Reading Comprehension

PT155 · S3 · P3 · Q21 Nanoscale Computer Chips

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This passage was adapted from an article published in 2000.

Topic

Belcher and Hu's research using peptides — short amino-acid chains — to build nanoscale electronic components.

Framework

Highlight Noteworthy. The author isn't arguing against anyone; the author is showcasing a promising approach to a coming problem in chip miniaturization.

Main Point

Conventional miniaturization is about to hit a hard physical limit, and Belcher and Hu's peptide-based approach is a promising route to building electronics below that limit. They have already identified hundreds of peptides that bind to specific semiconductor crystals and are now designing peptides that can act as molecular "glue" — exactly the kind of finesse needed for self-assembling nanocircuits.

P1: Why this work matters

The race to make computer chips smaller is approaching a wall (~2010): current transistors can't go below 25 nanometers. Living cells, however, routinely build complex structures at smaller scales. So researchers want to harness biological molecules. Most work focuses on DNA — Belcher and Hu are pursuing peptides instead.

P2: How they got there

The idea grew out of Belcher's discovery that a specific peptide directs calcium-carbonate crystallization in abalone shells. She and Hu reasoned that peptides able to direct crystal growth in semiconductor materials could be a tool for building nanoscale electronics. Since no known peptide had this property, they screened a billion random peptides against three semiconductor materials and isolated ones that bound to specific faces of specific crystals — then refined them via accelerated-evolution-style methods.

P3: Where things stand and what's next

To assemble a real toolkit, many more binding peptides are needed. They're making progress: hundreds of crystal-manipulating peptides across 20+ semiconductor materials, plus newly designed peptides that bind to two different crystals at once — molecular glue. That kind of nanoscale finesse is what self-assembling circuits will require.

21.

The passage most strongly supports which one of the following?

  1. Some peptides that bind to

    Too Specific

    The final paragraph tells us that "they are also designing new peptides that bind to two different crystals at once", and gallium arsenide and indium phosphide are two different crystals. But we don't know if those two crystals are the ones being referred to in the final paragraph. Maybe it's binding silicon to one of these two crystals.

    11% picked this

  2. Researchers besides Belcher and Hu

    Out of Scope: other peptide researchers

    The end of the 1st paragraph says that "much current research is aimed at harnessing DNA to make nanocircuits, but Belcher and Hu are investigating a different maker: peptides". We don't ever hear about any other researchers working on peptides.

    8% picked this

  3. Neither Belcher nor Hu has

    Too Strong: nothing major but peptides

    This passage only talks about Belcher and Hu's works with peptides, but that doesn't mean that they've only worked on peptides. We have no idea if they've done major scientific research on other topics.

    2% picked this

  4. Correct

    Silicon, gallium arsenide, and indium

    Why this is right

    This is supported in the final paragraph. Hu and Belcher are "making progress on the quest to identify many additional organic compounds that bind to circuit-component materials. As they have expanded their targets to 20 more semiconductor materials, their cache of crystal-manipulating peptides has ballooned into the hundreds". There's a causal logic to saying, "As I have started stretching before playing basketball, my day-after injuries have lessened". It suggests that stretching is having an effect on injury reduction. Here it's saying that "As they have started looking at 20 other semiconductor materials beyond silicon / gallium / indium, their collection of crystal-manipulating peptides has ballooned." That implies that as they've been looking at other semiconductor materials, they've been finding peptides that can successfully manipulate those (and have added them to their collection).

    Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

    69% picked this

  5. Peptides have been used in

    Out of Scope: other industrial applications

    This passage has only told us about peptides causing calcium carbonate to crystallize into the abalone shell, and about peptides being able to manipulate semiconductor crystals. We don't hear about using peptides for any other reason.

    9% picked this

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