An Intro to CRISPR Cas-9 Gene Editing

An Introduction to CRISPR

Imagine the power to create super-athletes or cure sickle cell anemia. Now, with CRISPR-Cas9 gene editing technology, we can do just that. This technology is fast becoming increasingly popular. In fact, some companies are already selling do-it-yourself CRISPR kits. But how does CRISPR work? How can it be used? Why might this technology not be widely accepted?

Necessary Knowledge

This is the knowledge that you will need to know for this article. It is just a quick skim and only covers the basic things, so don’t use this to learn about cells or anything else covered in this section.

Cells

Your body is made up of tiny things called cells. Inside cells, there are small things called organelles(pronounced ôrɡəˈnel). Organelles act as organs for a cell. There are many different organelles with different functions. Ribosomes make proteins. There are many ribosomes in a single cell.  The nucleus is in the middle of the cell. It stores DNA. There are also much more with different functions that are equally important, but these are the ones needed for the rest of this article. The nutrients are allowed into the cell through the cell membrane. The cell membrane is like security for a cell. It keeps the bad stuff out and lets the good stuff in. There is also fluid in a cell containing all of the necessary nutrients for it to live. This is called cytoplasm or cytosol. It makes up 70% of a cell. The nutrients in the cytosol come into a cell through a process called diffusion. Diffusion is when things go from more concentrated to less concentrated. The nutrients diffuse through the holes in the cell membrane.

DNA

DNA makes up genes, and genes make chromosomes. A chromosome is like a schedule for a cell. Your body has 24 chromosomes. Continuing with the analogy, a gene is like an event in the schedule, and DNA is like each moment in the event. DNA is made up of pairs of chemicals called base pairs. These bases are called adenine, guanine, thymine, and cytosine. Cytosine always forms a base pair with guanine, and adenine, with thymine. DNA is the instructions for building proteins. First, a cell splits a segment of DNA in half. By splitting it in half, the cell turns the DNA into mRNA. Unlike other RNA, mRNA in an animal cell uses thymine instead of uracil. The mRNA then floats around in the cytoplasm until it hits a ribosome. The ribosome takes the mRNA and takes it into itself, three bases at a time. The three bases code for a certain protein. The ribosome then takes the amino acids out of the cytoplasm and puts them together into a protein. Cancer sometimes occurs when a mutation occurs in DNA.

Proteins

                   Proteins are made of things called amino acids. They are in meat and are needed to grow muscles. There are many different kinds of proteins. The human body can make proteins too. Ribosomes make proteins by reading the messenger RNA that your cell makes. They get the amino acids from the cytoplasm that they float in. Proteins affect how our bodies react to the world and our appearances.

RNA

RNA is similar to DNA except for the fact that RNA is a different shape that DNA. Whereas DNA is a double helix, RNA can fold itself into many different shapes. It does this because it has only one side, and its bases pair with each other, folding it. RNA also uses one different base. Instead of thymine, it uses uracil. Some viruses use RNA as their genetic material. These include zika, influenza a, dengue, west nile, and many more. Human cells use it to transmit information to the rest of the cell. RNA in animal and plant cells still uses thymine.

Other Information

Although there are similar techniques that function in similar ways, here we will focus on CRISPR. CRISPR is a better gene editor because it is much cheaper and is more accurate. It can also be attached to other proteins to make genes more or less expressive. There are also many other proteins that have been developed. Many of these work the same as Cas9, the protein that this article is about, but are just different.

CRISPR

What is it?

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. Essentially, it is a bunch of base pairs repeating in a pattern. It is a part of DNA in certain archaea and bacteria and was discovered in 2015 by Jennifer Doudna.  CRISPR was originally a archaea defense system to fix mutations. It was later discovered in bacteria being used to destroy viral DNA.

How does it work?

It works by cutting out sections of DNA by using guide RNA and the Cas9 protein. First, the guide RNA and CRISPR RNA is inserted into the Cas9 protein. The Cas9 folds the RNA into a shape that can cut DNA. It can cut out sections of DNA. Cas9 is programmed by putting in guide RNA sequences of up to twenty letters. When the Cas9 comes across a match, it will cut the sequence out. In order for it to be able to modify DNA, there must be replacement DNA in the near vicinity. When the cell starts to repair its DNA, it will grab the replacement DNA instead of the old DNA and put it back in. Its accuracy varies because there are different versions of the Cas9 protein that have different accuracy levels. There are even completely different proteins that work the same way. Cas9 is programmed by inserting CRISPR RNA and mRNA into it.

What does this process look like?

All of this happens in a test tube, petri dish, or maybe even some places in the body depending on what it is being used for. The dish would need to have a solution containing lots of both pre-programmed Cas9 programmed for the location in the DNA, and replacement DNA. The ingredients would then diffuse into the cell through the cell membrane. As the Cas9 accumulated, it would find its way into the nucleus. There, it would enter one of 24 chromosomes and zip around looking for a match to its guide RNA. While this was happening, the replacement DNA would also be floating around. If the Cas9 cut some DNA, but the cell put it back instead of the replacement, the Cas9 could simply re-cut until it works right. This process would continue until the Cas9 protein breaks apart.

Uses

CRISPR is a powerful technique with many uses. There are some that are known and some that are yet to be discovered.

There are many human uses to CRISPR, some of which are only possible before birth. With CRISPR, humans can now make people taller or shorter, faster or slower, and more or less muscular. This edit must occur in the womb when a baby is just an embryo so this change affects all or most of the cells. Using CRISPR we can also cure some genetic diseases such as sickle cell anemia. For sickle cell, the change could happen after birth because the edit only happens in a few cells, then spreads as the cells split. This technology could also prevent diseases that are not genetic like malaria.Allergies This would need to occur very soon after fertilization because all of the cells need to be equipped with this gene. Also occurring soon after fertilization or even before it, is edits to the brain preventing diseases or allowing for people to finish school in less time.

CRISPR can benefit humans indirectly through its use on animals there are at least four ways:

1. Every year, many people die on the waiting list for new organs. This could be solved if humans created animals such as pigs with identical organs to ours. This change would have to be done before the egg is fertilized because it is critical that every cell in the animal has the update.
2. Humans can also make animals that are better for business. We can use this in two ways. Before fertilization, we can edit farm animals to be bigger, have better meat, or have long hair. Also, we can make race animals that are more aggressive or have a balance of muscle and leanness to perform better in races.
3. There are also pet pigs that stay mini created by CRISPR. These animals used to exist earlier, but they only stayed small for 10% of the time. These CRISPR pigs stay smaller most of the time. Along with pet pigs, there are many other animals that could be miniaturized to be pets. Scientists are now trying to create pigs with customized fur to sell. This could also be applicable to other species like dogs and cats.

Some of the most useful benefits are in the field of plant uses. There have already been many modifications to the crop gene pool by unnatural selection, but CRISPR is much faster at making these changes. All of these modifications would occur before the seed is planted. First, a scientist would extract DNA from the seed. Then they would modify it and put it back in the seed. Plants are much easier to make changes to because they can stay dormant and do not immediately start growing. This is already being done to crops.

The uses for CRISPR in plants could possibly change the world and maybe even solve world hunger. By making a plant whose roots grow downward instead of sideways, farmers can plant plants closer together, allowing for more food to be grown on the same amount of land. People can also make plants that look more aesthetically pleasing. This is important because a lot of food is wasted because it doesn't look good. Parents could also get kids to eat their veggies easier if there were veggies with different flavors like chocolate flavored broccoli.