Question

SOS Can someone PLEASE help me out with Calculating isoelectric (PI) point?

Answer 1

@ganeshie8 @Somy

Answer 2

@rvc

Answer 3

the answer is 10.97

Answer 4

oh and they wrote calculate it without the end groups (Coo-,NH+)

Answer 5

@JFraser can do it better i believe :)

Answer 6

Sorry to prove @somy wrong, but I don't know this at all

Answer 7

no!!!!!!!!!!

Answer 8

I never took a biochem course, so I know nothing about amino acids and peptides

Answer 9

thanks though! Anyone?

Answer 10

oh i see @JFraser :)

Answer 11

@Somy isn't the PI the average of the pKas? that's at the isoelectric point .

Answer 12

@Photon336 please enlighten me!

Answer 13

for example for Asp you take the average of the three pKa's to get the PI it;'s been a while

Answer 14

I don't think so @Photon336

Answer 15

@ganeshie8

Answer 16

i think it's this The pI is given by the average of the pKas that involve the zwitterion

Answer 17

@Photon336 yes it is

Answer 18

I have done this last year but i didnt remember much, i just reviewed it but i think this video will be better for you https://www.youtube.com/watch?v=Zrw793WkTco

Answer 19

yeah I've seen it but still it's not enough... Thanks though!

Answer 20

@ParthKohli

Answer 21

@Luigi0210

Answer 22

do you have a peptide or a mix of amino acids? if you have a peptide you need to know the sequence or at least what is the amino and the carboxyl terminal amino acids. for all the others you have to consider only the side chain. In the example you have a 3 and a 4 aa chains.

Answer 23

PI= (10.5+9.2)/2=9.85 if Asp is N-ter
PI= (10.5+9.6)/2=10.05 if His is N-ter
PI= (10.5+8.9)/2=9.7 if Lys is N-ter
PI= (10.5+9.0)/2=9.75 if Arg is N-ter

(-) (-) (-) (+) (+) (+)
COOH Aspx6 Hisx2 Lysx4 Argx5 NH3 net
2.2-1.9 3.6 6.0 10.5 1 2.5 9.6-8.9
1 0 0 0 4 5 1 10
2 0 0 0 4 5 1 10
3 -1 0 0 4 5 1 9
4 -1 -6 0 4 5 1 3
5 -1 -6 0 4 5 1 3
6 -1 -6 0 4 5 1 3
7 -1 -6 -2 4 5 1 1
8 -1 -6 -2 4 5 1 1
9 -1 -6 -2 4 5 1 1
10 -1 -6 -2 4 5 0 0
11 -1 -6 -2 0 5 0 -4
12 -1 -6 -2 0 5 0 -4
13 -1 -6 -2 0 0 0 -9

Answer 24

hmmm that's not the answer though

Answer 25

it says that those amino acids are attached, that's all the information I was given

Answer 26

a online pI calculator gives PI=9.98

Answer 27

http://web.expasy.org/compute_pi/
insert the following sequence
DDDDDDHHKKKKRRRRR

Answer 28

but they wrote IGNORE THE SIDE GROUPS @Cuanchi

Answer 29

where it said that? IGNORE THE SIDE GROUPS

Answer 30

I forgot to upload it, I re-wrote the question, so I posted at the beginning

Answer 31

What do you mean?? how you can ignore the side groups?? why they give you the pKs?

Answer 32

idk anymore

Answer 33

but thanks though!

Answer 34

Ok NP