Biology Chapter 4 Notes Nucleic Acids
4.1 What is a Nucleic Acid?
- Nucleic acid is polymers made of monomer units of nucleotides
- -Anucleotide components- a phosphate group, a sugar, a nitrogenous base
- -Figure 4.1- phosphate attached to carbon #5,nitrogen base attached to carbon # 1, and OH- group on carbon 3
to bond with next nucleotide
- -Nucleotides- ribonucleotide (sugar is ribose) and deoxyribonucleotide (sugar is deoxribose `
o Deoxyribose is one less oxygen. Ribose has 0H- on carbon 2, while deoxyribose has hydrogen atom
o Nitrogenous bases can be either purines (adenine/guanine) or pyrimidine (cytosine, uracil, thymine)
o Purines are double ring and pyrimidine are single ring, therefore purines are larger than pyrimidine
o Study figure c. in figure 4.1
How to nucleotides polymerize to form nucleic acids?
- DNAand RNAare polynucleotides
- Phosphodiester bond links nucleotides together to form nucleic acid
o Condensation reaction joining the phosphate group of one nucleotide and the hydroxyl group of
o Joins 5’carbon (phosphate) of one ribose to the 3’carbon (hydroxyl) of another ribose
- In RNAand DNA, there will be unlinked 5’carbon while the other end has unlinked 3’end. Sequences of
bases found in nucleotide always written in 5’to 3’direction because DNAsynthesized in this manner(bases
added to 3’end of growing molecule
- Polymerization of nucleotides is endergonic because addition of phosphate groups raises potential energy of
substrate molecule enough to make reaction endergonic
- RNAhas a sugar/phosphate backbone. Refer to figure 4.3
4.2 DNAStructure and Function
What is nature of DNA’s secondary structure?
- Watson and Crick proposed a secondary structure of DNAthat explained the following observation:
o Chemists know structure of nucleotides and that DNApolymerized though Phosphodiester
linkages. So, W and C know that molecule had sugar phosphate backbone.
o By analyzing nitrogenous bases in the DNAsamples, Chargaff established 2 empirical rules: 1)
number of purines and pyrimidine in DNAare the same and 2) number of T andAand C and G
equal in DNA
o By bombarding DNAwith X-ray and seeing how it scattered, Rosalind and Maurice calculated
distances between groups of atoms and molecules. Technique called x-ray crystallography (Bio
skills 8). The scattering patterns repeated multiple times suggesting DNA was helical and spiral
molecule in nature.
- Watson and Crick explained the helical structure of D