00:01
Okay, so what we're going to do here is we are going to see how many codons can mutate to become nonsense codons.
00:08
The first thing we need to do is write out all the nonsense codons.
00:11
So that's u, a, a.
00:14
These are the stop codons.
00:16
U, a, g, and u, g, a.
00:21
And this is a super tough question because it's just any codon that could become a nonsense codon through a single base change.
00:29
I'll just point out there's three positions that can mutate to become a nonsense codon.
00:35
And so we're actually going to have to be super, super thorough in our analysis.
00:40
We don't double count or miss anything.
00:43
So what i'm going to do is i'm going to set up a little table for us.
00:46
And we're going to use this table to stay organized.
00:49
And what we're going to do is we're going to for each stop codon first analyze the third position, second position, and then finally first position and tally up how many different amino acids we could, or codons we could think of that would, with a single base pair change, become the stop codon that we're working with.
01:11
And then make sure that we check, you know, what those are in terms of amino acids using the genetic code because that's the second part of your question, which amino acids do they encode? so let's do the first one and we'll get the pattern and the hang of it and then continue on.
01:28
So we're going to work with this stop codon first and think about what different codons could have mutated.
01:36
So with just the third position.
01:39
So that would be uasomething, uasomething, and uasomething.
01:45
So that would be uau, uac, or uag.
01:55
Ok, now i'm going to eliminate uag because this is already a stop codon.
02:00
So that does not meet the requirement of becoming a stop codon.
02:04
Now i'm going to check the genetic code and i'll write the abbreviation for the amino acids, tyrosine, and that's how we'll do this.
02:17
Ok, so for now, we're going to work with the second position here.
02:23
Right.
02:24
And we'll think about, all right, what could have gone there? so u blank a, u blank a, u blank a.
02:35
Right.
02:35
Instead of a, that could have been a g or color coded red consistency g.
02:44
Could have been a c or could have been a u.
02:47
Right.
02:48
Now, uga is already a stop codon.
02:52
So we're going to eliminate that one for the same reason as before.
02:55
It doesn't meet the requirement of becoming a stop codon.
02:58
And then we'll check these in the genetic code.
03:00
So this is serine and leucine.
03:05
And we'll do the same thing here now, focusing on that third position, this u.
03:11
So blank aa, blank aa, blank aa.
03:17
So this could have been a g, could have been a c, could have been an a.
03:22
Right.
03:23
And mutated to be a u.
03:24
So we'll check the genetic code, glue and lysine.
03:33
Ok, so if i tally up here, one, two, three, four, five, six, seven, seven total from this column.
03:42
Now we'll do the same thing here with the uag.
03:45
So it could have been ua something, ua something, ua something.
03:48
So ua u, ua c, uaa.
03:55
So ua u, we already actually counted, i believe, ua u is right here.
04:05
So i'm going to eliminate this one, not because it doesn't count as an answer, but because i already counted that one because we're asked a total number, how many codons.
04:13
I don't want to double count that.
04:14
And i'm going to eliminate this one for the same reason, because we already have uac in our count.
04:18
And then uaa is actually a stop codon.
04:21
So i'm going to eliminate that one because that's already a stop codon...