Chemical Digestion and Enzymes
Introduction
Chemical digestion
o Aids in preparing food particles for absorption.
o Takes place through the action of
.
o Large food molecules are chemically changed into smaller molecules
The types of nutrients that are digested through mechanical and chemical action are
.
Carbohydrates
o Made up of carbon, hydrogen, and oxygen
o Quick sources of energy and include both simple molecules (
and complex molecules (
)
o Common food sources are breads, pasta, and fruit
)
Proteins
o Large complex molecules that contain ______________________________
__________________________________________________________.
o Serve as the structural framework of most living tissue and also serve as
enzymes, but are not usually used as an energy source.
o Made up of smaller molecules called
.
o Common food sources include meat, eggs, and nuts.
Lipids
o Make up fats, oils, and waxes.
o Contain carbon, hydrogen and oxygen.
o Capable of storing great amounts of energy in their chemical bonds.
o Common food sources include margarine, cooking oil, and animal fat found in
meat.
- biological catalyst that can speed up chemical reactions
without being altered in the process.
Grade 11 Biology
Unit 2: Digestion and Nutrition
Digestive Enzymes
Enzymes are very specific; they only act on certain molecules called a ___________.
Each type of enzyme is very specific in terms of which substrate it will act on. The
names for enzymes start with the name of the substrate involved and end in
"__________". For example, an enzyme that acts on a protein molecule is a
. An enzyme that acts on a carbohydrate molecule is a
. And an enzyme that acts on a lipid molecule is a _______.
An analogy that is often used to understand enzyme action is the
“____________________“ concept in which the substrate acts as the __________
and the enzyme is the _____________.
2
Grade 11 Biology
Unit 2: Digestion and Nutrition
Chemical Digestion in the Human Digestive Tract
Type of
Enzyme
Location
Secretion
Action
Mouth
Saliva
Begins digestion of starch to
simple sugars.
Stomach
Gastric Juice
Begins digestion of proteins.
Completes digestion of starch to
simple sugars.
Pancreatic
Juice
Continues digestion of proteins.
Completes digestion of lipids to
fatty acids and glycerol with the
help of bile.
Small
Intestine
Completes digestion of proteins
to amino acids.
Intestinal
Juice
Completes digestion of
carbohydrates to simple sugars.
In addition to carbohydrates, proteins, and lipids, nucleic acids are also nutrient
molecules that are broken down in the digestive system. When nucleic acids are
broken down chemically, the results are nucleotides, which contain nitrogen,
phosphorus, and sugars.
Once nutrient molecules are broken down chemically and mechanically, they are
absorbed into the circulatory system. Most absorption occurs in the small intestine
except vitamins, minerals, and water are absorbed in the large intestine.
3
Grade 11 Biology
Unit 2: Digestion and Nutrition
Factors that Affect Enzyme Action
1. ____________
o The pH of a solution refers to how acidic or basic it is.
o An enzyme that is structurally changed as a result of pH is said to be
___________________; which leads to a loss of enzymatic activity.
o The _________________ in the stomach, _____________, is activated by
this acidic environment and becomes deactivated when it enters the basic
environment of the small intestine
o Less acidic environment of the small intestine allows the enzymes produced by
the small intestine and pancreas to be more effective in digestion.
2. ________________________
o When a food particle is mechanically broken down by chewing it into a number
of smaller particles, the total surface area of exposed particles _________.
o An increased surface area allows more enzymes to act on the food particles.
3. ________________________
o Small organic molecules that are not proteins that help to facilitate the
enzyme-substrate connection and are often produced from various vitamins
o They are located at the active site of the enzyme molecule and facilitate the
"lock and key" action of the enzyme and substrate molecules.
o They are not themselves affected by the action of the enzyme on the
substrate molecule.
4. ________________________
o Compete with substrate molecules for the active sites of the enzymes.
o Binds to the enzyme, rendering the enzyme ineffective on the substrate
molecule that it was designed to act on.
5. _________________________
o Most reactions in the human body that involve enzyme activity occur within a
fairly small temperature range — usually from about 30°C to 40°C .
o Temperatures outside of this range can cause denaturation of the enzyme.
Enzymes are very important in the human digestive system. Their production and
accumulation in the body are carefully controlled so that homeostasis is maintained.
4
Grade 11 Biology
Unit 2: Digestion and Nutrition
The Liver: Introduction
o Almost all the blood circulating from the
intestines to the heart passes through
the liver.
o Everything you eat that gets into the
bloodstream passes through your liver.
o The liver then either stores nutrients or
breaks them down even more.
o The liver transforms nutrients into
proteins, fats, and cholesterol and
stores vitamins (A, D, K, and B12),
minerals, and carbohydrates.
