Introduction

A scientist studying DNA

If you ever saw Jurassic Park, you know that DNA is an important part of any animal’s biological makeup. DNA is more important than you know, and more important than we realize as we go about our daily lives. 

We can get DNA tests to test for parentage, lineage, and to look back and find our ancestors and where our family lines originated from. However, DNA does much more than just tell us? 

DNA is a set of instructions that are necessary to live. Coding within our DNA provides directions on how to make proteins that are necessary for our growth, development, and overall health. 

 

What is DNA?

a female scientist studying DNA

DNA is an acronym for deoxyribonucleic acid. It is created by a variety of building blocks in our biology known as nucleotides. DNA is vitally important as a molecule, for all organisms, not just people and animals, plants have DNA too! DNA contains the hereditary material from our ancestors, and our genetics, it is what makes us unique. 

Back in the 40s, Biologists struggled to accept that DNA is the genetic material of organisms, simply because it is much simpler in its chemistry than you might expect. DNA was known to be a long polymer which is composed of only a simple four types of subunits, which resemble each other chemically. 

Before we carry on, let’s have a look at these four chemical bases that make DNA. 

 

DNA Is Stored As A Code Made Up of Four Chemical Bases 

Information inside DNA is stored as code which is made up from four chemical bases, these are; adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA is made up of around 3 billion vases, and more than 99% of these bases are the same in all humans. The order and sequencing of these babes are what determines the information available for building and maintaining a living organism, similar to how the letters in the alphabet are morphed into different words and sentences that we then understand. 

DNA bases will pair up with each other, A will pair with T, and C with G in order to form the base pairs. Each base will then also be attached to a sugar molecule and a phosphate molecule. Combines a base pair, a sugar molecule, and a phosphate molecule are called a nucleotide. 

Nucleotides are then arranged in two long strands that form a double helix, which is kind of like a ladder, with base pairs forming the rungs of the ladder, and the sugar and phosphate molecules forming vertical side pieces of the ladder. 

One epic thing about DNA is that it can replicate or produce copies of itself. Each strand of DNA in a double helix can serve as a pattern for duplicating the sequence of bases. 

Let’s learn a little more about each of the four chemical bases that make up DNA. 

 

Adenine (A) 

Adenine is a nucleobase in the nucleic acid of DNA. Adenine has roles in protein synthesis and as a chemical component of RNA and DNA. When Adenine is connected into DNA, a covalent bond is formed between deoxyribose sugar and nitrogen. 

Adenine is one of the two purine nucleases that is used in the formation of nucleotides of the nucleic acids. It binds to thymine via two hydrogen bonds and assists in stabilizing the nucleic acid structures. 

Adenine forms adenosine, which is a nucleoside, when it is attracted to ribose, and deoxyadenosine when it is attached to deoxyribose.  

 

Guanine (G)

Guanine has long been known to aggregate in solution, in the nucleoside, oligonucleotide, and polynucleotide forms. It is a purine nucleobase, oligonucleotide. Guanine can be distinguished from adenine by its amine group. Guanine complementary pairs with cytosine via three hydrogen bonds in RNA and DNA molecules. This is different from Adenine, which bonds to thymine in DNA via two hydrogen bonds. 

Both guanine and adenine are derived from the nucleotide inosine monophosphate, as purines are synthesized as ribonucleotides as not as free nucleobases. 

Guanine has been associated with camouflage, display, and vision. It has been found to occur in iridocytes which are the specialized skin cells of fish. 

 

Cytosine (C)

Cytosine bonds to guanine in DNA. In a DNA molecule, cytosine bases located on one stand form a chemical bond with the guanine bases on the opposing stand. 

Guanine and cytosine bond together in DNA, forming three hydrogen bonds. Cytosine is relatively unstable and can be converted into uracil, which can be corrected by DNA repair systems such as the use of the enzyme uracil glycosylase. If this is not repaired, it can actually lead to a point mutation. 

 

Thymine (T) 

Thymine is the final of the four nitrogenous nucleobases that form the basic building blocks of deoxyribonucleic acid. It pairs with adenine, and they are joined together by two hydrogen bonds which stabilize the nucleic acid structures within DNA. When they are stacked with the other base pair; guanine and cytosine, the helical structure we know as DNA is formed. 

In the structure of RNA, thymine is actually replaced by the uracil nucleobase. The alternative name of thymine is 5-methyluracil, suggesting that thymine can be derived by the methylation of uracil at the 5th carbon. 

Thymine is just as guilty of causing mutations as other nucleobases. When it is exposed to ultraviolet radiation such as light from the sun, covalent bonds are formed between adjacent thymine molecules on the same DNA strand, which create thymine dimers. This is a process that causes damage and causes the DNA to form kinks, and inhibits the usual function of the DNA, which cannot then be replicated or transcribed. However, most cells are able to repair damaged DNA. 

