You share more than 60% of your DNA with a banana. We all have heard about DNA, the building blocks of life, but do we know what it actually is? What is it made out of? And why does it look so weird? DNA stands for deoxyribonucleic acid and is found in the cells of ALL living beings - it is what makes us different from a banana and a monkey. DNA tells our cells what to do and is essentially the instruction manual for our body.
The Structure of DNA
DNA is formed from small and complex molecules we call nucleotides, and the number of them can range from 250 to over 2 MILLION nucleotides in a gene. All nucleotides have 3 essential parts: a sugar, a phosphate group, and a nitrogenous base.
In DNA, the 4 nitrogenous bases are:
Adenosine [A]
Thymine [T]
Guanine [G]
Cytosine [C]
The nucleotides in a single strand of DNA are linked through their phosphate and sugar (resulting in them being dubbed the sugar-phosphate backbone, go figure), creating a nucleotide chain. However, only half of the two stands create a double helix; this is where complementary bases come in.
Nitrogenous bases match in specific pairs called complementary bases and cannot be randomly stuck together. Imagine these bases as four types of jigsaw pieces. A saying I use to remember the pairs is “apple under a tree” and “car in a garage”.
Adenosine MUST pair with Thymine [A-T]
Cytosine MUST pair with Guanine [C-G]
Why are Complementary Bases Necessary?
Adenine and guanine are larger than thymine and cytosine (see photo below). Due to spatial requirements, a pairing with thymine and cytosine would be too small, while a pairing with guanine and adenine would be too large. Furthermore, a pairing between adenine and cytosine is molecularly incompatible, as adenine and thymine are held together by two hydrogen bonds, while guanine and cytosine are held together by three.
This is also the cause of the DNA’s double helix shape, because the different lengths between the 2 base pairings make the DNA wonky, forcing it to twist.
How is DNA stored?
There are roughly 36 trillion cells in an adult male’s body or 28 trillion in an adult female’s body. Needless to say, you have A LOT of DNA crammed inside your tiny cells.
Your DNA is stored in ‘varying levels’ that form the next structure:
Nucleotides join together to form DNA.
DNA is then wound tightly around numerous proteins called histones, which act as a spool and keep the DNA nice and organized.
Together, histones and DNA form chromatin.
These chromatins then cluster together to form a chromosome.
Through this process, DNA achieves a highly compact state, stored inside of your nucleus.
It should be noted that for the majority of a cell’s life, your DNA is not fully compacted into the shape of a chromosome. It is partly diffused across your nucleus to allow access to its genetic code, and only takes the form of a chromosome during cell division.
To learn more about chromosomes, click here!
Where Does the Name Deoxyribonucleic Acid Come From?
Let’s break down the word deoxyribonucleic acid:
Deoxy → a lack of the presence of oxygen
Ribo(se) → an organic sugar created by your body
Together, deoxyribo(se) is a type of sugar that has hydrogen (no oxygen) as a component, compared to ribose which has a hydroxyl (OH) group.
Nucleic acid → any of various complex organic acids that are composed of nucleotide chains.
Creating Life - What Does DNA Do?
Now that we know the structure of DNA, let’s briefly talk about what it does.
1. DNA acts as a template to make copies of itself (DNA replication) →
If two strands unwind, they can each be used as a pattern for a complementary strand by pairing the nitrogenous bases with their complementary match, creating a duplicate of the original strand. DNA replication occurs during cell division and is used in cells across your body, such as your skin.
2. DNA carries information →
The order of nitrogenous bases carries instructions for protein synthesis. These proteins are used to create amino acids, which help form substances such as enzymes, cytokines, and antibodies as well as the basis of body structures, such as the protein keratin, which is used in hair and nails. The word protein is a vague word that refers to fascinating molecules that are used all over the body with varying functions. Click here to read more about them!
