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Slide 1 – Organic Compounds
Now that we have learned a little bit about chemistry, we will turn our attention to
molecules that are important in biology. We are going to examine four classes of organic
compounds: carbohydrates; lipids; proteins; and nucleic acids. Organic molecules are
compounds that contain carbon and hydrogen. All of the organic molecules that we are
going to look at are made of small building blocks called monomers that are linked
together to form polymers. Think of about how the cars of a train are linked together to
form they entire train. This is similar to how monomers are linked to form larger
Slide 2 – Synthesis
Monomers of organic compounds are joined together in a process called synthesis to
form polymers. In the process of synthesis one molecule of water is removed, in order to
join two monomers together.
Slide 3 – Hydrolysis
In addition to synthesizing polymers, organisms also need to break down polymers into
monomers. This process is called hydrolysis. In hydrolysis, one molecule of water is
added to break the bond between two monomers.
Slide 4 – Hydrolysis and synthesis
These two reactions can be seen in the diagram on this slide. Hydrolysis is represented
by the reaction on the right, while synthesis is represented by the reaction on the left.
Slide 5 – Check Your Understanding
Now that we have learned about small and large molecules, let’s check your knowledge
of the subject. The following slides will have a series of questions on the topic. Be sure to
click “Submit” after answering each question.
Slides 6 through 12 – Small and Large Molecules Interactive Quiz
A non–graded assessment to test your understanding of small and large molecules.
Slide 13 – Carbohydrates
The first group of organic molecules that we will look at is carbohydrates. You may have
heard of carbohydrates because they are an important source of energy for the body. You
may have also heard the term carbo loading, which is when athletes eat foods high in
carbohydrates such as potatoes and pasta before a sporting event. Carbohydrates are a
class of compounds that are composed of the elements carbon, hydrogen, and oxygen in a
ratio of 1:2:1. This means that for every carbon atom, there are twice as many hydrogen
atoms, and an equal amount of oxygen atoms. You have already learned about one
important carbohydrate in Unit 1, glucose. The chemical formula for glucose is C6H12O6.
If you divide the formula by 6, you can see that you get the 1:2:1 ratio described earlier.
Carbohydrates serve three important functions in living organisms. The first is as a
source of energy. Plants store extra glucose energy as starch, which can quickly be
broken down into glucose again when needed. Starch is a carbohydrate used for energy
storage. Humans store energy in the liver as the carbohydrate glycogen. Plants also have
another polymer of glucose that serves as a structural component, a molecule is called
cellulose. Think about the rigidness of a stalk of celery. This property comes from the
Slide 14 – Monosaccharides, Disaccharides, and Polysaccharides
The monomers or building blocks of carbohydrates are called monosaccharides or simple
sugars. Glucose is an example of a monosaccharide. The sugar that you may have put in
your coffee this morning is known as a disaccharide. A disaccharide is formed when two
monosaccharides are combined. A large chain of monosaccharides is called a
polysaccharide. Starch, glycogen, and cellulose are all example of polysaccharides.
Slide 15 – Polysaccharides
Let’s look at the three polysaccharides we mentioned earlier in more detail. Starch is a
plant storage form of glucose. It is a long chain of glucose, but the chain is twisted into a
coil that resembles a slinky. Only plants can make starch. Humans and animals store
extra glucose in the liver in the form of glycogen. We will discuss how and why we
make glycogen in unit 3. Glycogen is a highly branched polysaccharide. Cellulose is the
structural material found in plants, it is what makes plants stiff. Cellulose is different
from starch and glucose. Cellulose has a different type of bond between the glucose
molecules. This is why most organisms cannot digest cellulose.
Slide 16 – Fiber
Your body has the ability to breakdown both starch and glycogen. You can taste the
breakdown of starch into glucose by chewing on a piece of bread or a cracker and letting
the bolus of food sit on your tongue for a few minute. You will start to notice a sweet
sensation on your tongue. This is the salivary amylase in your salvia converting the
starch in the bread or cracker into glucose.
Cellulose cannot be broken down by humans. This is why we can not eat wood.
However, cellulose is important for your health; it is one of the types of dietary fiber.
Many fruits and vegetables contain fiber and you should eat between 25 and 30 grams of
fiber per day. Because you cannot digest fiber, it passes through your digestive tract
helping to keep you regular, as well as decreasing your risk of colon cancer. Eating
enough fiber will also help lower your cholesterol. As we will see in unit 3 high
cholesterol levels can lead to heart disease.
Slide 17 – Isomers
The last thing to mention about carbohydrates is the term isomer. The monosaccharides
fructose and glucose have the same chemical formula C6H12O6. Looking at the structures
of these two molecules, we can see that they are arranged slightly differently from each
other. Chemicals with the same chemical formula, but different structures are called
isomers. Do you recall earlier that we said that cellulose can not be broken down by
humans because of the way the glucose molecules were arranged? The body recognizes
each the structure of each molecule and will not confuse fructose for glucose. Only
glucose can be used for cellular respiration.
