24 ch03proteins2008
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Transcript of 24 ch03proteins2008
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AP Biology
Proteins
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2008-2009 AP Biology
ProteinsMultipurpose
molecules
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AP Biology
Proteins Most structurally & functionally diverse group Function: involved in almost everything
enzymes (pepsin, DNA polymerase) structure (keratin, collagen) carriers & transport (hemoglobin, aquaporin) cell communication
signals (insulin & other hormones) receptors
defense (antibodies) movement (actin & myosin) storage (bean seed proteins)
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AP Biology
Proteins Structure
monomer = amino acids 20 different amino acids
polymer = polypeptide protein can be one or more polypeptide
chains folded & bonded together large & complex molecules complex 3-D shape
Rubisco
hemoglobin
growthhormones
H2O
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AP Biology
Amino acids Structure
central carbon amino group carboxyl group (acid) R group (side chain)
variable group different for each amino acid confers unique chemical
properties to each amino acid like 20 different letters of an
alphabet can make many words (proteins)
—N—H
HC—OH
||O
R
|—C—
|
H
Oh, I get it!amino = NH2 acid = COOH
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AP Biology
Effect of different R groups:Nonpolar amino acids
Why are these nonpolar & hydrophobic?Why are these nonpolar & hydrophobic?
nonpolar & hydrophobic
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AP Biology
Effect of different R groups:Polar amino acids
polar or charged & hydrophilic
Why are these polar & hydrophillic?Why are these polar & hydrophillic?
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AP Biology
Ionizing in cellular waters H+ donorsH+ donors
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AP Biology
Ionizing in cellular waters H+ acceptorsH+ acceptors
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AP Biology
Sulfur containing amino acids Form disulfide bridges
covalent cross links betweens sulfhydryls stabilizes 3-D structure
You wonderedwhy permssmell like
rotten eggs?
H-S – S-HH-S – S-H
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AP Biology
Building proteins Peptide bonds
covalent bond between NH2 (amine) of one amino acid & COOH (carboxyl) of another
C–N bond
peptidebond
dehydration synthesisH2O
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AP Biology
Building proteins Polypeptide chains have direction
N-terminus = NH2 end C-terminus = COOH end repeated sequence (N-C-C) is the
polypeptide backbone can only grow in one direction
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AP Biology
Protein structure & function
hemoglobin
Function depends on structure 3-D structure
twisted, folded, coiled into unique shape
collagen
pepsin
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AP Biology
Primary (1°) structure Order of amino acids in chain
amino acid sequence determined by gene (DNA)
slight change in amino acid sequence can affect protein’s structure & its function even just one amino acid change
can make all the difference!
lysozyme: enzyme in tears & mucus that kills bacteria
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AP Biology
Sickle cell anemia
I’mhydrophilic!
But I’mhydrophobic!
Just 1out of 146
amino acids!
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AP Biology
Secondary (2°) structure “Local folding”
folding along short sections of polypeptide interactions between
adjacent amino acids H bonds
weak bonds between R groups
forms sections of 3-D structure -helix -pleated sheet
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AP Biology
Secondary (2°) structure
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AP Biology
Tertiary (3°) structure “Whole molecule folding”
interactions between distant amino acids hydrophobic interactions
cytoplasm is water-based
nonpolar amino acids cluster away from water
H bonds & ionic bonds disulfide bridges
covalent bonds between sulfurs in sulfhydryls (S–H)
anchors 3-D shape
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AP Biology
Quaternary (4°) structure More than one polypeptide chain bonded
together only then does polypeptide become
functional protein hydrophobic interactions
collagen = skin & tendons hemoglobin
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AP Biology
Protein structure (review)
amino acid sequence
peptide bonds
1°
determinedby DNA R groups
H bonds
R groupshydrophobic interactions
disulfide bridges(H & ionic bonds)
3°multiple
polypeptideshydrophobic interactions
4°
2°
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AP Biology
Protein denaturation Unfolding a protein
conditions that disrupt H bonds, ionic bonds, disulfide bridges temperature pH salinity
alter 2° & 3° structure alter 3-D shape
destroys functionality some proteins can return to their functional shape
after denaturation, many cannot
In Biology,size doesn’t matter,
SHAPE matters!
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2008-2009 AP Biology
Let’s build some
Proteins!
EATX
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2007-2008 AP Biology
Ghosts of Lectures Past(storage)
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AP Biology
Chaperonin proteins Guide protein folding
provide shelter for folding polypeptides keep the new protein segregated from
cytoplasmic influences
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AP Biology
Protein models Protein structure visualized by
X-ray crystallography extrapolating from amino acid sequence computer modelling
lysozyme