Your DNA is incredibly important. Your cells make up every single part of your body, and your DNA controls them. This is why viruses target your DNA by inserting their genetic code into a cell. This way, when the cell ‘reads’ the DNA it starts creating more viruses, instead of the protein they should be producing, effectively becoming a virus machine and working against you to infect other cells.
Now, you have the BASIC knowledge of the structure of deoxyribonucleic acid and know just how complicated our bodies are. Try to tell a friend about the wonders of the hydrogen bonds between complementary nitrogenous bases and why cytosine and guanine do not go together. I’m sure they’ll love it!
Fun Facts
Humans share 99.9% of DNA with each other!
The DNA from your stomach is the same DNA from the cells in your eyes. The only difference is that certain genes in our DNA are deactivated.
That’s a good thing, we don’t want stomach acid in our eyes!
In the double-helix shape, DNA completes one full turn every ten base pairs.
Humans have 46 chromosomes. However, other animals have varying amounts, such as the koala with 16 chromosomes or the Atlas Blue butterfly whose chromosomes surpass hundreds.
Glossary
DNA: Deoxyribonucleic Acid, which contains the genetic code [information for the development and functioning of an organism] of you, located in your nucleus.
Gene: a distinct sequence of nucleotides forming part of a chromosome - the order of which determines the order of monomers in a polypeptide or nucleic acid molecule which a cell (or virus) may synthesize.
Nucleotide: a complex molecule consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit of nucleic acids.
Double-Helix: a term used to describe the physical structure of DNA → two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape.
Complementary base: a nucleotide base that pairs with its partner nucleotide on the alternative DNA strand - adenine pairs with thymine, cytosine pairs with guanine.
Hydrogen bond: a type of weak chemical bond between two groups of atoms; the bond between two nitrogen bases in the DNA helix complementary base.
Nucleic acid: a polynucleotide chain made up of nucleotides.
Protein: A molecule made up of amino acids and needed for the human body to function properly.
Works Cited
Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2002). The Structure and Function of DNA. Molecular Biology of the Cell. , [online] 4th edition. Available at: https://www.ncbi.nlm.nih.gov/books/NBK26821/. [Accessed 27 Mar. 2024].
BYJUS. (n.d.). Difference Between Deoxyribose And Ribose - An Overview. [online] Available at: https://byjus.com/biology/difference-between-deoxyribose-and-ribose/. [Accessed: 18 March 2021].
Farthing, E., Boldú, L.O., Shingles, S., Haydon, E., Monaghan, J., Smidt, C. and Gale, F. (n.d.). What Is a chromosome? [online] www.yourgenome.org. Available at: https://www.yourgenome.org/theme/what-is-a-chromosome/. [Accessed 23 Mar. 2024].
Farthing, E., Boldú, L.O., Shingles, S., Haydon, E., Monaghan, J., Smidt, C. and Gale, F. (n.d.). What Is a chromosome? [online] www.yourgenome.org. Available at: https://www.yourgenome.org/theme/what-is-a-chromosome/. [Accessed 23 Mar. 2024].
Fessenden, J. (2018). Study Answers 100-year-old Question about How Chromosomes Get Their Distinctive X-shape. [online] UMass Chan Medical School. Available at: https://www.umassmed.edu/news/news-archives/2018/01/study-answers-100-year-old-question-about-how-chromosomes-get-their-distinctive-x-shape/. [Accessed 23 Mar. 2024].
Gilchrist, D.A. (2024). Histone. [online] Genome.gov. Available at: https://www.genome.gov/genetics-glossary/histone. [Accessed 22 Mar. 2024].
Shively, V. and Kim, K. (2021). National DNA Day - DNA Facts & History. [online] www.luriechildrens.org. Available at: https://www.luriechildrens.org/en/blog/happy-dna-day/. [Accessed: 20 March 2024].
Silvester. H. (2023). Oxford Science 10 Australian Curriculum Student obook pro. (2nd ed.). Oxford University Press [Accessed: 12 March 2024]
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