The article is taken from CREATION MAGAZINE Vol 36, Issue 3, 2024

Biological cells are like tiny cities bustling with machines performing numerous tasks to keep cells alive. For decades, one class of these machines, SMCs (for Structural Maintenance of Chromosomes), have been known to fold DNA strands into intricate three-dimensional structures. This is crucial for the proper organization and function of the genome.

Insights gained from multiple studies have paved the way toward a step-by-step model of how these machines might extrude loops of DNA as part of this process. An SMC is like an arm with two hands at one end. Each hand holds either end of a stretch of DNA. One of these hands holds continuously while the other periodically ‘let go’ when the arm is bending, during which time the DNA loop becomes a little larger. The hand then re-grabs the DNA before the arm re-extends. In this way, SMCs can extrude longer and longer loops of DNA.

The conundrum for evolution: this machine, useless until fully functional, is needed for reproduction, so natural selection (differential reproduction) can’t explain it.

Dekker, C. et al., How do molecular motors fold the genome? Science 382(6671): 646–648, 2023.