scigirl

No. It would only affect that gene (unless you are talking about certain bacterial genes which are in tandem).

Each gene has its own promotor and start site, which are not dependent on the orientation of the other genes. Some genes are in the +1 reading frame, others are in the +2, and still others in the +3. Then you can have genes on the other strand, which are called the - reading frames.

Here's a simple analogy--imagine this string of letters is a chromosome, and the words in the sentence are genes:

*Angie giengienasoiejioefjaie *goes ngeisntiosentel *to teiognaelsineaiotne *the iosngoesiangiod *store.

(I put spaces in so you can see the words.)

Most of the sentence is junk. The words are indicated by a * (the "promotor" in this case)
If you deleted the bold letter above, you could still pick out the words and make a sentence, right?

hope that helps,

Scigirl

CodeMason

Thanks, both. I understand now.

Writer@Large

Wish I could say the same! Genetics just ain't my thang ...

--W@L

Peez

The important thing to note is that the molecular machinery that translates genetic information "searches" for a start code to start translating, then stops translating when it reaches a stop code. If a frame-shift occurs before the start code, or after the stop code, nothing is changed in the translation. Only if the frame-shift occurs after the start code but before the following stop code would there be any change in the translation.

There are many start-to-stop code sequences on the same strand, but the distance between these sequences is not important. Thus, a frame-shift after a stop code but before the next start code has no effect.

Peez

MortalWombat

It may help to think of genes (in a very simplistic manner) as sentences. If you delete one word in one sentence, it usually messes up the meaning of that sentence, but it has no effect on subsequent sentences.

tronvillain

Well, if you want to try to illustrate a frame shift with actual sentences, deleting the first t in what you said:

Deleting an entire word would be closer to deleting a codon.

EDIT: it's frame not phrase

[ January 20, 2002: Message edited by: tronvillain ]</p>

Writer@Large

Thanks, all. I went back and read the whole thread again, in the context of the last few posts, and it made more sense. This is why I became an English major!

--W@L

Theophage

So when is DavidH going to look at SciGirl's post and attampt to understand? Somehow, I doubt he will...

davidH

Thanks for all the info!! Just got to try and keep all that I have learnt in my head now!! So just correct me if I get mixed up!

Ok, so deletions or insertations or alterations that occur in the "junk" DNA before the start and stop codons aren't going to affect the cell at all because the "junk" DNA doesn't code for anything.

Right, one thing that comes to mind here is the DNA replication. Are there enzymes that cut/remove the interons when repliction takes place? Or am I getting it mixed up with DNA technology? - I'm not sure about this so keep me right.

Yeah, just picked this out. So if a deletion or addition occurs somewhere in the intron it could alter the base sequence that the enzyme cuts to remove the intron so causing the enzyme to be unable to remove that intron?
Keep me right on this please.


One question I'm still not sure about - what are the point of these introns (junk DNA)? What purpose do they serve if any at all?

No, it doesn't prove that we are of common descent. It only proves that the intron/exon structure is similar in all organisms.
I too could argue that it shows a common creator.

Don't go on debating this though for the moment because I want to get a better understanding of the DNA business.

Thanks.

scigirl

Hello davidH,

You are quite welcome.
We will!

Most likely yes. However it is possible that the "junk" could take on a new function and turn into a gene or a promoter (the switch that turns on the genes).

There are. They are called the "spliceosome" and they find certain sequences in the introns and loop them out (at this point, we are talking about RNA, not DNA). Then a ligase comes by and glues the RNA bits back together.

No, DNA technology is possible because of nature's enzymes. Scientists like Kathy in my lab (not me--i'm a cell bio gal ) take advantage of these enzymes to "engineer" DNA. For instance, the weird viral enzyme that turns RNA into DNA (like in HIV) is used in a proceedure called PCR to study gene expression.
Any other questions that you have?

I highly recommend <a href="http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookTOC.html" target="_blank">this on-line biology text</a>. It's got great pictures and explanations of many biological concepts.

scigirl