Protein Structure and Functions

Protein Structure:

It is a three-dimensional structure. Polypeptides are folded to produce a globular shape. The structure is stabilized by intermolecular bonds between amino acids.

Primary Structure:

Is the sequence of amino acids in the polypeptide chain. It is codified by a gene. The sequence of nucleotides in a gene codify the sequence of amino acids in a polypeptide chain.

Secondary Structure:

3-dimensional conformation. It's the formation of beta-pleated and alpha helices, established by hydrogen bonds. It's the bond formed between the carboxyl group and the amino group.

Tertiary Structure:

The polypeptide chain is folded and established by interactions between R groups. The conformation is established by intramolecular bonds and interactions that form between amino acids and polypeptide, especially between their R groups. It also has in their surrounding water medium. Types of interactions:

• Ionic bonds between R groups
• Hydrogen bonds between R groups
• Van der Waals (attraction between hydrophilic parts of the protein, outwards attraction of the hydrophilic portion of the protein)
• Di-sulfide bridges adjacent to the amino acids

Quaternary Structure:

When a protein is formed by more than one polypeptide chain. It exists when a polypeptide chain links together between each other and also with nonprotein parts. Ex: hemoglobin is formed by 4 polypeptide chains linked to a heme group which is the non-protein portion called the prosthetic group.

Functions:

Catalysis - enzymes catalyze specific chemical reactions within the cell or outside it.
Muscle contraction – used in contraction of muscle in location and transport around the body.
Cytoskeletons – Tubulin is the subunit of microtubules that give animals their cells shape and pull chromosomes during mitosis.
Blood clotting – plasma proteins – they act as a clotting factor that causes blood to turn from a liquid to a gel in wounds.
Transport of nutrients and gases – they move molecules from one place to another around the body, they transport oxygen, CO2, iron, and lipids.
Cell adhesion - membrane proteins - molecules help cells stick to each other and to their surroundings.

Enzyme Inhibitors:

The substrate binds to the enzymes reduce the activity of the enzyme. There are two main types, competitive and non-competitive. The result of this is the change of shape in the enzyme so that it cannot bind to the substrate.Competitive are the ones that interfere with the active site so the substrate cannot bind, it has a similar structure to the substrate, it is reversible, the substrate concentration increases, it outcompetes with the inhibitor and occupies the vacant sites.Non-competitive binds to another location than the active site (allosteric site), when it combines to the allosteric site it changes and the substrate cannot bind to it.

Lactose Intolerance:

Lactose is the sugar in milk. Lactose is digested into glucose and galactose (monosaccharides) by the enzyme lactase. Advantages: As a source of dairy for lactose-intolerant individuals. Galactose and glucose are sweeter than lactose, so less sugar is needed. Lactose tends to crystallize during production of ice cream, because glucose and galactose are more soluble, they remain dissolved giving a smoother texture.