Nucleic acids are biopolymers that are essential for all forms of life. RNA and DNA are the two types of nucleic acids that exist in living organisms.
Both DNA and RNA are composed of nucleotides, joined via condensation reactions to form a long strand. Nucleotides have three components:
There are four types of nitrogenous bases:
Below is a RNA nucleotide from VCAA’s 2006 Exam 1 Examination report.
When drawing nucleotides be wary of where each component joins. When drawing a DNA or RNA nucleotide make sure you specify the sugar (deoxyribose or ribose).
DNA is composed of two strands of nucleotides. The phosphate end of the nucleotide is called the 5′ end (pronounced 5-prime), and the sugar end is the 3′ end. In DNA, the two chains are anti-parallel, which means they run in opposite directions – one chain has 5′ at the top and 3′ at the bottom, while the other chain runs from 3′ to 5′.
The two strands are held together by hydrogen bonds between nitrogenous bases. Due to a rule called complementary base pairing, only C can bind with G (with three hydrogen bonds), and only A can bind with T (with two hydrogen bonds).
The double-stranded anti-parallel chain then twists into a structure called a double helix.
Differences between DNA and RNA include:
The three main types of RNA are:
You’ll learn about their roles when you learn about gene expression in Unit 4.
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