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In this simulation, I will learn about the different macromolecules found in food: carbohydrates, protein, and fats. I will help my friend get a healthy diet. I will investigate the types of macromolecules found in food. By performing a series of biochemistry tests, I will know the contents of various food items.
Bob and Alice are partners in a biology class. After they’ve
been working together for several weeks, Bob asks Alice for a date in the
Bob: Wow, you sure seem to love cabbage salad.
Alice: Yes, it’s delicious.
Bob: I wonder if we could survive on only cabbage salad. Does it have all the essential macro-molecules we need?
Alice: Cabbage salad has high nutrients, but I’m not sure if it has all the macro-molecules we need.
Bob: Wanna take this date to the lab, and maybe we can find an answer together?
Alice: I do love nerds. Let’s go.
Tracy: I’m Tracy, a food scientist. Molecules in food can be
divided into two main groups: micro (small) and macro (large).
Micro-molecules include vitamins and minerals. Macro-molecules include carbohydrates, proteins, and lipids (fats). In this lab, I will learn about and perform a test for each of the macro-molecules.
Macromolecules are large molecules. Macro means large, and
molecules refer to atoms held together by chemical bonds.
Macromolecules are huge molecules created by the polymerization of small units called monomers. Most macromolecules are present in everyday life, for instance, in food (although nucleic acids are not considered food macro-molecules).
There are several types of biological macromolecules:
All macromolecules except lipids are polymers. A polymer is
a long molecule composed of chains of monomers. Monomers are small molecules
that serve as building blocks of polymers.
Besides, there are also oligomers in nature. Oligomers
are molecular complexes made out of a few monomer units as opposed to polymers
which are theoretically unlimited. Dimers and trimers are, for instance,
oligomers composed of two and three monomers, respectively, such as the lactose in
However, in biochemistry, an oligomer usually refers to a macromolecular complex formed by non-covalent bonding of a few macro-molecules like nucleic acids or proteins. Clear examples of this are oligomers related to many neurodegenerative diseases such as the alpha-synuclein aggregations in Parkinson’s Disease.
Which of the following molecules is NOT a macromolecule?
In biochemistry, we know four types of macromolecules:
carbohydrates, proteins, lipids, and nucleic acids. In food, we are mainly
concerned about carbohydrates, proteins, and lipids (fats).
Let’s start by taking a look at a few different types of
There are three macromolecules found in food: carbohydrates,
protein, and fats. I can see them all in front of me here.
Look at all this food? Are we allowed to eat it after the
No, we shouldn’t eat the food in the lab.
You may be exposed to hazardous biological chemical
materials through the consumption of potentially contaminated food and drinks.
Never prepare, store, or consume food and drink in the lab.
Click on the food that contains a high amount of
There are apples, rice, chicken breast, butter, eggs, and
broccoli on Workbench 2. Pick the food that contains a high amount of
Carbohydrates include simple sugars and complex sugars. They
are a source of energy for the body. They can be found in healthy and
unhealthy food such as rice, bread, popcorn, cookies, pasta, apple pie, milk,
potatoes, and soft drinks.
Click on the food that contains a high level of protein.
Protein is found throughout our bodies. Protein builds our
enzymes, cells, hormones, and antibodies. If your body lacks protein, you will
experience muscle loss, weakening of the heart and respiratory system, and
decreased immunity. High protein foods contain fish, chicken, beans, nuts, and
Click on the food that contains a high amount of lipids.
Lipids include fats. The major function of fat is to store
energy. It also maintains your core body temperature. Fats are mostly found in
the oil, butter, cheese, and processed food such as pastries, cakes, and biscuits.
Delicious time to make a hypothesis. We are curious about
Alice’s cabbage salad. What type of macromolecules do you hypothesize to find in Alice’s salad primarily?
Alice’s salad mainly consists of cabbage. I can perform a
series of biochemistry experiments to determine what type of macromolecules are
most common in the salad.
Some macromolecules are polymers. What is a polymer?
A polymer is a long molecule that consists of small
repeating units called monomers. I can imagine a polymer as a train with the individual
monomers as the cars.
