ap biology proteins ap biology 2006-2007 proteins multipurpose molecules
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AP Biology
Proteins Most structurally & functionally diverse
group of biomolecules Function:
involved in almost everything enzymes (pepsin, polymerase, etc.) structure (keratin, collagen) carriers & transport (membrane channels) receptors & binding (defense: antibodies) contraction (actin & myosin) signaling (hormones: insulin) storage (bean seed proteins)
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
AP Biology
Amino acids Structure:
central carbon amino group carboxyl group (acid) R group (side chain)
variable group confers unique
chemical properties of the amino acid —N—
H
HC—OH
||O
R
|—C—
|
H
AP Biology
Nonpolar amino acids nonpolar & hydrophobic
Why are these nonpolar & hydrophobic?Why are these nonpolar & hydrophobic?
AP Biology
Polar amino acids polar or charged & hydrophilic
Why are these polar & hydrophillic?Why are these polar & hydrophillic?
AP Biology
Sulfur containing amino acids Form disulfide bridges
cross links betweens sulfurs in amino acids
You wonderedwhy perms
smelled like rotten eggs?
H-S – S-HH-S – S-H
AP Biology
Building proteins Peptide bonds
linking NH2 of one amino acid to COOH of another
C–N bond
peptidebond
dehydration synthesis
AP Biology
Protein models Protein structure visualized by
X-ray crystallography extrapolating from amino acid sequence computer modelling
lysozyme
AP Biology
Building proteins Polypeptide chains
N-terminus = NH2 end C-terminus = COOH end repeated sequence (N-C-C) is the
polypeptide backbone can only grow in one direction
AP Biology
Protein structure & function
hemoglobin
Function depends on structure 3-D structure
twisted, folded, coiled into unique shape
collagen
pepsin
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 & it’s function even just one amino acid change
can make all the difference!
lysozyme: enzyme in tears & mucus that kills bacteria
AP Biology
Secondary (2°) structure “Local folding”
folding along short sections of polypeptide interaction between
adjacent amino acids
H bonds between R groups
-helix -pleated sheet
AP Biology
Tertiary (3°) structure “Whole molecule folding”
determined by interactions between R groups hydrophobic
interactionseffect of water
in cell anchored by
disulfide bridges(H & ionic bonds)
AP Biology
Quaternary (4°) structure More than one polypeptide chain
joined together only then is it a functional protein
hydrophobic interactions
hemoglobin
collagen = skin & tendons
AP Biology
Chaperonin proteins Guide protein folding
provide shelter for folding polypeptides keep the new protein segregated from
cytoplasmic influences
AP Biology
Denature a protein Unfolding a protein
disrupt 3° structure pH salt temperature
unravels or denatures protein disrupts H bonds, ionic bonds &
disulfide bridges destroys functionality
Some proteins can return to their functional shape after denaturation, many cannot
In Biology,size doesn’t matter,
SHAPE matters!
AP Biology
Protein structure (review)
1°
2°
3°
4°
aa sequencepeptide bonds
R groupsH bonds
R groups hydrophobic interactions,
disulfide bridges
determinedby DNA
multiplepolypeptideshydrophobic interactions
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