Proteins

Proteins, Polypeptides and Amino Acids

Biggest

Smallest

Proteins

Polypeptides

Amino Acids

• Amino acids bond together to form polypeptides.

• Proteins are made up of one or more polypeptide, precisely twisted, folded and coiled into a molecule of unique shape

Amino Acids

• These are the monomers of proteins.• An amino acid is an organic molecule

possessing both an amino group and a carboxyl group.

Amino Acid Structure

• Amino acids have one central carbon atom (called the alpha carbon)

• It has four different partners:– A hydrogen atom (H)– An amino group (H3N)– A carboxyl group (COOH)– An R group (R)

Amino Acid Variation

• The R group, also called the side chain, differs with each amino acid.

• There are 20 different amino acids that cells use to build their thousands of proteins. (you don’t need to memorise them!)

• The R group may be as simple as a hydrogen atom (glycine) or it may be a carbon skeleton with various functional groups attached, like glutamine.

Significance

All most all of the living organisms on Earth use the same 20 amino acids to synthesize proteins.

What does this mean? Why is this significant?

Polypeptides

• Polypeptides form from amino acids linking together.

• This occurs through condensation reactions between the carboxyl group of one amino acid and the amino group of another ( C – N)

• A water molecule (H2O) is removed and a covalent bond is formed.

• These are called peptide bonds

Drawing practice

Draw two amino acids forming a peptide bond.

Remember, the bond forms between the Carboxyl group and amino group (carbon bonding with nitrogen)

The double bonded oxygen remains, and water is a product of the reaction

Peptide Bonds

R R R

Polypeptides

• Peptide bonds are formed over and over, resulting in a polypeptide.

• Each polypeptide has a unique combination of the 20 amino acids, resulting in an infinite number of polypeptides.

• Every polypeptide always has an amino group end and a carboxyl group end.

Proteins

• Proteins may consist of a single polypeptide or more than one polypeptide linked together.

• Proteins have a precise 3D shape, determined by the amino acid sequence

The enzyme:

Lysozyme

Functions of Proteins

• Proteins have many different functions, depending on their structure and shape.

• Diverse functions:– Defense– Storage– Transport – Cellular communication– Movement– Structural support

Specific proteins

You need to know the specific functions of the following proteins:

– RubBisCo– Insulin– Immunoglobulins– Rhodopsin– Collagen– Spider silk

Use the information in your IB guide, the worksheet and your own research to summarize the functions and structure of each protein.

Proteome

A proteome is all of the proteins produced by a cell, a tissue or an organism. These proteins are coded for by genes in DNA.

Do you think all organisms in the same species, for example humans, have the same proteome? Explain your answer.

Denaturation

Denaturation of proteins can be caused by heat or a change in pH level.

Summarize the process of denaturation, giving examples.