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YOU ARE WHAT YOU EAT
Fact Sheet #1: Carbohydrates
Introduction
Carbohydrates are the main energy source for human bodies. Our bodies can use a variety of
carbohydrates immediately, or store the energy for later use. Found in table sugar, milk, fruit, bread
and pasta, the energy-rich carbohydrate macromolecule is a staple in every diet around the world. The
bodies or fruits of plants, where energy is stored as glucose, fructose, or starch are usually the source
of carbohydrates. Humans harvest and refine these plant crops into diverse products which all contain
sugar or starch. Complex carbohydrates, usually starches, are referred to as polysaccharides. (Poly =
many, Saccharide = sugar) In their simplest sugar form of one or two molecules, carbohydrates are
called monosaccharides and disaccharides. (Mono = one, Di = two.)
Digestion
Digestion of carbohydrates begins in the mouth. As the teeth and tongue mash the food, amylase,
an enzyme found in saliva, breaks down starch into simple sugars. Not all starch is broken down by
amylase; as the chewed and moistened food is swallowed, the amylase enzyme from saliva breaks
down in the acidic environment of the stomach. After the food leaves the stomach as a lump called
chyme, it enters the beginning of the small intestine. This region is named the duodenum. In the
duodenum, enzymes from the pancreas will mix with the chyme to continue the breakdown of
polysaccharides into simple sugars. This enzyme is called pancreatic amylase. The small intestine also
has enzymes in its lining that break down disaccharides into monosaccharides. The broken down
carbohydrates are now small enough to be absorbed through the wall of the small intestine into the
blood stream.
There are some types of carbohydrates for which our body does not make enzymes. This means
that these types of carbohydrates cannot be broken down in human bodies without the help of
bacteria. There are about 5 pounds of bacteria in the intestine. Many types of bacteria in the digestive
tract can digest small amounts of fiber. The by-product of bacteria digesting fiber in our diet is the
creation of gas in our lower digestive tracts. The majority of the fiber is not digested by bacteria, and
instead forms a major component of stool, which is essentially made of the parts of our diet that our
body cannot digest. Because our intestine is sensitive to fiber and expels it from the body, diets high in
fiber from whole grains, beans, and fruits can relieve constipation. A high fiber diet may also lower the
risk of developing heart disease and colon cancer.
Assimilation
As the monosaccharides from the small intestine flow into the blood stream, many of these
microscopic sugars are picked up by the liver. The liver is a large organ on the right side of your body,
near the bottom of your rib cage. It has many functions, one of which is to store monosaccharides
called glucose in large chains. The chains of glucose are polysaccharides called glycogen. Glycogen is
used to pack and store glucose molecules until the body needs more energy. Most of these glucose
molecules will only be stored as glycogen for 24 hours or less. When the glucose in the blood stream is
lower than normal, the liver will use enzymes to break apart the glycogen chains and release the
glucose molecules into the blood. The glucose then circulates through the body until it is absorbed into
a cell.
Insulin is a protein that allows glucose to enter a cell. Without proper amounts of insulin in the
body, glucose cannot enter cells. This is a serious health problem that results in diabetes. Basically, a
person with diabetes could have very high amounts of glucose in the blood, but the cells would receive
little to no energy without the help of insulin. As a result, water is pulled into the hypertonic
environment of the bloodstream, causing increased urination. Because cells are not receiving the
energy they require, symptoms of diabetes also include blurred vision, fatigue, extreme thirst and
hunger, and at worst, a person with diabetes can enter a coma.
Cellular Use
Cells break the bonds of glucose molecules to release energy that is used to make ATP. ATP is the
main type of energy a cell can use. This is the process of respiration. It can occur with or without
oxygen, although humans mainly use the type of respiration that occurs in the presence of oxygen. The
mitochondria are devoted to this process, and ultimately make 36-38 ATP from each molecule of
glucose.
The ATP produced by breaking down glucose is used for most jobs in the cell. Some jobs in the cell
make or use carbohydrates for specific functions. The smooth and rough endoplasmic reticulum
synthesize glycoprotein. This molecule is a protein with a carbohydrate tail. Glycolipids are also
manufactured in the cell, and are membrane lipids with short chains of glucose attached. Both
glycoprotein and glycolipids are added into the cell membrane, where the carbohydrate tail helps with
cell to cell interactions and cellular recognition. Ribose is a type of carbohydrate which is used to
assemble DNA and RNA in the nucleus of cells. These molecules are responsible for storing and relaying
genetic information. Carbohydrates are the main source of energy for our cells but can be found
playing other important roles, as well.
