Reflection VII: AMINO ACIDS & PROTEINS P2!!!

Amino Acids form undergo a condensation reaction to form a dipeptide.

Formation of Peptide Bond

This dipeptide can remain or link with more amino acids to form a polypeptide.

Polypeptide Chain

-The unique sequence of amino acids in the  polypeptide chain give rise to unique proteins that code for many things such as hair, skin, nails and enzymes.

Structure-Function Relationship

-Polypeptides must be folded to be functional proteins.

-Protein structure dictates protein function.

-Proteins have four levels of structure.

• Primary Structure
• Secondary Structure
• Tertiary Structure
• Quaternary Structure

Primary Structure.

-This the sequence of amino acid units, and comprises the protein’s overall biomolecular structure.

Primary Protein Structure

Secondary Structure 

This is the specific geometric shape caused by intramolecular and intermolecular hydrogen bonding of amide groups. Consists of two types alpha helix and beta pleated sheet.

Secondary Structure of Proteins

Tertiary Structure

This is the final specific geometric shape that a protein assumes. This is determined by a variety of bonding interactions between the “side chains” on the amino acids. These bonding interactions may be stronger than the hydrogen bonds between amide groups holding the helical structure. As a result, bonding interactions between “side chains” may cause a number of folds, bends, and loops in the protein chain. Different fragments of the same chain may become bonded together.

There are four types of bonding interactions:

1. Disulfide bonds are formed by oxidation of the sulfhydryl groups on cysteine. Different protein chains or loops within a single chain are held together by the strong covalent disulfide bonds.
2. Hydrogen bonding between “side chains” occurs in a variety of circumstances. The most usual cases are between two alcohols, an alcohol and an acid, two acids, or an alcohol and an amine or amide.
3. Salt bridges/ Ionic bonds result from the neutralization of an acid and amine on side chains. The final interaction is ionic between the positive ammonium group and the negative acid group. Any combination of the various acidic or amine amino acid side chains will have this effect.

4.  Non-Polar Hydrophobic Interactions: are believed to contribute significantly to the stabilizing of the tertiary structures in proteins. This interaction is really just an application of the solubility rule that “likes dissolve likes”. The non-polar groups mutually repel water and other polar groups and results in a net attraction of the non-polar groups for each other.

The four types of bonding that takes place within a protein’s tertiary structure that give it it’s geometrical shape.

Quaternary Structure

This involves the clustering of several individual peptide or protein chains into a final specific shape. A variety of bonding interactions including hydrogen bonding, salt bridges, and disulfide bonds hold the various chains into a particular geometry.

Quaternary Structure of Haemoglobin

There are two major categories of proteins with Quaternary structure:.

1. Fibrous Proteins: the result of the interaction of many individual protein chains. Some are composed of hydrogen bonding on amide groups on different chains is the basis of beta-pleated sheet as seen in silk proteins.While other fibrous proteins such as keratins  are composed of coiled alpha helical protein chains with other various coils analogous to those found in a rope.  Fibrous proteins are insoluble, and play a structural or supportive role in the body, and are also involved in movement (as in muscle and ciliary proteins).
2. Globular Proteins:  globular proteins fold back on themselves to produce compact, nearly spherical shapes. Most globular proteins are water soluble and hence are relatively mobile within a cell. Some examples are enzymes, antibodies, hormones, toxins, and substances such as hemoglobin.

Fibrous and Globular Proteins

Well that’s all I can remember; time to re-watch the lectures 😛

Good luck my fellow Biochemians