We will perform four biochemistry tests to evaluate the
macromolecule content of Alice’s cabbage salad. We will also check other food
samples for their carbohydrate, protein, and fat content.
Let’s begin with our first experiment. At this workbench,
we’ll take Alice’s salad for carbohydrates.
Carbohydrates provide the body with energy. They’re often
known as sugars or saccharides. Carbohydrates are commonly divided into simple
sugars (monosaccharides and disaccharides) and complex sugars (starch).
Benedict’s solution is used to detect reducing sugars,
typically monosaccharides and disaccharides. It will show a positive result for
reducing sugars such as glucose, fructose, lactose, maltose, galactose. It will
show a negative result for non-reducing sugars such as sucrose, starch.
Benedict’s solution is a blue-colored liquid that contains
copper sulfate. Copper binds to oxygen in the free aldehyde or ketone group
forming a copper oxide. The copper oxide transmits a brown color.
Click on the syrup.
Carbohydrates are organic compounds that are composed of
carbon, oxygen, and hydrogen. Their empirical formula is (CH2O)n,
virtually a carbon, water, or hydrated carbon, hence the name carbohydrate.
Carbohydrates include sugars (simple carbohydrates) and
polymers of sugars (complex carbohydrates). The simplest type of carbohydrates
are monosaccharides or simple sugars.
Monosaccharides or simple sugars can be aldose or aldehyde
sugars or ketose or ketone sugars. It depends on the location of the carbonyl
group (C = O).
Which of these is an aldehyde?
An aldehyde has one alkyl or aryl group and one hydrogen-bonded to the carbonyl carbon. A ketone has two alkyls or aryl bonded to the
carbonyl carbon. This functional group determines the type of monosaccharides.
Monosaccharides can exist as a linear chain or as
ring-shaped molecules. This is the linear shape of glucose, an example of a
monosaccharide (simple sugar).
In aqueous solutions, monosaccharides (simple sugars) are
usually found in ring forms. Monosaccharides can link together, forming
oligosaccharides (2-10 sugar monomers). Oligosaccharides with two sugar
molecules are known as disaccharides with three as trisaccharides with four as
tetrasaccharides, and so on.
Sucrose, an example of a disaccharide, is a combination of
two monosaccharides: glucose and fructose.
What forms after the glycosidic linkage reaction between
glucose and galactose are complete?
Glucose and galactose combine via a glycosidic linkage,
forming lactose and water. Lactose is a sugar mostly found in milk.
Glucose and fructose form a covalent bond between them. This
bond is called a glycosidic linkage. Both glucose and fructose are hexoses
(they have six carbons) though fructose forms a live-carbon ring, while glucose
forms a six-carbon ring.
Remember that monosaccharides are the same as simple sugars
or simple carbohydrates.
I covered the basics of carbohydrates in the animation. To
sum up, there are two types of carbohydrates: simple sugars and complex sugars.
Benedict’s reagent is a chemical reagent that detects the
presence of simple sugars: monosaccharides and most disaccharides (lactose,
maltose, and mannose). Table sugar (sucrose) cannot be detected using this
Let’s see if Alice’s salad contains simple sugars.
Tubes contain Alice’s cabbage salad, baked
potato, milk, glucose, apple, water, egg, bread, and vegetable oil. I added
Benedict’s reagent to each tube. I picked up the first tube containing the
baked potato sample and Benedict’s reagent, placed it in a beaker, and boiled
it on a hot plate at 100 degrees C for 5 minutes. I did this for all of the
other samples as well. Every tube was boiled manually. Once the 5 minutes were
up, I put the test tubes from the beaker into the tube rack using the test tube
Add 1 mL of Benedict’s reagent to each tube. Usethe dropper to add Benedict’s reagent to the test tube (highlighted).
the first tube containing Benedict’s reagent using the test tube holder.
Boil the samples on the hot plate for 5 minutes.
Place the test tube holder on the table and wait
Put the test tube from the beaker into the tube
rack using a test tube holder.
Pick up the tubes from the hot plate.
Place the test tube holder back on the table.
All of the tubes were boiled manually.
The change of color indicates the presence of simple sugars (carbohydrates). In Benedict’s experiment, the positive control is
glucose and negative control is water.
