BIO - Nucleic Acids [LESSON]
Nucleic Acids
The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals. DNA bears the hereditary information that’s passed on from parents to children, providing instructions for how (and when) to make the many proteins needed to build and maintain functioning cells, tissues, and organisms. It’s amazing to think that inside the same organism, all cells have the same DNA! Adenosine triphosphate (ATP) is also considered to be in this biomolecule category. The role of nucleic acids is to transfer the genetic code from DNA to a messenger RNA (mRNA) molecule in order for the ribosome to read it and create a functional protein. Since structure determines function, if there is a mistake in the genetic code, then the correct protein cannot be produced and it cannot do its job in the cell.
Nucleic acids are built from repeating monomers called nucleotides. A nucleotide has three parts: a 5-carbon sugar, a phosphate group (PO43-), and a nitrogenous base. The four possible nitrogenous bases in DNA are guanine, cytosine, adenine, and thymine. It is helpful to remember the mnemonic device G-CAT because G pairs with C and A pairs with T. RNA does not contain thymine but has an additional nitrogenous base called uracil. Another difference between DNA and RNA is the sugar found in each nucleotide. DNA contains the sugar deoxyribose and RNA contains the sugar ribose. You can see the differences in structure in the image below.
Each strand of DNA is joined together in the middle by hydrogen bonds between the bases. Guanine and cytosine (G-C) base pairs have three hydrogen bonds and adenine and thymine (A-T) base pairs have two hydrogen bonds. Please watch the following video for a nice summary of nucleic acid structure.
Watch the Introduction to Nucleic Acids and Nucleotides video below.
As shown above, the two strands of DNA run in opposite directions. The term antiparallel means one is upside down compared to the other. The sugar-phosphate backbone is located on the outside, and the bases are in the middle. The strands run from the 5’ to 3’ direction, and this is named for the position of the carbon in the sugar to which the free functional group is attached. We’ll look at this more in the molecular genetics unit.
Try the DNA Directionality activity below.
Make sure you found all the differences between DNA and RNA by sorting into this DNA RNA Venn diagram activity (select the arrow after each question to move to the next question):
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