Contains DNA in the form of Chromosomes which store the genetic code. The nucleus is where DNA replication, repair and transcription occur. Surrounded by the nuclear membrane which contains nuclear pores which tightly regulate what can get in and out. The nucleus also contains the nucleolus – responsible for generating ribosomes and regulating the function of proteins in the nucleus
Polymeric macromolecules made from monomers called nucleotides. There are two main types: DNA and RNA. Like proteins, DNA and RNA are unbranched polymers
Has 3 main components: a phosphate group, a sugar (ribose in RNA, deoxyribose in DNA), and a base. The phosphate and sugar form the backbone of the molecule while the base encodes the genetic information
The phosphate attached to the 5' position of one nucleotide bonds to the 3' position of the next. This is called a condensation reaction (because water is released) and the new bond is called a phosphodiester bond
Bases can interact through Hydrogen bonding. In DNA and RNA bases pair in specific ways: A always bonds with T (or U in the case of RNA), G always bonds with C. A-T form 2 Hydrogen bonds whereas G-C form 3 Hydrogen bonds
Consists of two anti-parallel strands held together by the base-pair hydrogen bonds. The sugar-phosphate backbone is on the outside with the base pairs in the centre. The two strands then wind into a right-handed double helix. One full turn of the helix contains 10 base pairs and is around 3.4 nm in length
Has 3 important differences from DNA: Ribose instead of deoxyribose in the backbone, Uracil takes the place of Thiamine as a base, and RNA generally does not form a double helix, but instead exists as a single strand. Small portions of the strand might be self-complimentary – causing the RNA to fold into complex formations. RNA can have a structural role e.g. in ribosomes
DNA Polymerase can only add nucleotides in the 5' to 3' direction and can only elongate a chain – not start a new one because it also does proof-reading
1. DNA Primase forms a new chain from RNA not DNA. It forms a chain ~10 nucleotides long which DNA Polymerase can then extend. This chain is called a primer and is ultimately replaced by a DNA version by an enzyme called Exonuclease
2. The primer is extended by DNA polymerase into small sections called Okazaki fragments which are then join together by an enzyme called DNA Ligase
DNA Polymerase can only add nucleotides in the 5' to 3' direction and DNA polymerise can only elongate a chain – not start a new one because it also does proof-reading
There are 3 possible reading frames – but only one gives a meaningful amino acid sequence. It is the job of RNA Polymerase to get the right reading frame