Embedded Files
In the following topics covered on our website, we will be exploring DNA and RNA along with their significance.
Discovery of DNA Structure
In the 1950s, Rosalind Franklin performed X-ray crystallography on DNA structures. This revealed a consistent pattern that appeared repetitive. She although passed away before her recognition, made the true discovery about the structure of DNA.
Her significant contributions went unacknowledged during her lifetime, having a Nobel Prize awarded following her death. With prejudices remarked against her, we must still recognize her major discovery about the helical structure with phosphate groups surrounding the helix. Paving the way for future scientists, remarkably Watson and Crick.
Simultaneously another biochemist, Erwin Chargaff analyzed DNA samples discover a set of rules. The amount of adenine (A) equals the amount of thymine (T), and the amount of cytosine (C) equals the amount of guanine (G). These findings were found from a variety of different species.
This leads us to the nucleotide structure, where we classify into two separate groups. Purines and Pyrmidines.
Nucleotides and what are their functions?
Purines = A, G; Pyramidines = C, U, T
Purines are classified as a double ring structure. Adenine and Guanine are classified within this group.
Pyrimidines are classified as a single ring structure. Cytosine, Uracil, and Thymine are the three within this group. (CUT is the abbreviation think to a physical pyramid which are sharp, and similarly enough CUT can be associated with this) A quick pneumonic to help memorization.
The base of these pairs are held via hydrogen bonding. Adenine and Thymine have two hydrogen bonds (II). Cytosine and Guanine have three hydrogen bonds (III).
With Watson and Crick combining the findings of Franklin's (helix shape) as mentioned earlier and Chargaff's (base pairing) findings they were able to create the first 3D double helix model of DNA.
Key Qualities of DNA Structure
DNA is a double stranded helix (think about the D to memorize Double-helix)
The backbone is a sugar phosphate, while the center is where nucleotides pair up (A, G, C, U, T). Visualize a zipper of a sweater.
2. DNA strands are antiparallel
By antiparallel, I am describing how one strand runs in the opposite direction in respect to the other. We call this 5' to 3' (pronounced 5 prime to 3 prime). One strand runs in this direction, while the other strand runs in the opposite the 3' to 5' direction.
The 5' end is named the "free phosphate group". The 3' end is named "free hydroxyl group"
DNA is the primary source of heritable information. This implies that genetic information is stored and passed from one generation to the next via DNA. Caveat: RNA is the primary source of heritable information as seen in particular viruses. We will explore this concept in the following topics.
Prokaryotic vs. Eukaryotic DNA
In eukaryotic cells, DNA is found within the nucleus as linear chromosomes. (animals, plants, etc.)
In prokaryotic cells DNA is found within the nucleoid region as circular chromosomes. (bacteria, fungi, etc.)
What are Plasmids?
Prokaryotes and some eukaryotes contain "plasmids". These are small, circular, DNA molecules that are separate from chromosomes.
These plasmids replicate independently from chromosomal DNA, primarily found in prokaryotes. Plasmids contain genes that may be useful to the prokaryote cell in particular environments. Although it may NOT be required for survival.
Plasmids are typically manipulated within laboratories. Plasmids can be removed from bacteria, then a gene can be inserted into the plasmid thus forming a recombinant plasmid DNA. (recombinant= DNA, protein, cell, or organism that has been created by combining genetic material from two different sources)
When the recombinant plasmid is inserted back into the bacteria, the gene will be expressed.
Bacteria can exchange genes found on plasmid with neighboring bacteria. Once the DNA is expressed the bacteria can express the genes acquired, which helps with the survival of prokaryotes.
DNA vs. RNA
DNA is a deoxyribonucleic acid, which is double stranded (just recall the D), with nucleotide base pairing A=T, and C=G.
RNA is a ribonucleic acid, which is single stranded, with nucleotide base pairing A=U and C=G.
Key differences = DNA is double stranded, and typically circular, but RNA is single stranded and can be either circular/linear
Google Sites
Report abuse