when IcsA genes are transferred into E. coli, they develop actin tails.
III. Shigella flexneri without the IcsA gene do not grow tails formed from actin filaments.

I only
II only
I and II only
I and III only
II and III only

[Reveal] Spoiler:
C

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA

Last edited by NickHalden on 20 Jul 2015, 07:43, edited 1 time in total.

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 20 Jul 2015, 02:27
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The first and Second question of the passage are same. Is it a Typo?

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Manager
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Kudos [?]: 143 [0], given: 216

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 20 Jul 2015, 07:48
RaviChandra,
Thanks for pointing out. I have modified the question.

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 11 Oct 2017, 01:32
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plz explain the question no 3 ??
though (ii) has been mentioned but I didn't get whether (i) is in the RC ?

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 12 Oct 2017, 16:13
About Question 3, can someone explain the reason why 1 is true, I understand that 2 is mentioned, but why 1? Abhishek009, msk0657

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 16 Oct 2017, 01:04
soumya170293 wrote:
plz explain the question no 3 ??
though (ii) has been mentioned but I didn't get whether (i) is in the RC ?

Same problem! Someone can help me?

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Re: Many dangerous microbes co-opt their host’s own molecular structures. [#permalink]

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New post 20 Nov 2017, 21:37
Right answer for Q3 is B

I am sure

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Re: Many dangerous microbes co-opt their host’s own molecular structures.   [#permalink] 20 Nov 2017, 21:37
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Many dangerous microbes co-opt their host’s own molecular structures.

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