IB Biology Sub-topic A1.2 Notes

Nucleotides

Organic molecules are typically divided into four types. The first of these you need to know about is nucleic acids, whose function is to code for proteins. Nucleic acids all have base units (monomers), called nucleotides. These have three main components:

1. Phosphate group - a PO₄^3- group connected to the 5' carbon of the pentose sugar.
2. Sugar ring - deoxy-D-ribose or D-ribose pentose ring connected to a nitrogenous base at the 1' carbon and a phosphate group at the 5' carbon. 
3. Nitrogenous base - one of adenine, thymine, cytosine, guanine, or uracil, connected to the 1' carbon of the pentose sugar.

Nucleotides are subsequently connected together via condensation reactions, forming a connection between the 3' carbon of one nucleotide and the phosphate group of another nucleotide. Altogether this forms an alternating pattern of phosphates and sugars, called the sugar-phosphate backbone.

Nucleic acids

Connecting many nucleotides together via this sugar-phosphate backbone begins to form nucleic acids. There are two forms you need to be aware of: DNA and RNA.

1. DNA, deoxyribonucleic acid, is a helical double stranded structure.
2. RNA, ribonucleic acid, is a linear single stranded structure.