00:01
The yeast gene encode a protein found in mitotic spindle was cloned by a laboratory studying mitosis.
00:08
The gene encode a protein of 477 amino acid.
00:12
What is the minimum length of the nucleotide of this protein coding part of this yeast gene? so we know that every amino acid comes from one codon and each codon will have three nucleotides.
00:30
So the minimum length of a 477 amino acid long protein you have to times three.
00:39
This is the number of nucleotide for the amino acid and also you have to include the stop codon.
00:46
The stop codon does not give you any amino acid.
00:48
However, it is required for coding region because it gives the termination signal to the ribosome to release the polypeptide.
00:56
And a stop codon needs three nucleotides.
01:00
So this is 1431 plus three, you end up having 1434 base pair.
01:11
So this is the minimum length of this nucleotide of the protein coding part of the yeast gene.
01:21
The second part of question b.
01:23
Now you have a partial dna sequence which is the middle of the coding region of the yeast gene.
01:29
What is the sequence of the mrna and also what is the amino acid sequence in this part of the gene? so since this is the middle part, so we know that it's an axon and it should not have a stop codon.
01:47
And we don't know if this is strand that you see here is template strand or coding strand.
01:53
If it's the coding strand, then the mrna will have the same sequence as a coding strand.
02:00
But then when there is a t in the sequence, it will be replaced by a u in the mrna.
02:06
Now if it's a template strand, then mrna is going to be complementary to the sequence.
02:11
So before we know that, let's write down the complementary strand in dna.
02:16
So g pair with c, a pair with t.
02:20
I'm going to write down the complementary sequence first.
02:50
Now if the top strand is the coding strand, and then mrna again as i just mentioned should have the same sequence as the coding strand except for this there's a t, it's going to be a u in mrna.
03:03
And let's look at all six reading frames to see which frame has our coding region.
03:10
Again we have to make sure that there's no stop codon in any of the frame.
03:16
So let's look at the first frame.
03:17
The first frame starts from the first g here.
03:20
So every three nucleotide is a codon.
03:22
G, t, a, first codon, a, g, t, second.
03:27
Now the third one taa actually is going to be a stop codon.
03:32
In mrna it will be a uaa.
03:35
Uaa is a stop codon which will tell the ribosome to release polypeptide.
03:43
So it's in the middle of the coding region so you can't have a stop codon.
03:47
So this is not the right frame.
03:49
Let's start from the second frame.
03:51
This is a t.
03:52
Again the first one taa is a stop codon.
03:58
So this is not right.
04:00
The third frame starts from a here.
04:03
So you have a, a, g, u, t, t, a, a, c, t, t, c, g, a, c, and then again you have a t, a, g.
04:17
T, a, g in dna become a u, a, g in mrna.
04:23
Again u, a, g is a stop codon and we can't have stop codon in the middle of a coding region.
04:31
This means all three frames for the top strand is gone.
04:36
So they all have stop codon which means the top strand is not the coding strip.
04:42
So let's take a look at the bottom.
04:45
So again the first codon from the bottom.
04:48
So i guess i would call the fourth frame a, c, c.
04:52
The second is c, t, g, g, a, c.
04:58
Again you're gonna have a t, a, g which is a stop codon.
05:04
So i'm going to just write a sequence here maybe for you to easier to see.
05:09
U, a, a or t, a, a.
05:13
U, a, g or t, a, g in dna and u, g, a or t, g, a in dna.
05:22
So the all three are stop codons.
05:26
So if you see any of those in your sequence you know it's not the right frame.
05:30
So the fourth frame is out and the fifth frame starts from the c here.
05:37
C, c, c.
05:39
T, g, g.
05:43
A, c, t...