THE CENTRAL DOGMA

Information Transfer

DNA

• Blueprint for protein synthesis• Polymer of nucleotides• Nucleotide = a 5 carbon sugar (deoxyribose), a

phosphate group and a nitrogenous base (adenine, thymine, cytosine and guanine)

• A + G = purines = 2 rings; T and C = pyrimidines = 1 ring

• Base pairing rules = C + G and A + T

DNA Double Helix

• 2 nucleotide chains wrapped in a double spiral (twisted ladder)

• Structure discovered by Watson, Crick and Wilkins – Nobel Prize; Rosalind Franklin

• Alternating sugar - phosphate – sugar – phosphate ….. Covalently bonded – make up sides of ladder (AKA backbone)

• Bases covalently bonded to sugar; rungs of ladder are A, T, G and C hydrogen bonded

DNA Replication

• Process by which DNA is copied – S Phase of Interphase

• 2 nucleotide chains separate (helicase breaks H bonds) -> replication fork

• Topoisomerase = allows swiveling by nicking strand

• RNA Primase = sets down about 10 nucleotides first (complementary)

• DNA Polymerase binds and adds complementary nucleotides to parent strand – can only add 5’ -> 3’

• Discontinuous replication on lagging strand – Okazaki fragments – eventually linked together by ligase

• Other strand is leading strand; replication is continuous

• When replication is completed, 2 new exact copies of original DNA molecule are produced -> cell can now divide

• Replication = accurate; repair enzymes fix mutations (changes in nucleotide sequence)

Sites to Visit

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#

• http://bcs.whfreeman.com/thelifewire/content/chp11/1102003.html