| View previous topic :: View next topic |
| Author |
Message |
ssitaf26625
Joined: 10 Jul 2007
Posts: 2
|
 Posted: Mon Aug 06, 2007 11:45 am Post subject: Question 41 |
 |
|
| I dont understand how it's tyrosine. Could you explain how to find which one has the greatest point? what does that even mean? |
|
| Back to top |
|
 |
admin
Site Admin
Joined: 08 Dec 2003
Posts: 1795
|
| Posted: Mon Aug 06, 2007 9:53 pm Post subject: |
|
|
Don't worry about this question. You did great on this test! Normally on the MCAT, they will just ask about the isoelectric point of an amino acid with 2 ionizable groups (common). In that case, you must memorize the fact that the pI (isoelectric point) is the average of the pKa's of the 2 ionizable groups.
If you really want to understand why it depends on the top 2 pKa's when there are 3 groups (very very rare on the MCAT), then this was discussed in detail regarding a previous problem: www.mcat-prep.com/forum/viewtopic.php?t=773 |
|
| Back to top |
|
|
jvuofm1709
Joined: 31 Dec 1969
Posts: 19
|
| Posted: Thu May 20, 2010 3:30 am Post subject: |
|
|
| ....the iso electric point of tyrosine is pH=5.66. 2.2+9.11/2=5.66. It is the point where the CHARGES ARE NEUTRAL, and the neutral zwitterion is at its highest concentration. the alcohol on tyrosine is NEUTRAL, so once the carboxylic acid is deprotonated, it has a net neutral charge, further deprotonation of the tyrosine -OH would yield a net negative charge. |
|
| Back to top |
|
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
