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Instruction 1-8

Cell Membrane | Enzymes | Prokaryotic and Eukaryotic Cells | RNA's Role | The Role of the Endoplasmic Reticulum and the Golgi Apparatus | Energy Capture and Storage | Mitochondria | Macromolecules | What Determines the Eukaryotic Cell's Shape? | Summary

CA GR 9-12  Biology Biology 1.h..

Small organic molecules are the basic stuff of life. Scientists call them monomers. Mono means one. These monomers actually make up building blocks for bigger things. You can think of them as one brick that makes up a brick wall. When monomers (small molecules) are joined together, they form larger molecules called polymers. Poly means many. Think of the polymers as that brick wall. And when polymers are joined together, they form “giant” molecules called macromolecules. Macro means big. You can think of these macromolecules as the building that is made up of those brick walls. So, you need the bricks (monomers) to form the walls (polymers) which when put together actually make up the building (macromolecules). Macromolecules are what this Instruction is mostly going to be about.

But first we'd probably better review a little basic chemistry. That's because even though this lesson is called Cell Biology, we’re really talking biochemistry here Don’t let the term freak you out. It is just the chemistry of living things (like cells). So here’s a little dictionary to remind you about some of the words that we'll be using in this Instruction. Don’t worry, you don’t have to memorize all of these terms. Use them for reference later if you have questions while reading this lesson. You will actually run across words like compound, molecule and bond.

Words from Chemistry

atom: The smallest component of an element that has all the properties of that element. An atom is made up of protons, neutrons and electrons. The electrons play an important role in chemical bonding.
element: A substance composed of atoms that are alike. For example, oxygen is made up of two atoms of oxygen (O). This means that the formula for oxygen is O2.
compound:  A substance composed of atoms that are different. Water is a good example, since water is made up of two atoms of hydrogen (H) plus one of oxygen (O). The chemical formula for water is H2O.
molecule:  The smallest part of a substance that can exist on its own without losing its chemical properties.

he molecule of an element consists of two or more of the same atoms bonded together, like the two atoms that make up oxygen.

The molecule of a compound consists of two or more different atoms bonded together (like water, H2O).

bond:  When atoms, elements or compounds join together they bond by sharing their electrons. The electrons of certain atoms only bond with the electrons of certain other atoms.
formula: A written representation or structural model that tells you or shows you which elements go into what compound and how. There are many different kinds of formulae (formulae is the plural of formula) but the two most useful for our purpose are:
  • the molecular formula, in which the chemical compounds
    are written like a sentence, and
  • the Kekule model in which they are drawn and look something like a graph

We’ll use a simple example to show you what we mean. Methane
gas is made up of one atom of carbon and four atoms of hydrogen.

So the molecular (written) formula would be CH4.

The Kekule model would look like this:


 Now let’s get back to macromolecules. Just refer back to the chemistry terms if you get confused about the meaning of one of them.


All macromolecules (polymers) are produced from a very small group of about 50 monomers (molecules). These monomers can be put together to form many different substances. But the process by which they’re put together is always the same. And so is the process by which they’re broken apart  to release energy.

Polymers are put together by an anabolic (building) process called dehydration synthesis. Sounds scary right? Well, actually when you translate the words, dehydration is just removal of water, and synthesis just means to build. In dehydration synthesis, two molecules are chemically bonded through the use of enzymes and the removal of water. So, you build something and take water away in the process.

Polymers are broken apart by a catabolic (destruction) process called hydrolysis. Another potentially scary term right? Wrong, all you need to do is break the word down. Hydro refers to water and lyse is to break. You are breaking something apart and adding water. Let’s see how this all works with something we’ve just been learning about – carbohydrates (sugars).


Carbohydrates (sugars) and their polymers are the main source of food for all living things. Chemists call these sugars saccharides.

This brings us to something you’ve probably already noticed. Different kinds of scientists have different words for the same thing. They have their reasons, but it can be pretty confusing.

