Proteins. These are polymers of 20 common amino acids linked in various sequences. Proteins differ in molecular mass, molecular structure and shape

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1 Proteins These are polymers of 20 common amino acids linked in various sequences. Proteins differ in molecular mass, molecular structure and shape

2 Characteristics if protein Amino acids are linked by covalent peptide bonds. Polypeptide chain is flexible, therefore protein molecule gains 3-D shape. structure

3 Classification of proteins By function: Catalytic proteins (enzymes) Defense proteins immunoglobulins Regulatory proteins (transcription factors) Signalling proteins (hormons) Transfer and store proteins (myoglobin, transferrin) Structural baltymai (colagen, elastin) Motor proteins (myosin, kinesin)

4 Classification of proteins By structural features (by number of polypeptide chains) : - Protomeric (monomeric) proteins with 1 polypeptide chains in molecule; - Dimeric protein with 2 polypeptide chains; - Olygomeric protein with more tan 2 polypeptide chains (prefixes tri-, tetra-, penta- indicate number of chains )

5 Classification of proteins By molecular shape: Fibril proteins- thread like molecules. Globular proteins irregular spheric molecules. Transmembrane proteins.

6 Classification of proteins By complexity of molecule - Simple proteins produce only amino acids after hydrolysis -Conjugated proteins produce amino acids and another compound after hydrolysis

7 Conjugated proteins Contains fragment with non-protein structure. If the fragment is titly attached it is referred as prosthetic group. By structure of prosthetic group conjugated proteins are classified as: Nucleoproteins Flavoproteins Metaloproteinsi Glycoproteins Phosphoproteins

8 Structural unit of peptide molecule

9 Structure of protein molecule As proteins have 3-D structure they can be unfolded Unfolded protein is known as polypeptide or peptide. In polypeptide, amino acids are linked by peptide bond. A polypeptide has free amino group at its left side, this is N-terminus. There is free carboxyl group at another side of polypeptide; this is C- terminus.

10 Structure of proteins As polypeptide chain undergoes folding, this occurs in 4 steps. Each step of folding has a particular structure, therefore there are primary, secondary, tertiary and quaternary structures of proteins. Primary structure of a protein is a linear chain of amino acids bonded by peptide bonds. In other words, it is a polypeptide chain. The prefix added to the word peptide specifies the number of amino acids present there. For exampe, di for peptide containing only 2 amino acids; tri for 3 amino acids. If there are amino acids in peptide, we name it as oligopeptide. If there are more than 20 included, we say polypeptide.

11 Secondary structure In beginning of folding, regions within polypeptide can form regular, recurring, localized structures that result from hydrogen bonding between atoms of the peptide bonds. These regions are known as secondary structures. The types of secondary structure: alpha helix, Beta-pleated sheet, beta-turn and irregular coil Hydrogen bonding

12 Regions of scondary structures in folded ppolypeptide chain Beta-turn Beta-pleated Protein can contain different numbers of regions with helical and beta-pleated structures and et.c. helical Irregular coil

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15 Strucural levels of proteins Polypeptide chain Alpha-helix; Coiled polypeptide chain Polypeptide chaine folded by various ways Two or more polypeptide chains folded independently And associated into a single molecule.

16 Loss of structural integrity and functions of proteins Denaturation results from heating, shaking of proteins, action of acids, basis, heavy metal salts. Mild denaturation can be reversed, this is renaturation.

17 Protein folding and re-folding Mild denaturation is reversed by action of protein folding machinery, which also provides newly produced proteins with their proper 3-D structure.

18 Abnormalities of protein folding Prion stands from proteinaceous Infectious agent.

19 Characteristics of prion diseases Types Infectious, e.g. bovine spongiform encephalopathy (mad-cow disease). Inherited, caused by point mutations in the gene encoding Pr C protein, e.g. Creutzfeld-Jakob disease. Characteristics Degeneration and astrocytic gliosis in the CNS. Symptoms convulsions, dementia, ataxia (balance and coordination dysfunction), behavioural or personality changes Microscopic view prion affected tissue. Vacuoles are formed in place of prion Damaged cells.