Hello! Bea here, and welcome back to integrated physics and chemistry. Over the last 20 years,
the word organic has become a part of most people's everyday vocabulary. There is
organic food, organic drinks — even organic clothing! This definition of organic refers
to the lack of fertilizers, pesticides, or additives. Organic, in the sense of goods,
is referring to how the item is produced. In chemistry, the word organic refers to molecules,
reactions, and processes that involve carbon-based molecules. If you think back to your life science
classes, you may remember that carbon-based molecules are the basis for all living things.
Knowing this, it makes sense that industries use the word organic to describe goods and foods made
without chemicals. But, it is important to also understand that the word organic
in science refers to carbon-based molecules! In fact, organic chemistry is an entire branch of
chemistry that studies carbon molecules. These molecules are the basis of today's lesson.
Before we get started, let's look at our goals for this lesson. By the end, you'll be able
to describe the structure and function of the four main categories of carbon-based molecules.
Carbon-based molecules are the foundation for all living things. Whether a plant, animal,
large or small, the basis for the structure and function of that organism is carbon!
Carbon is located in Group 4 on the periodic table, which means that it
has four valence electrons. As we learned in our previous lesson, elements with four valence
electrons prefer to share their electrons with other atoms to achieve the octet rule.
This means that carbon can form covalent bonds with up to four other atoms.
These four bonds provide carbon with the flexibility to make molecules of all different
sizes and shapes. Most carbon-based molecules fall into three main categories of shapes. There
are straight-chained molecules, such as oleic acid; branched molecules, such as cholesterol;
and ringed molecules, such as aspirin. In all of these molecules, the single bar connecting
two atoms represents a shared pair of electrons. And unless otherwise stated,
black atoms represent carbon, red represents oxygen, and white atoms represent hydrogen.
Occasionally, you will see a blue atom, like in dopamine; this represents a nitrogen atom.
Have you ever wondered why endurance athletes will carb-load the night before a big event?
Well, complex carbohydrates, such as those found in whole grains and legumes, take a long time for
your body to break down. This provides energy for your body during long workouts without causing the
crash that follows the digestion of simple sugars, such as those found in candy and sugary drinks.
Simple carbohydrates are sugars that are made of carbon, hydrogen, and oxygen. These organic
molecules, such as glucose and fructose, are often bonded in a ring shape made of five or six carbon
atoms. Sometimes two rings will bond together to form a slightly larger sugar, like sucrose.
Sucrose is made of one fructose molecule and one glucose molecule.
Sucrose is the sugar we use when baking. Complex carbohydrates, such as the cellulose found in cell
walls, form when anywhere from several hundred to several thousands of simple carbohydrates bond
together to form very large molecules. Cellulose molecules contain hundreds to thousands of glucose
molecules bonded together. Because the actual number of glucose molecules bonded together to
form a cellulose molecule can vary, the formula is often represented by two glucose molecules with
a small "n" to represent the varying number of glucose molecules in any given cellulose molecule.
Our next category of organic molecules is proteins. I'm sure you've heard about proteins
in terms of nutrition. We need to consume protein in order for our cells and bodies to
function properly; some ways that we can attain protein is by eating meat, legumes, and soy.
All protein molecules are made of a combination of the 20 amino acids. Your body is able to make
11 out of the 20 amino acids that are needed to build proteins and help your body function
properly. The other nine must be attained through your diet and are called essential amino acids.
Amino acids all have the same basic structure. They have a central carbon atom with a hydrogen,
an amino group, and a carboxyl group, all bonded to that central carbon.
The fourth bond off of the central carbon atom will vary for each of the 20 amino acids.
These range from ring structures, like in tryptophan, to the long branches in lysine.
We all know that DNA is what makes us who we are and that it is found in all of our cells. DNA
stands for deoxyribonucleic acid and is one of two types of the category of organic molecules called
nucleic acids. Nucleic acids are long carbon-based molecules. Both DNA and RNA, or ribonucleic acid,
are nucleic acids and are made of a long chain of nucleotides. Every nucleotide is made of a sugar,
a phosphate group, and one of five different nitrogen-containing molecules called a base.
One DNA molecule could contain 30,000 nucleotides! These two nucleic acids are found in every one of
our cells and have key roles in our body. DNA stores information for how to make proteins;
it's like the instruction manual for building proteins and is the basis of genes and heredity!
RNA is the actual machinery to make the proteins. Our body could not function
properly without both of these types of nucleic acids working together!
Do you know anyone who has high cholesterol? If you do, chances are they are trying to
limit the amount of fatty food they eat so that they can lower their cholesterol.
Cholesterol is an example of a molecule in our final category of organic molecules:
lipids. Lipids include molecules such as fats, oils, and cholesterol. Lipids are present in
foods as fatty acids or long chains of carbon and hydrogen. These chains are known as hydrocarbons.
While fatty acids tend to have a bad rep when present in food, some are actually good for you!
These include omega-3 fatty acids found in food like salmon, olive oil, chia seeds, and avocados.
You will learn a lot more about hydrocarbons during the organic
chemistry unit in your chemistry course later in high school.
As we went through the lesson today, we learned about the four main categories
of carbon-based molecules. These molecules make up all living things and are essential to life.
In our next lesson, we are going to explore a different category of molecules: polar molecules.
Until next time, remember, the universe is vast and full of surprises, so never stop exploring!