DNA Structure

DNA = D eoxyribo N ucleic A cid  DNA is a polymer (chain of monomers)  Nucleotide = monomer of nucleic acids  DNA is in a double helix structure  two long strands of nucleotides twisted around each other, like a spiral staircase

DNA Structure DNA Nucleotide Structure: (3 parts)  Phosphate group  1 phosphate (P) atom bonded to 4 oxygen (O) atoms  5- Carbon Sugar = Deoxyribose  Nitrogenous Base

DNA Structure 4 Types of Nitrogenous Bases:  Pyrimidines (single rings)  Thymine (T)  Cytosine (C)  Purines (double rings)  Adenine (A)  Guanine (G)

DNA Structure Complementary Base Pairing Rules  Adenine (A) pairs with Thymine (T)  AT&T  Guanine (G) pairs with Cytosine (C)  They look alike!  Every complementary base pair contains one double-ringed purine and one single-ringed pyrimidine

DNA Structure Bonds hold DNA together  DNA double helix resembles a spiral staircase  Alternating phosphate and sugar molecules form the “side rails” of the staircase – phosphate sugar backbone  Covalent bonds between sugar of one nucleotide to a phosphate of another nucleotide

DNA Structure Bonds hold DNA together  DNA double helix resembles a spiral staircase  Nitrogenous bases face toward the center of DNA  Bases of one strand of DNA form hydrogen bonds with the bases on the other strand – “steps” of the staircase

DNA Structure Bonds hold DNA together ….strong or weak bonds? 3’3’ 5’5’ 3’3’ 5’5’ covalent bonds hydrogen bonds

DNA Structure Complementary Base Pairing Rules  2 hydrogen bonds form between A : T  3 hydrogen bonds form between G : C

DNA Structure Directionality of DNA  Nucleotide:  Phosphate  5 C Sugar  N Base  Refer to the 3’ and 5’ ends of DNA nucleotide depending on the trailing carbon... super important! OH CH 2 O 4’4’ 5’5’ 3’3’ 2’2’ 1’1’ PO 4 N base ribose nucleotide

DNA Structure DNA is antiparallel  A single strand is different at each end  5’ (5 prime) and a 3’ (3 prime) end  The two strands in the helix run in opposite directions = antiparallel

DNA Structure Lets practice!  Draw an entire DNA molecule with the 5’  3’ sequence reading A C T A G C A T

DNA Structure  DNA Construction