"Several recent papers show how cleanup crews play essential roles in the cell's quality control systems. Here's what three scientists in Germany say about "In vivo aspects of protein folding and quality control" in Science Magazine:
We see here that the cleanup crews work right alongside the construction crews and surveillance
crews. "Chaperones are a kind of Technical Inspection Authority for cells," Phys.org explains. "They are proteins that inspect other proteins for quality defects before they are allowed to leave the cell." When molecular chaperones cannot fold a protein properly in time, the surveillance crew must make a go/no-go decision, because some amino acids might clump into toxic aggregates. Figures in the Science paper illustrate the "Proteostasis Network" involving cleanup crews like the proteasome system, autophagy, and the lysosome system.
Aberrant proteins are tagged with ubiquitin, a small protein, by two independent surveillance crews. A shredding machine called the proteasome recognizes the tags and provides docking points for them. These quality-control measures ensure that only the bad proteins are degraded.
A cell needs just the right number of these trash recyclers. Consequently, their numbers also are regulated for quality control.
This brief survey of cell cleanup provides glimpses into a wondrous array of networks of complex molecular machines that know just what to do to keep cells humming. When evolution is mentioned at all, the main thing said is that the machines are "evolutionarily conserved." In other words, they have not evolved. It's important that we look at the details inside the cell occasionally. That's where the evidence for design often shines the brightest." EN&V
Proteins are synthesized on ribosomes as linear chains of amino acids and must fold into unique three-dimensional structures to fulfill their biological functions. Protein folding is intrinsically error-prone, and how it is accomplished efficiently represents a problem of great biological and medical importance. During folding, the nascent polypeptide must navigate a complex energy landscape. As a result, misfolded molecules may accumulate that expose hydrophobic amino acid residues and thus are in danger of forming potentially toxic aggregates. To ensure efficient folding and prevent aggregation, cells in all domains of life express various classes of proteins called molecular chaperones. These proteins receive the nascent polypeptide chain emerging from the ribosome and guide it along a productive folding pathway. Because proteins are structurally dynamic, constant surveillance of the proteome by an integrated network of chaperones and protein degradation machineries, the proteostasis network (PN), is required to maintain protein homeostasis in a range of external and endogenous stress conditions.
We see here that the cleanup crews work right alongside the construction crews and surveillance
Aberrant proteins are tagged with ubiquitin, a small protein, by two independent surveillance crews. A shredding machine called the proteasome recognizes the tags and provides docking points for them. These quality-control measures ensure that only the bad proteins are degraded.
A cell needs just the right number of these trash recyclers. Consequently, their numbers also are regulated for quality control.
This brief survey of cell cleanup provides glimpses into a wondrous array of networks of complex molecular machines that know just what to do to keep cells humming. When evolution is mentioned at all, the main thing said is that the machines are "evolutionarily conserved." In other words, they have not evolved. It's important that we look at the details inside the cell occasionally. That's where the evidence for design often shines the brightest." EN&V
...for I am fearfully and wonderfully made:
Psalm 139:14
