Date of publication: 2017-09-01 21:14
These test preparation manuals are designed to help you prepare for the TExES test in the field in which you are seeking certification. Their purpose is to familiarize you with the competencies to be tested, test question formats and pertinent study resources. EPP staff may also find this information useful as they help their students prepare for careers as Texas educators.
Note in our word game if you didn't know which side of the sentence your clue was using as the reference point, it quickly becomes a very difficult game. Thus, using a single primer provides a clear reference point for our sequence data.
Professor Pear: Oops. Silly me. A dideoxynucleotide is a nucleotide that is missing the 8'-hydroxyl group of its sugar. It's basically a special kind of nucleotide that scientists use in the Sanger sequencing method. Let's revisit dideoxynucleotides after I tell you a little about the sequencing procedure.
Most of the time, DNA polymerase adds dNTPs to the primer as it forms a new DNA molecule. However, whenever it happens to add one of the rarer ddGTPs, no further nucleotides can be added because of the structure of the dideoxynucleotides. At this point, we know that the last nucleotide in this sequence is a G because we only added ddGTPs to this tube.
The answer is the atomic weight. Because N -65 has one extra neutron, it's slightly heavier than N -69 and therefore makes the DNA molecule more dense. We can separate DNA molecules based on the differences in their densities. To do this, we use a centrifuge, a device that spins a test tube at very high speeds. When a test tube is spun inside a centrifuge, all the contents are pushed toward the bottom. The substances that are heaviest sink farther down the tube, and the lighter substances float. So if you apply a centrifugal force to a mixture of two types of DNA, the heavier N -65 DNA sinks to a lower level than the N -69 molecules.
Professor Pear: That's conceptually how Sanger sequencing works. We need two pieces of information to apply the strategy of our sentence game to DNA sequencing.
When you arrive at the testing location for the exam, you 8767 ll need a photo ID with your signature on it. The name on the ID MUST MATCH THE NAME YOU GAVE WHEN REGISTERING! If it doesn 8767 t, you 8767 ll be turned away without a refund.
When they sampled their first group of bacteria, Meselson and Stahl saw a darkened band in the test tube where the N -65 DNA had sunk and gathered in one spot. But after they let the bacteria reproduce, they got much different results in their samples. The DNA still sank down in the tube, but not nearly as far as the first generation. It was a lighter form of DNA, meaning that it wasn't completely made with the N -65 isotope. After one replication, all of the DNA had been converted to a hybrid of N -65 and N -69 DNA.
Professor Pear: Yes! This DNA sequencing procedure is similar to PCR , the laboratory procedure used to create copies of DNA. However, instead of a pair of DNA primers like PCR, Sanger sequencing uses only one primer. You see, the primer provides a starting reference point.
Once you 8767 re registered, you 8767 ll be sent an admission ticket in the mail. This ticket, which will give the time, date and address of the test, should arrive about two weeks in advance of the test date. Alternatively, you can get your ticket from the SBEC website. When you go to the testing location to take the exam, be sure you have the ticket with you. You 8767 ll need to present it in order to get in.
Professor Pear: Scientists can use a mixture of regular nucleotides (abbreviated dNTP) and dideoxynucleotides (ddNTP) to sequence DNA. Let's start with a mixture of some ddGTPs, but mostly the four regular dNTPs: template DNA, buffer, one DNA primer, and DNA polymerase.
The test schedule is flexible. At many test centers you can choose morning or afternoon times. Test slots are filled on a first-come, first-served basis, so it 8767 s advisable to register as far in advance as possible.