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)

Question

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)

In: 7

Answer 1

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!