Howard Hughes Medical Institute researchers have successfully created a protocell, a basic cell structure encapsulated with a membrane, capable of intaking nutrients and creating copies of its own DNA.
Szostak’s lab had already created membrane sacs out of molecules called fatty acids—long chains of carbon atoms that make up part of the lipids in modern cell membranes. In the current study, they substituted different fatty acids with specific structural characteristics until they created a membrane with the appropriate permeability. They found that fatty acids that were branched, and therefore unable to pack tightly together, allowed sugar molecules (key building blocks of nucleotides, which in turn make up RNA and DNA) to pass through. Fatty acids with shorter carbon chains or bulky “headgroups” had a similar effect.
Guided by these findings, the group created a protocell out of fatty acids that were likely present in the earth’s early environment. They were able to get nucleotides themselves to cross the membrane, showing that early cells could have taken up such molecules without protein channels.
Szostak says that’s important, but only a part of the problem. Once inside the cell, the nucleotides need to be able to assemble into polymers that—like the DNA in modern cells—store genetic information. Modern cells replicate their DNA by “unzipping” the two strands of the molecule, and then using the individual strands as templates to create two daughter strands, again with the help of proteins. The second half of Szostak’s experiment showed that his protocell could have carried out the template-copying part of the reaction.
The group created a protocell containing a single-stranded genetic molecule—a DNA template. Then, says Szostak, “we added nucleotides to the outside of the [protocell], let them diffuse across the membrane to the inside, and then take part in a template-copying reaction”—all without the help of proteins.
Full story at HHMI: Researchers Build Model Protocell Capable of Copying DNA …