• Biology Genetics Molecular Genetics
  • Molecular Genetics

    Have you ever noticed how well things are organized at your local library? Imagine you wanted to find a certain book among the thousands. You’d need to find its call number, head to the right bookshelf, then scan along the rows of books to find the precise book you’re looking for.

    Imagine how long it would take to find your book if all the books were scattered around in disorganized piles—forever! But thanks to the careful and precise organization of the information, you’re able to quickly get the information you need, find the book, read it, and then take that knowledge out of the library and into the world.

    Did you know that you have your own little libraries that work in a similar fashion but on a smaller scale: inside every single cell in your body?

    We’re going to explain how your own mini-libraries works. See the list at right for other in-depth articles on genetics!

    Major Genetics Molecules

    Libraries contain a lot more than just books. They have CDs, DVDs, periodicals, classes, etc. Your own body is the same. Your genetic information is contained in several different types of materials.

    DNA

    Much like most information in libraries is contained in books, the master copy of all your genetic information is contained in your DNA. DNA is famous for its unique shape—imagine if you had a small bendable ladder and twisted it around your finger. Scientists call it a double helix.

    DNA is really cool because it actually stores information within its structure. The “rungs” of the ladder are actually a code, believe it or not! There are four “letters” in the code, called nucleotides. The order of the nucleotides translates into building instructions for your body, just like the letters in the word “dog” translate into a furry, lovable creature.

    Scientists work hard at understanding the DNA code because if we know the code and what it produces, theoretically we can engineer organisms similar to the ways we engineer machines. We might even be able to bring back extinct organisms, like the wooly mammoth:

    RNA

    Have you ever noticed how some books in the library are too important or rare to be checked out? If you want to take that information out of the library, you have to make a copy of the parts you’re interested in.

    It works the same way in your body. If DNA is the master copy of your body’s blueprints, then RNA serves as the temporary copies that can be taken elsewhere in the cell so the master copy can stay safe in the nucleus (the cell’s version of a vault).

    RNA is very similar in structure to DNA, with a few differences. It’s copied directly from a DNA molecule, so it maintains the original order of the code, with one difference: it replaces one specific nucleotide, thymine, with another RNA-specific nucleotide, uracil. It’s also single-stranded, rather than double-stranded.

    Your body uses RNA for a lot of things. It’s mostly used as temporary blueprint copies that get taken out into the construction area (the cytoplasm, or jelly-like material inside the cell), so the originals can stay in the vault (the nucleus) and not get damaged. RNA is also used to make up the structure of the cellular construction machines (the ribosomes) that actually translate the code into a real product to build your body.

    Chromosomes

    Sometimes, libraries need to move to a new location. To make sure they don’t lose track of their books, they have an orderly system of packing books into boxes, transporting the books to their new location, and then unpacking them back onto their new shelves. It’s a big job!

    Your body does the same thing. Sometimes your cells divide, and each new cell needs to get the same “books”. Your body carefully packages the DNA (the “books”) into chromosomes (the “boxes”) which get transported to the new cells before being unpacked again.

    DNA poses some unique packing challenges, though. You have a ton of DNA—enough that if all of it were stretched end-to-end, it would reach from the Earth to the sun and back 300 times! In order to wrangle up all of that DNA, it’s carefully wound around proteins called histones, similar to line on a fishing reel.

    Those histones are organized even further and crammed together to form a long, hot-dog-shaped bundle of DNA called a chromatid. Finally, two chromatids are bound together at the middle with a centromere to create the final chromosome.

    Each cell in your body has 46 chromosomes. They’re actually large enough that when they form, it’s possible to see them under a microscope. Some genetic diseases are caused by abnormalities within the chromosomes. If this is suspected, scientists can make a karyotype—a picture of each of the 46 chromosomes—to check if the chromosomes are normal or not.

    Proteins

    Your body goes through a lot of fuss dealing with DNA, RNA, and chromosomes. It’s all to produce one thing—proteins!

    You might see “protein” and picture your food’s nutritional labels, but there is a much wider definition to consider. No one knows exactly how many proteins there are, but the worldwide Protein Data Bank lists information for 114,983 proteins as of October 2016.

    Proteins are like Legos. They serve as the building blocks for your body, doing everything from making up the structure of your muscles (composed of the two proteins myosin and actin) to bringing oxygen to your muscles via the protein called hemoglobin. Every protein has at least one job, and there’s a lot of things they do to build you up and keep you alive!

