During human digestion, what specifically happens to dietary proteins as they move through the digestive tract?

Introduction / Context:
Proteins in our diet come from foods like meat, eggs, pulses and dairy products. These proteins are large molecules made of long chains of amino acids. For the body to use these amino acids for growth, repair and other functions, the digestive system must first break the proteins down into smaller units. This question asks what specifically happens to proteins during digestion and which substances are responsible for that process.

Given Data / Assumptions:

• The focus is on dietary proteins and their fate during digestion.
• Key terms include hormones, enzymes, simple sugars, complex starches and amino acids.
• We assume basic knowledge that proteins are different from carbohydrates and have different building blocks.

Concept / Approach:
Proteins are polymers composed of amino acid monomers linked by peptide bonds. In the digestive system, specialised enzymes called proteases and peptidases break these peptide bonds. Digestion of protein begins in the stomach with the enzyme pepsin and continues in the small intestine with enzymes like trypsin, chymotrypsin and various peptidases. The end products are mainly amino acids and small peptides that can be absorbed through the intestinal lining. Hormones play regulatory roles, such as stimulating the release of digestive juices, but they do not directly break proteins into sugars or starches.

Step-by-Step Solution:
Step 1: Recall that proteins are made of amino acids, not sugars, so the end products of protein digestion should be amino acids. Step 2: Recognise that digestive enzymes, not hormones, are the molecules that directly break chemical bonds in food macromolecules. Step 3: Identify the main enzymes involved in protein digestion, such as pepsin in the stomach and trypsin and other proteases in the small intestine. Step 4: Understand that these enzymes progressively break long protein chains into smaller peptides and eventually into individual amino acids. Step 5: Compare this process with the options and select the one that correctly states that specific digestive enzymes break down proteins into amino acids.

Verification / Alternative check:
Nutrition and biology textbooks usually have a table of digestive enzymes and their substrates. Under proteins, they list proteases and peptidases with final products described as amino acids and small peptides. Carbohydrate digestion is shown separately, ending in simple sugars like glucose, fructose and galactose. No reference book states that proteins are converted into sugars or starches during normal digestion. This clear separation between protein and carbohydrate digestion supports the correct option that emphasises enzymatic breakdown into amino acids.

Why Other Options Are Wrong:
Options A and B incorrectly say that hormones or enzymes break proteins into simple sugars, which are carbohydrate units, not protein units. Option C suggests that proteins are converted into complex starches, which again belong to the carbohydrate category and is not how digestion works. Option E claims that proteins pass through unchanged and are absorbed whole, which is generally false because whole proteins are too large to cross the intestinal wall under normal conditions.

Common Pitfalls:
Because digestion of carbohydrates and proteins is taught at the same time, students sometimes mix up the end products, thinking that all nutrients break down into sugars. Another confusion is the role of hormones versus enzymes. Hormones like gastrin and secretin regulate secretion and movement, while enzymes actually cut chemical bonds. To avoid these mistakes, always remember that carbohydrates end as simple sugars, proteins end as amino acids and lipids end as fatty acids and glycerol. Matching each nutrient to its specific enzymes and end products will make exam questions much easier.

Final Answer:
During digestion, Specific digestive enzymes break down proteins into their basic building blocks, amino acids.