PROTEINSPROTEINS

Learning Outcomes:Learning Outcomes:• B4 - describe the chemical structure of proteins• List functions of proteins• Draw and describe the structure of an amino acid• Describe the formation of peptide bonds• Describe the 4 levels of protein structure

ELEMENTSELEMENTS• All contain C, H, O, N• Some contain S

MONOMERSMONOMERS• Amino Acids consist of an acid (carboxyl) group,

an amino group, and a variable R group (R for “remainder”)

• There are 20 amino acids, each with a unique R group

• some of these are known as “essential amino acids” because our bodies can’t synthesize them• Examples: (see p. 37, note different R groups)

POLYMERSPOLYMERS• Proteins consist of

chains of amino acids

• A single protein may contain several hundred amino acids

• A dipeptide contains two amino acids joined by a peptide bond

Condenstation Condenstation SynthesisSynthesis

• A molecule of H2O is removed to form a peptide bond between two amino acids

HydrolysisHydrolysis• Proteins can be

broken down into amino acids

• A molecule of H2O is added when a peptide bond is broken

• A polypeptide is a chain of many amino acids joined by peptide bonds

LEVELS OF LEVELS OF STRUCTURESTRUCTURE

• Proteins have four levels of structure, resulting in large complex molecules with definite 3D shapes

Primary structurePrimary structure• The sequence of amino acids in the polypeptide

chain

Secondary structureSecondary structure• The chain forms a

shape such as a helix (coil) or pleated sheet

• Held together by hydrogen bonds between R groups

Amino acid basics

Tertiary structureTertiary structure• The coil or sheet

folds into a 3-dimensional shape -

• may be due to hydrogen, ionic or covalent bonding

• Hydrophobic parts on the inside, hydrophilic parts on the outside

Quaternary structureQuaternary structure• Two or more polypetide chains combine to form a

complex molecule• Ex. Hemoglobin contains 4 polypeptide chains

• The 3 dimensional shape of a protein is important to its function

FUNCTIONSFUNCTIONS1. Structural proteins in all parts of the body• Ex. Keratin in hair and nails; collagen in skin;

actin and myosin in muscle

• Muscle proteins form long fibers

2. Blood proteins such as hemoglobin, clotting proteins, antibodies

• Hemoglobin is the oxygen carrying protein in red blood cells

• consists of four polypeptide chains and an iron-containing heme group

3. Enzymes - very important!• Enzymes catalyze chemical reactions in all

parts of the body (we have over 2000 different ones)

• All enzymes are proteins• The specific shape of the enzyme molecule

allows it to bind to reactants

4. Cell membranes• proteins are found in cell membranes, where

they have various functions(along with phospholipids - more on this later!)