Objectives

Identify the structure and function of proteins.

Proteins

Proteins have many structures, resulting in a wide range of function

Proteins”

Elements: C H O N

Monomer: amino acids

(**They have nothing to do with acids or pH)

Amino acids

20 different kinds of amino acids

Each amino acid has the same basic structure- central C- H atom- amino group- carboxyl group- “R” group (side group)

“R” differs for each kind of amino acid

Building a Protein

polypeptide a chain of amino acids joined together by peptide bonds

proteinone or more polypeptides joined together, folded and coiled into a 3D shape

Peptide Bond Formation(dehydration synthesis or hydrolysis?)

4 Levels of Protein Structure

Primary Structure

Unique sequence of amino acids linked together to form a polymer

Sequence different in every protein

Secondary Structure

Primary structure is coiled and/or pleated

Pleats and coils held in place by hydrogen bonds

Tertiary Structure

Secondary structure is twisted and folded into a glob

Each globular protein has a unique shape

Quaternary structure

Two or more polypeptides linked together

Quaternary Structure

Ex. Hemoglobin: an oxygen carrying protein in red blood cells which is made of 4 parts

Shape is also influenced by environment

Usually proteins are in water

Water attracts hydrophilic sides groupsWater repels hydrophobic sides

Hydrophilic amino acids orient toward outside edge of protein

Hydrophobic amino acids cluster in the center

Function of a protein depends on the shape of the protein

Type 1: Structural Proteins (Secondary Structure)example: Keratin- used to make structures

examples: hair, tendons, ligaments

Type: Structural proteinExample: fibroin- spider web "silk"

Type 2: Contractile Proteins Ex: Myosin- found in muscle cells

Type 3: Storage proteins(primary structure)

Examples: albumin- egg white- stores food

Type 4: Defensive Proteins:used to fight invaders (ex. Globulin)

Example: antibodies (neutralize antigens) What is an antigen?An antigen refers to any molecule or molecular fragments. Antigens are usually parts of proteins or polysaccharides (coats, capsules, cell walls, flagella, and toxins that flake off or are released from bacteria, viruses, and other microorganisms in the body) Non-microbial exogenous (foreign) antigens can include pollen, egg white, and proteins from transplanted tissues and organs or on the surface of transfused blood cells.

Autoimmune disorders arise from the immune system reacting to its own antigens.

Type 5: Transport Proteins:move molecules (ex. Karyopherin)

Example

Proteins that help molecules enter and exit the cell

Type 6: Messenger proteins:carry messages from cell to cell

Protein hormonesEXAMPLES:Somatotropin- growth hormone (regulates

bone, muscle and liver growth)Leptin – adipose tissue (plays a key role in

regulating energy intake and energy expenditure, including appetite and metabolism)

Lutropin – pituitary (regulates production of estrogen and testosterone)

Type 7: ENZYMEScatalyze (speed up) all reactions within the body

We will learn MUCH more about this type of protein.

If a protein loses its shape, it loses its function.

A protein that has lost its shape is said to be denatured.

Example of denaturation

Frying an eggEgg white clear liquid changes to white solid the heat denatures the egg’s proteins.

Process: Heat breaks the attractions between the side groups

Protein then loses its shape and therefore its ability to work properly.

http://www.sumanasinc.com/webcontent/animations/content/proteinstructure.html

Can Acid Cook an Egg?

An egg is largely protein and when you cook the egg you are actually denaturing the protein (that is a good thing) using heat.

Vinegar, or lemon juice, makes the water acidic. Acid can penetrate the semi-permeable egg shell and denature the protein.

It usually just denatures the protein on the outside and you heat your egg to denature the rest of the protein. The solid denatured protein prevents any other still liquid protein from escaping until you have finished cooking your egg.

Interesting NoteIf you let an egg sit in acid (more concentrated is

better) such as vinegar or lemon juice, you can denature the entire egg without cooking it. It will also 'eat' the entire shell. the shell is largely calcium carbonate which will react with the acid to produce carbon dioxide and water.

http://scienceathome.cienciaviva.pt/ovonu_eng.html

Denaturizing

What two ways can a protein be denatured?