What are the structual differences between DNA and RNA?
DNA and RNA are similar, but different molecules. Both are made up of nucleic acids attached to a backbone made of phosphate and a sugar forming a nucleotide. DNA uses the nucleic acids Guanine, Cytosine, Adenine, and Thymine, while RNA replaces Thymine with Uridine. 


The nucleic acids can form pairs due to hydrogen bonding, which allows the DNA/RNA to store information, if one strand has a C, the other must have a G and vice versa. Same applies for A and T.


While both molecules are capable of forming double helices by hydrogen bonding between G and C or A and T/U, the types of helix tend to be different. DNA prefers to form what is known as a B type helix, while RNA prefers the A type. 



The left most helix is A type, the middle is B type, and the right helix is Z type, a highly unusual form found only under certain conditions.

DNA is almost always found as a double stranded molecule, and is primarily responsible for storing the information for making proteins and RNA and regulatory functions in cells. RNA is made by copying information from DNA through a process known as transcription and performs a variety of roles. Messenger RNA, or mRNA, carries information from DNA to ribosomes where it is used to build proteins through translation. Transfer RNA, or tRNA, carries amino acids to ribosomes to build proteins. The ribosome itself is made of RNA, known as rRNA, with proteins to help it function. Even through RNA is usually made up of only 1 strand, it can fold up and form complex shapes, such as the characteristic tRNA structure shown below. Some RNA molecules can even act as catalysts, carrying out chemical reactions such as cutting up other RNAs. These catalytic RNAs are known as ribozymes.