Nucleic Acids 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 (ribose in DNA) – Phosphoric acid – Organic base (always contains nitrogen) Phosphate sugar base Stay the same Changes Contains nitrogen & carbon Pentose sugar (5 Carbon atoms)

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

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

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

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

Type of BasePurinePyrimidine Structure Bonding relationships Adenine Guanine Thymine Cytosine = hydrogen bond

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

Phosphodiester Bonds: the sugar-phosphate-backbone

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

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

Strands run anti parallel

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

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

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

Points to remember: 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) 10 base pairs for every complete turn of the helix

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! tion/index.html tion/index.html Key words to look out for: –R–Replication fork –T–Template –C–Complementary base pairing –L–Leading strand –L–Lagging strand –O–Okazaki fragments –E–Enzymes: –h–helicase –d–dna polymerase –l–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

DNA Replication Meselson and Stahl Grew microbes in 15 N growth medium Then repeatedly on 14 N growth medium DNA was extracted and separated by centrifugation

DNA Replication