eli5 / if DNA codes for proteins, but each type of cell uses different proteins, how do the cells know which bits to use? Furthermore, how does that also translate to larger scale shapes in/on the organism? (Like the shape of my face, or the shape of a plants leaves)
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Stem cells, they have all info about how organs should be made and how everything looks like. They are basically like a program that can edit itself as its working.
We need a liver? Copy yourself and change in such a way to make a liver cell, rinse and repeat until ‘program’ comes to an end.
It’s too complex for ELI5 but yeah, basically EVERYTHING about you is written in your stem cells, which is why we can use them to recreate new organs. It has been done but it’s yet to be industrialized, its just too complex and expensive right now (and you also need to save those cells for each individual person. There are some treatments for specific genetic diseases that use stem cells so look into those as well for a bit more info)
Think of an American dollar bill. You can fold the note so the words “THE UNITED STATES OF AMERICA” shows the words “THE AMERICA” while hiding the words “UNITED STATES OF”. In the same way, each cell can fold its DNA to show which genes to use and which genes to not use. (For a non-ELI5 explanation look up epigenetics)
For the second question, cells can ‘talk’ to each other by sending signaling molecules that act like passing notes in class. Only certain cells can receive these signals, like only certain other kids have the cipher to make sense of these notes. There are lots of different types of signals that do different things like tell cells to divide, migrate, stick together, repel, make layers, etc. (For a non-ELI5 explanation look up morphogen signaling)
This is a fantastic question! This was one of the first things I wondered as a freshmen getting my degree. The answer is that DNA holds all the instructions but it’s expression is the heart of studying molecular biology. So buckle up for your mini crash course.
The absolute most basic form of this are operons in bacteria. Look up the lac operon. Basically the operon is a segment of DNA that codes for a protein that helps break down lactase. However, normally is not expressed due to another protein(a repressor) binding part of the segment. This blocks the DNA from being transcribed. But when lactose is present it binds to the repressor and the code for the protein lactase can be transcribed and expressed.
Now that is a super simple example. Humans are super complicated. Cells respond to a literal crap ton of signals from other cells and different parts of the body. But a good example you’ll probably know of is hormones. Hormones are basically signals for the cell to transcribe certain segments of DNA.
Now you are probably wondering why cells are different to begin with. Cells start differentiating very early based on the different signals they get very early on in life. But embryology is not my strong suite so I’ll allow someone else to explain the details but the important part is they differentiate early and different cells respond differently or not at all to different signals.
For how it translates on a larger scale you got to remember the shape of a face is or plant leaves are the process of trillions little signals happening. But in a sense they are just an emergent pattern from all those little signals. Kind of like how you can millions of people acting an economy but a countries economy develops patterns like recessions and industry specialization.
I hope that helps explain things a bit. Sorry to be a bit long winded!
Have you ever played these “choose your own adventure” game books? Where everytime you have to make a decision you choose a page and read a specific part of the text? Development kinda works like that. The book is our DNA, and the decisions are small signals that “tell” our cells who to become during development, and they “learn” how to “always” follow the same instructions. So it’s like, every cell has the entire instruction manual inside, but the order of instructions to be followed, thus the end result, varies depending on the type of cell.
(there are exceptions etc., I tried to make it as simplified as I could)
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