New Animal Cell Organelle Discovered
As design becomes more complex,
evolution becomes less likely
by Jerry Bergman, PhD
A new cell organelle discovery was announced last week by Harvard Medical School.[1] This is a surprise, after well over a century of cell biology research.
What Are Organelles?
Figure 1. The basic parts of the eukaryotic cell including the known organelles. (Wiki Commons)
Organelles are membrane-bound structures performing specific functions in all eukaryotic cells, as shown in Figure 1. After decades of research with no new finds, it was wrongly assumed that every organelle in eukaryotic cells had been discovered. This new organelle discovery was so significant that a Nature review article wrote: “Biology textbooks look set for an update: researchers have just discovered a new kind of organelle, a tiny organ-like structure inside cells.”[2]
What Was Discovered?
The function of the new organelle is to safely store phosphate so as to ensure that the cell has sufficient supply during times of stress. This is important because the phosphate nutrient is essential for all life, and depletion can result in the death of the organism. It is also very toxic when excess quantities are present in the cytoplasm. For this reason, it is critical that sufficient quantities can be safely stored in high concentrations and then released when needed.
Evidence for the storage function included the fact that, when the fruit fly’s cells were experimentally deprived of phosphate, the newly discovered organelles “broke apart and released the stored phospholipids into [the cytoplasm of] each cell,” supporting the conclusion that they functioned as phosphate reservoirs.[3]
How the Body Handles Phosphate Shortages
In the human body, inorganic phosphate starvation induces hyperproliferation and enterocyte differentiation in the digestive epithelium. These enterocytes result in increased phosphate absorption from the digestive tract, thereby increasing the level of phosphate in the body.
The team reasoned that, because inorganic phosphate is essential to cellular life, this was a survival mechanism designed to produce more enterocytes which, in turn, increases the amount of phosphate into the cell.[4]
The Link to Genetics
Other evidence of the new organelle’s function was that when cells were deprived of phosphate, a gene that encoded a phosphate-sensing protein was downloaded. This reduced gene expression kicked cell division into overdrive. Conversely, cell division slowed down when the researchers tweaked the gene to over express this protein. Thus, whenever this gene was down regulated or missing, the backup storage of phosphate was released into the cell cytoplasm, allowing the phosphate to serve its important cellular functions.
The geneticist and study co-author, Chiwei (Charles) Xu, observed: “The discovery highlights how much there is to learn about cell physiology.” This discovery supports the trend of the last century: more and more complexity is found as the living cell is examined at higher resolution. And increasing complexity within the cell further reduces the probability of evolution by unguided processes.
Figure 2. Three of the new phosphate-storing organelles as shown by a transmission electron microscope image. Note the dark triple membrane of each. From: Conroy, Gemma. New cellular ‘organelle’ discovered inside fruit-fly intestines. Nature, May 2023.
Details of the New Organelle P1
The new organelle was enclosed by several membrane layers in an onion-like structure separating it from the cytoplasm (Figure 2). PXo protein was observed transporting inorganic phosphate across the membrane layers into the newly discovered organelle.
Once inside the organelle, the inorganic phosphate was converted to phospholipids for storage. When inorganic phosphate is low, lysosomes, which contain degrading enzymes, allow the phosphate to be released into the cytoplasm and, consequently, to be used by the cell.[5]
Researchers made the discovery while investigating the role of phosphate in cell renewal of the fruit fly Drosophila melanogaster. The essential requirement for phosphate storage and release performed by this new organelle also likely exists for other chemical elements, an indication that many other organelles must exist that serve the same function as this newly discovered, but presently nameless, organelle. For example, just last year zinc was found to be stored in similar vesicles in flies.[6]
The Biological Function of the Element Phosphorus
Phosphate is a compound made of phosphorus and oxygen. Phosphorus will spontaneously ignite if exposed to air, so it must be stored under oil in a jar to prevent igniting. Phosphorus also reacts violently with oxidants, halogens (bromine, chlorine, fluorine, and iodine), some metals, nitrites, sulfur, and many other compounds, creating a fire hazard. For this reason phosphate is very unstable and must be tightly regulated in the cell.
One of its most important uses is in the compound adenosine triphosphate (ATP), called the “energy currency” of the cell.[7] ATP provides the energy to drive and support numerous processes in living cells, including muscle contraction, nerve impulse propagation and certain chemical synthesis reactions. Its importance is illustrated by the fact that the human body recycles the equivalent of its own body weight in ATP each day.[8] The consequences of its lack was detailed by genetic researchers Emily Strachan and Irene Miguel-Aliage:
Without inorganic phosphate (Pi), our cells would have no DNA, no ATP molecules to store energy and no phospholipids to form membranes. However, researchers do not fully understand how phosphate is metabolized or stored in animal cells, nor how it might act as a signal that allows cells to communicate.[9].
Furthermore, as far as is known, all organisms, from the simplest bacteria to humans, use ATP as their primary energy currency which powers virtually every activity of both the cell and the organism.
The energy level in ATP is just the right amount for most biological reactions. Energy is usually liberated from the ATP molecule to do work in the cell by a reaction that removes one of the phosphate-oxygen groups, leaving adenosine diphosphate (ADP). When the ATP converts to ADP, the ATP is said to be spent. Then the ADP is usually immediately recycled in the mitochondria where it is recharged by ATP synthase and comes out again as ATP. In short, “hooking and unhooking that last phosphate [on ATP] is what keeps the whole world operating.”[10]
Summary
This new organelle discovery illustrates how much there is yet to learn about cell anatomy and physiology. It was there all along, yet never noticed until the Harvard researchers realized it must be in the cell. As previously stated, this discovery supports the trend of the last century: finding increased complexity within the cell further reduces the probability of random-chance evolution. Because all elements, including iron, are toxic in the cell if above a certain threshold, it is likely that similar systems, such as the organelle described in this paper, exist in the cell to safely store other elements.
References
[1] Conroy, Gemma. 2023. New cellular ‘organelle’ discovered inside fruit-fly intestines;https://www.nature.com/articles/d41586-023-01518-8, 4 May 2023.
[2] Conroy, 2023.
[3] Conroy, 2023.
[4] Jackson, Justin. 2023. Fruit fly gut research leads to discovery of new phosphate-storing organelle; https://phys.org/news/2023-05-fruit-fly-gut-discovery-phosphate-storing.html, 5 May 2023.
[5] Strachan, Emily, and Irene Miguel-Aliaga. 2023. Phosphate-storing organelle found in flies. Nature: News and Views doi: 10.1038/d41586-023-01410-5, 3 May pp. 1-2.
[6] Garay, E. et al. 2022. Proceedings of the National. Academy of Science USA 119, e2117807119.
[7] Bergman, Jerry. 1999. ATP: The Perfect Energy Currency for the Cell. Creation Research Society Quarterly 36(1):199, 1999.
[8] Törnroth-Horsefield, Susanna, and Richard Neutze. 2008. Opening and closing the metabolite gate. Proceedings of the National. Academy of Science USA. 105(50):19565–19566, 16 December.
[9] Strachan, Emily, and Irene Miguel-Aliaga. 2023. Phosphate-storing organelle found in flies. Nature: News and Views doi: 10.1038/d41586-023-01410-5, 3 May.
[10] Trefil, James. 1001 Things Everyone Should Know About Science. Doubleday, New York, New York, 93, 1992.
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.