 

What Does DNA Look Like?

Back on April 25th 1952 Francis Crick and James Watson published their famous article which showed DNA’s shape to be a double helix. They were unable to see DNA directly, as it is far too miniscule for that, however they came to their conclusion based on calculations and X-ray diffraction images. The famous photo-51 gave them crucial information. 

Ever since then the double helix structure has become the iconic image of DNA, in logos and stock images, as well as in Jurassic Park of course. It’s even been added to the official list of emojis you can use. In terms of that, the announcement of the DNA emoji annoyed scientists, not because it was turned into an emoji, but because the helix was twisted in the wrong direction, however, they fixed this issue before the emoji was officially released to the world. 

It’s not surprising of course, that many artistic interpretations of the DNA double helix do not claim to be fully scientifically accurate of course, and they will often let the helix turn in whichever way looks best. However, in our bodies, and in the bodies of every other living thing on earth, from monkeys to dolphins, to elephants to that large oak tree in the local park, the characteristic DNA helix will only ever have a right-handed turn. 

The kind of DNA helix we can see are only models, you cannot see real DNA with the naked eye, have you ever seen some helix spirals pop out when you pricked your finger and bled? No, of course not. 

You couldn’t even see DNA with a microscope. The only reason we are aware that DNA exists in the shape of a double helix is because it is the only shape that can explain the X-ray diffraction patterns that it forms. We know this, not only from Rosalind Franklin’s image, but also from many other images that have been taken over the years by a whole multitude of other scientists. It is simply not just something you can clearly see under a microscope, as it is just so tiny! 

A double helix strand is a tiny 2 nanometers wide, your finger is a good 5 million times wider than that, it’s so incredibly small, but so absolutely vital to existence.  

You might be able to see DNA in a few instances, however, one would be if you had a lot of DNA in one test tube. High school projects and science fairs will often involve DNA extraction from vegetables and fruits. They remove the DNA from the plant’s cells and place it in alcohol. Here you will be able to see it as a kind of snotty and white blob in the tube. This is not all that far from the kind of experiment molecular biologists will regularly do in their laboratories, however, they do it at a much, much smaller scale to analyze the DNA samples. 

There is one more well known DNA shape, the chromosome. One individual chromosome contains several million base pairs of DNA, covering a few hundred genes on average. With chromosomes, what you are actually seeing is a very tightly wound long double strand of DNA. Although, it does not always exist in this shape in your cells, it will only look this way during cell division, however, this bunched up shape we refer to is visible under a microscope. 

If you are lucky enough to have access to an electron microscope, you could zoom in even more, and at this resolution you may be able to see a strand of DNA inside a cell. However, there still is not a huge amount of detail at this level of scope. The best way that you could visualize an individual helix would be to create a model based on indirect images, perhaps from X-ray crystallography, or nuclear magnetic resonance spectroscopy. The resulting images would not be a true image of one single piece of DNA, but an average image of several molecules. 

Then, in 2014, Pyne and some of her colleagues were able to look at the structure of a DNA helix using a technique they called Atomic Force Microscopy. Using this method they were able to see details that were not visible in the past, all the way to the characteristic grooves in the helix, both major grooves, and minor ones too. They started to get some structure to the image of a DNA helix. It was more detailed than most non-averaged DNA images, however, even at this level you still were not able to see the individual base pairs that make each piece of DNA unique. No microscope would see it, so usually the genetic code is simplified as simply, a code. 

 

Where is DNA Found?

DNA is not found just floating aimlessly around in the cells, a vast majority of DNA is stored in a small compartment inside cells called the nucleus. A small bit of DNA can also be found in another compartment of the   known as the mitochondrion. 

Every human cell has around six picograms of DNA, this is actually small in quantity, and is much tinier than a grain of rice. 

The location of DNA depends on the organism, in a bacterium or archaebacterium you would find all the DNA is stored in the cytoplasm of the cell. In terms of bacteria or archaebacteriums (prokaryotes) then the cytoplasm is basically everything inside a cell. 

However, for eukaryotes, this means plants, animals, fungus, or a variety of microscopic beasties which are not prokaryotes. If you are reading this, you’re most likely human and thus a eukaryote. While these beings have cytoplasm, they also have membrane-bound organelles which act as small compartments where different activities can take place within the cell. A majority of a eukaryote’s DNA is stored in just one of these organelles, called the nucleus. A small bit of eukaryotic DNA can also be found in two other organelles; the mitochondria, which is relevant for organisms which can photosynthesize, and also chloroplasts. 

Nuclear DNA is organized into linear molecules, which we know as chromosomes. The size and number of chromosomes varies between species. A fruit fly will have only 4 chromosomes, whereas a toad will have 18. A majority of humans will have 46 chromosomes, 23 pairs. Exceptions to this can include mature red blood cells that contain no DNA, as well as sperm and egg cells which have 23 unpaired chromosomes, (you can guess why, right)?

