Common protein sources

Conditionally Essential Amino Acids (CEAAs): These are usually non-essential but become essential under specific circumstances, such as illness, stress, or periods of rapid growth, when the body's demand exceeds its ability to synthesize them (e.g., Arginine, Glutamine).5

2. Protein Digestion, Absorption, and Transportation

Protein must be broken down into individual amino acids or short peptide chains before the body can use it.6

Outline of the Process

Mouth: Mechanical breakdown (chewing) occurs, but no chemical protein digestion takes place here.

Stomach:

Denaturation: Hydrochloric acid (7$\text{HCl}$) uncoils the protein strands, making them accessible to enzymes.8

Enzymatic Digestion: 9$\text{HCl}$ activates the proenzyme pepsinogen into pepsin, which begins cleaving the long polypeptide chains into smaller polypeptides.10

Small Intestine: This is where the majority of digestion and absorption occurs.

Pancreatic Enzymes: The pancreas releases powerful enzymes (e.g., trypsin, chymotrypsin) that further break down polypeptides into tripeptides, dipeptides, and single amino acids.11

Sample Answer

Protein in the Diet: Sources, Digestion, and Function

This discussion covers common protein sources, the types of amino acids, the process of protein metabolism, its roles in health, recommended intakes (RDAs), and various vegetarian diets.

1. Protein Sources and Amino Acids

Protein is an indispensable macronutrient composed of amino acids (AAs), which are linked together in chains.1 Our diets incorporate protein from diverse sources.2

Common Protein Sources

Types of Amino Acids

Amino acids are categorized based on whether the body can produce them:

Essential Amino Acids (EAAs): There are nine essential amino acids (e.g., Leucine, Lysine).3 They cannot be synthesized by the body and must be obtained through the diet.4

Non-essential Amino Acids (NEAAs): These can be synthesized by the body from other amino acids or nitrogen-containing compounds.