Nucleic Acids Individual unit called a (mono)nucleotide Polymer Individual unit called a (mono)nucleotide DNA is a type of nucleic acid deoxyribonucleic acid

DNA is a polymer made up of individual units called nucleotides

Nucleotide Structure 3 components: Pentose sugar Organic base Phosphate sugar base Stay the same Changes Contains nitrogen & carbon Pentose sugar (5 Carbon atoms) 3 components: Pentose sugar (ribose in DNA) Phosphoric acid Organic base (always contains nitrogen)

4 Bases Purines – Pyrimidines – Double ringed structure Single ringed structure

Bondings The base and sugar join with a: glycosidic bond The phosphate and sugar join with an: ester bond Both require a condensation reaction to occur 

2 condensation reactions occur in the formation of a nucleotide: Phosphate 2 condensation reactions occur in the formation of a nucleotide: H Ester bond OH Glycosidic bond OH H Base Sugar

Tell me… 4 names of bases in DNA 3 components of a nucleotide 2 ends of a strand are called 1 place where a condensation reaction occurs 2 types of bonds in a nucleotide 1 difference between purine and pyrimidine bases

Compl mentary Base Pairing *Purines always pair with pyrimidines* A joins to T (2 hydrogen bonds) C joins to G (3 hydrogen bonds) Therefore, when discussing the proportions of a particular base, you will always find A=T and C=G or! A+C = G+T see e

Bonding relationships Type of Base Purine Pyrimidine Structure Bonding relationships Adenine Guanine Thymine Cytosine = hydrogen bond

5’ 3 hydrogen bonds 3’ C G 0.34nm A T 3’ 2 hydrogen bonds 5’ 2nm

Phosphodiester Bonds: the sugar-phosphate-backbone

G 5’ C 3’ C G T 3’ 5’ T 0.34nm A A 3C 5C 5C 3C 5C 5C 3C 5C 5C 3C 3C 5C

G C C G T T 5’ 3 hydrogen bonds 3’ 0.34nm 2 hydrogen bonds A 3’ A 5’

Strands run anti parallel

Points to remember: nucleotides DNA stands for deoxyribonucleic acid It is a polymer of mono Each nucleotide has three components: pentose sugar (deoxyribose) phosphate group organic base (4 types - purines/pyrimidines) 2 condensation reactions occur when the base and sugar form a glycosidic bond phosphate and sugar form an ester bond Phosphodiester bonds build a sugar phosphaphate backbone on each strand of DNA, with the bases all facing inwards The 2 strands of the DNA molecule form anti-parallel to one another; one strand runs 5’ to 3’ and the other strand runs 3’ to 5’ The strands wind around one another into a double helix (like a twisted ladder) nucleotides

4 Bases Purines – Pyrimidines – Double ringed structure Single ringed structure

DNA Replication – why? DNA carries the genetic code in the order of its bases (more info to come) To pass this information on the molecule needs to replicate itself DNA replication always occurs just before mitosis. This way the cell can make an exact copy of itself When might this occur in the cell?

Movie time! http://207.207.4.198/pub/flash/24/menu.swf Key words to look out for: Replication fork Template Complementary base pairing Leading strand Lagging strand Okazaki fragments Enzymes: helicase dna polymerase ligase

Summarise into 3 stages

Semi-conservative Replication ½ of the old strand of DNA is conserved in each new strand and the 2 new strands are identical