Chromosomes are made up of a single molecule of DNA wrapped around a small, spool-like protein called a histone. The wrapping of this DNA around a histone is very important, otherwise a majority of DNA molecules would not fit inside of cells. 

In humans, the total length of DNA in one cell, if you were to unwind it and stretch it end to end, would be about 6ft long. But that amount of DNA has to fit, tightly packed, into the nucleus of a cell, which has only a miniscule diameter of five to ten μm. The best way to imagine this is to think of packing 24 miles of a thin piece of sewing thread into a tennis ball. Which sounds physically impossible, but somehow science manages to make it happen with our DNA.

So, we know that DNA can be found in three organelles; the nucleus, mitochondrion, and the chloroplast. Only eukaryotes have a nucleus, which is a large structure surrounded by a membrane. Nuclear DNA comes in from the form of long, and linear pieces of DNA which we know as chromosomes. Humans have an amazing six feet of  DNA, but these six feet of DNA are usually spread out over 46 chromosomes. 

A majority of eukaryotes also have mitochondria as well, which are seen as the energy powerhouse of the cell. In this the DNA is known as mitochondrial DNA or mtDNA, and instead of being linear, it is circular. This usually only has a small fraction of the DNA that you could expect to find in the nucleus. 

Only plants and eukaryotic algae have chloroplasts. These can capture sunlight and turn it into energy in the process we know as photosynthesis. In a chloroplast, the DNA is called chloroplast DNA or cpDNA, and like the DNA you might find in mitochondria, it is circular. 

DNA is packed tightly into the nucleus of our cells as chromosomes. Humans are diploid organisms, meaning that they have two copies of every chromosome- one from each parent.

 

What Does DNA Do?

What Does DNA Do

Understanding the basics of DNA, what it looks like, and where you can find it is great. However, what DNA does is more important than this. DNA is something that literally affects how we live, who we are, and our physical traits. Mutations in DNA can create illnesses or unique features that stand us out from the crowd, so what DNA does is very important, and it is more than worth knowing. 

DNA contains the instructions needed for an organism to develop, survive and reproduce, basically, DNA is the key to existence. In order to do this, DNA sequences require to be converted into messages that are then used to produce proteins, which are the complex and skilled molecules that do a vast majority of the work inside our bodies. 

Every DNA sequence that has instructions on how to make a protein is known as a gene. The size of these genes can vary greatly, ranging from around 1,000 bases, to 1 million bases in humans. But genes only make up around one percent of the whole DNA sequence. Sequences outside of this tiny one percent are involved in regulating when, how and how much of a protein is made. In this sense, your body is a factory, the DNA is the overseers and supervisors who give instructions and information on the creation of proteins.  

DNA instructions are handed to the enzymes to read the information in a DNA molecule and transcribe it to an intermediary molecule called messenger ribonucleic acid or mRNA. Then, the information in the mRNA molecule is translated for the amino acids, which are the building blocks of proteins. 

It is an efficient work house, with DNA being the overseers and instructions, while the mRNA and amino acids do all the hard work in creating proteins. 

 

DNA Helps Your Body Grow

DNA is like the recipe instructions for a meal, however, instead of it being a meal, it is you. DNA gives mRNA instructions to translate for the amino acids to create… you. 

DNA contains the instructions to create us, or our cat, our dog, that plant we keep in the restroom. It gives instructions on how to grow, develop, and reproduce. Our cells read the code given to them by the DNA three bases at a time to generate the proteins that are essential for our growth and survival. Each group of three bases will correspond to specific amino acids, which are the building blocks of proteins, as we previously noted. An example of this would be the base pairs T-G-G which specify the amino acid tryptophan, the base pairs G-G-C would specify the amino acid glycine. 

Proteins are made up of different amino acid combinations, when they are placed together in the correct order, every protein will have a unique structure and function inside your body. 

DNA makes us grow, exist, develop, and eventually reproduce. We wouldn’t be here without it…. Literally. 

 

The Structure Of DNA Provides a Mechanism for Heredity. 

DNA is very important in terms of heredity. It is what packs in all the genetic information and passes it on to the next generation, and the next, and the next. It is how we can do DNA tests that will tell us where our ancestors came from. 

The basis for this lies in the way that DNA makes genes and genes make up chromosomes. As we have 23 pairs of chromosomes. Twenty-two of these pairs which are called autosomes look the same in either gender. The 23rd pair are the sex chromosomes, which create the biological differences between males and females. Females will have two copies of the X chromosome (XX), and males will have one X and Y chromosome. 

Both parents of a child will have reproductive cells, the sperms in a male and the eggs (ovum) in a female, and these contain half the number of chromosomes, 23 each. When the sperm fertilizes an egg, this gives rise to a cell with a complete set of chromosomes, therefore the child will inherit half of their genes from each of their biological parents. 

