DNA structure DNA is made of subunits called Nucleotides Nucleotides are made of 3 parts 1) one 5 carbon sugar 2) phosphate 3) nitrogen containing base

Nucleotides are bonded together in long chains Strong covalent bonds hold one nucleotide to the next The strong bonds between phosphates & sugars forms backbone of the double helix

The double helix shape is formed when 2 chains of nucleotides are stuck together by weak Hydrogen bonds between their bases

The two joined strands are twisted into a double helix. Cells store DNA wrapped around proteins called histones Further wrapping of DNA forms the X-shape Seen in mitosis http://www.youtube.com/watch?v=yqESR7E4b_8

Cells can Reproduce by dividing in 1/2 Before dividing cells need to make a copy of their DNA So that each cell can get one copy The process used to copy the DNA is called Semiconservative replication

Semiconservative Replication http://www.wiley.com/college/boyer/0470003790/animations/replication/replication.swf One double helix is copied so there are 2 double helixes. 1 molecule of DNA becomes 2 molecules of DNA Each molecule retains one of the original chains of nucleotides And has one new chain of nucleotides formed by replication

Parent vs Daughter Strands Original chains of nucleotides = Parent strand. New chain of nucleotides = daughter strands Daughter strands are complimentary to parent strands Two new molecules are Identical The two strands are antiparallel (face in opposite directions)

Helicase – breaks H-bonds between bases and unwinds double helix Replication Enzymes Helicase – breaks H-bonds between bases and unwinds double helix DNA polymerase – assembles new nucleotides on daughter chain of nucleotides covalently bonds them in place

http://sites.fas.harvard.edu/~biotext/animations/replication1.swf http://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/inde x.html