Slide down the lab pad to examine the color of the food
samples. Benedict’s reagent detects the presence of simple sugars in food. What
color indicates the presence of a high level of simple sugars?
Benedict’s reagent is used to test for glucose but not
sucrose. In the experiment, the test sample is heated and analyzed for color
change. A change from blue to red or orange indicates a high level of simple
sugars (e.g., glucose, fructose, maltose) in the food sample. A low level of
sugar is indicated by the colors yellow and green. Blue means no simple sugar
is present in the food sample.
Observe the color of each tube to determine the presence of
Cabbage salad and benedict’s mix – yellow-green
baked potato and benedict’s mix – yellow-green
milk and benedict’s mix – orange
glucose and benedict’s mix – red
apple and benedict’s mix – red
water and benedict’s mix – blue
egg and benedict’s mix – blue
bread and benedict’s mix – orange
vegetable oil and benedict’s mix – blue
Negative result Pos.
(reducing) sugars Blue Red, Orange Glucose solutions
Iodine solution Complex
Carbohydrate Dark Red, black, dark blue starch solutions
Yellow, Brown, White
Biuret’s Protein Blue Violet,
Black egg albumin
Sudan IV Lipid Red,
Orange (one Top layer: vegetable oil
Click the tube that contains food with a low level of
No simple sugars present in the food (negative result): blue
Low level of simple sugars present in the food: yellow or green
High level of simple sugars present in the food (red or orange)
The tube that contains food with a low level of glucose is baked
potato and benedict’s mix.
Examples of foods that contain a high level of simple sugar
are cookies, cakes, soft drinks, honey, milk, and fruits. Simple sugars are
digested quickly by the body or enter the bloodstream quickly. Having excess
sugar in your blood can contribute to gaining weight and developing type 2 diabetes and heart disease.
I’ll now complete a test for complex sugars. Benedict’s
test is over.
Click on the baked potato.
Potatoes are an example of a food with a high carbohydrate
content. Remember that carbohydrates include monosaccharides (simple sugar)
and complex carbohydrates. I’ll learn the basic structure of complex
This is the structure of starch, an example of a complex
carbohydrate mostly found in plants. Complex carbohydrates are polymers called
polysaccharides that are composed of many sugar building blocks.
Sucrose is part of the carbohydrate group. DNA is a nucleic
acid. Insulin is a peptide hormone, so it’s a protein. Wax is part of the lipid
The sugar building blocks are monosaccharides (simple
sugars) such as glucose. The glucose monomers in starch can also be joined by
1-6 linkages (number 1 carbon to number 6 carbon), forming a branch in the structure.
There are two types of starch: amylopectin and amylose.
Amylopectin is branched while amylose is unbranched.
As you might know, plants store energy as starch. Animals
store energy in a similar structure called glycogen.
Take a look at broccoli. It has a crunchy structure thanks
to another complex carbohydrate called cellulose. Unlike starch, whose main
function is to store energy, cellulose’s main purpose is to maintain cell
structure. Even though starch and cellulose have different functions, their
structure is pretty similar. Cellulose is also a polymer of glucose.
The difference between cellulose and starch is in the type
of glucose building blocks. In starch, the glucose is an alpha-glucose, while
in cellulose, it is beta-glucose. That’s why cellulose is mainly straight,
while starch is helical.
What is the difference between the structure of alpha and
the structure of beta glucose?
The alpha and beta glucose differ in the hydroxyl group’s position attached to the number 1 carbon. The hydroxyl group is upside
down when we compare the two glucose structures.
So the glucose in starch is an alpha-glucose, while the
glucose in cellulose is a beta-glucose. Humans have the enzyme to break down
the glycosidic linkage in starch but not in cellulose. That’s why we can’t
digest the cellulose in vegetables.
Nutrition facts labels tell you the number of macromolecules
in the food.
What does insoluble fiber refer to?
Insoluble fiber refers to the type of carbohydrate that your
body couldn’t digest. A human doesn’t possess the proper enzyme to break down
cellulose. Foods that contain a high level of cellulose are brown rice, whole
wheat bread, fruits, and vegetables.
