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Fundamentals ofProtein Structure
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Proteins play key roles in a
living systemThree examples of protein functions
Catalysis:Almost all chemical reactions in a
living cell are catalyzed by proteinenzymes.
Transport:Some proteins transports varioussubstances, such as oxygen, ions,
and so on.Information transfer:For example, hormones.
Alcoholdehydrogenaseoxidizes alcoholsto aldehydes or
ketones
Haemoglobincarries oxygen
Insulin controlsthe amount ofsugar in theblood
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Amino acid: Basic unit of
protein
COO-NH3+ C
R
HAn amino acid
Different side chains,R, determin theproperties of 20amino acids.
Amino group Carboxylic
acid group
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20 Amino acidsGlycine (G)
Glutamic acid (E)Asparatic acid (D)
Methionine (M)
Threonine (T)Serine (S)Glutamine (Q)
Asparagine (N)Tryptophan (W)Phenylalanine (F)
Cysteine (C)
Proline (P)
Leucine (L)Isoleucine (I)Valine (V)Alanine (A)
Histidine (H)Lysine (K)
Tyrosine (Y)
Arginine (R)
White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic
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Proteins are linear polymers ofamino acids
R1
NH3 C CO
H
R2
NH C CO
H
R3
NH C CO
H
R2
NH3 C COO
H
R1
NH3 C COO
H
H2OH2O
Peptidebond PeptidebondThe amino acid
sequence is called as
primary structure
A AF
NG GS
T
S
DK
A carboxylic acid
condenses with an aminogroup with the release of awater
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Amino acid sequence is encoded
by DNA base sequence in a geneCGCGAATTCGCG
GCGCTTAAGCGC
DNAmolecule
DNA basesequence
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Amino acid sequence is encoded
by DNA base sequence in a geneSecond letterT C A G
Firstle
tter
T
TTTPhe
TCT
Ser
TATTyr
TGTCys
T
Thirdle
tter
TTC TCC TAC TGC C
TTA Leu TCA TAA Stop TGA Stop ATTG TCG TAG TGG Trp G
C
CTT
Leu
CCT
Pro
CATHis
CGT
Arg
T
CTC CCC CAC CGC C
CTA CCA CAAGln
CGA A
CTG CCG CAG CGG G
A
ATT
Ile
ACT
Thr
AAT
Asn
AGT
Ser
T
ATC ACC AAC AGC C
ATA ACA AAALys
AGAArg
A
ATG Met ACG AAG AGG G
G
GTT
Val
GCT
Ala
GATAsp
GGT
Gly
T
GTC GCC GAC GGC C
GTA GCA GAAGlu
GGA A
GTG GCG GAG GGG G
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Gene is proteins blueprint,
genome is lifes blueprint
Gene
DNA
Protein
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Each Protein has a unique
structure
Amino acid sequence
NLKTEWPELVGKSVEEAKKVILQDKPEAQIIVLPVGTIVTMEYRIDRVRLFVDKLDNIAEVPRVG
Folding!
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Basic structural units of proteins:Secondary structure
-helix -sheet
Secondary structures, -helixand -sheet, have regularhydrogen-bonding patterns.
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Three-dimensional structure of
proteins
Tertiarystructure
Quaternary structure
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Hierarchical nature of protein
structurePrimary structure (Amino acid sequence)
Secondary structure -helix, -sheet
Tertiary structure Three-dimensional structureformed by assembly of secondary structures
Quaternary structure Structure formed by morethan one polypeptide chains
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Close relationship between
protein structure and its function
enzyme A
B
A
Binding to A
Digestion
of A!
enzyme
Matching
the shapeto A
Hormone receptor AntibodyExample of enzyme reaction
enzyme
substrates
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