DNA

DNA StructureMonomer (basic subunit) = nucleotide

Nucleotide composed of:(1)Phosphate group(2)5C sugar (deoxyribose)(3)Nitrogenous-base

* 5C sugar covalently bonded to both phosphate group AND nitrogenous base

Nitrogenous bases

Only FOUR bases found in all DNA structures:1- Adenine (A)2-Thymine (T)3-Guanine (G)4-Cytosine (C)

Adenine forms 2 H-bonds with Thymine

Guanine forms 3 H-bonds with Cytosine

Phosphate groups bond to sugars with bases attaching at right angles

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Double helix structure

Chromosome structure

Strands of DNA wrap around a protein (histone) forming nucleosomes. Nucleosomes coil together forming chromatin. Chromatin loops and coils together forming supercoils. Supercoils bunch together forming chromsomes.

DNA ReplicationProblem: In order to duplicate (replicate) double-stranded DNA, the two strands must be separated from each other exposing nucleotide bases with complimentary base pairs being added to the “open” strand forming a new double strand.Multiple steps:1.UNZIP the two strands2.Allow matching base pair nucleotides to form new hydrogen bonds with exposed nucleotides3.The new double strands must be exact duplicates of the original bases and be stable

Helicase used with other proteins to UNZIP double strand.

DNA polymerase – primary enzyme used to add new complimentary base nucleotides to unzipped DNA at replication forks.

Ligase used to close gaps and help repair incorrect sequences.

Replication enzymes