Issues
It is popular in some diet programs to severely limit someone’s carbohydrate intake. Diets that
are too low in carbohydrates can cause problems. If you do not eat enough carbohydrates your body is
forced to break down muscle (proteins) for energy. Low levels of carbohydrates actually cause your
appetite to increase. So, people who are on low carbohydrate diets suffer from increased hunger.
In America diabetes is the seventh leading cause of death. Diabetes is the major cause of heart
disease and stroke and the leading cause of kidney failure, nontraumatic lowerlimb amputations, and
new cases of blindness. Recently a study found that women who have diabetes are two times as likely
to have a child with autism. Diabetes is a disease where blood glucose levels are above normal. Insulin
is the hormone that your body uses to help get glucose out of the blood and delivered to your cells. If
you have diabetes you either do not make enough insulin or your cells cannot respond to insulin.
YOU ARE WHAT YOU EAT
Fact Sheet #2: Protein
Introduction
The protein macromolecule plays critical roles in cells and organisms. Proteins make up the
structural tissue for muscles and tendons, carry oxygen in the form of hemoglobin, catalyze all
biochemical reaction as enzymes, regulate reactions as hormones, form antibodies that fight infection,
supply nitrogen for DNA and RNA genetic material and can even supply energy. The building blocks of
proteins are 20 amino acids that can be joined or linked together to form long strands or polypeptides
that become the scaffold for 3 dimensional proteins. Out of the 20 amino acids, 8 of them cannot be
synthesized in the human body and are called the essential amino acids. The remaining amino acids
can be synthesized in the cell from other chemicals.
Digestion
When proteins are ingested in our diet, the proteins are broken down in the digestive system
through a series of chemical and physical reactions that break the large polymer into smaller and
smaller monomers, which eventually are absorbed into the bloodstream and are transported to the
liver and to all the cells. The chemical digestion of proteins begins in the stomach with the aid of
digestive acid and pepsin. The resulting smaller peptides enter the small intestine and are introduced
to pancreatic proteases where the peptide chains are further broken down into medium and smaller
peptides (oligopeptides). The border cells of the small intestine contain peptidases that break down
these small peptides into free amino acids that are now ready to be absorbed into the membrane cells
using active transport. From there, the free amino acids are absorbed into the bloodstream and are
transported into the liver via the hepatic portal system.
Assimilation
Inside the liver, amino acids can be used for a variety of functions. Some amino acids can be
converted into glucose if the organism is experiencing starvation. Other amino acids, like those
essential to the ATP-producing citric acid cycle, can be changed by transamination. Transamination is
the transfer of an amine group from one molecule to another, thus synthesizing one amino acid from
another. The transamination process takes place in the liver and can synthesize amino acids not
present in the diet. Amino acids not used by the liver to produce proteins in the liver are sent
elsewhere to be utilized by other cells.
Cellular Use
The human body is dependent on proteins and its cells are built to assemble amino acids and
synthesize necessary proteins. The nucleolus of eukaryotic cells assembles ribosomes. The ribosomes
utilize the free amino acids in the cytoplasm to translate the mRNA transcript (a short, single copy of
the DNA) creating proteins that serve many roles such as hormone receptors in the cell membrane,
structural components (cytoskeleton) in the cell, channel proteins in the membranes, hydrolytic
enzymes and a variety of enzymes that catalyze each and every reaction in the cell.
Issues
A deficiency of a certain amino acid or the mutation of an enzyme that regulates the synthesis or
degradation of specific amino acids can lead to a variety of disorders. The most common disorder
caused by a mutation or deficiency of a necessary protein/enzyme is phenyketonuria (PKU). This
disorder which results in cognitive and behavioral abnormalities is caused by elevated serum (i.e.
blood) phenylalanine due to a deficiency in the enzyme phenylalanine hydroxylase. Other disorders
can be caused by a deficiency of certain amino acids due to malnutrition. Kwashiorkor results from an
inadequate consumption of protein and leads to the reduction of proteins in internal organs. Reduced
levels of protein in blood lead to fluid accumulation in the vascular system and can result in edema (i.e.
draining of fluids) in the extremities, like feet or legs.
If someone eats more protein than they need, the liver converts the excess protein into ketones.
Ketones can cause serious damage to the central nervous system. Your kidneys work to filter out the
ketones before they do harm. Unfortunately this can overwork the kidneys and hurt them. Also, you
need more water to help get rid of the ketones, which can cause dehydration.
YOU ARE WHAT YOU EAT
Fact Sheet #3: Lipids
Introduction
Lipids include a large number of diverse molecules. The one characteristic that all lipids share is that
they are hydrophobic (do not mix with water). There are several types of lipids such as glyderides,
steroids, and terpenoids. Among glycerides the most well-known are saturated and unsaturated fats.
