Macromolecules Part 3 Proteins

Proteins!

Functions of Proteins – Structural support – Storage – Transport – Cellular communications – Movement – Defense against foreign substances

Proteins Monomer: amino acids – 20 amino acids – Amine (NH 2 ) and carboxyl (COOH) groups attached to carbon – Only thing different is side chain…R-group Polymer: polypeptide chains (proteins) Link between monomers is called: polypeptide bond – Made by a dehydration reaction – (between amine group of one aa and carboxyl group of another aa) STRUCTURE of A.A. – Amino group on one end (-NH 2 ) – Carboxyl group on one end (COOH) – Hydrogen – R-group/side chain (changes)  ALANINE Proteins account for more than 50% of the dry mass of most cells

Polypeptide bonds

Some famous proteins… – Essential components of cell membranes – Oxygen-carrying pigment hemoglobin (hemoglobin) – Antibodies which attack and destroy invading microorganisms

Protein Structure Primary structure 1’ – Order of amino acids in a polypeptide chain Secondary structure 2’ – Polypeptide chain folds because of interactions between amino acids – HYDROGEN BONDING Tertiary Structure 3’ – Gives proteins 3-D shape VERY IMPORTANT to function of protein – Beta pleated sheets and alpha helices fold based on interactions between R-groups of a.a. – Hydrogen bonds, polar/non-polar interactions, acid/base interactions, disulfide bonds, van der Waals forces Quaternary Structure 4’ – the association of the polypeptide chains – some proteins contain more than one polypeptide chain – Each polypeptide chain in the protein is called a subunit – Two or more subunits come together for a specific function – HEMOGLOBIN On Red blood cells Its shape allows RBCs to carry oxygen all around your body!

Primary Structure Sequence of AA in a long polypeptide chain AA= letters of alphabet Sequence of AA= arrangement of letters to make words HUGE amount of different primary structures Changing ONE AA is polypeptide chain GREATLY changes the properties of the polypeptide chain and PROTEIN

Secondary Structure The order of AA in polypeptide chain determine interactions between functional groups of AA Functional groups interact via HYDROGEN BONDS – Attraction between oxygen in the –CO end of one AA and the hydrogen in the – NH end of another AA – H-bond easily broken Change pH and change Temperature – Three possible 2 o structures Determined by order R- groups – No particular arrangement – Alpha helix Polypeptide chains that coil tightly – Beta pleated sheet Looser, straighter shape created by hydrogen bonds

Tertiary Structure Secondary structure gets coiled and folded Precise 3D shape Folding is determined by interactions between R-groups – Hydrogen bonds Tryptophan Arginine Asparigine – Disulphide bonds Between 2 cystine molecules – Ionic bonds b/t R groups containing amine and carboxyl groups – Hydrophobic interactions b/t R groups that are non-polar (hydrophobic)

Quaternary Structure Proteins are made up of multiple polypeptide chains, sometimes with an inorganic component (for example, a haem group in haemoglogin) – Prosthetic Group (inorganic component of protein) These proteins will only be able to function if all subunits are present Made by same bonds found in tertiary structure Interactions between R-groups – Hydrogen bonds Tryptophan Arginine Asparigine – Disulphide bonds Between 2 cystine molecules – Ionic bonds b/t R groups containing amine and carboxyl groups – Hydrophobic interactions b/t R groups that are non-polar (hydrophobic)

Denaturation Unraveling/unfolding of protein Why would this be a problem? When protein loses its 3-D shape and thus its specific function Caused by: – Unfavorable changes in pH, temperature or other environmental condition – Disrupts the interactions between side chains and causes loss of shape Examples: – Frying an egg – Straightening your hair