1 Chapter 8 DNA & RNA
2 #1. DNA Structure (an overview)DNA has three main components 1. deoxyribose (a pentose sugar) 2. base (there are four different ones) 3. phosphate
3 #2. The Bases They are divided into two groupsPyrimidines and purines Pyrimidines (made of one 6 member ring) Thymine Cytosine Purines (made of a 6 member ring, fused to a 5 member ring) Adenine Guanine The rings are not only made of carbon (specific formulas and structures are not required for IB)
4 Nucleotides Units that make up DNA molecule Made of three parts5 carbon sugar (deoxyribose) Phosphate group Nitrogen bases
5 #3. Nucleotide StructureNucleotides are formed by the condensation of a pentose sugar, phosphate and one of the 4 bases The following illustration represents one nucleotide
6 #3. Nucleotide StructureNucleotides are linked together by covalent bonds called phosphodiester linkage
7 #4. DNA Double Helix and Hydrogen BondingMade of two strands of nucleotides that are joined together by hydrogen bonding Hydrogen bonding occurs as a result of complimentary base pairing Adenine and thymine pair up Cytosine and guanine pair up Each pair is connected through hydrogen bonding Hydrogen bonding always occurs between one pyrimidine and one purine
8 #4. DNA Double Helix and Hydrogen BondingComplimentary base pairing of pyrimidines and purines
9 #4. DNA Double Helix and Hydrogen Bonding
10 Watson and Crick later discovered what held the two strands togetherHydrogen bonds could form between certain nitrogen bases and provide enough force to hold the two strands together Hydrogen bonds could only form between certain base pairs adenine and thymine and guanine and cytosine This principal is called Base pairing This explains Chargaff’s Rule
11 #4. DNA Double Helix and Hydrogen BondingAdenine always pairs with thymine because they form two H bonds with each other Cytosine always pairs with guanine because they form three hydrogen bonds with each other
12 #5. DNA Double Helix The ‘backbones’ of DNA molecules are made of alternating sugar and phosphates The ‘rungs on the ladder’ are made of bases that are hydrogen bonded to each other
13 #6. Antiparallel strands5’ 3’ The strands run opposite of each other. The 5’ end always has the phosphate attached. 5’ 3’
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