1. PROTEINS
FOLDED POLYPEPTIDES
© 2016 Paul Billiet ODWS

2. PRIMARY STRUCTURE The sequence of amino acids MIL1 sequence:
>gi| |ref|NP_ | MIL1 protein [Homo sapiens]
MEDCLAHLGEKVSQELKEPLHKALQMLLSQPVTYQAFRECTLETTVHASGWNKILVPLVLLRQMLLELTRLGQEPLSALLQFGVTYLEDYSAEYIIQQGGWGTVFSLESEEEEYPGITAEDSNDIYILPSDNSGQVSPPESPTVTTSWQSESLPVSLSASQSWHTESLPVSLGPESWQQIAMDPEEVKSLDSNGAGEKSENNSSNSDIVHVEKEEVPEGMEEAAVASVVLPARELQEALPEAPAPLLPHITATSLLGTREPDTEVITVEKSSPATSLFVELDEEEVKAATTEPTEVEEVVPALEPTETLLSEKEINAREESLVEELSPASEKKPVPPSEGKSRLSPAGEMKPMPLSEGKSILLFGGAAAVAILAVAIGVALALRKK
length: 386amino acids
kachkeis.com/ img/essay2_pic0.jpg

3. PRIMARY STRUCTURE
The numbers of amino acids vary (e.g. insulin 51, lysozyme 129, haemoglobin 574, gamma globulin 1250, titin )
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.
© 2016 Paul Billiet ODWS

4. 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 = possible combinations
Most are useless Natural selection picks out the best.
© 2016 Paul Billiet ODWS

5. SECONDARY STRUCTURE
The folding of the N-C-C backbone of the polypeptide chain using weak hydrogen bonds
student.ccbcmd.edu/.../ images/alphahelix.jpg
© 2016 Paul Billiet ODWS

6. 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)
student.ccbcmd.edu/.../ images/betasheet.jpg
© 2016 Paul Billiet ODWS

7. TERTIARY STRUCTURE
The folding of the polypeptide into domains whose chemical properties are determined by the amino acids in the chain
MIL1 protein
kachkeis.com/ img/essay2_pic0.jpg
© 2016 Paul Billiet ODWS

8. 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.
© 2016 Paul Billiet ODWS

9. Chain B of Protein Kinase C
lectures/quaternary.gif

10. QUATERNARY STRUCTURE
Some proteins are made of several polypeptide subunits (e.g. haemoglobin has four)
Protein Kinase C
lectures/quaternary.gif
© 2016 Paul Billiet ODWS

11. 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.
© 2016 Paul Billiet ODWS

12. Result
Protein 3-D structure depends upon the amino acid sequence This, in turn, depends upon the sequence of bases in the gene.
© 2016 Paul Billiet ODWS

13. 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.
© 2016 Paul Billiet ODWS

14. 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).
© 2016 Paul Billiet ODWS

15. Globular proteins
most proteins which move around (e.g. albumen, casein in milk)
Proteins with binding sites: enzymes, haemoglobin, immunoglobulins, membrane receptor sites.
© 2016 Paul Billiet ODWS

16. Proteins classified by function
CATALYTIC: enzymes e.g. rubisco
STORAGE: ovalbumen (in eggs), casein (in milk), zein (in maize)
TRANSPORT: hemoglobin
COMMUNICATION: hormones (e.g. 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.
PIGMENTS: e.g. Rhodopsin, melanin
© 2016 Paul Billiet ODWS