Proteins

From last week we know that genes are recipes written out with nitrogen bases, but who reads these recipes and what gets made? 

First, let’s talk a little bit more about the structure of a gene. Genes are made of DNA that have two distinct parts, introns and exons, typed out in a repeating pattern (intron, exon, intron, etc). The nitrogen bases in the exon regions are the letters that will make up the words for the recipe, but in DNA the introns interrupt the exons and make the recipe unreadable. Think of the instructions to your favorite recipe, and instead of space in between words, the word “unreadable” separates the words so it reads something like this:

“Preheatunreadabletheunreadableovenunreadabletounreadable350unreadabledegrees.Firstunreadablecreamunreadabletheunreadablebutterunreadableforunreadablethreeunreadableminutesunreadableuntilunreadableitunreadableisunreadablelightunreadableandunreadablefluffy.”

Tough to make out the directions, right?

So, these introns (the word “unreadable”) must be removed. However, our original copy of DNA (which includes exons AND introns) must be preserved within the cell first. A machine protein, called RNA polymerase, will copy the gene into a separate molecule in a process known as transcription. This copy of the gene is called pre-messenger RNA (pre-mRNA)

Now we have pre-mRNA, but the words of the recipe are still broken up by introns. To fix this, another machine protein, the spliceosome, removes all of the introns and connects the exons, in a process called splicing. With the introns removed, the new exon-only product is known as messenger RNA (mRNA) and the recipe can now be read as full sentences:

“Preheat the oven to 350 degrees. First, cream the butter for three minutes until it is light and fluffy.”

A lot easier to read and interpret, right? All thanks to splicesosomes! 

The cell now brings in the protein chef, or the ribosome. The ribosome reads the recipe, grabs the small chemical components, amino acids, and makes the protein. Amino acids are the building blocks of the proteins. They are the ingredients that are required for making your favorite recipe. There are 21 different amino acids and they can be linked in countless ways to create different flavors or combinations of proteins. This process is called translation.

Proteins form very distinct three dimensional shapes, known as conformations. Their conformation is determined by their amino acid sequence, as different amino acid sequences have different properties and behaviors. All proteins have the ability to bind to other molecules. Binding is like the connection of two molecules. Think of a lock and key, the lock has a hole that only certain shaped keys will fit into. In a similar way, proteins can have little pockets that other molecules can sit in. Proteins have varying specificity depending on how many different molecules it can bind. The binding capabilities of proteins are essential for their jobs and functions. 

Transcription factors help control how often the recipe is read and protein is made. They either increase or decrease transcription, the copying of the gene into pre-mRNA, by hugging regions of DNA close to the gene. These transcription factors are called activators or repressors, respectively.

To summarize, the DNA sequence is the recipe for making these proteins. The process from DNA to proteins is: RNA polymerase converts DNA into pre-mRNA through transcription, spliceosomes remove introns and create mRNA, then ribosomes bring in the correct amino acids based on the mRNA sequence and make the protein in a process called translation.

But, what do proteins do? Why do we need them? 

Proteins do all of the work inside of the cell; they are essential for structure, function and regulation of tissues and organs. Proteins are the machines, the workers, and the messengers bringing information into and out of the cell from the outside world. With that said, this article could be a whole textbook on its own, but we’ll save you the time and include only a few examples of their many functions. 

Protein FunctionDescription ExamplesApplication 
Antibody A protein released by immune cells that targets a specific part of a virus or bacteria to help the immune system. Immunoglobulin G (IgG)
Vaccines introduce the body to the virus or bacteria so antibodies can be made before there is a true infection. 
EnzymesProteins that help make a chemical reaction go faster. They can also read genes and produce new molecules, like pre-mRNA.   -DNA Polymerase-RNA polymerase -LactaseLactase breaks down lactose, a sugar in milk. People who are lactose intolerant lack this enzyme and have problems digesting milk.
Messenger proteins Proteins that help the cells and organs in the body communicate so everything functions synchronously. Hormones: insulin, testosterone, growth hormone, adrenaline, etc.Fight or flight: when your body needs to react quickly, it will release adrenaline to speed up your heart rate, for example, so you are ready to fight or flee. 

As you can see by the few examples, proteins are essential for many diverse components of life. They are important for helping us stay healthy, digest milk and react to intense situations. 

While DNA is the recipe that codes for our specific proteins, proteins themselves are the diverse results (cookies, pizza, pasta, roast beef, chicken, cake, bread and any other tasty meal you can think of) that keeps everything in check, satisfied and happy! But, what happens when too much or too little of certain proteins are being made? Diseases like cancer can result. More on this later!

Thanks for reading and make sure to check back next week for the launch of our CELL SIGNALING introductory post! In the meantime, let us know if you have any questions, comments or feedback and don’t forget to follow/ like us!

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Written by Annah and Denys
Illustrated by Rhea

Disclaimer: We are not medical professionals. This post is not meant to be used as a diagnostic tool or as medical advice. Further, the opinions in this post are our opinions and in no way reflect the opinions of our mentors or Medical University of South Carolina.

References
https://ghr.nlm.nih.gov/primer/howgeneswork/makingprotein
https://www.ncbi.nlm.nih.gov/books/NBK26911/
https://ghr.nlm.nih.gov/primer/howgeneswork/protein

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