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Proteins
AP Biology
Proteins
________________
________________
AP Biology
2008-2009
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

H2O
monomer = _____________
 20 different amino acids

polymer = _____________
 protein can be one or more polypeptide
chains folded & bonded together
 large & complex molecules
 complex 3-D shape
hemoglobin
AP Biology
Rubisco
growth
hormones
Amino acids
 Structure
central carbon
 amino group
 carboxyl group (acid)
 R group (side chain)

H O
H
| ||
—C— C—OH
—N—
|
H
R
 variable group
 different for each amino acid
 confers unique chemical
properties to each amino acid
 like 20 different letters of an
AP Biology
alphabet
 can make many words (proteins)
Oh, I get it!
amino = NH2
acid = COOH
Effect of different R groups:
Nonpolar amino acids
 nonpolar & hydrophobic
Why are these nonpolar & hydrophobic?
AP Biology
Effect of different R groups:
Polar amino acids
 polar or charged & hydrophilic
AP Biology
Why are these polar & hydrophillic?
Ionizing in cellular waters
AP Biology
H+ donors
Ionizing in cellular waters
AP Biology
H+ acceptors
Sulfur containing amino acids
 Form ________________________


covalent cross links betweens sulfhydryls
stabilizes 3-D structure
H-S – S-H
You wondered
why perms
smell like
rotten eggs?
AP Biology
Building proteins
 _______________________
covalent bond between NH2 (amine) of
one amino acid & COOH (carboxyl) of
another
 C–N bond

H2O
dehydration synthesis
AP Biology
peptide
bond
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
AP Biology
Protein structure & function
 Function depends on structure

3-D structure
 twisted, folded, coiled into unique shape
pepsin
hemoglobin
AP Biology
collagen
Primary (1°) structure
 __________________________
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!
AP Biology
lysozyme: enzyme
in tears & mucus
that kills bacteria
Sickle cell anemia
I’m
hydrophilic!
AP Biology
Just 1
out of 146
amino acids!
But I’m
hydrophobic!
Secondary (2°) structure
 __________________________
folding along short sections of polypeptide
 interactions between
adjacent amino acids

 __________________
 weak bonds
between R groups

forms sections of
3-D structure
 __________________
 __________________
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
AP Biology
sulfurs in sulfhydryls (S–H)
 anchors 3-D shape
Quaternary (4°) structure
 _____________________________________
_____________________________________

only then does polypeptide become
functional protein
 ________________________________
AP Biology = skin & tendons
collagen
hemoglobin
Protein structure (review)
R groups
hydrophobic interactions
disulfide bridges
(H & ionic bonds)
3°
multiple
polypeptides
hydrophobic
interactions
1°
amino acid
sequence
peptide bonds
determined
by DNA
AP Biology
4°
2°
R groups
H bonds
Protein denaturation
 Unfolding a protein

In Biology,
size doesn’t matter,
SHAPE matters!
___________________________________
___________________________________
 ______________
 ______________
 ______________

________________________
 alter 3-D shape

________________________
 some proteins can return to their functional shape
after denaturation, many cannot
AP Biology
Let’s build some
Proteins!
AP Biology
2008-2009