Amino Acids and
the Primary
Structures of
Proteins
Firefly Luciferase and Luciferin
Hemoglobin in erythrocytes
Keratin
Chemical structure of
an amino acid
R = side chain
Amino terminus
Carboxyl terminus
C = alpha carbon
R = side chain
The alpha carbon of amino acids is chiral (except glycine).
There are two stereoisomers of amino acids (L and D).
Proteins contain L-amino acids
L-amino acid
at neutral pH
Figure 3.1
Amino acids with aliphatic R groups
Amino acids with aliphatic R groups
The amino acid proline is a cyclic molecule
Amino acids with aromatic R groups
Amino acids with sulfur-containing R groups
Oxidation can form cystine from two cysteines
Figure 3.4
Side chains with alcohol groups
Amino acids with basic R groups
Amino acids with acidic R groups
Amide derivatives of acidic R groups
Other amino acids and amino acid derivatives
Figure 3.5
Selenocysteine is the 21st amino acid
Ionization of amino acids
Pages 60 – 64
pH ?
pH ?
Ionization of amino acids
Pages 60 – 64
pH 1
pH 7
Ionization of amino acids
Pages 60 – 64
pH 7
pH ?
Ionization of amino acids
Pages 60 – 64
pH 7
pH 12
Ionization of histidine
Figure 3.7
Ionization of histidine
Figure 3.7
Ionization of glutamate
Figure 3.8
Ionization of arginine
Figure 3.8
Peptide bonds link amino acids in proteins
Figure 3.9
Peptide bonds link amino acids in proteins
Figure 3.9
Alanine Ala (A)
Serine Ser (S)
Dipeptide
Ala – Ser or AS
Practice Problem
Draw the chemical structure of the tripeptide Ala – Thr– Cys at pH 7.
Answer the following with regard to this tripeptide:
1. Indicate the charge present on any ionizable group(s).
2. Indicate, using an arrow, which covalent bond is the peptide bond.
3. What is the net, overall charge of this tripeptide at pH 7? __________
4. What is this peptide called using the one-letter code system for amino acids? ______
Proteins can be very large, hundreds of amino acids long
The enzyme HMG-CoA reductase
MLSRLFRMHGLFVASHPWEVIVGTVTLTICMMSMNMFTGNNKICGWNYECPK
FEEDVLSSDIIILTITRCIAILYIYFQFQNLRQLGSKYILGIAGLFTIFSSFVFSTVVIH
FLDKELTGLNEALPFFLLLIDLSRASTLAKFALSSNSQDEVRENIARGMAILGPTF
TLDALVECLVIGVGTMSGVRQLEIMCCFGCMSVLANYFVFMTFFPACVSLVLEL
SRESREGRPIWQLSHFARVLEEEENKPNPVTQRVKMIMSLGLVLVHAHSRWIAD
PSPQNSTADTSKVSLGLDENVSKRIEPSVSLWQFYLSKMISMDIEQVITLSLALL
LAVKYIFFEQTETESTLSLKNPITSPVVTQKKVPDNCCRREPMLVRNNQKCDSV
EEETGINRERKVEVIKPLVAETDTPNRATFVVGNSSLLDTSSVLVTQEPEIELPRE
PRPNEECLQILGNAEKGAKFLSDAEIIQLVNAKHIPAYKLETLMETHERGVSIRR
QLLSKKLSEPSSLQYLPYRDYNYSLVMGACCENVIGYMPIPVGVAGPLCLDEKE
FQVPMATTEGCLVASTNRGCRAIGLGGGASSRVLADGMTRGPVVRLPRACDSA
EVKAWLETSEGFAVIKEAFDSTSRFARLQKLHTSIAGRNLYIRFQSRSGDAMGM
NMISKGTEKALSKLHEYFPEMQILAVSGNYCTDKKPAAINWIEGRGKSVVCEA
VIPAKVVREVLKTTTEAMIEVNINKNLVGSAMAGSIGGYNAHAANIVTAIYIAC
GQDAAQNVGSSNCITLMEASGPTNEDLYISCTMPSIEIGTVGGGTNLLPQQACL
QMLGVQGACKDNPGENARQLARIVCGTVMAGELSLMAALAAGHLVKSHMIH
NRSKINLQDLQGACTKKTA
Next:
Chapter 4
Proteins: Three-Dimensional
Structure and Function