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AP Biology
Proteins
AP Biology 2008-2009
Proteins______________________________
AP Biology
Proteins Most structurally & functionally diverse group Function: involved in almost everything
(pepsin, DNA polymerase) (keratin, collagen) (hemoglobin, aquaporin)
(insulin & other hormones)
(antibodies) (actin & myosin) (bean seed proteins)
AP Biology
Proteins Structure
monomer = 20 different amino acids
polymer = protein can be one or more polypeptide
chains folded & bonded together
Rubisco
hemoglobin
growthhormones
H2O
AP Biology
Amino acids Structure
(acid) (side chain)
variable group different for 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
AP Biology
Effect of different R groups:Nonpolar amino acids
Why are these nonpolar & hydrophobic?Why are these nonpolar & hydrophobic?
AP Biology
Effect of different R groups:Polar amino acids
Why are these polar & hydrophillic?Why are these polar & hydrophillic?
AP Biology
Ionizing in cellular waters H+ donorsH+ donors
AP Biology
Ionizing in cellular waters H+ acceptorsH+ acceptors
AP Biology
Sulfur containing amino acids Form
covalent cross links betweens sulfhydryls
You wonderedwhy permssmell like
rotten eggs?
H-S – S-HH-S – S-H
AP Biology
Building proteins Peptide bonds
C–N bond
peptidebond
dehydration synthesisH2O
AP Biology
Building proteins Polypeptide chains have direction
repeated sequence (N-C-C) is the
_____________________ can only grow in one direction
AP Biology
Protein structure & function
hemoglobin
3-D structure
twisted, folded, coiled into unique shape
collagen
pepsin
AP Biology
Primary (1°) structure
slight change in amino acid sequence can affect protein’s structure & its function
lysozyme: enzyme in tears & mucus that kills bacteria
AP Biology
Sickle cell anemiaJust 1
out of 146amino acids!
AP Biology
Secondary (2°) structure “ ”
folding along short sections of polypeptide
weak bonds
between R groups
-helix -pleated sheet
AP Biology
Secondary (2°) structure
AP Biology
Tertiary (3°) structure “ ”
interactions between distant amino acids
cytoplasm is water-based
nonpolar amino acids cluster away from water
covalent bonds between sulfurs in sulfhydryls (S–H)
anchors 3-D shape
AP Biology
Quaternary (4°) structure
only then does polypeptide become functional protein hydrophobic interactions
collagen = skin & tendons hemoglobin
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°
AP Biology
Protein denaturation
conditions that disrupt H bonds, ionic bonds, disulfide bridges
alter 2° & 3° structure
destroys functionality
In Biology,size doesn’t matter,
SHAPE matters!