More Genetics!

Corn...kernels...so many kernels. I don't think I can look at a corn on the cob the same way ever again. We were given cobs of corn in class and had to determine the corn's parents' genotype and phenotype. This involved the counting of corn kernels. SO MANY KERNELS! I 'm pretty sure I had to start counting over so many times because I kept getting lost in the kernels. But eventually we did it and were able to determine the genotype and phenotype using what we learned from the past two classes.

We reviewed and practiced some genetic problems again. I think I'm starting to understand it a little more. However, I still really need to sit down and practice some genetic problems, because I am seriously slow. Everyone in my class will know the answer way before me while I'm still writing down the trait information. It's a slight problem. We also went over sex chromosomes and worked on some problems about Labradors. The test is coming soon, so I better get studying and perfecting my knowledge on genetics. But now it is time for Thanksgiving break and I can relax! Oh, just kidding, I have a bio project to do...hooray. 

Genetics! (2 Classes)

Yay! Genetics! For this class we started learning about Mendelian genetics. In the last unit, we read something about how Mendel used pea plants to examine genetics. In this class, we learned how to find genotype and phenotype ratios using a Punnett Square. In other words, we were taught the necessary steps for solving genetics problems. We also practiced some of those problems in class, and then took a quiz on it, which I got a 3 on. I think that means I should retake it, and that I need to practice a few more problems.

The next class consisted was focused entirely on genetic problems. We went over the steps again and did some more problems. Quick even showed us two different ways of finding the phenotype and genotype ratios; the Fitz way and the Quick way. Someone tried explaining to me how to the Fitz way but I just could not grasp it. Especially since this person was basically doing all of the problems in their head. So when it came to take a quiz, I used the Quick way. It took me a little longer than the rest of my class...actually it too me a lot longer than everyone else, but it doesn't matter because i got a 1! So I understand how to solve the problems, it just takes me a really long time to do them. Maybe if I keep practicing, I can get better and faster. 

The Test...DUN DUN DUUUUUUN!

We took our Unit 3 test a couple of weeks ago, and I did a lot better than I thought I would. Perhaps I did better because this unit was on stuff I am genuinely interested in. I have always been fascinated by DNA, genetics, and forensics. This unit was all about DNA and I seemed to get a grasp on all of the concepts pretty easily. I took me a while to understand DNA replication, but I found an animation online that explained the whole process and I think it really helped. Overall, I think I did well. However, there was this one question that had to do with chemistry that I did not get right. I always seem to miss the chemistry questions. Hmmm...I wonder why that is. Oh yeah, because I hate chemistry! I'm sorry, no offense to the subject, but I really don't get it. But no matter what, it seems to always find a way back into my life.

Operons

Today in class, we talked about operons. An operon is a unit made up of a bunch of genes. These genes regulate other genes responsible for protein synthesis. We were shown two examples of operons today. The first one had to do with tryptophan, a type of amino acid. This operon is on, meaning it is repressible. This operon has to be stopped. There is a regulatory gene in the front of this operon, and it has to be read by RNA polymerase. Next, an mRNA is created which then creates a repressor. This repressor is inactive; therefore, the RNA polymerase can go down the system of genes and read them. They create the polypeptides that make up the enzymes for tryptophan synthesis. When there is enough tryptophan, it can go into the repressor and activate it, which can then lock the system of genes. Furthermore, no RNA is made. The repressor is like a wall blocking the RNA from going through, and because of this more tryptophan cannot be made.

We also learned about an inducible operon, meaning it is off. This a lactose operon. Everything is pretty much the same as the tryptophan one. There is a repressor, a promoter, and an operator. One difference, however, is that the represoor starts off active, obviously, because it starts off stopped. So no RNA can be made due to the "wall." This happens when lactose is not present. When lactose is present, it is inducible. Therefore, repressor is inactive, the operon is on, and transcription occurs. In other words, RNA polymerase can pass through and RNA is made. 

