PROTEINS FOLDED POLYPEPTIDES © 2007 Paul Billiet ODWSODWS.

PROTEINS

FOLDED POLYPEPTIDES

© 2007 Paul Billiet ODWS

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

PRIMARY STRUCTURE The numbers of amino acids vary

(e.g. insulin 51, lysozyme 129, haemoglobin 574, 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 the outside of the protein.

Non-polar (hydrophobic) amino acids tend to be placed on the inside of the protein


Infinite variety

The number of possible sequences is infinite An average protein has 300 amino acids, At each position there could be one of 20 different amino acids = 10390 possible combinations

Most are uselessNatural selection picks out the best


SECONDARY STRUCTURE

The folding of the N-C-C backbone of the polypeptide chain using weak hydrogen bonds

© Science Student

© Text 2007 Paul Billiet ODWS

SECONDARY STRUCTURE

This produces the alpha helix and beta pleating The length of the helix or pleat is determined by certain amino acids that will not

participate in these structures (e.g. proline)

© Dr Gary Kaiser © Text2007 Paul Billiet ODWS

TERTIARY STRUCTURE The 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

TERTIARY STRUCTURE

This folding is sometimes held together by strong covalent bonds (e.g. cysteine-cysteine disulphide bridge)

Bending of the chain takes place at certain amino acids (e.g. proline)

Hydrophobic amino acids tend to arrange themselves inside the molecule

Hydrophilic amino acids arrange themselves on the outside


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

QUATERNARY STRUCTURE

These subunits fit together to form the functional protein

Therefore, the sequence of the amino acids in the primary structure will influence the protein's structure at two, three or more levels


Result

Protein structure depends upon the amino acid sequence

This, in turn, depends upon the sequence of bases in the gene


PROTEIN FUNCTIONS

Protein structure determines protein function

Denaturation or inhibition which may change protein structure will change its function

Coenzymes and cofactors in general may enhance the protein's structure


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)


Globular proteins

most proteins which move around (e.g. albumen, casein in milk)

Proteins with binding sites: enzymes, haemoglobin, immunoglobulins, membrane receptor sites


Proteins classified by function CATALYTIC: enzymes STORAGE: ovalbumen (in eggs), casein (in milk), zein

(in maize) TRANSPORT: haemoglobin COMMUNICATION: hormones (eg insulin) and

neurotransmitters CONTRACTILE: actin, myosin, dynein (in microtubules) PROTECTIVE: Immunoglobulin, fibrinogen, blood

clotting factors TOXINS: snake venom STRUCTURAL: cell membrane proteins, keratin (hair),

collagen


PROTEINS FOLDED POLYPEPTIDES © 2007 Paul Billiet ODWSODWS.

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Transcript of PROTEINS FOLDED POLYPEPTIDES © 2007 Paul Billiet ODWSODWS.