 

How Does DNA Create Proteins?

We covered this briefly before. Understanding the workings of the factory going on inside you, where the DNA transfers information on how to create proteins to the mRNA which translates this information for the amino acids which then create the proteins. 

The function of how DNA does this is simply laid in how DNA stores information for other cells and parts of our biological makeup to do what they are supposed to in order to create a functional life form. 

Remember that our inner workings are much like a factory with DNA, genes, mRNA, amino acids, and proteins all having their individual functions and all working together to create you as a living organism. 

 

Origin of DNA

Origin Of DNA

The origin of DNA would be the universe. DNA came into being as life began, as life cannot exist without DNA in reality. 

However, something that is worth talking about in DNA origins in the RNA replication origin. 

DNA replication origins are characterized by three structures; the sites for binding proteins, mainly initiation and auxiliary proteins, a characteristically AT-rich region that is unwound, and sites and structural properties involved in regulating initiation events. 

The ability to replicate is essential for every living being, the duplication of genetic information is carried out by replication proteins. It is physically visible in many viruses, consider the herpes virus for example, this is a prime example of DNA replication. How this happens is through mechanisms, and this is something worth discussing, as DNA replication is not only something that happens normally in every living being, but it is also something that happens in viruses, thus allowing the spread of these viruses. 

 

Viral DNA Replication Mechanisms

Cellular genomes have double-stranded DNA, however, viral DNA genomes are diverse, some may have circular or linear double stranded DNA genomes while others may have circular single stranded DNA genomes. 

Single stranded DNA genomes are replicated via a rolling circle replication with a double-stranded DNA intermediate. On the other hand, double-stranded viral DNA genomes are replicated via either classical theta or Y-shape replication, by rolling circle, or by linear strand replacement. 

Replications can also be symmetric, or it can be asymmetric, in which both strands are replicated one after the other rather than simultaneously. Some viral replication mechanisms are also used by plasmids (rolling circles) and some of these will encode DNA replication proteins homologous to viral ones, this suggests that plasmids may have originated from very ancient viruses and have simply lost their capsid genes. 

The initiation of viral DNA replication needs to have a specific viral encoded initiator protein which can be a site-specific endonuclease, or a protein that can trigger double-stranded unwinding. Plasmid and viral endonucleases involved in this rolling-circle replication are actually evolutionary related. 

The minimal need for DNA chain elongation is a DNA polymerase (which is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates- i.e. the molecular precursors of DNA). 

 

When and Where DNA Replication Mechanisms Originated

There is no clear answer to this. You could argue that archaeal and eukaryal versions of DNA replication proteins were already present in LUCA (Last Universal Common Ancestor) then they may have appeared successively in the same lineages ancestral to LUCA, or perhaps in different lineages, thus being later mixed in LUCA. However, it is unclear how a new DNA replication machinery could be selected in any organisms that is already containing a more advanced/ evolved version 

However, if bacterial and archaeal/ eukaryal versions of DNA replication proteins appear in different lineages, then you could still imagine that they have evolved differing properties, which would explain their ability to coexist in a singular cell. 

It is also thought that there are two distinct sets of DNA replication proteins that originated after LUCA, one in a common lineage to archaea and eukarya, and one in a proto-bacterium. This would make sense, however, the rooting of this is highly disputed. In fact phylogenetic data that supports this rooting is not valid, although not wrong, and instead it is proposed that instead there is eukaryal rooting or a fusion between proto-bacterium and proto-archaeon to give eukarya

However, the dispute goes on, perhaps one day we will know. 

 

Summary

Scientist explaining DNA

DNA is both immensely basic, and immensely complicated. It is the foundation of all life, trees have DNA, your cat, your dog, your hamster, the ant on the sidewalk, and yes, of course, you. 

DNA is made from a spiraling helix made from four chemical bases; adenine, guanine, cytosine, and thymine. It makes up your body, instructs mRNA, amino acids and proteins on how to create and maintain your body and being. It decides the color of your eyes, your hair, your facial structure, and we get a great deal of it from our parents. 

DNA is found in our genetics and every person, male or female, has 23 single chromosomes, containing DNA in our sperm or eggs that is then passed onto our children. 

Thanks to DNA we can do fantastic things, fight viruses and diseases, understand the core functioning of the human body, animal bodies, and plant bodies. You might not believe it, but the basic photosynthesis classes you had to take in school as part of biology were teaching you a little something about plant DNA! 

DNA can also help people connect with long-lost relatives, and find out where their ancestors came from. In all of us, most of our genes are the same, with only a few differences that make each of us unique. However, at the very core, in the deepest roots of our DNA, we are all the same, made up of proteins created by hardworking amino acids. If nothing else can tell you we are all alike, DNA surely can.