Proteins

Proteins!

This is the most abundant biological macromolecules.

>40% found in skeletal muscle

>25% found in organs

Remaining found mostly in the skin and blood.

Proteins are essential nutritionally because of their constituent AAs. The body needs AA to synthesize a variety of proteins and nitrogen-containing molecules.

Amino acid classification: net electrical charge

AAs in an aq solution are ionized

Essentiality

AAs that the body cannot make and must be supplied by the diet, and also AAs that the body can make.

Conditionally or acquired indispensable are AAs with rate limitations to synthesis, e.g., if a precursor isn’t available or improper organ function. Cirrhosis, impaired liver function = transformation of phe and met into tyr and cys. Thus phe and met would become indispensable until normal organ function is established.

Primary structure proteins

AAs covalently linked by peptide bonds formed by removal of water (polypeptide chain).

Synthesized on ribosomes, and energy is required to form the peptide linkage.

Secondary structure

The conformation of the peptide chain/backbone: the conformation of a protein can vary in different areas of the peptide chain.

alpha

⍺-helix

This is the structure wound around an imaginary axis in the middle. It is stabilized by intrachain hydrogen bonding between the carbonyl O₂ atom

β-pleated sheet

Sheetlike arrangement in which two or more extended polypeptide chains (or separate regions on the same chain) are aligned side by side. the aligned segments are connected by interchain hydrogen bonding.

Tertiary structure

• Fibrous