I covered the basics of complex carbohydrates. So complex
carbohydrates have longer chains of sugars than simple sugars. The chains
can have branches or not depending on their origin and function.
Iodine solution is a chemical reagent that detects the
presence of starch. The positive control of this experiment is a potato, and the
negative control is water.
Add drops of iodine reagent to each tube on the right hand
set of tube racks. I added drops of this to each tube. I put the pipette
dropper back into the bottle and watched the colors change over time. The baked
potato iodine mix turned black; the milk iodine mix turned white, the glucose
iodine mix turned yellow, and the apple iodine mix turned brown, the water iodine
the mix turned yellow, and the egg iodine mix turned yellow, the bread iodine mix
turned dark blue, the vegetable oil iodine mix turned yellow, and the cabbage
salad iodine mix turned dark blue.
The tube that contains a high amount of starch is baked
potato. Iodine reagent reacts with and binds to a structure in the starch
molecule, forming a structure that has a dark bluish-black color. Therefore,
food that contains a high level of starch, such as potato, will exhibit a black
color, whereas food that doesn’t contain complex carbohydrates will exhibit a
The tubes contain the following: baked potato, milk, glucose,
apple, water, egg, bread, and vegetable oil, and Alice’s cabbage salad.
Click on the bottle that contains the iodine
reagent. Use the dropper to add the iodine reagent to each highlighted test
Put the pipette dropper back into the bottle,
and then watch the colors change over time.
Click on the tube that contains food with a high
amount of starch
no complex carbohydrates are present in the food (negative result): yellow
a significant level of complex carbohydrates found in the food: dark blue or
What do you call a sample for
which no response is expected?
A negative control
The negative control is essential
to check that the positive result is actually positive and not because of an
error in the procedure.
I can observe the benedict’s test results for simple sugars and the iodine for complex sugars. Now it’s
time to input and assess the results in the test results table.
Fill out the test results table
correctly on the screen.
Examine each sample’s color for Benedict’s
test for simple sugar and Iodine test for complex sugar.
Check the white box in each column for simple
and complex carbohydrates to indicate which sample contains it.
Leave the white box blank if the food doesn’t
contain any carbohydrates.
Click check if you have completed filling out
Now let’s continue to the next mission. We will make a final
assessment of Alice’s cabbage after we performed all four biochemistry tests.
Biuret experiment for protein
Proteins are organic molecules made up of amino acids. It’s
important to consume enough protein. Our body needs it to produce important
molecules such as enzymes, hormones, antibodies, neurotransmitters, and cell structure parts. Good sources of protein are eggs, beans, milk, fish, and
Click on the eggs to dive into proteins.
Genetic information is stored as DNA and copied as the messenger
RNA (mRNA) during transcription. In mRNA, genetic information is encoded in
three-letter units – codons – made up of the bases uracil (U), cytosine C,
adenine (A), and guanine (g). in the ribosome, each codon is translated into
one amino acid.
Covalent peptide bonds link amino acids. The
formation of a peptide bond produces one water molecule.
Covalent peptide bonds link amino acids. The
reaction of a peptide bond produces one water molecule. Multiple amino acids
are linked together by
Covalent peptide bonds. A covalent peptide bond links two
amino acids, thereby forming a long chain. Peptide bonds occur between the amino
group and the carboxyl group of neighboring amino acids. The process of making
a peptide bond results in one water molecule.
An amino acid molecule consists of three components: a
carboxyl group, an amino group, and a side chain symbolized by it. A peptide
bond occurs between the amino acid and the carboxyl groups of neighboring amino
acids. A sequence of amino acids called a polypeptide grows from the
N-terminus to the C-terminus. This polypeptide chain represents the primary
structure of a protein.
A sequence of amino acids or a polypeptide grows from the
N-terminus to the C-terminus. The linear sequence of amino acids within a
protein is considered the primary structure of a protein.
The primary structure of a protein is the linear sequence of
Which protein structure level is formed by the weak bonds
between oxygen and hydrogen atoms within the polypeptide backbone?
The secondary structure
The oxygen and hydrogen atoms within the polypeptide
backbone can form hydrogen bonds. These weak bonds result in the local folded
structure known as the secondary structure.
