PROTEINS INTRODUCTION

Useful Proteins There are thousands and thousands of different combinations of amino acids that can make up proteins and that would increase if each one had multiple shapes Proteins usually have only one useful conformation Natural selection has eliminated proteins that do not perform a specific function in the cell

Functions / importance of Proteins Type Examples Structural tendons, cartilage, hair, nails Contractile muscles Transport hemoglobin, albumin Storage ferritin Hormonal eg. insulin, growth hormone Enzyme eg. hydroxylases Protection immunoglobulins Energy 4.1 k.cal/gm Motor Signalling Receptors Motor proteins kinesin

Protein Families Enzymes Have similarities in amino acid sequence and 3-D structure Have similar functions such as breakdown proteins but do it differently

Proteins at Work The conformation of a protein gives it a unique function To work proteins must interact with other molecules, usually 1 or a few molecules from the thousands to 1 protein Ligand – the molecule that a protein can bind Binding site – part of the protein that interacts with the ligand Consists of a cavity formed by a specific arrangement of amino acids

Ligand Binding

Enzymes as Catalysts Enzymes are proteins that bind to their ligand as the 1st step in a process An enzyme’s ligand is called a substrate May be 1 or more molecules Output of the reaction is called the product Enzymes can repeat these steps many times and rapidly, called catalysts

Enzymes at Work Lysozyme is an important enzyme that protects us from bacteria by making holes in the bacterial cell wall and causing it to break Lysozyme adds H2O to the glycosidic bond in the cell wall Active site is a special binding site in enzymes where the chemical reaction takes place

Antibodies Y-shaped molecules with 2 binding sites at the upper ends of the Y The loops of polypeptides on the end of the binding site are what imparts the recognition of the antigen Changes in the sequence of the loops make the antibody recognize different antigens - specificity

Antibodies

Antibody Family A family of proteins that can be created to bind to almost any molecule Antibodies (immunoglobulins) are made in response to a foreign molecule ie. bacteria, virus, pollen… called the antigen Bind together tightly and therefore inactivates the antigen or marks it for destruction

Motor Proteins Proteins can move in the cell, say up and down a DNA strand but with very little uniformity The hydrolysis of ATP can direct the the movement as well as make it unidirectional The motor proteins that move things along the actin filaments or myosin

Protein Machines Complexes of 10 or more proteins that work together such as DNA replication, RNA or protein synthesis, trans-membrane signaling etc. Usually driven by ATP or GTP hydrolysis