Science roundup: the pillars inside your mitochondria, and resetting a cell’s clock
Two studies from late October caught our eye because they rest on concepts you’ll see on your exam: mitochondrial structure, stem cells and epigenetics. Here’s what each one found, and where it shows up on test day.
A pillar that holds mitochondrial membranes apart
Mitochondria have two membranes, an outer membrane and an inner membrane, with a narrow gap between them called the intermembrane space. That gap isn’t empty real estate. During cellular respiration, the electron transport chain pumps protons into the intermembrane space, and ATP synthase uses the resulting gradient to make ATP.
A team led by Dr. Luca Pellegrini at the University of Ottawa, with first author Raman Shulinski, reported in Science Advances that a protein called SPRIZ (also known as CCDC127) bridges the two membranes and acts as a rigid pillar that sets the width of the intermembrane space. Most membrane tethers just bring membranes close enough to exchange material. SPRIZ holds them a defined distance apart.
Changing SPRIZ levels changed the size of the intermembrane space and how much calcium the mitochondria took up. As Pellegrini put it, “A change of only a few nanometers in the height of that room is enough to slow the calcium.” Mice without the gene were still viable, and their mitochondria kept their overall structure, but the membrane spacing changed. When the team engineered a longer version of the protein, the space got wider.
SPRIZ appears in vertebrates but not in plants, fungi or invertebrates such as insects and worms. The authors estimate it emerged around the origin of vertebrates, roughly 500 million years ago. They suggest it may be relevant to diseases involving mitochondrial energy failure, such as Parkinson’s disease, but that’s a question for future work.
Where it shows up on your exam
- MCAT Bio/Biochem and DAT/OAT Biology: mitochondrial structure, the electron transport chain and chemiosmosis. Protons are pumped into the intermembrane space and flow back through ATP synthase.
- MCAT Bio/Biochem: knockout models as a way to test what a gene does.
- DAT/OAT Biology: evolution and shared ancestry, using which groups of organisms have a gene and which don’t.
Turning back a cell’s epigenetic clock
Researchers at the University Hospital of Bonn and the University of Bonn, with teams from RWTH Aachen University, reported in Aging Cell that they converted immature red blood cell precursors directly into neural stem cells. They used a combination of transcription factors and skipped the pluripotent stem cell stage that earlier two-step methods relied on.
To measure age, they used epigenetic clocks, which estimate a cell’s biological age from chemical marks on DNA, such as methylation, that change predictably over a lifetime. Cells from an 80-year-old donor had an epigenetic age below 20 after conversion. The rejuvenation happened gradually over about 50 days and could be tracked for more than 100.
The headline number is about molecular age, not a person getting younger. The researchers say the work does not establish a treatment that can reverse aging in people. They see it as a lab model for studying how rejuvenation works, and for testing factors that speed it up or slow it down.
Where it shows up on your exam
- MCAT Bio/Biochem: epigenetics, including DNA methylation and how it regulates gene expression without changing the DNA sequence.
- MCAT Bio/Biochem and DAT/OAT Biology: stem cells and differentiation, including the difference between pluripotent and more specialized stem cells.
- MCAT Bio/Biochem: transcription factors and how they control which genes a cell expresses.
- MCAT Psych/Soc and research design: reading a headline carefully. Ask what was actually measured before you accept the claim.
The takeaway
Both studies reward the same skill the MCAT, DAT and OAT test: knowing a mechanism well enough to apply it to a situation you’ve never seen. Join our free Introduction to the PA-CAT on Sunday, November 22, or our Introduction to the MCAT on Sunday, December 6, at 12 pm Pacific on Zoom, or book a consult at icosaprep.com/consult.