Which of the following is a secondary protein structure?
Two basic secondary protein structures are alpha
helixes (a-helix) and beta sheets (B-sheet). The a-helix is a right-handed
coil. The b sheet can be formed by two or more segments of the polypeptide
chain lying side by side. The entire 3d structure of the folded protein is
known as the tertiary structure.
Proteins are modified in many ways after translation. Here I
can observe a protein that undergoes post-translational modification called
glycosylation before being considered biologically active. Glycosylation is
the addition of sugars.
Now I know that proteins consist of long chains of amino
acids. The chains are folded up in specific ways to become functional. The
Biuret reagent will reveal the presence of protein. A positive result is
indicated by changes in color from blue to dark purple.
I added Biuret reagent to each tube. Again, the tubes contained
Alice’s cabbage salad, a baked potato, milk, glucose, apple, water, egg, bread,
and vegetable oil. I then watched the colors change.
Baked potato: pale purple
Glucose: pale blue
Apple: pale blue
Water: pale blue (negative control)
Egg: dark purple (positive control)
Bread: pale purple
Vegetable Oil: blue
Cabbage Salad: pale blue
Add 0.5 ml of the Biuret reagent to each tube.
Put the pipette dropper in the bottle and watch
the colors change.
Click on the positive control of the Biuret test.
no protein present in the food (negative result): blue
low level of protein present in the food: pale purple
high level of protein present in the food: dark purple
Now that I have completed the Biuret test for protein let’s
assess the results just the way I did with the carbohydrate biochemistry test
Fill out the table of biochemistry test result correctly on
the Biuret test.
Examine the color of each sample for the biuret
test for protein.
Check the white box in the protein column if
that particular food sample contains proteins.
Leave the white box blank if the food doesn’t
Click check if you have completed filling out
We can use these results to help make a final assessment of
the macromolecules in Alice’s cabbage salad.
The positive control for the Biuret experiment is an egg.
Eggs are high in protein content; therefore, they will exhibit a purple color
after this biochemistry test. Water, on the other hand, the negative control,
will exhibit a blue color.
A positive control is a sample known to give positive
results for the given test. What is the purpose of a positive control?
Verify that the negative results are valid.
Controls are needed to make sure the procedure is working
correctly. A positive result from the positive control, even if the samples are
negative, will indicate the procedure is optimized and working. It will verify
that any negative results are valid. If there is no positive control and the
sample is negative, we can’t be certain whether the sample was truly negative or
if the procedure didn’t work.
Go to workbench 3 to begin investigating fats.
You’ve tested the food samples for carbohydrates and
protein. Now let’s check whether it contains any fats.
Lipids are a group of molecules that do not mix well with
water. Lipids include fats, sterols, and phospholipids. When it comes to food,
we focus on fats. Fats provide insulation, energy, and a cushion for organs.
Good sources of fats are avocados, fatty fish, egg yolks, and vegetable oils.
Click on the butter to dive into the fat.
Lipids are not true polymers. Lipids include fats,
phospholipids, steroids, wax, and certain pigments. These compounds are grouped
into a class of molecules called lipids because they share one important trait:
they mix poorly with water.
Fats are composed of two kinds of smaller molecules:
glycerol and fatty acids.
Glycerol is alcohol. Glycerol has three carbons. Each of
them bears a hydroxyl carbon.
Fatty acids have a long carbon skeleton (16 or 18 carbons).
The acid in fatty acids refers to the carboxyl group (-COOH) at one end of the
carbon skeleton (left). The rest of the skeleton consists of a hydrocarbon
chain. This hydrocarbon chain is hydrophobic, which means it separates from the
Each fatty acid is linked to the glycerol by an ester
linkage, resulting in a fat, also called a triacylglycerol.
Lipids are mostly composed of non-polar molecules
Lipids are organic molecules that are insoluble in solutions
of high polarity such as water. For example, think of the interaction between
oil (a lipid) and water. Lipids are insoluble in water because they are largely
composed of non-polar regions. Non-polar regions are hydrophobic. A fatty acid
has a large non-polar region and a small polar region.
