Class 4 Flashcards
Are amino acids amphoteric?
Yes, they can act as both an acid and a base.
What is the difference between L and D amino acids?
L = amino group on the left D = amino group on the right
Which form (L or D) is that naturally occurring form of amino acids?
L
What is the only amino acid that is achiral?
Glycine (Gly)
What amino acid forms disulfide bonds?
Cysteine (Cys)
-SH thiols bind
What is the only secondary amino acid?
Proline (Pro)
This makes it bulky and formation of hydrogen bonds for secondary structure can be difficult.
How do you form an imine?
Carbonyl + NH4Cl -> imine (double bond to N in place of O)
What are the basic steps for amino acid formation?
Aldehyde -> imine formation -> KCN adds carbon to become COOH -> H3O+ converts CN to COOH
This will form an L,D racemic mixture!
What is the Gabriel Malonic ester synthesis?
A second way to form an amino acid:
Phthalimide -> treat with base pulling an H of N -> treat with malonic ester that has a good LG -> treat with alkyl halide with an R group of interest -> treat with H3O+ -> heat
Will form an L,D racemic mixture!
Lower (even into the negatives) = strong _________.
Acids!
Think low pH, low pKa, HIGH Ka
What are the different Ka values for strong and weak acids?
Strong acid: Ka > 1; pKa 0
What is the pKa of RCOOH?
and RNH3+?
RCOOH: pKa =2
RNH3+: pKa = 9-10
When pH > pKa a group will…
be deprotonated
What is the isoelectric point?
The pH at which an amino acid has no net charge. 100% will be in the zwitterionic form (+ charge on amino group, - charge on carboxyl group; net charge =0)
How do you calculate the isoelectric point?
pI = (pKa1 + pKa2)/2
Acidic amino acids will have a ______ isoelectric point than basic amino acids.
Lower
If your pH is
positive because your solution is more acidic than your molecule and will thus put protons on
If your pH is > pI what net charge will your amino acid have?
negative because your solution is basic relative to your AA and thus will pull off protons.
What are some peptide bond characteristics? Caused by what?
Due to resonance:
Partial double bond character
Cannot rotate
Planar
Amide H is slightly acidic
What is the difference between D and L carbohydrates?
Location of the OH group.
L = OH group on the left
D = OH group on the right
What is the naturally occurring form (L or D) of carbohydrates?
D
Which OH will you look at when trying to determine D or L configuration?
Penultimate carbon
What does the +/- mean in sugars?
direction of rotation of polarized light
What is the stereochemical relationship between D and L sugars?
Enantiomers
