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Fibrous. Proteins. 1 o structure. amino acid sequence. - helix -sheet. H - bonding between C = O and N - H of backbone. 2 o structure. +. -. some proteins only have 1 o and 2 o structure:. fibroin (silk). -sheet. insoluble in H 2 O. hair skin. - PowerPoint PPT Presentation
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Proteins
1o structure amino acid sequence
2o structure - helix -sheet
H-bonding betweenC=O and N-H of backbone
- +
some proteins only have 1o and 2o structure:
fibroin (silk) -sheet
keratincollagen
hairskin
- helixinsoluble in H2O
non-polar residues
Fibrous
Gly-Glu- His-Ala-Phe-Ser-Ser-Val- His-Ile-Met-Arg-Asp-Val- Asn-
Tertiary structurePrimary structure sequence of amino acids
Alanine
Non-polar
Phenylalanine
Polar
Serine
Valine
Acidic or Basic
Glutamic acidHistidine
Isoleusine Methionine
Arginine
AsperagineAspartic acid
Glycine
Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly
Tertiary structureAla-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly
arrange these in an -helix
Ala 1
Phe2
Ser3
Ser
4
Val 5Glu
6
His7
Ile8
Met9
Arg10
Asp11
Val 12
His13
Asn14
Gly15
non-polarpolarinterior
exterior
Tertiary structure
interaction of the R-groups-
-
+
-+
-
- +
proteins fold aroundnon-polar groups
globular proteins
hydrophobic residues inside
polar and charged residues outside
Tertiary structure
1. Hydrophobic interactions non-polar R-groups
LDF2. Hydrogen bonding
between H-bonddonors and acceptors
polar R-groups
3. Ionic bonds (salt bridges) acidic and basic R-groups
4. Covalent bonds (disulfide) cysteins
ion-ion
interactions of R-groups
CH3
NH+
N-terminus
C-terminus
Pro
Ala Phe
Arg
Asp
Pro
SS Cys
Cys
His
His
-O-CH O
= Fe2+
Quaternary Structuresubunits
hemoglobin heme groups 4 - Fe
globin chains 2 -chains2 - chains
held in position by interaction of R-groups
polar histidine inside - holds Fe2+
pKa = 6.1
C
H
H3N+
CO
O-
NH
N
Denaturationform is function
loss of native configuration denaturation
denaturation peptide bonds not affected
H-bondsdisulfide bondsionic bondsL.D.F.
disrupted
Denaturation
4o structure disrupted first subunits separate
3o structure disrupted protein unfolds
2o structure disrupted H-bonds broken
treatments are sometimes reversible renaturedsometimes irreversible
insulin
Denaturing treatments
1. Heat above 50-60oC frying eggsunburn
2. pH disrupt salt bridgesapproach pHI
3. detergents unfold globular proteins SDS
SO4-
Na+
-
-
+
-+
-
- +
Denaturing treatments4. reducing agents
S-S SH HS
5. Metal salts Hg+, Pb+, Ag+ S-Hg
C =O_O-
Hg+
6. H-bonding solvents alcoholacetone
7. “Chaotropes”
urea guanidine
oxidizing agents
CH2N NH2
O
CH2N NH2
NH
Words of Wisdom
3. detergents
6. H-bonding solvents alcohol
1. Heat sunburn