8Tell me… 4 names of bases in DNA 3 components of a nucleotide 2 ends of a strand are called1 place where a condensation reaction occurs2 types of bonds in a nucleotide1 difference between purine and pyrimidine bases
9Compl 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=Gor! A+C = G+Tseee
10Bonding relationships Type of BasePurinePyrimidineStructureBonding relationshipsAdenineGuanineThymineCytosine= hydrogen bond
16Points to remember: nucleotides DNA stands for deoxyribonucleic acid It is a polymer of monoEach nucleotide has three components:pentose sugar (deoxyribose)phosphate grouporganic base (4 types - purines/pyrimidines)2 condensation reactions occur when thebase and sugar form a glycosidic bondphosphate and sugar form an ester bondPhosphodiester bonds build a sugar phosphaphate backbone on each strand of DNA, with the bases all facing inwardsThe 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
18DNA 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 itselfDNA replication always occurs just before mitosis. This way the cell can make an exact copy of itselfWhen might this occur in the cell?
19Movie time! http://220.127.116.11/pub/flash/24/menu.swf Key words to look out for:Replication forkTemplateComplementary base pairingLeading strandLagging strandOkazaki fragmentsEnzymes:helicasedna polymeraseligase