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Proteins
AP Biology
Proteins
Multipurpose
molecules
AP Biology
2006-2007
Proteins
 Most structurally & functionally diverse

group of biomolecules
Function:

involved in almost everything
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AP Biology
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)
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
hemoglobin
AP Biology
growth
hormones
Amino acids
 Structure:
central carbon
 amino group
 carboxyl group (acid)
 R group (side chain)

 variable group
 confers unique
chemical properties
of the amino acid
AP Biology
H O
H
| ||
—C— C—OH
—N—
|
H
R
Nonpolar amino acids
 nonpolar & hydrophobic
AP Biology
Polar amino acids
 polar or charged & hydrophilic
AP Biology
Sulfur containing amino acids
 Form disulfide bridges

cross links betweens sulfurs in amino acids
H-S – S-H
You wondered
why perms
smelled like
rotten eggs?
AP Biology
Building proteins
 Peptide bonds
linking NH2 of one amino acid to
COOH of another
 C–N bond

dehydration synthesis
AP Biology
peptide
bond
Protein structure & function
 Function depends on structure

3-D structure
 twisted, folded, coiled into unique shape
pepsin
hemoglobin
AP Biology
collagen
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!
AP Biology
lysozyme: enzyme
in tears & mucus
that kills bacteria
Sickle cell anemia
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
interactions
 effect 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
collagen =
skin & tendons
AP Biology
hemoglobin
Protein structure (review)
R groups
hydrophobic interactions,
disulfide bridges
3°
1
°
multiple
polypeptides
hydrophobic
interactions
aa sequence
peptide bonds
determined
by DNA
AP Biology
2°
R groups
H bonds
4°
Let’s build some
Proteins!
AP Biology
2006-2007
Protein models
 Protein structure visualized by
X-ray crystallography
 extrapolating from amino acid sequence
 computer modelling

lysozyme
AP Biology
Any Questions??
AP Biology
2006-2007