Important Notes:
The Quiz on Ch. 17 is on Monday. It will be 15 multiple choice questions.
Test Corrections from the last test are due on Monday at 3:05.
Bring in any coats you want to donate to the Coat Drive! These will be donated to needy Bellevue families on December 15-17.
(for videos and notes on Transcription and Transcript Processing see Blog entry from Wednesday, Dec. 8th)
Translation
Watch the video below and then construct your understanding of translation using the following key words: small ribosomal subunit, large ribosomal subunit, tRNA, amino acid, codon, anticodon, A and P site, release factor. Note that the process of translation is separated into initiation, elongation and termination. Make sure that you know the key events of each stage.
Post Translational Modification
You will not be quizzed on this, but you should understand that proteins are not "ready to go" when they come off the ribosome. They often need specialized assistance in folding, removal of certain segments, addition of chemical groups, like sugars or phosphate groups and they may need "tags" that identify where the protein needs to go. The best way to learn more about this process in on pp. 325-6 of your text.
These animated cartoons are really cool. Unfortunately this cartoon didn't talk about gene regulation, so the view they gave of transcription factors was too simple to prepare you for what I will say in January. There are also one or two places I think their simple view was a little misleading.
ReplyDeleteFor instance, in the "translation" cartoon they mention an "enhancer", and show it as a part of the DNA close to the transcription initiation site; unfortunately, that is wrong. They also don't explain the role of the enhancer at all, they just say it's there.
When I come speak with you in January, I will call the DNA close to the transcription initiation site the PROMOTER. The promoter is a part of the DNA that proteins bind in order for the cell to REGULATE transcription.
At any given time, most of our genes are not being transcribed; they are only transcribed when they are needed. Something controls (REGULATES) whether to transcribe each gene based on what else is happening in the cell. This control process happens at the promoter, right next to where the transcription could start. Every transcription initiation site has a place where this control happens, so every transcription initiation site has a promoter.
The only part of the promoter this video shows is the TATAA box. As shown in the cartoon, the TATAA box is bound by parts of the RNA polymerase that builds the new mRNA molecule. The rest of the promoter contains binding sites for other proteins which are usually not part of the RNA polymerase. These proteins only help control whether transcription starts, they don't help build the mRNA. Which proteins bind to the promoter, and how those proteins interact with each other, helps determine whether transcription will start.
I will also talk about enhancers. Like the promoter, ENHANCERS are parts of the DNA that are bound by proteins to regulate transcription. In the cartoon "the enhancer" was shown close to the TATAA box, but enhancers are usually FAR AWAY from the TATAA box; hundreds, thousands, even millions of nucleotides away from the promoter, either direction along the DNA. Just like two parts of your shoelace are far apart along the shoelace but close together in the knot, in a living cell the enhancers end up close to the promoter, and the proteins bound to the promoter and enhancers can interact. All of these proteins and the interactions between them contribute to controlling whether transcription will start. Some genes have no enhancers but some have many, depending on how complex it is for the cell to identify the conditions under which the gene is transcribed.
Finally, this cartoon calls some proteins TRANSCRIPTION FACTORS, and I will talk about these too.
Any protein that binds DNA and is involved in transcribing genes can be called a transcription factor. The transcription factors mentioned in this cartoon are ones I would call GENERAL TRANSCRIPTION FACTORS, because these transcription factors are parts of the RNA polymerase that is used to transcribe every gene. However, most of the transcription factors I will talk about are the proteins that bind the promoter or enhancers to regulate transcription. Since different genes are needed by the cell under different conditions, it makes sense that the proteins that bind to the promoter or the enhancers may be different for different genes. These transcription factors are therefore not "general", i.e. they aren't involved in transcription of every gene.
The main things I want you to remember about promoters, enhancers, and transcription factors are:
1. Both the promoter and enhancers are regions of DNA that are bound by transcription factors to regulate transcription.
2. Every transcription initiation site MUST have a promoter next to it, but enhancers are optional.
3. The promoter MUST be adjacent to the transcription start site, but enhancers are usually far from the promoter along the DNA.
Oops! That comment is about the cartoon about transcription, which is in the Dec 8 blog entry.
ReplyDeleteGreat clarifications, Max! I don't think the students will have to "unlearn" too much during your talk. A few of the comments you have added above are similar to things I pointed out during class and I love that you took to time to really spell them out here on the blog.
ReplyDelete