BCH 2333 Lecture Notes - Lecture 4: Guanidine, Acid Dissociation Constant, Amine

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19 Jan 2017

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Amino acids in which r-group contains a carboxyl group. Have a negative charge at ph 7. Carboxyl groups act as nucleophiles in enzymatic interactions. Lysine when it is deprotonated it is an amine. Arginine, when it is protonated, is in the guanidinium state (it will be protonated by anything with a pka less than it) R-groups have net positive charges at ph 7. Alpha acid group pka on an amino acid is ~ 2. 2 pka of alpha amino group ~ 9. 4. Side chain pkas of 7 amino acids are important. Amino and carbonyl groups allow amino acids to polymerize. React in a head to tail fashion. Proteins are molecules that consist of one or more polypeptide chains. ** always start at the n terminus go towards the c terminus, when writing out a polypeptide. Draw a peptide from its sequence (3 letter or 1 letter codes) Also be able to go from structure to name.

Related Questions

Answer the following seven questions (a through g) based upon a tripeptide sequence with the following amino acids (one-letter symbols are given):

S I D

a) What are the full names of the amino acids? Spelling counts, but capitalization does not. For an acidic amino acid, assume it is ionized and use the âate ending instead of âic acid.

S: I: D:

b) What are the three-letter abbreviations for the amino acids?

S: I: D:

c) What is the overall charge of the most abundant tripeptide species at neutral pH (pH 7.0)?

d) At physiological pH, what is the best description of the chemical properties of the side chain (R group)? (1. Hydrophobic, 2. Polar,Uncharged, 3. Negatively Charged, or 4. Positively Charged).

S: I: D:

e) What is the overall charge of the most abundant tripeptide species below pH 1.0?

f) What is the overall charge of the most abundant tripeptide species at pH 11.5?

g) What type of intermolecular force could the side chains form with water? (Note that these are interactions are with water, not with other amino acids.) A. Hydrophobic Interactions, B. Ionic Interactions, or C. Hydrogen Bonds.

silverchinchilla971

Tyrosine has a polar side chain because:
a.) It is asymmetrical
b.) It has two types of atoms that have large differences inelectronegativity
c.) It is symmetrical
d.) both a and b
e.) both b and c

2. Consider the amino acid T at pH 9.23. Its alpha carboxyl grouphas a pKa of 2.63. What is the ratio of
base to acid for this group at this pH?
a.) 1:1
b.) 45637:1
c.) 2,634,678:1
d.) 3,981,072:1
e.) 9,364,345:1

3. Which statement about pKa is not true?
a.) It represents a pH at which 50% of the titratable group is inthe acid form and 50% is in the
base form.
b.) If the pH is less than the pKa, more than 50% of the titratablegroups are unprotonated.
c.) If the pH is greater than the pKa, more than 50% of thetitratable groups are in the base
form.
d.) If the pH is less than the pKa, more than 50% of the titratablegroups are in the acid form.
e.) All of the above are true.

4. At what approximate pH will D most likely exist as azwitterion?
a.) 3.0
b.) 4.0
c.) 5.0
d.) 6.0
e.) 7.0

5. Cysteine is the only amino acid that can form covalent bondswith other amino acids (i.e. cysteine)
through its side chain.
a.) true
b.) false

6. At pH 2, will the R group of H likely be charged OR uncharged?

BCH 2333 Lecture Notes - Lecture 4: Guanidine, Acid Dissociation Constant, Amine

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