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PROTEINS
FOLDED POLYPEPTIDES
2007 Paul Billiet ODWS
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PRIMARY STRUCTURE
The sequence of amino acids
MIL1 sequence:>gi|7662506|ref|NP_056182.1| MIL1 protein [Homo sapiens]
MEDCLAHLGEKVSQELKEPLHKALQMLLSQPVTYQAFRECTLETTVHASGWNKILVPLVLLRQMLLELTRLGQEPLSALLQFGVTYLEDYSAEYIIQQGGWGTVFSLESEEEEYPGITAEDSNDIYILPSDNSGQVSPPESPTVTTSWQSESLPVSLSASQSWHTESLPVSLGPESWQQIAMDPEEVKSLDSNGAGEKSENNSSNSDIVHVEKEEVPEGMEEAAVASVVLPARELQEALPEAPAPLLPHITATSLLGTREPDTEVITVEKSSPATSLFVELDEEEVKAATTEPTEVEEVVPALEPTETLLSEKEINAREESLVEELSPASEKKPVPPSEGKSRLSPAGEMKPMPLSEGKSILLFGGAAAVAILAVAIGVALALRKK
length: 386amino acids Anne-Marie Ternes
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PRIMARY STRUCTURE The numbers of amino acids vary
(e.g. insulin 51, lysozyme 129, haemoglobin574, gamma globulin 1250)
The primary structure determines the folding of
the polypeptide to give a functional protein Polar amino acids (acidic, basic and neutral)
are hydrophilic and tend to be placed on theoutside of the protein.
Non-polar (hydrophobic) amino acids tend to beplaced on the inside of the protein
2007 Paul Billiet ODWS
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Infinite variety
The number of possible sequences isinfinite
An average protein has 300 amino acids,At each position there could be one of 20different amino acids= 10390 possible combinations
Most are uselessNatural selection picks out the best
2007 Paul Billiet ODWS
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SECONDARY STRUCTURE
The folding of the N-C-
C backbone of the
polypeptide chainusing weak hydrogen
bonds
Science Student
Text 2007 Paul Billiet ODWS
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SECONDARY STRUCTURE
This produces the alpha helix and beta pleating
The length of the helix or pleat is determined by certainamino acids that will not participate in these structures
(e.g. proline)
Dr Gary Kaiser Text2007 Paul Billiet ODWS
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TERTIARY STRUCTUREThe folding of the polypeptide into
domains whose chemical properties are
determined by the amino acids in the
chain
MIL1 protein
Anne-Marie Ternes
2007 Paul Billiet ODWS
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TERTIARY STRUCTURE
This folding is sometimes held together bystrong covalent bonds(e.g. cysteine-cysteine disulphide bridge)
Bending of the chain takes place at certainamino acids(e.g. proline)
Hydrophobic amino acids tend to arrange
themselves inside the molecule Hydrophilic amino acids arrange themselves
on the outside
2007 Paul Billiet ODWS
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Max Planck Institute for Molecular Genetics
Chain B of Protein Kinase C
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QUATERNARY STRUCTURE
Some proteins are
made of several
polypeptide subunits(e.g. haemoglobin has
four)
Protein Kinase C
Max Planck Institute for Molecular Genetics
Text 2007 Paul Billiet ODWS
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QUATERNARY STRUCTURE
These subunits fit together to form the
functional protein
Therefore, the sequence of the aminoacids in the primary structure will influence
the protein's structure at two, three or
more levels
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Result
Protein structure depends upon the
amino acid sequence
This, in turn, depends upon the sequenceof bases in the gene
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PROTEIN FUNCTIONS
Protein structure determines protein
function
Denaturation or inhibition which maychange protein structure will change its
function
Coenzymes and cofactors in general mayenhance the protein's structure
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Fibrous proteins
Involved in structure: tendons ligaments
blood clots
(e.g. collagen and keratin) Contractile proteins in movement: muscle,
microtubules
(cytoskelton, mitotic spindle, cilia, flagella)
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Globular proteins
most proteins which move around (e.g.
albumen, casein in milk)
Proteins with binding sites:enzymes, haemoglobin, immunoglobulins,
membrane receptor sites
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Proteins classified by function CATALYTIC: enzymes
STORAGE: ovalbumen (in eggs), casein (in milk), zein(in maize)
TRANSPORT: haemoglobin
COMMUNICATION: hormones (eg insulin) andneurotransmitters
CONTRACTILE: actin, myosin, dynein (in microtubules)
PROTECTIVE: Immunoglobulin, fibrinogen, blood
clotting factors TOXINS: snake venom
STRUCTURAL: cell membrane proteins, keratin (hair),collagen
2007 Paul Billiet ODWS
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