PROTEINS Unlike Carbohydrates and Fats, which are primarily used as an energy source; Proteins are primarily used to structurally build and repair the body of an organism or to form enzymes which facilitate chemical reactions to occur.

Fig. 2.1 C.H.N.O.P.S. With Carbs and Fats, the primary elements were C.H.and O. With Proteins we will not only see C.H.O. but we will also see Nitrogen.

Just like Carbs and Fats, Protein macromolecules can be built by stringing together smaller monomer molecules together through “Dehydration Synthesis” Reactions. In this case the monomer molecules are called “AMINO ACIDS” fats glycerol and F.A’s Table Sugar

Fig. 2b The body prefers to burn Fatty Acids and Monosaccharides (like Glucose) for energy. But the body may also transform Amino Acids to a useable form of energy. But AA’s are usually used to rebuild structural proteins such as Hemoglobin, Keratin, Blood Clotting Proteins and Enzymes etc.

AMINO ACIDS are the basic building blocks of PROTEINS All amino acids live up to their name, they will have an “amino group” coming off of their central carbon and an “acid group” coming off the other side of the central carbon. Carboxylic Acid Group You need to be able to draw this structure so practice it.

Fig. 2.25 There are over 20 different amino acids used by the body, the only thing that differs between one and another is what comes down off the central carbon

To start building a protein, your body will take the amino acids that have formed from the digestion of the proteins you ate, and your cells will run reactions to link them back together in a specific order to build a specific protein that you need. Just like building Fats and Complex carbs, a dehydration synthesis (condensation synthesis) reaction is used to link the two monomers. During this process, an “H” is taken from one monomer and an “OH” from the other, these then combine to form a Water molecule (H2O)

Amino group of second amino acid Tap. 38 Where one Amino Acid joins to another a unique covalent bond forms called a PEPTIDE bond. Around this peptide bond there are polar regions. Even though the bond is totally neutral, there are regions of positive and negative that all balance out. Amino group of second amino acid Carboxylic acid group of the first amino acid

Protein – Levels of Structure When the body starts linking amino acids together, the amino acid chain takes on different levels of structure. The most important level for determining that a protein has its proper shape so that it can perform its proper function is the specific order that the AA’s are linked together. This is known as the “PRIMARY STRUCTURE” of the protein. It is crucial that each amino acid end up in the specific spot that it needs to be in. If not, the protein will not take its proper shape and will not properly function. Sometimes even if a single amino acid is in the wrong spot, the protein will not function.

Very weak Hydrogen bonds are used to hold the Alpha Helix together. Secondary Structure Very weak Hydrogen bonds are used to hold the Alpha Helix together. As a long polypeptide chain is built by adding on more and more amino acids, the polar regions around each peptide bond start to cling to other peptide bond regions further down the chain. This attraction causes the polypeptide to take on an “alpha helix” spiral shape. This is called the “SECONDARY STRUCTURE” of this specific protein.

Tertiary Structure This R-group bonding may be via a covalent bond, ionic or a hydrogen bond. Depending on which two R-groups are forming the bond Recall that the only difference between one AA and another is the R-group coming off of the central carbon. These R-groups have their own unique molecular structures. Some of these R-groups are attracted to other R-groups found further down the polypeptide chain. As they are drawn to each other to form a bond, the polypeptide folds over on itself to take a three-dimensional globular shape, this folding over creates the “Tertiary Structure”

Quaternary Structure To reach the fourth level of structure, some proteins will combine one Polypeptide chain that has reached its 3-dimensional tertiary structure with at least one more polypeptide that has also reached its 3-dimensional tertiary structure.

Here all four levels of structure are illustrated Fig. 2.27 Here all four levels of structure are illustrated

Fig. 2.27a

Fig. 2.27b The other type of secondary structure known as a “pleated sheet” (on the right) is not a learning outcome for the course. Both secondary structures are held together by weak H-Bonding

Fig. 2.27c

Protein Denaturation Whether it be very weak H-bonding, or stronger Covalent or Ionic Bonding that contributes to the protein taking its final proper 3-D shape. These bonds, especially the H-Bonding may be broken by adding heat or changing the pH of the environment. When this happens, the protein loses its proper shape and no longer is able to perform its function, this is known as DENATURATION of the protein.