# 12 &13 DNA & RNA

 DNA and RNA are two different nucleic acids found in the cells of every living organism. Both have significant roles to play in cell biology. DNA and RNA structure are similar because they both consist of long chains of nucleotide units. However, there are a few structural details that distinguish them from each other, and if you are to compare DNA and RNA, these would be the results:

(1) RNA is single-stranded while DNA is a double-stranded helix. (2) RNA also has uracil as its base while the DNA base is thymine. However, even with the differences in their structures, DNA and RNA have cooperating roles in the field of Cell Biology.

 DNA contains the genetic information of an organism, and this information dictates how the body’s cells would construct new proteins according to the genetic code of the organism. Within the cell structure, DNA is organized into structures called chromosomes, which are duplicated during cell division.

These chromosomes would then release the genetic codes that will be transcribed and carried by the RNA (specifically the messenger RNA) to the ribosome. The ribosome will then synthesize new proteins that will help the body grow. This is the how the DNA and RNA work together in the body.

#13

• DNA replication begins with the "unzipping" of the parent molecule as the hydrogen bonds between the base pairs are broken.
• Once exposed, the sequence of bases on each of the separated strands serves as a template to guide the insertion of a complementary set of bases on the strand being synthesized.
• The new strands are assembled from deoxynucleoside triphosphates.
• Each incoming nucleotide is covalently linked to the "free" 3' carbon atom on the pentose (figure) as
• the second and third phosphates are removed together as a molecule of pyrophosphate (PPi).
• The nucleotides are assembled in the order that complements the order of bases on the strand serving as the template.
• Thus each C on the template guides the insertion of a G on the new strand, each G a C, and so on.
• When the process is complete, two DNA molecules have been formed identical to each other and to the parent molecule.

The Enzymes

• A portion of the double helix is unwound by a helicase.
• A molecule of a DNA polymerase binds to one strand of the DNA and begins moving along it in the 3' to 5' direction, using it as a template for assembling a leading strand of nucleotides and reforming a double helix. In eukaryotes, this molecule is called DNA polymerase delta (δ).
• Because DNA synthesis can only occur 5' to 3', a molecule of a second type of DNA polymerase (epsilon, ε, in eukaryotes) binds to the other template strand as the double helix opens. This molecule must synthesize discontinuous segments of polynucleotides (called Okazaki fragments). Another enzyme, DNA ligase I then stitches these together into the lagging strand.