Question

Gastric juice normally has a pH of 2. Given this, what happens to the activity of salivary amylase, a starch-digesting enzyme in saliva, when it arrives in the stomach?

Short answer

Salivary amylase, the enzyme in saliva that digests starch, functions most effectively in neutral or slightly alkaline conditions. However, the gastric juice in the stomach is highly acidic, with a pH of 2. When the salivary amylase enters the acidic environment of the stomach, its structure gets modified due to denaturation and it loses its activity. Therefore, the starch-digesting activity of salivary amylase will decrease or stop. So, the drastic change in pH from the mouth to the stomach negatively impacts the functionality of salivary amylase.

Step-by-step solution

Understanding salivary amylase and acidity of the stomach

The first step is to understand that salivary amylase, an enzyme found in saliva, aids in the digestion of starch. This enzyme works best in neutral or slightly alkaline conditions, which is the normal pH in the mouth. On the other hand, the gastric juice in the stomach is acidic in nature with a pH of 2.

Effect of acidity on enzyme activity

The next step is to understand what happens when the pH changes. Enzymes have an optimal pH range within which they function effectively. When conditions are too acidic or basic, the enzymes can get denatured, implying that their structure is modified and they lose their activity.

Apply the concept to salivary amylase

Given that the optimal working conditions for salivary amylase are neutral or slightly alkaline, it will not function effectively in the stomach. This is because the stomach's gastric juice has a pH of 2, which is highly acidic. Thus, upon reaching the stomach, the salivary amylase will get denatured due to the acidic environment. It means that the starch-digesting activity of salivary amylase will decrease or stop. Hence, the change in pH from the neutral or slightly alkaline conditions in the mouth to the highly acidic environment in the stomach affects the functionality of salivary amylase, causing its starch-digesting activity to decline or cease.

Key concepts

Enzyme pH Sensitivity

Enzymes are like specialized molecular machines; they are crucial for speeding up chemical reactions in our bodies, such as digesting food. But these remarkable proteins have a set of conditions under which they work best, akin to a preferred working environment.

pH, a measure of how acidic or basic a solution is, is one of these conditions. Enzyme pH sensitivity refers to how enzyme activity changes when pH levels fluctuate. Each enzyme has an optimal pH range, and when conditions fall outside this range, the enzyme's efficiency can drop significantly.

Why pH Matters for Enzymes

The structure of an enzyme is maintained by delicate interactions between its amino acids. Changes in pH can disrupt these interactions, as can potentially unfold the enzyme's structure. If the structure is altered, the active site of the enzyme - where the magic happens - can't hold the substrate properly, and thus, enzyme activity diminishes.

Digestive Enzymes

Our digestive system is like a well-coordinated assembly line, with various enzymes each specializing in breaking down different types of nutrients. Digestive enzymes specifically break down foods into nutrients that can be absorbed and utilized by our bodies.

Types of Digestive Enzymes

There are several types of digestive enzymes, each targeting specific substances:

• Amylases break down starches into simple sugars.
• Proteases break down proteins into amino acids.
• Lipases break down fats into fatty acids and glycerol.

These enzymes are secreted in different parts of the digestive system, including your saliva, stomach, and small intestine, each working best within the pH range appropriate for their location.

Protein Denaturation

Proteins are like origami figures; they need a specific shape to perform their jobs correctly. Protein denaturation is the process where these elaborate folding patterns are disturbed, leading to loss of function.

Causes of Denaturation

Proteins can become denatured due to various factors, including extreme pH levels, high temperatures, or exposure to harsh chemicals. Think of denaturation like unfolding a paper crane - once it's unfolded and flattened, you can't use it as a crane anymore. Similarly, when an enzyme denatures, it can't perform its catalytic functions, which may have significant implications for biological processes, such as digestion.

Gastric Juice Acidity

The stomach is a vat of highly acidic liquid known as gastric juice. This mixture, primarily composed of hydrochloric acid, creates the necessity for a low pH in the stomach, usually around pH 2.

Role in Digestion

The acidic environment serves several purposes: it aids in the breakdown of food; it activates specific enzymes, like pepsin which digests proteins; and it serves as a barrier to pathogens that enter the body through what we eat. However, this same acidity can deactivate enzymes, like salivary amylase, that are not designed to function in such harsh conditions.