S-STEM Scholar Melanie Castaneda's Blog

Tuesday, November 8, 2022 - Thursday, November 10, 2022  In the lab, we talked about plasmids and plasmid  extractions and I spent time on my own reading up about what plasmids are. A plasmid is essentially a small circular piece of DNA found in bacterial cells that replicate independently from the host’s chromosomal DNA.  Plasmids can exist naturally in archaea and eukaryotes. For example, they can exist in yeast and plants. There are also plasmids utilized in the lab. These are typically artificial and designed to introduce foreign DNA into another cell. These plasmids have an origin or replication, selection marker, and cloning site.  The origin of replication is a DNA sequence which allows initiation of replication within a plasmic by recruiting replication machinery proteins. A selection marker is the antibiotic resistance gene which allows for selection in the bacteria. The cloning site is a short segment of DNA which contains many restriction sites. After rea...

  Tuesday October 1, 2022  On Tuesday, Dr. Tuohy asked my partner and I to take some time and get familiar with restriction enzymes. I had heard the term before in the lab but I didn’t know what it meant or what it was for. After doing a little bit of research, I feel as if I have a basic understanding of the term.  A restriction enzyme is a protein from bacteria that cleaves DNA sequences at a specific site and cuts the DNA only at that specific site, known as the restriction site or target sequence. The use of restriction enzymes is critical to laboratory methods such as genetic engineering. They can be isolated from bacterial cells and used to manipulate fragments of DNA.  A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages, or phages. When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into...