Reading Comprehension

PT155 · S3 · P3 · Q22 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.

22.

Which one of the following, if true, lends the most support to a prediction of an eventual commercial application of Belcher and Hu's research into peptides and semiconductors?

  1. Belcher and Hu’s early successes

    Opposite, if anything

    DNA-based circuits are essentially a competitor for peptide-based circuits, so sparking renewed interest in DNA technology does not strengthen the idea that peptide technology will have commercial applications.

    35% picked this

  2. Correct

    For almost any semiconductor material

    Why this is right

    This is a super confusing answer, but it's at least somewhat attractive because it's a very strong answer, so it has the potential to be impactful. It actually ties back to that sentence at the beginning of the final paragraph where we're told was the success of this whole peptide enterprise hinges on: In order to use such a method to assemble a set of circuit-building tools (i.e. an eventual commercial application), it would be necessary to identify many additional organic compounds that bind to circuit-component materials (i.e. semiconductor materials). This answer is saying that for almost any semiconductor material used in a circuit, there are a lot of other equally good options. So if we can't identify an organic compound that binds to "silicon, gallium arsenide, or indium phosphide crystals", this answer is saying we could swap out any of those materials and use a different material instead, one which me might have more luck with in terms of finding an organic compound that binds to it. In essence, this answer is just saying, "When it comes to solving the crucial problem of finding organic compounds that can bind to circuit-component materials, we have LOTS of options for circuit-component materials", which increases the odds that we'll be able to find an organic compound that binds to at least one of them.

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

    47% picked this

  3. The number of peptides that

    Weakens, if anything

    It's a great thing when a peptide can bind to two different crystals at once. That gives us a lot of flexibility --- "it will take that kind of finesse at the nanoscale to produce selfassembling circuits". But this answer is saying there aren't that many of those peptides. That would seem to threaten the commercial viability of this technique. If there aren't many peptides that can act like a daub of glue to bind two different crystals at once, then we might not have all the options we need to build a selfassembling circuit.

    8% picked this

  4. The one billion peptides that

    No Impact

    This doesn't seem to speak to anything that seems particularly encouraging when it comes to commercial viability. Initially, they made about 1 billion peptides. Once they had found some peptides that worked, they tried to make slight variations on those, and this is telling us that there were about 250 million of those. Okay?

    6% picked this

  5. Expectations of continuing high costs

    Weakens

    This undermines the hope that peptide circuits will be commercially viable. There are high costs involved in trying to find the right peptides and it's discouraging the number of scientists even willing to try.

    4% picked this

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