2.4 Proteins

2.4 Poteins

Functions

Examples of proteins

- Muscle development/contraction.

- Crucial for the inmune system. Proteins create antibodies.

- They work as catalysts, speeding up reactions, thus helping survival.

- Cytoskeleton, maintaining cell shape.

- Strengthens tissues, they become more resistant.

- When bruised, proteins helps in blood clotting.

- They create our body (structure) by cell adhesion.

- Proteins are hormones, like insulin.

- Proteins work as receptors.

- Proteins pack DNA.

Rubisco (Ribulose bisphosphate carboxylase): an enzyme working in photosynthesis. It ia able to catalyse the reaction that fixes CO2 from the atmosphere. It provides a source of carbon from which living organisms produce carbon compounds.

Insulin: A hormone with is able to absorb glucose, hence reducing glucose concentration of the blood.

Immunoglobulin (antibodies): Its arms bind to antigens, bacteria or pathogens, causing a response engulfing the pathogen.

Rhodopsin: A membrane protein of the retina. Its is one of the pigments from which vision depends on.

Collagen: rope-like protein which enables skin and blood vessel walls to resist tearing. It provides strength.

Amino acid

Monomer: Amino acid

Dimer: Dipeptide

Polymer: Polypeptide

An amino acid molecule is composed by three main sections. center section includes the "center" C. Below, an H, and above an R (radical). This radical is replaced by other (CHON) element which make up different amino acids. The left section or amino group is made of N and two H. Finally, the right section or carboxyl group is made of one C, two O and one H (C, O, OH).

There are 20 types of amino acids. Their endless combinations (which form long chains (polypeptides) which make un proteins) provide a variety of different functions. This sequences are determined by genes.

The amino acid chains had different chemical properties. Some amino acids are hydrophilic/hydrophobic and polar/non-polar. This characteristics will determine how the chain folds.

Protein Structure

Amino acids are joined by condensation (anabolism) to create a dipeptide. Therefore, the result of joining two amino acids will be a molecule of water.

The carboxyl group of one molecule will join with the amino group of another molecule. As by condensation, the OH is taken from the carboxyl group and joined by one H of the amino group (of the other molecule) will create a molecule of water and both amino acids will joining creating a dipeptide.

Primary Structure: It is a simple amino acid sequence (chain-like). The amino acids are joined by condensation, forming peptide bonds. A primary structure can form a large bond. This primary structure takes into account the amino acid sequence but not its folds.

Denaturation

Secondary Structure: Amino acids will fold in two types of three dimensional structures (stable structures).

Structure 1. Alpha Helices: they occur when the amino acid sequence fold into a 3d spiral.

Structure 2. Beta Pleated Sheet: they occur when the amino acid sequence adopts a sheet wavy-like structure.

Both structures result from hydrogen bonds.

Tertiary Structure: They are three dimensional arrangements.Tertiary structures take into account both helix and pleated sheer structures, but acknowledging charges (polar/non-polar, hydrophilic/hydrophobic). Hydrophilic amino acids will maintain on the exterior of the folded chain, while hydrophilic will be in the interior.

Quaternary Structure: Two or more polypeptides in their tertiary states.

Denaturation is a structural change in a protein which usually results in the permanent loss of its biological properties.

It involves the breaking of weak bonds. Amino acids have a large amount of weak bonds due to positive and negative charges. Molecules in amino acids are temporarily attracted, therefore they easily break apart.

Denaturation is caused by exposition to temperatures and pH.

Protein conformations: Main tertiary structures. This structures define the function of the protein.

Fibrous proteins are composted of long and narrow straps, similar to a hair braid. Their function is mainly structural, they provide strenght and support. They are mostly insoluble. They are arranges by repetitive amino acid sequence. They are less sensitive to changes in heat and pH (which cause denaturation). Some examples are collagen and keratin.

Globular proteins have a more compact and rounded not organized shape. Their role is functional, they catalyse and transport. They are mostly soluble. They have an irregular amino acid sequence. They are more sensitive to changes in heat and pH. Insulin is a perfect example.