How heavy are human chromosomes? A difficult question scientists managed to answer

Human cell has 46 chromosomes. From your school biology class you know that they contain instructions for life – your DNA is in them. And while we know about chromosomes for 130 years there are still many details that have escaped scientists’ eyes for decades. For example, scientists at UCL only now figured out the mass of the human chromosome group.

Chromosomes contain DNA and are very small. Image credit: AJC1 via Wikimedia (CC BY-SA 4.0)

2 metres of a DNA strand, instructions to read it, information about cells splitting – chromosomes basically contain software of the human body. We don’t read about them too often, because DNA that they contain is getting more attention. In fact, the Human Genome Project allowed scientists to know the mass of DNA. This is very interesting, because now if we knew the mass of chromosomes we could compare the two and understand whether something else is happening inside of them that we didn’t know before.

Scientists used Diamond Light Source X-ray beam at the UK’s national synchrotron facility and variou microscopy techniques to determine the number of electrons in a spread of 46 chromosomes. They used this information to calculate the mass of chromosomes. It turns out our 23 pairs of chromosomes have a mass of 242 picograms (trillionths of a gram). This is an incredibly small mass and yet chromosomes are heavier than scientists expected. In fact, chromosomes are about 20 times heavier than the DNA they contain, which is a fascinating observation. Scientists say that these findings suggest that there might be missing components in chromosomes that are yet to be discovered.

Scientists employed a technique known as X-ray ptychography in this research. Basically, a strong X-ray beam was passed through the chromosomes at metaphase (just before they were about to divide into two daughter cells) and then diffraction patterns were stitched together to create a highly sensitive 3D reconstruction. This allowed scientists to count electrons and calculate the mass of chromosomes. While we know about chromosomes for 130 years, these kinds of methods have only been available for several decades. This means that only now we can begin to understand the intricate internal structures of chromosomes.

Archana Bhartiya, lead author of the study, said: “A better understanding of chromosomes may have important implications for human health. A vast amount of study of chromosomes is undertaken in medical labs to diagnose cancer from patient samples. Any improvements in our abilities to image chromosomes would therefore be highly valuable.”

Wear and tear on chromosomes is strongly linked to aging. They also contain answers about various genetic disorders. We need to research chromosomes further to understand their structure better. But for now it is interesting to know that every cell in your body contains 242 picograms of chromosomes that have the instructions for your entire life.


Source: UCL