davidH

Wow that's quite alot of bases in a cell!

Yo, what would happen if one base in that cell was removed? Like from anywhere along the strand.
Would that change the whole DNA strand? Like change all the bases in 3s?
I'm sure there must be something to stop that happening you know what it is?
Thanks.

hezekiah jones

Removed by chance, or removed by natural selection?

<img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" /> <img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" />

Daggah

In bacteria, probably, but more advanced cells contain their genetic information separated into chromosomes. What you're talking about is a frame shift mutation, and yes, it can cause massive changes. And yes, there are mechanisms to prevent it from occurring.

tribalbeeyatch

A frame shift might have profound consequences for the gene in which it occurred, but this wouldn't affect other genes on the same chromosome.

Queen of Swords

There may be short stretches of DNA between the points where one gene ends and where another's start codon begins (assuming they're in the same operon - and I'm thinking of motB and cheA of Salmonella typhimurium here). I don't think a loss of one base there would have serious consequences for the cell.

[ January 17, 2002: Message edited by: QueenofSwords ]</p>

CodeMason

A single deletion will pretty much scramble all of the following information on that strand.

CodeMason

Say we have the nucleotide sequence:
ATG__ GAT TAC ACT AAG TGA_ CAT
START Asp Tyr Thr Lys STOP His
The bold base is the one that's going to be deleted.

So now we have:
ATG__ GAT TCA CTA AGT GAC AT... and so on
START Asp Ser Leu Ser Asp ?...

Get the picture? Everything after that base removal is now scrambled.
But frameshifts have lead to beneficial, new information, for instance nylon waste product metabolizing bacteria.
And, although very rare, a single base addition later on, further down in the code, can restore the rest of the sequence so that only a few genes were radically altered. I suspect this is what happened with the nylon-eating bacteria.

[ January 17, 2002: Message edited by: CodeMason ]</p>

stryder2112

This is pedantic, but a frame shift mutation requires a base pair be deleted. I'm sure CodeMason knows this, but for the slower ones in the class it's an important distinction. DNA is not a single strand but a pair of complementary strands.

If one (or even a fews) base is deleted/destroyed/removed from one strand, it can be accurately replaced because it's complement still exists in the complementing DNA strand. Molecular machinery exists in the cell that recognizes the missing nucleotide and puts the proper one into the open spot by "reading" the complementary base opposite the hole. This redundancy (two DNA strands) helps to protect the integrity of the information encoded from such deletions.

Stryder

[ January 17, 2002: Message edited by: stryder2112 ]</p>

MortalWombat

But this is not foolproof. No DNA repair mechanism is. Otherwise, there would be no evolution.

[ January 17, 2002: Message edited by: MortalWombat ]</p>

tribalbeeyatch

I can't tell whether everybody is trying to say the same thing or there is some disagreement here. A frameshift within a gene will profoundly alter that gene, but other genes up or downstream of the frameshift will still be in frame with their start codons, so they will still be expressed normally.