A cell\'s genome is its blueprint for life. However, what is the bare minimum nu

Question

A cell's genome is its blueprint for life. However, what is the bare minimum number of genes needed to sustain a free-living cell? This is a question that microbiologists at the J. Craig Venter Institute (JCVI) have attempted to answer ever since they sequenced the genomes of several Mycoplasma species in the 1990s. Because Mycoplasma species are parasitic bacteria, their genomes are already reduced in size and hence provide an excellent foundation for creating a "minimal cell." However, little did the scientists at JCVI suspect that it would take 20 years to satisfy their scientific curiosity!

Instead of beginning by genetically manipulating a Mycoplasma species, microbiologists at JCVI wanted to have more control. To begin unraveling the genetic requirements for life, they first generated a synthetic self-replicating Mycoplasma (described in this chapter). The genome of this pioneering synthetic life form was synthesized from scratch based on its known genome sequence. The synthetic cell did not possess a "designer genome," or even a minimal one; it simply contained its own genome, but one completely constructed in the laboratory. This breakthrough in synthetic biology provided the technology needed for microbiologists to create designer genomes.

Using comparative genomics and prior knowledge about specific gene sequences, microbiologists at JCVI continued their work by designing and synthesizing several minimal genomes that they hypothesized would sustain life. To their dismay, none of these resulted in a viable cell. So instead, they generated modules of DNA corresponding to a Mycoplasma genome and sewed different combinations together to form synthetic genomes. Once viable cells were obtained from transplanting these genomes, nonessential genes from the smallest genome were identified by transposon mutagenesis. After removing these unnecessary genes, a synthetic minimal cell coined JCVI-syn3.0 was created (see photo). This autonomous life form possesses a 531-kilobase genome encoding 473 genes; JCVI-syn3.0 thus contains a genome smaller than any other free-living cell.

While this work showcases the amazing advancements in synthetic biology and the potential for creating designer cells with novel functions, a surprising mystery surrounds this minimal cell: The roles for almost a third of JCVI-syn3.0's genes remain unknown, highlighting how much we still need to learn about the genetic foundation of a living cell.

1. The introductory passage describes work to develop increasingly synthetic cells. What are some reasons that researchers are so interested in developing synthetic life, as opposed to simply developing more approaches to work with existing species of organisms? You should speculate about realistic options, as these are not all listed in the chapter.

Select all that apply.

2. Which of the following is NOT an example of an impediment to the development of entirely synthetic cells, beyond even JCVI-syn3.0?

Select all that apply.

Before JCVI-syn3.0 was produced, what steps were used to create a synthetic Mycoplasma cell? Put the events below into the correct order.

place the events into the proper sequence from left to right. first step to last step.

The synthetic chromosome
is transformed into
Mycoplasma capricolum.

Transformed cells are
detected by the presence
of lacZ, which causes
them to cleave Xgal and
produce a blue color.

Yeast is transformed
using Mycoplasma mycoides
fragments.

DNA fragments
assemble through
homologous recombination
in yeast.

The synthetic
Mycoplasma mycoides
chromosome is purified.

4. In the chapter, transformed Mycoplasma cells are identified because they produce a blue color. There are other ways to identify cells that have taken up genetic material. For example, a piece of DNA containing genes for green fluorescent protein (GFP) and a yeast DNA-binding protein gene is used to identify yeast nuclei. What is the name for this construct?

5. Drag the choices below to indicate whether each represents a statement about genomic editing or a statement about synthetic biology.

can involve transforming a cell with an artificial chromosome

often uses either homologous recombination or the DNA break repair pathway to join fragments after DNA is deleted

involves the removal of specific gene sequences, allowing them to be deleted or replaced with pieces of foreign DNA

uses the CRISPR/Cas9 system

6.

The polymerase chain reaction (PCR) is a powerful tool for amplifying genetic material (i.e., making many copies of it). This technique can be used for a wide range of applications. What are the steps of PCR required to amplify DNA?

Drag and drop the events into the proper sequence from left to right. first to last step

A probe is used to
identify a particular
sequence of interest
known to exist in the
microbe of interest.

The sample is
cooled to allow
short oligonucleotides,
used as primers, to
anneal to the DNA.

The sample is heated
to denature the
double-stranded DNA.

The product is
visualized through
a technique such
as electrophoresis.

Cycles of heating and
cooling are repeated
20-30 times.

DNA must be
extracted from the
sample to be tested.

The sample is heated,
and DNA polymerase
extends the primers
using the original
DNA as a template.

Synthetic cells will allow researchers to determine the minimum number of genes necessary for a cell to function. Synthetic cells can be modified to facilitate their use for a wide variety of manipulations (e.g., by inserting convenient restriction sites). Synthetic cells will always divide more rapidly and be more easily cultured than existing cells. Synthetic cells can be used to make products, which cannot be done with current techniques using genetically modified cells.

Explanation / Answer

1. The introductory passage describes work to develop increasingly synthetic cells. What are some reasons that researchers are so interested in developing synthetic life, as opposed to simply developing more approaches to work with existing species of organisms? You should speculate about realistic options, as these are not all listed in the chapter.

2. Which of the following is NOT an example of an impediment to the development of entirely synthetic cells, beyond even JCVI-syn3.0?

Before JCVI-syn3.0 was produced, what steps were used to create a synthetic Mycoplasma cell? Put the events below into the correct order.

4. In the chapter, transformed Mycoplasma cells are identified because they produce a blue color. There are other ways to identify cells that have taken up genetic material. For example, a piece of DNA containing genes for green fluorescent protein (GFP) and a yeast DNA-binding protein gene is used to identify yeast nuclei. What is the name for this construct?

5. Drag the choices below to indicate whether each represents a statement about genomic editing or a statement about synthetic biology.

6.

The polymerase chain reaction (PCR) is a powerful tool for amplifying genetic material (i.e., making many copies of it). This technique can be used for a wide range of applications. What are the steps of PCR required to amplify DNA?

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