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SDS & Science Snapshots (2024-02-03)

In this issue: Unveiling the Mysteries: CZI Blog Breaks Down Your Body's Building Blocks – Surprising Answers to Your FAQs

Welcome to our timely updates on all things SDS, Science, and Advocacy. We bring you a digest of recent scientific publications, conferences, and other newsworthy content - all relevant to SDS - with links to more details and learning opportunities. Are you interested in anything specific? Did we miss something? Let us know. Email or message us on Facebook! This is all for you!

The Science Snapshot this week contains content modified from a blog post published by the Chan Zuckerburg Initiative (CZI) and written by Samantha Yammine.


Revealing the Mysteries of Human Cells

In a previous Science Snapshot on Understanding the Role of Genes, we briefly reviewed what cells are, the role of genes as instructions for these cells, and the difference between germline/hereditary variants (i.e., mutations) and somatic/acquired variants.

Our bodies are composed of trillions of cells that have many different roles – to help us grow, digest food, protect us against infections, and more. These different tasks are controlled by a set of instructions known as genes. (We even have genes whose purpose is to protect us against cancer!) Genes are made up of DNA, which you inherit from your parents, and they determine things like your eye color, height, and even your risk for certain health conditions.

In this week’s Science Snapshot, we will be highlighting an interactive and informative blog post published by the Chan Zuckerburg Initiative (CZI) and written by Samantha Yammine, which answered some of the frequently asked questions about the cells that make up our bodies.

How many cells are there in the human body?

The current best estimate is that the average body contains about 37.2 trillion human cells. There are more cells making up the human body than the number of seconds in one million years. And about 372 times as many cells making just one body than there are stars in our home galaxy, the Milky Way. And that’s without factoring in the trillions of single-celled microbes living throughout the human body in symbiosis (i.e., these microbes positively benefit the function of the human body just as our bodies support their survival).

These trillions of cells are the basic functional unit of our biology, coming together to form the different organ systems in our body. Cells come in many forms and functions — from elongated cardiomyocytes that help the heart contract, to the tree-shaped neurons that transmit electrochemical messages throughout the brain, and biconcave, disc-shaped cells carrying iron throughout our blood. Researchers are working to map all of these different cells in our body to better understand health and disease.

How big is a cell?

Human cells come in a range of sizes, though most are too small to be seen with the naked eye. The main exception to that is the ovum, or egg cell, which is among the largest cells in the body at about 0.1 millimeters (or 100 micrometers) across. Rival to the unusually large size of the ovum are motor neurons emanating from the spinal cord down to the biggest toe. These are about 100 times thinner in diameter than the ovum, but have a single projection running the length of the leg, reaching up to one meter long.

Most other human cells average about 10-100 micrometers in diameter. To picture that scale, imagine a single grain of salt cut into five pieces. Each of those pieces would be about the size of the average human cell — no longer visible without magnification, and so small that about 635 of these cells could fit across the diameter of a penny.

The size and shape of a cell is closely tied to its function, and can change over time. The growth and division of cells are very carefully regulated to maintain a healthy state.

Does every single cell in my body have the same DNA?

For the most part, yes, every cell in the body has roughly the same set of DNA. That’s because all cells in the body originate from the fertilized egg, created through many, many rounds of cell division. Each time the cell divides, it makes a copy of its genetic material so there is enough to be passed on to the new cell.

While there are many “proofreading” steps to reduce errors in the process of duplicating DNA, there are approximately 120,000 copying mistakes across the 6 billion bases in the genetic code every time a cell divides. While most of these changes do not amount to any significant changes in the genetic code, they can accumulate as cells in the body continue to divide over our lifetime.

While every cell in a person’s body has nearly the same set of DNA, cells become different depending on the subset of the DNA being used. It’s similar to how an orchestra works: all of the instruments are there, but not all of them are getting played at once, and depending on the timing and combination of instruments you can get completely different music from the same set of instruments. While every cell has the full set of DNA, as a cell develops and specializes it uncoils the parts of DNA it needs to use and coils up the parts that are less relevant to its functions. That’s how a muscle cell ends up different from a skin cell, even though they have the same set of genetic instructions.

Researchers want to learn more about how differences in people’s DNA, environments, and lifestyles impact their health to formulate more precise treatments and prevention strategies. CZI has partnered with the US’ four historically Black medical colleges to further support their cutting-edge scientific research in this field to accelerate precision health for all.

How many different types of cells are there in the human body?

Historically the answer has been that there are about 200 different types of cells in the human body, but new technology in the last decade has uncovered many more than that, totalling a couple thousand.

For example, we’ve known for over a century that there are four main types of cells in the brain: message-conducting neurons, star-shaped support cells called astrocytes, cells that insulate neuronal connections called oligodendrocytes, and specialized immune cells that survey and respond to changes in the brain called microglia. From the first glimpses of these cells through the earliest of microscopes it became clear there are many subcategories of each of these cell types.

But it’s taken advances of imaging technology and molecular biology to fully begin to realize just how varied cells can be. For example, the Tabula Sapiens is a project by the Chan Zuckerberg Biohub San Francisco and CZI to map cells of the human body using molecular data. They have already characterized over 400 different cell types using molecular data from studying 500,000 cells from 24 different tissues and organs. The data in these comprehensive cell atlases put a spotlight on the subtle differences between cells that are key to maintaining health, and help us better detect the early changes that lead to disease.

How does understanding the cell’s response to disease allow us to develop new therapies?

Diseases result from a change in our body’s function, right down to the level of our cells. By studying which cells are affected in a disease and what changes are happening to everyday cell processes, researchers will be better poised to treat the root cause of a disease. That’s because understanding more about the biology of a disease can enable researchers to identify new targets for medications, better understand disease progression, make more personalized predictions of how someone may respond to a treatment, and develop preventative measures for disease.

For example, rare diseases often involve specific genetic mutations or changes to how genes and proteins are regulated, which point to the role they play in our cells. Through the CZI Patient-Partnered Collaborations for Rare Neurodegenerative Disease and Single-Cell Analysis of Rare Inflammatory Pediatric Disease, researchers and patient organizations are partnering to accelerate our understanding of some of the more than 7,000 rare diseases affecting more than 300 million people worldwide. This work not only advances us towards new treatments for these diseases, but gives us a better understanding of basic cellular processes that are important to treating common diseases, too.

What are some unsolved problems in cell biology?

Each of the 37.2 trillion cells in the human body is like a whole city of biological activity. Each cell is complex with many parts interacting within an ever-changing environment. There is so much we still don’t know about how individual cells in our bodies change over time and how they interact as systems in our tissues and organs.

While new technology is giving researchers a front-row seat to that activity, collaboration and open sharing of data and tools is key to transforming this new information into scientific breakthroughs.

CZI is building open source software tools to accelerate science, funding important research and launching institutes to do research that can’t be done in conventional environments.

For the next 10 years, our goal (of the CZI and SDS Alliance!) is to understand the biggest biological mystery about the human body — the cell. A foundational understanding of how they work will lead to discoveries that will change medicine in the decades that follow.


For more information about what are some of the important cellular components, like ribosomes and mitochondria, you can review this previously published Science Snapshot or watch this YouTube video.


10 Questions Revealing the Mysteries of Human Cells.

Chan-Zuckerburg Initiative

Blog Post Written by Samantha Yammine

July 27, 2023

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