DNA and RNA are nucleic acids which store and transport genetic information. DNA is a double stranded helix structure found in the nucleus. To produce proteins, the DNA is copied into a type of a single stranded nucleic acid called RNA (more specifically, a type of RNA called mRNA) which goes to the ribosome to be translated into a protein. In other words, the DNA is like an original instruction manual, and the mRNA is a photocopied version which can be transported! There are also 2 other types of RNA - so you need to explain what each type does:
1. mRNA (messenger RNA) - transports genetic information from the nucleus to the ribsosome for protein synthesis
2. tRNA (transfer RNA) - transports SPECIFIC amino acids to the ribosome during protein synthesis
3. rRNA (ribosomal RNA) - a part of ribosomes
Nucleic acids are made up of monomers including a phosphate group, sugar and nitrogenous base. There are however some differences between RNA and DNA, so I would know the differences in structure, monomers, bonding and function. I've attached an image which illustrates the differences.
NB You are supposed to know that phosphodiester bonds, a type of covalent bond, form between the sugar of one nucleotide and the phosphate of another nucleotide in nucleic acids. The reaction to form these bonds is called a condensation reaction where water is removed - just remember that the molecule will be more condensed if water is removed!