The 2 different types of macromolecules that we will focus on this post are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Organic macromolecules, like DNA and RNA, are biopolymers in living organisms that help store and transfer biological information from one generation to the next. They are great at storing nitrogen in their aromatic rings because both purines and pyrimidines contain nitrogen in their aromatic rings. They therefore have exceptional stability due to the fact that the delocalized electrons can travel throughout the entire compound using available molecular orbitals!
A. DNA Structure: DNA, a polydeoxyribonucleotide, is composed of multiple nucleotide monomers called deoxyribonucleotides. The helix in DNA makes a turn every 3.4 nm, has about 10 bases within that span, and have major and minor grooves between the interlocking strands.
1. Nucleosides and Nucleotides:
Nucleosides are composed of 5-carbon sugar (pentose) that is linked to a nitrogenous base. Nucleotides, on the other hand, are similar to nucleosides. The only difference is that they also have one or more phosphate groups attached to C-5 (5th carbon) as well.
a) Pentose (five-carbon sugar group): Nucleic acids can either have a ribose or a deoxyribose as their pentose. A ribose has an -OH group at C-2 while a deoxyribose has -H (as seen in figure 1). If the five-carbon sugar is a ribose, the nucleic acid is called RNA. If it has a deoxyribose, on the other hand, then the nucleic acid is called DNA.
b) Sugar Phosphate Group: If you take a look at the DNA structure on the right (see figure 3), you will see that the backbone of DNA is consisted of sugar and phosphate groups. The nucleotides (or bases) are joined by 3'-'5 phosphodiester linkages. This means that the phosphate group links the 3rd carbon on the pentose to the 5th carbon on the phosphate group.
These two DNA strands run antiparallel to one another and each strand of DNA has distinct 5' to 3' ends. The two nucleotide chains wound together in a spiral orientation to create a double helix with sugar-phosphate groups directed toward the outside and nitrogenous bases are directed toward the inside.
B. Purines and Pyrimidines: The 2 different families of nitrogen-containing (nitrogenous) bases that we see in nucleotides are purines and pyrimidines. Adenine (A) and guanine (G) are purines and both are found in DNA and RNA. Cytosine (C), thymine (T) and uracil (U) are pyrimidines and instead of having 2 rings in their structures, they only have 1. While cytosine is found in both DNA and RNA, uracil is only found in RNA and thymine is only found in DNA.
These bases are special because they help pair one DNA strand to another. In order for two strands to wound together and form a helix structure, we need these bases to be complimentary to each together, and that's how the term complementary base-pairing comes about. Adenine is always paired with a thymine using 2 hydrogen bonds and a guanine always pair with cytosine via 3 hydrogen bonds. Because these bases have specific pairing, the amount of adenine equals the amount of thymine and the amount of G equals the amount of C. This is known as Chargaff's rules.
C. DNA Denaturation, Reannealing, Hybridization: DNA structure is normally stabilized by hydrogen bonding between base pairs along the length of the molecule. High temperature, high pH, and denaturing agents like urea can disrupt hydrogen bonds between the base pairings and cause the DNA helix to denature. Denatured DNA, though, can be brought back together (reannealed) if we reverse the conditions (ie: cooler temperature, lower pH). Singled-stranded DNA can bind to another strand of DNA if the pairs of bases match each other. This process is called hybridization.
I'm Linh - a science geek who loves experimenting and tinkering with recipes! I hope that this blog brings more ideas into your kitchens! Happy eating folks! XOXO