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. 

DNA has a history????

This week in AP biology we covered the history of DNA. There are 11 prominent names that we associate with this subject. The first being T.H. Morgan who worked with fruit flies to find that chromosomes are located on genes. A second name is Freferick Griffith who was working to find a cure for pneumonia by working with Strepococcus pneumonia bacteria. Griffith discovered that there is a "Transforming Factor" that can turn harmless live bacteria into harmful bacteria when combined with heat-killed infectious bacteria. The next three names discovered just what that "Transforming Factor" was. In 1944 scientists Avery, McCarty, and MacLeod purified both proteins and DNA from Strepococcus pneumonia bacteria and injected both into bacteria. It turned out that when protein was injected into bacteria there was no effect, but when DNA was injected into bacteria it transformed the harmless bacteria into virulent bacteria. Hershey and Chase worked with bacteriophage to confirm that DNA was the "Transforming Factor." The next two names are very commonly associated with DNA having won a Novel Prize for their work with DNA. Watson and Crick are two men that discovered the double helix structure of DNA. A controversy surrounds this because it can be believed that they stole Rosalind Franklin's work.Meselson and Stahl worked with transcription, replication, and translation to try and guess where bands would be. These 11 names have forever changed the world because of their wonderful discoveries involving DNA. 

Chi Squared... and not its not the straightener.

This week in AP Biology we went over chi² (sounds like ky). Chi² is used to test a null hypothesis, in other words it can be used to see if there is a significant difference in what is observed and what is expected. The formula for chi squared is:

The X²_c  represents chi²

The ∑ is a symbol for a summation.

O_i is the observed data, the data you have collected

E_i  is the expected data, what you would get in a perfect world.

To determine if the discrepancies between the numbers are to large you look at the critical value and degrees of freedom chart.

The chart gives you the number that your answer from the chi² formula must be under for you to accept the null hypothesis.

Chi² is commonly used in genetics to determine phenotypes.

Genetic... chromosomes, chromosomes, and chromosomes!!!

This week in AP Biology we further travelled through genetics. We learned about sex-linked traits, co-dominance, incomplete dominance among other things. From there we went even deeper into the chromosomal basis of inheritance.

                Sex-linked traits are genes that are located on the x or y chromosome.  These genes on the chromosomes bring forth diseases such as hemophilia and color blindness. Co-dominance in genetics is when both alleles are expressed. This is exemplified in the blood type AB and calico cats. Calico cats are also always female which makes it a sex-linked trait. Incomplete dominance is when the dominant allele doesn’t completely mask the other such creating a sort of blending. This can be seen in blending a red and white snapdragon together and it producing a pink.

                The chromosomal basis of inheritance is connected with Thomas Hunt and the, Chromosome Theory of Inheritance which states that Mendelian genes have specific loci on chromosomes that undergo segregation and independent assortment. Thomas Hunt Morgan contributed a lot to his specific subject. He produced a lot of research with fruit flies that had to do with linked genes. Link genes are genes that tend to be inherited together because they are so close on the chromosomes.  He also helped with recombinant offspring. These are offspring that have features from both parents.

                We also looked at genetic disorders such as Huntington’s and Down Syndrome. The fertilization of these gametes cells that produce these disorders is called aneuploidy.

Genetics

This week for AP Biology we reviewed and studied genetics. On Tuesday we went to Sam Ryan's genetic conference at Lubbock High. At the conference we went over genetics and the recent discoveries in the field. 

An interesting thing I learned about was Barr bodies. Barr bodies are little black dots in female cells. They're only in females because the bodies are a disabled X chromosome. When a cell begins to form it randomly picks an X to follow and then disables the other one. This lead to questions about fixing Down syndrome by taking the third chromosome at 21 and disabling it so that it would turn into a Barr body. 

A fun fact I learned was that our phenotype which is the physical representation of our genotype is actually expressed in all of our cells.  

Another concept that I was enlightened about was that you can take skin cells and turn them into stem cells by reprogramming the cell. This can lead to many things. Such as growing new organs and allowing blind people to see again. The stem cells that have been reprogrammed can form new organs by using scaffolds of organs. If an organ cannot be replicated perfectly they use a dead organ and drain the cells out of it. The stem cells can also be used to replace corneas that have become too cloudy for people to see out of and thus making it possible for the replacement of their vision. This procedure has already been done in a young boy. The procedure requires no stiches or blood and the patient is under local anesthesia and last around thirty minutes. 

I also learned about alternative splicing which allows our genes to code for different proteins and telomerase. 

 Telomerase is an enzyme that builds up the telomeres which are caps at the end of chromosomes. Every time a cell divides the telomeres get shorter and shorter until eventually there is next nothing there. At that point the chromosome stops dividing, unless it has telomerase. The shortening of the telomeres is a major component in age. Unfortunately telomerase is only found in testis, ovaries, and cancer cells. If researchers can discover a way to put telomerase in all areas there might be a chance to postpone aging. 

 The Genetics Conference was super interesting and I advise everyone to take the opportunity to go to it if they can.