The liver also plays the role of a filtering system. Toxic substances, including alcohol,
are transformed into less harmful substances.
The Role of the Liver in Homeostasis
Glucose is necessary for cells to produce ATP. The amount of ATP that the body
needs at any one time changes; therefore, the body needs to be able to store glucose
when it is not needed, but release glucose when it is needed.
o Two hormones responsible for controlling the concentration of glucose in the
blood are ______________ and ____________, which are produced in the
_________________.
o The liver also plays an important role in blood glucose control. It is here that
excess glucose is stored in the form of __________________.
o When you eat a meal, blood glucose levels start to ________. When they reach a
certain concentration, receptors in the pancreas stimulate the production of
______________. This hormone reaches the liver, which then converts blood
glucose into glycogen. Blood glucose levels ________ and return to a _________.
o If blood glucose levels drop below a certain level, receptors in the pancreas
stimulate the production of ___________. This hormone reaches the liver, which
then converts glycogen into glucose. Glucose is released into the bloodstream and
blood glucose levels _________ until they return to a ____________________.
5
Grade 11 Biology
Unit 2: Digestion and Nutrition
Negative Feedback Mechanism
The maintenance of adequate blood glucose levels is an example of a negative
feedback mechanism.
6
Grade 11 Biology
Unit 2: Digestion and Nutrition
Digestion and Nutrition
Introduction
There are six basic types of nutrients (carbohydrates, lipids, proteins, vitamins,
minerals, and water) used by the human body. Some of the uses that your body makes
of nutrients are ___________________ and others are ____________________
in nature.
Carbohydrates
o Used by the cells of the body to produce _________________.
o The human body cannot produce its own carbohydrates and must rely on eating
other organisms to acquire them.
o Primary source of energy for humans, supplying 50 to 80% of the total energy
required.
o Provide short-term energy to cells through the process of cellular respiration.
There are 3 main types of carbohydrates
1. Monosaccharides
o ______________________________________
o Most common is glucose which provides energy for
cellular respiration and the production of ATP and
fructose which is found in fruit
2. Disaccharides
o _________________________________
o Made by joining together simple sugars with
chemical bonds.
o Most common are sucrose (white table sugar),
and lactose (dairy products)
Sucrose
7
Grade 11 Biology
Unit 2: Digestion and Nutrition
3. Polysaccharides
o Complex sugars made of many simple sugars joined by __________________.
o Several hundred glucose molecules join together to form ________________
which are the primary form of storage carbohydrate used by plants.
o ___________________, which is found in the cell wall of plants, is the fibre
we need in our diets; which our digestive system requires to function correctly.
Food Sources of Carbohydrates
Simple Carbohydrates
o Usually sweet-tasting like cookies, candy, pop, pastries, fruits, and juices.
o Good sources of carbohydrates, but do not always contain vitamins or minerals.
o Considered “__________________________”
Complex Carbohydrates
o Starchy carbohydrates take _______________ to be digested than simple
carbohydrates and therefore provide a more ________________________
source of energy for the body.
o Complex carbs, are found in breads, pasta, rice, and potatoes and most
vegetables like corn, tomatoes, carrots, and lettuce
Lipids (Fats)
o Are only used for _____________________ when the supply of carbohydrates
in the bloodstream is _____________
o Difficult to break down
o Stored source of ____________________ energy for the body
o About ______________ as energetic as one gram of carbohydrate
o Important in helping the body absorb vitamins effectively
o Key structural components of cell membranes, a form of insulation for the body
and serve as protection for delicate vital organs
o The raw material from which ____________________ are produced
o An important component in the transmission of nerve impulses in the nervous
system
8
Grade 11 Biology
Unit 2: Digestion and Nutrition
Cholesterol
o ____________________________ that occurs naturally in the body
o Produced by the ________________ and is transported by the blood to cells
o Found in all animal products
o Very important component of _________________________________.
o The body processes cholesterol in the diet in different ways, depending on
what type of food contained the cholesterol that was ingested.
There are two types of cholesterol in the blood:
1.
LDL ( ________” cholesterol)
o ______________________________________
o Can accumulate on artery walls and restrict blood flow.
o Liver maintains a "normal" level of cholesterol by removing excess LDL
from the blood
2. HDL ("__________” cholesterol)
o ______________________________________
o Lowers blood cholesterol by carrying LDLs back to the liver which can
break down the LDL molecule
o The level of HDL in the blood can be increased if you decrease the
amount of saturated fat in your diet and if you increase your physical
activity.
o HDL can reduce the risk of heart attack and stroke
9
Grade 11 Biology
Unit 2: Digestion and Nutrition
Comparison between Unsaturated and Saturated Fats
Unsaturated Fats
Saturated Fats
It is recommended that no more than 30% of your total energy intake should be in
the form of lipids, since lipid molecules store about twice as much chemical energy
as carbohydrate molecules.
