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Proteins
Regents Biology
Proteins:
Multipurpose molecules
Regents Biology
2006-2007
Proteins
Examples


muscle
skin, hair, fingernails, claws
 collagen, keratin

insulin
pepsin
pepsin
 digestive enzyme
in stomach

insulin
 hormone that controls blood
sugar levels
Regents Biology
collagen (skin)
Proteins
 Function:

many, many functions
 hormones
 signals from one body system to another
 insulin
 movement
 muscle
 immune system
 protect against germs
 enzymes
Regents Biology  help chemical reactions
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
alphabet
Regents Biology can make many words (proteins)
Oh, I get it!
amino = NH2
acid = COOH
Proteins
 Building block = amino acids
amino amino amino amino amino
acid – acid – acid – acid – acid

20 different amino acids
H O
H
| ||
—N—
—C—C—OH
|
H variable
Regents Biology
group
There’s
20 of us…
like 20 different
letters in an
alphabet!
Can make lots of
different
words
Effect of different R groups:
Nonpolar amino acids
 nonpolar & hydrophobic
Why are these nonpolar & hydrophobic?
Regents Biology
Effect of different R groups:
Polar amino acids
 polar or charged & hydrophilic
Why are these polar & hydrophillic?
Regents Biology
Ionizing in cellular waters
Regents Biology
H+ donors
Ionizing in cellular waters
Regents Biology
H+ acceptors
Sulfur containing amino acids
 Form disulfide bridges


covalent cross links betweens sulfhydryls
stabilizes 3-D structure
H-S – S-H
You wondered
why perms
smell like
rotten eggs?
Regents Biology
Amino Acids
 Essential Amino acids

Amino acids that the body cannot
synthesize from simpler compounds;
they must be obtained from the diet
Regents Biology
Amino acid chains
 Proteins

amino acids chained into a polymer
H O
H
| ||
—N—
—C—C—OH
|
H
R
Regents Biology
H O
H
| ||
—N—
—C—C—OH
|
H
R
Amino acid chains
 Proteins

amino acids chained into a polymer
H O
H
| ||
—N—
—C—C—OH
|
H
R
Regents Biology
Carboxyl
group
H O
H
| ||
—N—
—C—C—OH
|
H
R
Amino
group
Amino acid chains
 Proteins

amino acids chained into a polymer
H O
H O
H
| ||
H
| ||
—N—
—C— C—
—N—
—C—C—OH
|
|
H
R
R
OH H
Regents Biology
Amino acid chains
 Proteins

amino acids chained into a polymer
H O H H O
H
| ||
|
||
—
—C—C—OH
—N—
—C— C— N—
|
|
H
R
R
H 2O
Regents Biology
Peptide bond- The amide linkage that
holds amino acids together in
polypeptides
Amino acid chains
 Proteins

amino acids chained into a polymer
amino acid
amino acid
amino acid
amino acid
amino acid
 Each amino acid is different

some “like” water & dissolve in it

some “fear” water & separate from it
Regents Biology
Amino acid chains
 Amino terminus

The free amino group at one end of the
polypeptide
amino acid
amino acid
amino acid
amino acid
amino acid
 Carboxyl terminus

The free carboxyl group at one end of a
polypeptide
Regents Biology
Water-fearing amino acids
 Hydrophobic
“water fearing” amino acids
 try to get away from water in cell

 the protein folds
Regents Biology
Water-loving amino acids
 Hydrophillic
“water loving” amino acids
 try to stay in water in cell

 the protein folds
Regents Biology
For proteins: SHAPE matters!
 Proteins fold & twist into 3-D shape

that’s what happens in the cell!
 Different shapes = different jobs
growth
hormone
Regents Biology
hemoglobin
pepsin
collagen
It’s SHAPE that matters!
 Proteins do their jobs, because
of their shape (conformation)
 Unfolding a protein destroys its shape
wrong shape = can’t do its job
 unfolding proteins = “denature”

 temperature
unfolded
“denatured”
 pH (acidity)
In Biology,
it’s not the size,
it’s the SHAPE
that matters!
Regents Biology
folded
Protein Folding
 Shape comes from how the protein
folds
 There are 4 levels of folding in proteins
Regents 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!
Regents Biology
lysozyme: enzyme
in tears & mucus
that kills bacteria
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
Regents Biology
Secondary (2°) structure
Regents 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)
Regents Biology anchors 3-D shape
Quaternary (4°) structure
 More than one polypeptide chain bonded
together

only then does polypeptide become
functional protein
 hydrophobic interactions
 Protein structure video
Regents Biology
collagen
= skin & tendons
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
Regents Biology
4°
2°
R groups
H bonds