All of this connects to a lab we did a few days ago. The lab was on pGLO. In our lab, we had four different containers with bacteria, but only the container containing arabinase was able to glow. This is because of the arabinose (sugar) which turns on the gene, allowing the RNA polymerase passage and causing it the bacteria to glow.

DNA Replication and Protein Synthesis

So DNA replication begins at a specific point in the DNA molecule called the origin of replication. First, the enzyme Helicase separates (or unzips) a portion of the DNA molecule.This causes two single stranded regions of DNA to form. Next, RNA primase comes along on the lagging strand and builds RNA primer. RNA primer is necessary in DNA replication because without it DNA polymrase III cannot not begin a new chain of DNA. And so, the next step is obviously DNA pulymerase III building a new chain of DNA. Then, DNA polymerase I comes in and replaces the RNA primer with DNA nucleotides, leaving fragments know as Okazaki fragments. Lastly, the DNA ligase enzyme swoops in and bonds these fragments together, completing the process of replication. 

It is also important to know that you read the strand from 3' to 5', but it is built from 5' to 3'. 



Protein synthesis is a whole other process. It starts off with Transcription, which is the separation of the double helix. This happens in a eukeryotic cell, a cell with a nucleus. The double helix has to be separated because a full DNA strand is too big to leave the nucleus. Therefore, it must transcribe so that it can fit and change from DNA to mRNA. Before the mRNA can leave the nucleus, the introns on the strand must be cut out (splicesome). The exons are then glued together. A G-cap (Guanine nucleotide) and Poly-A tail (Adenine nucleotides) are put on each end of the strand so that it does not get eaten by enzymes. These two protect the message. Finally, it can leave the nucleus.

Next, Translation occurs. The mRNA will now translate into an amino acid.The mRNA is decode by the ribosome to produce a specific amino acid chain. Met (AUG) is always the first amino acid in the chain. The ribosome reads the codons from 5' to 3'. Translation occurs in the cell's cytoplasm, where the ribosome are located, and they bind to the mRNA. The ribosome makes decoding easier by binding tRNAs with anticodon sequences on the mRNA. tRNA acts as a bus for amino acids and carries them to the mRNA. These amino acids are binded together by peptide bonds into a polypeptide. The amino acids are chained together into polypeptides while the mRNA passes through the ribosome and is read by the ribosome. 

The DNA Structure

So our main topic for this class was DNA. We talked about the double helix DNA structure and even created a paper model of it. The double helix structure was discovered by James D. Watson and Francis Crick. A man, Erwin Chargaff, found that a a composition of DNA varied one species to another, but all organisms had the same bases. These bases are Adenine (A), Cytosine (C), Thymine (T), and Guanine (G). Adenine is equal to Thymine and Cytosine is equal to Guanine. Hydrogen bonds are what hold together the Adenines with the Thymines and the Cytosines with the Guanines. Thymine and Cytosine are Pyrimidines. Adenine and Guanine are Purines. The bonds between the sugar and phosphate in the strucutre are called phosphodiester bonds. We began making a DNA model today and will begin the replication of it next class.

But what does it mean?

This picture is an example of an outcome of plant mutation. You see, mutations can occur when organisms are expose to some type of radiation or chemicals. According to Survival of the Sickest, Chapter 6, before we were able to modify our food on a molecular level with genetic engineering, plant breeders who wanted to grow more efficient crops would irradiate seeds by blasting them with a ray gun. The majority of the time, the seeds were not able to sprout after being irradiated; however, there were rare occasions when this genetic manipulation produced a beneficial trait. This flower could be a survivor of an irradiated seed. The mutation that has occurred in this flower, however, has nothing to do with efficient crops but with color. This flower has streaks of purple and white, which could be the cause of a change in the genes that control flower color.



This photo is an example of a half normal Sonic Hedgehog. Sonic hedgehog is one of dozens of genes that act to sculpt our limbs from shoulder to fingertip by turning on and off at the right time. According to Your Inner Fish, Chapter 3, something had to have gone wrong with Sonic hedgehog. Usually, when something goes wrong, the hands end up looking like a broad paddle with as many as twelve fingers, or eight as shown above, that all look alike.