Unit 2.2a - Proteins (Amino Acids - General Info) Flashcards
composition of amino acids
- amino group
- carboxyl group
(both bonded to the a-carbon)
functional group of amino group
NH2 (positive)
functional group of carboxyl group
COOH (negative)
What does the carboxyl group dissociate into?
carboxylate anion (–COO-)
hydrogen ion (H+)
Which group can accept electrons and which can donate electrons?
amino group: accept
carboxyl group: donate
To which is the a-carbon bonded to?
to a hydrogen and to the side chain group, R
portion of an amino acid that determines its identity
side chain group
Two streoisomers of amino acids are designated as __- and __-amino acids based on similarity to glyceraldehyde.
L and D
Two streoisomers of amino acids are designated as L- and D-amino acids based on?
similarity to glyceraldehyde
molecules that differ from each other only in their configuration
stereoisomers
Streoisomers are molecules that differ from each other only in their?
configuration
All amino acids have at least one chiral center (a-carbon) and are chiral (stereoisomers), except?
glycine
Except glycine, all amino acids have at least one ______ ________ (a-carbon) and are _______ (stereoisomers).
chiral center
chiral
Vast majority of a-amino acids have the __ configuration at the a-carbon
L
________ is usually in the L form
Proline
Side chain carbons in amino acids other than glycine are designated with _______ symbols, starting at a-carbon.
Greek
Amino acids can be referred to by ____-letter or __-letter codes
three
one
group of amino acids that has nonpolar side chains
nonpolar amino acids
9 nonpolar amino acids
Alanine
Valine
Leucine
Isoleucine
Glycine
Proline
Phenylalanine
Tryptophan
Methionine
Structure (nonpolar)
Alanine
Valine
Leucine
Isoleucine
contain aliphatic hydrocarbon group
Structure (nonpolar):
Proline
Has an aliphatic cyclic structure
Structure (nonpolar):
Phenylalanine
Hydrocarbon is aromatic
Structure (nonpolar):
Tryptophan
The side chains contain an indole ring (aromatic)
Structure (nonpolar):
Methionine
The side chain contains a sulfur atom in addition to aliphatic hydrocarbon groupings
group of amino acids that has polar side chains that are electrically neutral at neutral pH
polar-neutral amino acids
Principle in polar-neutral amino acids
+ and - cancel out
6 polar-neutral amino acids
Serine
Threonine
Tyrosine
Cysteine
Glutamine
Asparagine
Structure (polar-neutral):
Serine
Threonine
the polar group is a hydroxyl (-OH) bonded to aliphatic hydrocarbon groups
Structure (polar-neutral):
Tyrosine
the hydroxyl group (phenol) is bonded to an aromatic hydrocarbon group
Structure (polar-neutral):
Cysteine
the polar side chain contains a thiol group (-SH)
Structure (polar-neutral):
Glutamine
Asparagine
contain amide groups in their side chains
2 Acidic Amino Acids
Aspartic Acid
Glutamic Acid
Structure (Acidic):
Aspartic Acid
Glutamic Acid
have carboxyl groups in their side chains in addition to the one present in all amino acids
In acidic amino acids, describe what happens to the carboxyl group.
carboxyl group can lose a proton, forming carboxylate anions
In acidic amino acids, what is the charge of the side chains?
negatively charged at neutral pH
3 Basic Amino Acids
Histidine
Lysine
Arginine
In basic amino acids, what is the charge of the side chains?
side chains are positively charged at or near neutral pH
Structure (Basic):
Lysine
side-chain amino group is attached to an aliphatic hydrocarbon chain
Structure (Basic):
Arginine
side chain is a guanidino group bonded to an aliphatic hydrocarbon chain
Structure (Basic):
Histidine
side chain is an imidazole group
Average pKa of an a-carboxyl group
2.19
Which is more acidic, a-carboxyl group or acetic acid?
a-carboxyl group (2.19)
**acetic acid’s pKa: 4.76
Why do a-carboxyl groups have a greater acidity?
due to the electron-withdrawing inductive effect of the -NH3+ group
Average value of pKa for an a-NH3_ group
9.47
In a guanidine group, which is more basic, side chain of arginine or aliphatic amine?
side chain of arginine
Basicity of guanidino group is attributed to the large ________ ___________ of the protonated form relative to the neutral form.
resonance stabilization
side-chain imidazole group of histidine is a?
heterocyclic aromatic amine
