ProteinsUnit 2 – Chemistry of Life

Proteins

http://www.youtube.com/watch?v=g9G0zzdQx-M&feature=related

Contain: Carbon, hydrogen, oxygen, nitrogen, and

sometimes sulfur Form the basic structure of many

animal parts, such as muscle, skin, hair, and bone.

Enzymes are also proteins.

Proteins

Are formed from amino acids:

On the left: amine group On the right: carboxyl group “R” represents an atom or group of atoms

which varies with each different amino acid.

Proteins

20 different amino acids form proteins

They join by dehydration synthesis:

Polypeptides

Two or more amino acids bonded together are called a peptide.

A chain of many amino acids is referred to as a polypeptide.  The complete product, either one or more chains of amino acids, is called a protein.

There is unequal sharing of electrons in a peptide bond. The O and the N are negative and the H is positive.

Levels of Structure

Protein structure is described in 4 levels: 1. Primary structure 2. Secondary structure 3. Tertiary structure 4. Quaternary structure

Primary Structure

Is a chain of amino acids joined by dehydration synthesis and held together by peptide bonds (strong covalent bonds: C-N)

Organized in linear arrangements E.g. Cow insulin

Primary Structure

Proteins differ in 3 ways: 1. number of amino acids in the chain 2. types of amino acids 3. sequence of amino acids

Each different sequence is a different protein

Primary chains are 51 to thousands of amino acids long

There is an infinite number of different proteins

Secondary Structure

The straight primary chain of amino acids spontaneously coils, forming hydrogen bonds between amino acids.

Eg. Alpha-helix (hair)

hydrogen bonds

Secondary proteins are structural proteins (e.g. hair, cartilage) and are insoluble in water

Tertiary Structure

“Globs” Interactions (hydrogen bonds)

between R-groups of the amino acids hold these proteins in a 3-dimensional globular shape.

The specific globular shape is essential for the proteins of biological function.

Tertiary Structure

Primary chain of amino acids held together by peptide bond

Hydrogen bonds between some R-groups (weak bonds)

Quaternary Structure

Large globular proteins formed when 2 or more tertiary (globular) proteins join

E.g. hemoglobin – 4 globular proteins

Denaturation of Proteins

Globular proteins can easily be denatured.

For example, the hydrogen bonds holding the protein in its 3D shape are broken by acid, base, change in pH, or heat and the protein reverts back to its primary structure (chain of amino acids).

Denaturation

3D primary chain

The protein loses its biological function since its 3D shape is essential for it to function.

Once the heat, acid or base is removed, the protein may go back to its tertiary shape and resume its biological function.

Coagulation

A permanent change in protein shape caused by too much heat, acid, or base.

“Permanent denaturation” E.g. boiling an egg: no matter how

long the egg cools, the proteins of the egg will never assume their original shape

Hydrolysis of Protein

Hydrolysis of Protein

Hydrolysis is the reverse reaction to dehydration synthesis

Proteins you eat are hydrolyzed during digestion

Hydrolysis breaks the peptide bonds i.e. destroys the primary structure

Protein + many water molecules amino acids

Proteins

Video Intro for Protein Lab: http://www.youtube.com/watch?v=w-ctk

PUUpUc

Video closure for Protein Lab http://www.wisc-online.com/Objects/View

Object.aspx?ID=BIC007