The Terrorists of Cells

This week in AP Biology we went over viruses. Viruses are made of a protein coat called a capsid that encircles the middle which contains the genetic material and reverse transcriptase. Some viruses have a phospho-lipid bilayer called an envelope encircling them. In the envelope there are glycoproteins that are the key to the lock on plasma membranes. 

There are two different replication cycles min viruses. One is the lytic cycle this is when the cell is hijacked by the virus and uses the cell's machinery to synthesize more viruses. At the end of the cycle, the cell will burst setting the newly synthesized viruses loose. The other cycle is the lysogenic cycle. This is when the genetic material of the virus has been injected into the cell's DNA. Because the genetic material is in the cell'a DNA whenever the cell replicates the virus's genetic material is replicated too. The genetic material of the virus that is in the cell's DNA is called the prophage. The cell that has been affected by the virus can be in either one of these cycles depending on the circumstance. 

There are also viroids and prions. A viroid is a virus that affects plants. Prions are proteins that affect humans. Prions are associated with mad cow disease. 

Spikes are the glycoproteins. 

How to Make a Protein.

This week in AP Biology we reviewed transcription, RNA processing, and translation. These three processes are what enables helps DNA in the production of proteins. 

Transcription is the first of these processes. The enzyme RNA polymerase attaches to DNA, and starts adding nucleotides. Unlike DNA, in RNA strands adenine bonds with uracil instead of thymine. The strand of RNA then goes through RNA processing. During this process spicesomes cut out the introns in the RNA so that their is only extrinsic left. Next a 5' cap made of guanine is placed at the beginning of the strand and a poly A tail, A standing for adenine, is added to the end. These previous process all deal with mRNA and inside the nucleus. The next process takes place outside of the nucleus and deals with tRNA as well. 

Translation is the reading of mRNA and creating a protein made of amino acids. After RNA processing the smaller subunit of a ribosome will attach to mRNA and the larger subunit will follow. Next, the ribosome will read the mRNA and bring one amino acids per codon. These amino acids are brought by tRNA. The tRNA will dock at the docking site of a ribosome the amino acid it carries will form a peptide bond with amino acids that are already there, and then once getting rid of the amino acid it will leave the ribosome. Once the ribosome is finished with the mRNA the ribosome unattachs and the amino acid chain has formed a protein. From there it will either be used by the cell or a vesicle will transport it out of the cell. 

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DNA Clones and Suitcases

Last week in AP Biology we talked about DNA’s history this week we talked about how those discoveries would inspire future experiments. Once Watson and Crick discovered DNA’s structure the next question is, how does it replicate?

                DNA starts to separate at the origin of replication because of helicase. It then starts to create a replication bubble and fork. Next, single stranded proteins are added to the two parental strands to prevent them from reattaching. DNA polymerase III then starts to add nucleotides to the DNA. The polymerase adds the nucleotides in the direction of 5’ to 3’. Also, there is a leading strand and lagging strand during the replication process. The leading strand is replicated continuously, but the lagging strand is replicated in Okazaki fragments. Pieces of RNA mark the beginnings of the Okazaki fragments. Once pol III is done adding nucleotides pol I start to remove the RNA pieces and replacing them with pieces of DNA. DNA ligase then finishes it all up by connecting all the DNA fragments.

                Next we learned about how the DNA is packaged. In a mixture of DNA and histones we get nucleosomes which are looped in giant supercoils that created chromosomes. The histones have the ability to switch genes on and off and when the DNA spreads out it can be accessible for transcription.