Brother Gregory speaks to his class,

The subject for today is the structure and function of proteins. You must follow the lesson, answer the questions, then complete the research investigation, if required.

"Let us begin .......

"Proteins are one of the four major groups of macromolecules that are found in all living organisms. These giant molecules carry out many of the vital functions needed by cells.

"Proteins are involved in such processes as food digestion, cell structure, catalysis, movement, energy manipulation and much more. They are complex, huge associations of molecular subunits that appear impossibly difficult to understand. Fortunately they are all built using the same construction principle.

"As with all macromolecules, proteins are polymers, composed of smaller subuits - the amino acids - joined together in long chains.

"There are about 20-22 common amino acids found in most proteins. All but one of these small molecules has the same common structure, but varies in the nature of one chemical group - termed the "R-group". It is the varying structure and properties of these R-groups that make amino acids different from one another.

"Amino acids are joined together in long chains called "polypeptides", a name which comes from the type of bond holding the chains of amino acids together. The group of atoms that hold the amino acids together, is called a peptide bond. The order, or sequence of amino acids along a polypetide chain establishes the first critial property of proteins, its primary structure.

As you proceed through this lesson, test yourself as you go by answering some of these "true/false" questions.

Three dimentional shapes

"Most of the properties of most proteins, however, are based on the unique and special three dimensional shapes that proteins take up as the amino acids act and react with one another and with the surrounding water. Secondary, tertiary and quaternary structures are different levels of higher, three dimensional structure.

"Shape is very important. Amino acid R-groups can be grouped into four basic categories, and it is the interaction of these different R-groups that determines, to a considerable extent, the shape and role of the final protein.

"There are varying amounts of secondary structure in most proteins, but the two most common, recognizable repeating patterns of structure are the alpha-helix and beta-pleated sheet.

"Although it is the peptide bond that joins the amino acids together in their polypeptide chains, there are other, weaker, forces at work holding the polypeptide in its correct three-dimensional shape.

"These forces can "spot weld" two parts of the chain together, or simply provide a hydrophobic local environment from which water molecules are excluded.

"Once in shape, protein molecules are capable of coming together and forming complex arrangements or structures that are composed of more than one polypeptide subunit. Quite often, these larger structures also contain extra, non-protein material such as carbohydrate, lipid or even polynucleotides.

Roles Proteins Play - a few examples

"Proteins are involved in almost all aspects of cellular life and structure. They are also critical players in holding cells together into multicellular structures (like us!), and making sure that chemical reactions take place at "life speed".

"The following is a partical list giving a few examples of the roles that proteins play in life:

Research investigation
check your schedule to see if this is required
The Curse of Amun
Protein research Investigation
Concept questions
for the lesson

check your schedule to see if this is required
Protein Set
Concept Questions and personal question page
Required Readings
for the lesson
Key Concepts
Table of Contents -|- Polymers -|- Proteins

Protein shape -|- Weak Forces -|- Assembly

In the cytoskeleton -|- In holding cells together

In the membranes -|- In the muscles

Science@a Distance
© 2003, Professor John Blamire