Saturated and unsaturated fats refer to the structure of the
hydrocarbon chains of fatty acids. Saturated fats have no double bonds between
the carbon atoms. Hence, the structure is saturated with hydrogen. Unsaturated
fats have one or more double bonds between carbon atoms. The hydrocarbon chain
will bend at the position where a double bond occurs.
At room temperature, the molecules of saturated fat are
packed closely together, forming a solid. The unsaturated fats molecules
cannot pack together tightly enough because of the kinks in the fatty acid
A trans-fat is unsaturated fat that is uncommon in nature.
It is formed when unsaturated fats such as oil are synthetically converted to
saturated fats by adding hydrogen (hydrogenation).
Which of these is the structure of trans-fat?
Trans-fatty acid, or trans-fat, is an artificial unsaturated
fat. It contains a trans double bond between the carbon atoms.
You can find unsaturated fat in oil, saturated fat in
butter, and trans-fat in margarine.
Now I know the basics of lipid structures. Basically, fats
are made up of glycerol and fatty acids. The fatty acid chains can be
saturated, unsaturated, and trans-unsaturated.
Sudan IV is a red stain that detects the presence of lipids.
When Sudan IV is added to a mixture of lipids and water, the dye will move into
the lipid layer, coloring it reddish-orange.
I filled the tubes up halfway with water with a pipette and
changed out the tips for each tube.
Again, the tubes contained cabbage salad, baked potato,
milk, glucose, apple, water, egg, bread, and vegetable oil.
I mixed the contents of each tube using the vortex. Then, I
added drops of Sudan IV to each tube and mixed the contents of each tube in the
Fill the tubes halfway with water using the
Mix the contents of each tube using the vortex.
Put the tube back into the rack when the vortex
Do this for every tube.
Add drops of Sudan IV to each tube.
Again, mix the contents of the tube using the
Put the tube back into the rack when the vortex
Click on a test tube containing a food sample
with high-fat content.
Sudan IV assay:
no fats present in the food (negative result): one layer, red
a significant level of fats present in the food: two layers, orange (note: the
two layers may not be visible perfectly in this simulation)
Baked potato: red
Vegetable Oil: orange
Cabbage Salad: red
Vegetable oil has a high fat
content. Foods that contain a high level of fats are butter, oil, milk, and
I’ve now tested for the presence
of carbohydrates, protein, and fats in various food samples. Ultimately, I’m
close to concluding whether Alice’s salad is healthy or not.
Fill out the table of test results
correctly for the Sudan IV test for lipids.
Follow these steps to perform the
Examine the color of each sample for SudanIV test for lipids.
Check the white box in the lipid column if theparticular food sample contains it.
Leave the white box blank if the food doesn’t
Click check if you have completed filling out
I have completed tests to identify all food macromolecules
correctly. Now we’re ready to conclude. Before that, let’s test my ability
to recognize macromolecule structures.
I will now go to workbench 2 to conclude about
Alice’s cabbage salad.
Which food contains carbohydrates, proteins, and fats?
Based on the biochemical tests, only milk contains a
complete set of macromolecules except for complex sugars. Drinking
milk every day will supply you with all the macromolecules and minerals your
body needs to function properly.
Which of the samples contains no macromolecules at all?
Water does not contain any macromolecules. That’s why we
used it as the negative control in our four biochemistry experiments to detect
macromolecules. Despite the lack of macromolecules, you must drink enough water to keep your body hydrated.
Earlier, I made this hypothesis: Alice’s cabbage salad
mostly contains complex sugars. Was my hypothesis, right?
We have conducted four biochemistry tests to
detect simple sugars, complex sugars, proteins, and carbohydrates. Of the four
tests, two came out with a positive result: simple sugars and complex
carbohydrates. The level of simple sugars detected was, however, very low.
Based on the iodine test, Alice’s cabbage salad contains a high level of
complex carbohydrates. But it lacks the other important macromolecules:
proteins, and fats.
Based on the biochemistry tests, Alice’s cabbage salad lacks
some important macromolecules. What should Alice add to her salad to provide
the macromolecules she needs?
Egg and avocado
Alice’s salad lacks protein and fats. She can add an egg as a source of protein and an avocado as a source of fats.