Slide 18 – Check Your Understanding
Now that we have learned about complex carbohydrates, let’s check your knowledge of
the subject. The following slides will have a series of questions on the topic. Be sure to
click “Submit” after answering each question.
Slides 19 through 24 –Complex Carbohydrates Interactive Quiz
A non–graded assessment to test your understanding of complex carbohydrates.
Slide 25 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this
lecture. Be sure to review the questions you answered incorrectly.
Slide 26 – Lipids
The next class of organic molecules that we will examine is lipids. Lipids, like
carbohydrates, are composed of carbon, hydrogen, and oxygen, but lipids do not have the
same 1:2:1 ratio that we saw in carbohydrates. Lipids vary in both structure and function.
Examples of lipids include: oils, fats, waxes, steroids, sex hormones, and cholesterol. Fat
is used as long term energy storage and insulation. Waxes are used to lubricate and in
plants prevent their leaves from drying out. Cholesterol is a structural component of the
cell membrane, and sex hormones are chemical messengers.
Slide 27 – Saturated versus unsaturated fats
Let’s start by looking at fats and oils. Fats are composed of a glycerol head and three
fatty acid tails. There are two main types of fats: saturate and unsaturated. The types of
bonds found in the fatty acid tails determine whether the fat is saturated or unsaturated.
If the fatty acid tails do not contain double bonds between the carbon atoms, the fat is
called a saturated fat. If the fatty acid tails contain double bonds between the carbon
atoms, then the fat is called an unsaturated fat.
Slide 28 – Margarine is partially hydrogenated
Because the fatty acid tails are straight in a saturated fat, the fats pack together tightly.
At room temperature these fats will be solid. Some examples of saturated fats include
lard and shortening. In an unsaturated fat, the fatty acid tails are kinked and can not pack
together tightly. These fats are liquid at room temperature. Some examples of
unsaturated fats include sunflower and corn oils.
The process of hydrogenation adds hydrogen to an unsaturated fat to change them into
saturated fats. Many margarine are labeled are partially hydrogenated. This means that
some of the unsaturated fats have been changed to saturated fats. The end result is that
margarine is more solid at room temperature.
Slide 29 – Saturated fats, trans fatty acids, omega 3 fatty acids
Saturated fats are bad for you and can lead to heart disease. Other fats you may hear
about that may have health effects are omega three fatty acids. Omega three fatty acids
are found in fish and may held to decrease cholesterol. Recently trans fatty acids have
entered the new media. Trans fats have negative health effects and now appear on food
Slide 30 – Phospholipids
A second type of biologically important fat is phospholipids. A phospholipid has a
phosphate and glycerol head attached to two fatty acid tails. The phosphate group has a
negative charge. Phospholipids are a major component of the cell membrane.
Slide 31 – Phosopholipid arrangement
The phospholipids are arranged in a very specific way to form the lipid bilayer of the cell
membrane. The negatively charged phosphate heads are hydrophilic. This means they
are attracted to water. Recall that water is a polar molecule with a partial negative and a
partial positive charge, one at each end of the molecule. Substances that are polar or have
a charge are attracted to water. The fatty acid tails are made of non–polar covalent
hydrogen carbon bonds, making them hydrophobic. This means that they avoid water. It
also explains why oil and water so not mix. The phosphate head of the phospholipids
arrange themselves so that they point to the inside or outside of the cell where there is
water. The fatty acid tails stay to the inside.
Slide 32 – Lipid bilayer
The structure of the lipid bilayer makes it so that few things can pass into or out of the
cell. Substances that like water will not want to travel through the hydrophobic tails.
Substances that do not like water can not get past the phosphate heads; therefore most
substances either stay in or out of the cell. Embedded in the membrane are channels that
allow for the transport of substances that the cell needs.
Slide 33 – Steroids
Now let’s examine steroids and sex hormones. These lipids are different in structure
from the fatty acids we have discussed so far. These compounds consist of ringed
structures. An example of a steroid is cholesterol.
Slide 34 –Cholesterol and the Cell Membrane
Cholesterol is a necessary part of the cell membrane. Despite the fact that excess
cholesterol can cause heart disease, this lipid is necessary for cells to function properly.
Think about fats and oils, they are not very hard. The cell membrane is composed of
phospholipids which are similar in structure. Cholesterol helps to give your cell
membrane structure. This is similar to the role cellulose plays in plants. Problems occur
when individuals take in too much cholesterol, because all of the cholesterol your body
needs is manufactured in the liver. We will look at cholesterol and heart disease in more
detail in unit 3.
Slide 35 – Sex hormones
Cholesterol is the precursor for the anabolic steroids that include the sex hormones. The
sex hormones include testosterone, estrogen, and progesterone. We will examine these
more closely when we cover the reproductive system.
Slide 36 – Corticosteroids
Another class of steroids is the corticosteroids. Corticosteroids are associated with
reducing the signs of inflammation that include redness, swelling, and itching. If you
break out in a rash, you would use hydrocortisone cream on the rash to relieve the
itching. Hydrocortisone cream is a type of corticosteroid. If your rash also causes
swelling, you may be prescribed prednisone, another type of corticosteroid.
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