History of DNA
|History of DNA|
Avery, MacLeod, McCarty
Chase and Hershey
Rossalin Franklin and Wilkins
Watson and Crick
Human Genome Project
Nucleotides are individual units that make up the strands of DNA. Two strands of nucleotides make up a DNA molecule; Sugar and phosphate groups make up the backbone (two sides) of a DNA molecule (sugar-phosphate backbone). These two nucleotide strands are connected by a hydrogen bond between the nitrogen bases.
The three components of a DNA nucleotide include a phosphate group, a sugar (deoxyribose), and a nitrogen base. The nitrogen base could be either Adenine (A), Thymine (T), Cytosine (C), or Guanine (G). All of these nucleobases are represented by the letters G-C-A-T. Chargaff's law states that Thymine combines with Adenine (T-A or A-T) and Cytosine combines with Guanine (C-G or G-C). "Base pairing" is the same as Chargaff's law.
|Where is DNA located?||In the cytoplasm (no nucleus)||In a nucleus|
|Amount of DNA||Single Nucleoid (circle of DNA: Plasmid)||Multiple Chromosomes|
- See also w:Chromosomes
- Condensed Chromatin
Histones: The proteins that DNA wraps around.
Chromatin: Strands of DNA wrapped around histones.
- See also w:Gene
- Specific pieces of DNA that code for specific traits.
- Exons: The parts of genes that code for proteins.
- Introns: The parts of genes that do not code for proteins.
DNA Replication: The process of creating two new identical copies of a DNA molecule. This occurs during the S-phase (synthesis) in the Interphase of the cell cycle.
- The enzyme, helicase, unzips the original DNA molecule.
- The enzyme, DNA polymerase, joins the new nucleotides to the old nucleotides.
- The enzyme, ligase, zips back up. New 2 DNA.
In the end of DNA replication, each old strand of DNA has been copied to produce two new strands. Therefore, DNA replication is a semi-conservative process.
Origins of Replication
Replication of DNA begins at special sites called origins of replication. In prokaryotes, bacteria have a single origin of replication. On the other hand, eukaryotes have 100s or 1000s of origins of replication to help speed up the process of replication. Helicase (enzyme) helps to unwind DNA at "replication forks". DNA are antiparallel to each other... which means that the sugar-phosphate backbones run in opposite directions. This is how the new nucleotides are added to the old strands.
DNA polymerase (enzyme) can only add new nucleotides to the 3' end of a DNA strand. The new DNA strand created using the 3' to 5' strand of old DNA is called the leading strand.
The new DNA strand creating using the 5' to 3' strand of old DNA is called the lagging strand. The lagging strand creates DNA fragments called Okazaki fragments. The fragments are later joined together by ligase (enzyme).