Genetics
DNA
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Get access- Polymeric nucleic acid macromolecule composed of:
- Deoxyribose (a pentose sugar)
Nitrogen containing base (purines -adenine and guanine- and pyridamines -thymidine and cytosine)
- Phosphate group
- One terminal end has a hydroxyl group and the other has a phosphate group
- Adjacent nucleotides are linked by a 3’-5’ phosphodiester bond
- The two chains are joined by hydrogen bonds to form the double helix
- Most coils are right-handed
- Histones form complexes with DNA to produce chromatin
- Euchromatin is less densely packed than heterochromatin
- Less than 10% of the DNA in the genome encodes for genes
- Giemsa stain can reveal alternating dark and light bands
- DNA helix is unwound prior to replication by DNA helicase
- DNA polymerase commences DNA replication: it requires magnesium as a co-factor
- It works in a 5’ to 3’ direction
- This is straight forward for the leading strand
The second template (lagging strand) requires the synthesis of Okazaki fragments by a DNA polymerase
- The segments are then joined by DNA ligase