Saturated fats cause many health problems, but unsaturated fats (especially polyunsaturated fats) are
“good” fats. Steroids include testosterone, estrogen, and cortisone while the terpenoids include
vitamins A, D, E, and K. Because there are so many different types of lipids, there are many functions
of lipids. Some of the most important jobs are their use in energy storage, as structural components of
cell membranes, and as important signaling molecules.
Digestion
The digestion of fats and oils begins in the first section of the small intestine, the duodenum.
Globules of fat in the acidic chime, mixture leaving the stomach, are broken up by intestinal
movements. The smaller droplets of fats become coated with bile that entered the small intestine via
the common bile duct. The liver synthesizes bile and the bile is stored in the gall bladder. When
chyme enters the small intestine, the gall bladder walls contract and release the bile into the small
intestine via the common bile duct. The bile serves to break up or emulsify the large lipid droplet into
smaller micelles that present more surface area for the pancreatic enzymes. Enzymes called lipases
break up the lipids, also called triglycerides, into fatty acids and monoglycerides.
Assimilation
The fatty acids and monoglycerides are lipid soluble and are able to cross the mucosal membrane
of the small intestine. Once inside the epithelial cells, the fatty acids and monoglycerides diffuse into
the endoplasmic reticulum. There, they are re-synthesized into triglycerides and combined with
cholesterol, phospholipid and coated with a protein to form chylomicrons. Because chylomicrons are
water-soluble they are able to exit the cells via exocytosis. The chylomicrons enter the lymphatic
vessels in the submucosa. The lymphatic system will dump the chylomicrons via the thoracic duct into
the bloodstream.
There is usually a constant supply of lipids in the blood, although the concentration increases
immediately after a meal. The lipids will be absorbed by liver cells to provide energy for cellular
functions. The liver regulates the proper concentration of lipids in the blood. Excess lipids in the
bloodstream are eventually transported and stored in adipose tissue.
The stored fatty lipids can be used later for energy, if necessary. Under the skin, they serve as an
extra layer of insulation and cushioning. The fatty acids that enter the cells become important building
blocks for many different structures. Some will be transformed into phospholipids and will serve as the
flexible and semi-permeable membrane for cells and the organelles. Some of the fatty acids will serve
as intermediates such as for compounds like prostaglandins and leucotrienes which play a role in
physiological regulation. Some of the fatty acids will be metabolized to form Acetyl CoA which in turn
can be converted into many different types of compounds, including fatty acids.
Issues
Because fats (lipids) are an important source of energy for the body, they are constantly broken
down and reassembled to balance the body’s needs with the available food. Any mutations or defects
in the enzymes that catalyze the metabolism and synthesis of lipids can lead to the buildup of specific
fatty substances. The accumulation of these fatty substances can be harmful to many organs of the
body. Disorders caused by the buildup of lipids are called lipidoses. Abnormalities in enzymes that
prevent fat from being converted into energy are called fatty acid oxidation disorders.
Adrenoleukodystrophy (ALD) is a genetic disorder where certain fatty acids build up around nervous
tissue causing damage and eventually death. This is the disease that Lorenzo has in the movie,
Lorenzo’s Oil.
Name: ____________________________________________ Date: ___________________ Block: ____
Carbohydrates
1. Describe the pathway and the enzymes involved in the digestion of carbohydrates.
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2. Describe the advantage of having indigestible carbohydrates in the digestive system.
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3. The liver is one destination for digested monosacharides. Describe how monosaccharides are
utilized by the liver.___________________________________________________________
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4. Describe two ways that simple sugars are either incorporated or utilized within cells.
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5. If simple sugars were omitted from the diet and other organic compounds ceased to be converted
into simple sugars, how would this deficit disrupt life in an organism or a cell?
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Proteins
1. Describe the pathway and the enzymes involved in the digestion of proteins.
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2. Describe how amino acids are used by the liver. ____________________________________
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3. Describe how amino acids are incorporated or utilized within cells._____________________
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4. If certain amino acids are omitted from the diet and other amino acids cease to transform into
those specific amino acids, how might this deficit disrupt life in an organism or a cell?
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Lipids
1. Describe the pathway and the compounds involved in the digestion of lipids.
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2. Describe the pathway of lipids between the digestive system and the bloodstream. _______
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3. Besides long-term energy storage, what other functions do lipids serve in organisms and in cells?
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4. How might the deficit or accumulation of fats be detrimental to organism?
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CARBOHYDRATE GRAPHIC ORGANIZER
KEY
Ingestion – red ovals
Digestion – green rectangles
Assimilation – blue diamonds
PROTEIN GRAPHIC ORGANIZER
LIPID GRAPHIC ORGANIZER