What is the substrate of salivary amylase?

Appeared in: MNS 2015

Explanation

Salivary amylase, also known as ptyalin, is an enzyme in saliva that initiates the chemical digestion of carbohydrates in the mouth.
Its specific substrate is starch, which is a complex polysaccharide found in many foods like grains and potatoes.
The enzyme works by hydrolyzing the alpha-1,4 glycosidic bonds within the starch molecule.
This action breaks down the large starch polymer into smaller, simpler sugars, primarily the disaccharide maltose and various dextrins.

Option B: Proteins are macromolecules that are digested by a different class of enzymes called proteases, not amylases.
Option C: Glucose is a monosaccharide, which is the simplest form of sugar and an end-product of carbohydrate digestion. It is directly absorbed by the body and does not require further breakdown.
Option D: Maltose is a disaccharide that is a primary product of the breakdown of starch by salivary amylase. It is not the initial substance the enzyme acts upon.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Enzymatic digestion of carbohydrates as background academic context rather than a clinical decision trigger.
Understanding this initial digestive step emphasizes the importance of advising patients to chew their food thoroughly. Mastication increases the surface area of food and mixes it with saliva, allowing salivary amylase to work effectively.
The function of salivary amylase is pH-dependent and it is inactivated by the highly acidic environment of the stomach. This highlights why carbohydrate digestion pauses in the stomach and resumes in the small intestine.
What if? If a patient has a condition that causes severe dry mouth (xerostomia), such as Sjögren's syndrome or post-radiation therapy, the lack of saliva means a lack of salivary amylase. This can impair the initial phase of carbohydrate digestion and contribute to difficulty swallowing and poor oral hygiene.

How to Approach the Question

First, identify the key terms in the question: 'substrate' and 'salivary amylase'.
Recall the definition of a substrate: the specific substance upon which an enzyme acts.
Access your knowledge of the digestive system. Remember that chemical digestion begins in the mouth.
Identify salivary amylase as the primary digestive enzyme in saliva and recall its function is to break down carbohydrates.
Differentiate between the initial complex carbohydrate (starch) that needs digestion and the simpler sugars (maltose, glucose) that are the products of this digestion. Starch is the starting material, making it the substrate.

Concept Tested & Keywords

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E6 Physiology Ganong 27e Vol 2 Part 1 p. 24-26

E6 Nutrition Monika Sharma 3e p. 68-70

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 7-9

Practise the full MNS 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.