    Amino Acids

    If proteins are like Legos, then amino acids are the plastic and dyes that make the Legos. Proteins are actually just long chains of amino acids hooked together. The order of the amino acids is what determines what kind of protein it is.

    Your body uses 20 different amino acids to produce proteins. Your body can make most of them on its own, but nine of them you actually need to get from your diet. These are called essential amino acids.

    Your body can’t make all the proteins it needs without these essential amino acids. This is why some people on specialized diets (such as gluten-free) need to work with a dietician to make sure they’re getting a balanced diet; otherwise they could become malnourished.

    What does your body do with this genetic information?

    Now that you know the molecular major players in the game, let’s take a dive into how they all interact to produce you.

    Let’s say you’ve gone on a long hike with your family one weekend. The next day, you’re super sore. A tiny amount of your leg muscles have actually broken down and need to be replaced (don’t worry—you’ll be stronger afterwards!). Let’s look at how this process gets started.

    Transcription

    First, we need to get the blueprints to make more actin and myosin—the two types of muscle proteins.

    The blueprint for each protein is called a gene. A gene is a specific sequence of code written somewhere in your DNA. It begins with a promoter sequence (a line of code that says, “Hey! This gene starts here!”), has the code for the protein in the middle, and ends with a terminator sequence (a line of code that says, “Hey! This is the end of the gene!”).

    The molecular copy machine for each gene is an enzyme called RNA polymerase. It finds the promoter sequence of the correct gene and attaches to it on the DNA strand. Then, it splits that section of the DNA in half. It scans down the DNA, unzipping as it goes and re-zipping it back up after it passes through as it builds a single-stranded RNA copy from the DNA molecule.

    Finally, when it hits the terminator sequence, it drops off of the DNA (perhaps with an evil cry of “I’ll be back.”). The end result is an intact piece of DNA, a free-floating RNA polymerase molecule, and a new piece of RNA.

    This piece of RNA travels outside of the nucleus and now acts as a messenger template for proteins to be made, so scientists refer to it as messenger RNA, or mRNA.

    Here’s a cool video of it in action:

    Translation

    What good are the blueprints for new muscle proteins if we can’t read them? We need to find a translator to read the RNA code and turn it into a protein that we can use. This is where the process of translation comes in.

    By now, our little mRNA strand has made its way outside of the nucleus. It hooks up with a ribosome, a tiny cellular machine that has all the equipment in it to translate the mRNA into a protein. The ribosome has a special tool hidden up its sleeve: transfer RNA, or tRNA.

    tRNA is actually another piece of RNA (confusing, I know), but it has one job: translate the mRNA code into a series of amino acids that can be hooked together into a chain that makes the protein.

    tRNA does this by reading the code in 3-letter sequences called codons. In fact, the entire piece of DNA is a code that specifies the order of amino acids when broken up into 3-letter chunks. It works by starting out with an RNA strand full of nucleotides like this:

    AUGAUCGAUCAAUAUUAU……UAG

    tRNA reads it like this:

    AUG   AUC   GAU   CAA   UAU   UAU……UAG

    Next, tRNA finds the appropriate amino acid that each codon calls for, and hooks them together like this:

    Methionine-Isoleucine-Aspartate-Glutamine-Tyrosine-Tyrosine….Stop

    Methionine is always the amino acid that starts the chain. There isn’t an amino acid that ends the chain; rather, when the tRNA reads that code, it simply falls off and leaves a complete amino acid chain. To see the full list of how the code specifies each amino acid, click here.

    Here’s another cool video showing how the mRNA is translated into a protein:

    By the end, we have a fully-stitched-together chain of amino acids, now known as a protein. It’ll float on further in the cell for any post-translation processing. After that, the protein will be incorporated into muscle tissue so that the next time you go on a long hike (or take a long walk through the library), you’ll have a little more muscle and be a little less sore!

    Written by Lindsay VanSomeren

    Lindsay graduated with a master’s degree in wildlife biology and conservation from the University of Alaska Fairbanks. She also spent her time in Alaska racing sled dogs, and studying caribou and how well they are able to digest nutrients from their foods. Now, she enjoys sampling fine craft beers in Fort Collins, Colorado, knitting, and helping to inspire people to learn more about wildlife, nature, and science in general.

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