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Nucleic Acids: Function & Structure

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  • 0:01 What Are Nucleic Acids?
  • 1:58 Structure of DNA & RNA
  • 4:07 Function of Nucleic Acid
  • 5:30 Lesson Summary
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Lesson Transcript
Instructor: Marta Toran

Marta has taught high school and middle school Science and has a Master's degree in Science Education.

In this lesson, we will explore what nucleic acids are, including the oozing bodily fluid they were first found in, what makes them unique from other types of biological molecules, and why DNA is called the 'blueprint of life.'

What Are Nucleic Acids?

You probably hear about proteins, fats, and carbohydrates on a daily basis, and you may even plan your meals around them. What come up less often in everyday conversations are nucleic acids, which belong to the same group of compounds. Although you don't hear about nucleic acids as often, you likely consume them in every meal you eat. More importantly, your life depends on them.

So, what are nucleic acids? Up until 1868, scientists knew that every living thing was made of organic biomolecules (large, carbon-containing molecules made by living organisms), and they had been able to identify these as proteins, fats and carbohydrates. Then a young Swiss scientist named Friedrich Miescher made a discovery that would change the study of life forever: he isolated and identified a fourth type of biological molecule from white blood cells contained in pus he got from used hospital bandages.

Friedrich Miescher

He called the new molecule nuclein because it was extracted from the nucleus of the cells. The name would eventually be changed to nucleic acid, which is an organic substance found in the nucleus of living cells. From that moment, an exciting race began to try determine what the purpose of this new, mysterious biomolecule was, what its molecular structure looked like, and how it behaved.

Today we know that there are two types of nucleic acids found in every living organism: DNA (short for deoxyribonucleic acid) and RNA (ribonucleic acid). Together they are responsible for passing an organism's traits to the next generations, including what it will look like and how their body will work. This seems incredible for a mere chemical that looks like a blob of clear jelly in a test tube.

DNA Extracted from Kiwi
DNA Extracted from Kiwi Fruit

Structure of DNA and RNA

The structure of biological molecules is important because like the tools of any trade, their shape determines their function. It's difficult to imagine chemicals as having a 'shape,' so let's look a bit more into it to try to understand how the 3D shape of nucleic acids comes about.

Like other large organic molecules, nucleic acids are long chains made of individual, repeated units called monomers. The particular name for the units of nucleic acids are called nucleotides and each contains three things: a phosphate group, a sugar (deoxyribose in DNA and ribose in RNA) and a nitrogenous base.

There are six different nucleotides named according to the nitrogenous base they contain:

  • DNA is made up of different sequences of: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
  • RNA also contains A, G, and C but the T is replaced with Uracil (U)

The picture below shows the simplified structure of a nucleotide (in this case Adenine).

Basic Structure of a Nucleotide

Nucleotides are able to form chains because the phosphate of one can attach to the sugar of the one above it, creating a 'sugar phosphate backbone' with the nitrogenous bases sticking out of the side. The main difference between the 3D structure of DNA and RNA is that DNA is made up of two chains of nucleotides twisted together (forming a spiral or helix) and RNA only consists of a single chain of nucleotides. If you think of DNA as a ladder, with the sugar phosphate backbone being the sides of the ladder and the nitrogenous bases the rungs, then RNA would be a ladder cut down the middle.

DNA and RNA
DNA and RNA

Simple Representation of the DNA Structure
Simple Representation of DNA Structure

The famous 'Double Helix' structure of DNA is made possible because nitrogenous bases form complimentary pairs that can link together via hydrogen bonds like puzzle pieces. 'A' bases pair up with 'T' (via two hydrogen bonds), and 'C' bases form bonds with 'G.'

Molecular Model of DNA caption
Molecular Model of DNA

You might ask yourself: how could chemicals fit together like puzzle pieces? Recall that all molecules are three dimensional, they each have a shape and sometimes their 'nooks and crannies' fit together nicely. Chemical properties allow them to create bonds holding them close to each other.

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