10
Grade 11 Biology
Unit 2: Digestion and Nutrition
Proteins
o Primary __________________________ component of all cells
o Broken down by your digestive system into _____________________________
molecules which are then rebuilt into other proteins.
o Muscle, cartilage, ligaments, skin, and hair are all examples of protein molecules.
o Smaller protein molecules also play vital roles as hormones, antibodies, enzymes,
and hemoglobin.
o Vary in size and shape which allows for incredible diversity of functions
performed by proteins
Amino Acids
o 20 amino acids
o 9 of them cannot be made by the human body and are
referred to as the __________________________
_________________ because they must be eaten.
o All 20 "building blocks" allow the synthesis of all of
the many proteins that your body manufactures.
Example of the amino acid glycine:
Food Sources of Proteins
Complete Proteins
Incomplete Proteins
It is recommended that you consume 0.8 - 1.5 grams of protein per kilogram of body
weight. People who are on a vegetarian diet need to pay special attention to the foods
Vitamins
they eat to make sure that they acquire adequate amounts of all amino acids.
11
Grade 11 Biology
Unit 2: Digestion and Nutrition
o ____________________ substances (must
contain a carbon chain) that are needed in very
small amounts.
o Part of the structure of many ____________.
o If your diet is deficient in a certain vitamin, the
result could be an enzyme deficiency that can in
turn cause serious health problems.
o Are chemicals that are necessary for normal
growth and _________________________.
o Some vitamins are required for the chemical
reactions that result in the release of energy
from carbohydrates, fats, and proteins.
In all, there are 13 vitamins; that are divided into two groups:
i.
ii.
Fat-soluble vitamins (______________________________)
 are not as readily excreted from the body
 stored in the liver
Water-soluble vitamins (________________________________)
 can become depleted more quickly leading to a deficiency
 must be included regularly in your diet
12
Grade 11 Biology
Unit 2: Digestion and Nutrition
Minerals
Unlike vitamins, minerals are ______________________ — that is, they are not
based on a carbon chain. Most minerals are molecules of a single _______________.
Minerals do not provide ____________________ for the body, but they do play
very important roles in many cellular reactions. For example, minerals are vital in
maintaining nervous system functions, water balance, and skeletal health.
There are about 16 essential minerals.
o ______________ is found in table salt and helps maintain proper blood pressure.
o _____________________ is found in bananas and keeps nerves and muscles
working properly.
o ______________ is found in dairy products and is needed to build strong bones.
o ____________ is found in red meats and wholegrain vegetables; it is very
important in the production of red blood cells.
Water
o Water is an essential component of ____________________ — the intracellular
fluid that makes up all ____________.
o Water is an important _________________ because most chemical reactions in
the body occur between molecules that are dissolved in it.
o Water is also an important lubricant and bathes body cells.
o Water is a ________________ component of blood and _______________ vital
nutrients and unneeded wastes throughout the body.
o Water also serves an important role in ________________________________.
Water is acquired in many ways. Drinking water is the most obvious way that you
obtain water. However, many foods have a high water content, such as fruit and
vegetables. Also, many cellular processes involve the production of water. For these
reasons, it is suggested that you drink about 8 cups of water or other noncaffeinated fluids per day to maintain adequate hydration.
13
Grade 11 Biology
Unit 2: Digestion and Nutrition
Dietary Decisions
Labels on packaged foods are helpful in that they tell you what vitamins, minerals, and
nutrients are contained in the foods that you buy. An informative label might look like
this:
All the
information in
Nutrition Facts
is based on a
specific amount
of food.
The % Daily Value
(%DV) gives a
context to the actual
amount of a nutrient.
It indicates at a
glance how much of a
nutrient is in the
specific amount of
food.
The facts table
lists calories
and some core
nutrients.
This number is the
actual amount
(quantity) of the
nutrient in the specific
amount of food. Even if
the nutrient amount is
zero, it is listed.
Dieticians of Canada have identified a list of "Guidelines for Healthy Eating":
1. Enjoy a variety of foods.
2. Emphasize whole grain cereals, breads, other whole grain products, vegetables,
and fruit.
3. Choose lower-fat dairy products, leaner meats, and foods prepared with little
or no fat.
4. Achieve and maintain a healthy body weight by enjoying regular physical
activity and healthy eating.
5. Limit salt, alcohol, and caffeine.
They stress that there are no "good" or "bad" foods. Consumers do not have to give
up foods that they like but instead try to achieve variety and moderation in their
diet.
14