3.2 & 7.5 Proteins
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Transcript of 3.2 & 7.5 Proteins
3.2 & 7.5 Proteins
Pp 50 – 51 & 206 - 210 Pp 15 & 66 - 68
ProteinsProteins are polymers of amino acids Each has a unique 3D shapeAmino acid sequences varyProteins are major component of cell partsThe provide:
support and structural componentsstorage of amino acids
Several types of proteins are identified: receptor, contractile, defense, enzymes, structural
Building Blocks: Amino Acids There are 20 different types of amino acids
All have this general formular
The R group is a variable group
Polar vs. Non-polar Amino Acids
Some amino acids are polar while some are non-polar
This property causes proteins to fold into varied shapes
Significance of polar & non-polar amino acids
polar amino acids non-polar amino acids
hydrophiliccan make hydrogen
bonds
found in hydrophilic channels & parts of proteins projecting from membranes
found on surface of water-soluble proteins
hydrophobicforms van der Waals
(hydrophobic interactions) with other hydrophobic amino acids
found in proteins in interior of membranes
found in interior of water-soluble proteins
Peptide Bonds
Proteins are formed by condensation
A peptide bond is formed
Four levels of protein structure
Primary StructurePrimary structure is a
chain of amino acids number & unique
sequence of amino acids determine the properties of primary structure
each position is occupied by one of 20 different amino acids
sequence of amino acids is determined by DNA sequence in genes
linked by peptide bonds
Secondary structureformed by interaction
between amino and carboxyl i.e. -NH and -C=O groups
weak hydrogen bonds are formed between – H & = O
there are two types: a-helix and b-sheet
α- helix formed / polypeptide coils up e.g. sheep wool
β- pleated sheet formed e.g. silk in spider webregular repeated folding of
amino acid chainsecondary structure is
stabilized by hydrogen bonds
Tertiary structureThese are globular proteins
with irregular conformationtertiary structure is the
folding up of the polypeptide chain, secondary structure or alpha helix
it gives three dimensional globular shape i.e. shape of active site
the structure is stabilized by disulphide bridges, hydrogen, ionic& hydrophobic bonds
tertiary structure used as enzymes to catalyze biochemical reactions
Quaternary structuremade of several
polypeptide subunits joined together
they maybe conjugated proteins i.e. proteins which combine with a prosthetic group (non-protein molecules)
prosthetic groups includes: metals e.g. iron in haemoglobin, nucleic acids as in ribosomes , carbohydrates as in glycoprotein or lipids as in glycolipids
Denaturation of Proteinschange in
protein’s usual regular structure due to: High tempChange in pHAddition of
organic solvent (alcohol, acetone)
These factors break the bonds that stabilize the structure
Protein Functions Function Examples StructureTransport
Enzymes
Movement
HormonesAntibodiesstorage
– collagen/keratin/fibrin – myoglobin/hemoglobin, bind
& transport oxygen – lysozyme, speeding up
metabolic reactions – actin (and myosin tropomyosin
(and troponin)– insulin, regulate blood glucose – immunoglobulin– albumin in egg, casein in
milk
Difference between Fibrous and Globular Proteins
fibrous proteins are long and narrow strands or sheets whereas globular proteins are rounded, spherical or ball shaped
fibrous protein made of repetitive amino-acid sequences whereas globular proteins are made of irregular amino acid sequences
fibrous proteins are usually insoluble in water whereas globular proteins usually soluble in water
globular protein more sensitive to changes in pH, temperature & salt than fibrous proteins
fibrous proteins have structural or support functions (roles) whereas globular proteins have metabolic functions such as catalysis & transport function
Examples of fibrous proteins: keratin/fibrin/collagen/actin/myosin/silk protein
Examples of globular protein: insulin/immunoglobulin/hemoglobin/amylase
Revision QuestionsExplain how polar and non-polar amino acids help channel
proteins and enzymes carry out their functions. [5]Distinguish between fibrous and globular proteins with
reference to one example of each protein type. [6]Explain primary structures and tertiary structures of a
protein. [3]
Draw the structure of a generalized dipeptide. [4]Draw the basic structure of an amino acid, and label the
groups that are used in peptide bond formation. [4]List four functions of membrane proteins. [4]Giving a named example of each, state four functions of
proteins. [8]