Lesson #4: Structure and Function: Enzymes & the Stomach

Question 1

Enzymes

Answer 1

An enzyme is a biological catalyst that speeds up chemical reactions
without being consumed or altered.

An enzyme will lower the activation energy (the energy needed for a
reaction to occur). This makes it easier for a chemical reaction to take
place.

Enzymes are protein molecules

There are thousands of different enzymes in the body

Usually end in the suffix “ – ase”

Question 2

Enzyme Function

Answer 2

The Active Site

The active site is the region of the enzyme where the reactants
(substances that are going to react) bind and where the chemical
reaction takes place.

Substrate

A reactant that binds to the active site of an enzyme is called a
substrate.

There may be more than one substrate attached to the active site of an
enzyme depending on the type of reaction that will take place.The binding of the substrate to the active site forms the
Enzyme – Substrate Complex.

When the chemical change is complete, the products are
released from the active site and the enzyme remains
unchanged.Inhibitor

Enzyme activity must be controlled (homeostasis)

When enzyme activity is not needed an Inhibitor Molecule will bind to the
enzyme’s active site

This blocks the substrate molecules from being able to bind with the
enzyme thus preventing the chemical reaction from occurring.

Question 3

The Stomach

Answer 3

Once the bolus has been swallowed it moves down the esophagus into the
stomach.

The stomach is a J-shaped organ of the abdominal cavity where digestion
occurs.

Divided into 3 regions:

The Fundus – closest to the esophagus

The Body – the largest part, responsible for the formation of Chyme

The Pylorus – closest to the duodenum

The bolus spends 2-3 hours in the stomach

Question 4

Structure & Function

Answer 4

Entry into the stomach is
controlled by a ring of muscle
called the Cardiac Sphincter

This makes sure that food
enters the stomach slowly

This also prevents backflow
of food into the esophagus.

Question 5

The Body

Answer 5

The stomach is lined with a mucous membrane called the Mucosa.
This membrane is composed of gastric glands that contain the
following cells:

Parietal Cells – produce hydrochloric acid (HCl) that is
used to chemically breakdown proteins.

Epithelial Cells – produce mucous that protects the
stomach lining from the effects of HCl

Chief Cells – produce the enzyme pepsinogen.
When pepsinogen comes into contact with HCl it becomes active
and is called Pepsin.

Pepsin speeds up the process of protein digestion.The stomach lining also secretes the enzyme Rennin

Rennin slows the movement of milk and separates it into whey (protein)
and curds (carbohydrates) so that it can be digested and absorbed.

The combination of Pepsin, Rennin and HCl in the stomach is referred to as
“Gastric Juice”.The stomach is surrounded by a series of muscle layers that cause the
stomach cavity to expand and contract.

The mucosa contains ridges known as Rugae.

As the stomach “churns”, food is mixed up and dragged over these ridges
until it becomes liquid (mechanical digestion).

This liquid is called Chyme.When the stomach is empty only small amounts of gastric juice are present
but when food is eaten more is needed in order to digest it.

Three (3) mechanisms work to stimulate the flow of gastric juice:

1. The thought, sight, smell or taste of food.
2. Food touching the lining of the stomach.
3. The stretching of the stomach lining causes the stomach to secrete the
   hormone gastrin, which stimulates the gastric glands to produce gastric juice.

Question 6

The Fundus and
Pylorus

Answer 6

The Fundus is the top ¼ of the
stomach that holds gases
released during digestion

The pylorus is the exit point of
the stomach.

The Pyloric Sphincter controls
the flow of chyme from the
stomach to the duodenum of
the small intestine.