Carbohydrates (sugars or saccharides) are macromolecules made up of carbon, oxygen and hydrogen. The basic formula for carbohydrates is CH2O. You have your simple sugars, which are just made up of single (mono) sugars, when you put a couple of these things together, you form two (di) sugars. If you put many (poly) saccharides together you get an even bigger saccharide.

  • monosaccharides (single sugars) -- CH2O (glucose, fructose and galactose)
  • disaccharides (double sugars) -- C12H22011 (maltose, sucrose and lactose)
  • polysaccharides (multiple sugars; poly means many) -- C6H10O5n (starch and fiber; found in grain products, fruits and vegetables)

Monosaccharides and disaccharides (simple carbohydrates) are the most important source of nutrition for cells and bodies.

Polysaccharides (complex carbohydrates) do the work of building and storage.

Cellulose, which is the most abundant organic compound on earth, is a basic building material for plants. No, we didn’t say cellulite – but cellulite is made up of macromolecules, too.

Here is a diagram of a carbohydrate:

Another important macromolecule is fat.


Fats are large molecules composed of 2 types of monomers -- glycerol (an alcohol containing carbons) and 3 fatty acid molecules. Fatty acid contains oxygen, hydrogen and carbon. The bond connecting the glycerol and the fatty acids in the fat molecule is called an ester bond.

There are two types of fatty acid: saturated and unsaturated. The saturated fatty acids do not contain a double bond between their carbon atoms, while the unsaturated fatty acids do contain one or more double bonds between carbon atoms. You can read about them on any food label. If you see “unsaturated fats” on the label, it is referring to mostly plant fats. If you read “saturated fats” on the label, it is a reference to mostly animal fats. Which is better? Consider the fact that diets that are high in saturated fats have been linked to cardiovascular disease. These types of fats contribute to something called, artherosclerosis. It is pronounced, art heroes clear o sis. It is a big word that describes fatty deposits that build up on the insides of blood vessels. That means it will slow down blood flow. Also, beware of “hydrogentated fats” on your labels. What you see to describe this in the grocery store is the term “trans fats.” These fats are called hydrogenated because you take unsaturated fats and add hydrogen to make them saturated fats. These contribute to high cholesterol. There are a couple of kinds of cholesterol, one is good, one is bad, we will learn about those later. Trans fats contribute to a rise in bad cholesterol.

Now let’s see what protein looks like.


You should recall from an earlier instruction that proteins are the most diverse of all molecules. There are seven major classes of proteins. You don’t have to learn all of them here, but you do need to know that they make up things like hair, silk, antibodies, hormones and of course enzymes. You should remember learning all about enzymes from an earlier lesson. Like carbohydrates and lipids, proteins are made up of carbon (C), hydrogen (H) and oxygen (O). In addition to the C, the H and the O, they also contain nitrogen (N). All of these elements are arranged to form amino acids. Amino acids are the building blocks of proteins. Proteins are formed when these amino acids are linked in a chain. So if one amino acid (peptide) binds to another by dehydration synthesis, a dipeptide is formed. Do you remember, dehydration synthesis puts things together, while taking away water?

All amino acids (also called peptides) have the same basic structure – a central carbon (C) atom with a hydrogen (H) attached to it. Also bound to this central carbon is something called an “R” group. It is a strange name, but the “R” group refers to a bunch of different chemicals. You don’t have to learn all of these chemical groups, just know that there are different ones, and they are all referred to as R groups. When the R group changes, so does the amino acid. So look at the protein diagram and notice this central carbon with the hydrogen attached, also hanging off of the carbon is this R group. This central carbon (with the H and the “R” group) also connects to an amino group (NH2), and an acid group. It makes much more sense if you look at the diagram.

Here is a diagram of the basic monomer of protein. It is also an example of a monomer that would be attached to other monomers by a peptide (amino acid) bond.



There are two types of nucleic acids. Deoxyribonucleic Acid, more commonly known as DNA, and ribonucleic acid, more commonly known as RNA. You should recall from an earlier lesson what these nucleic acids do. They provide all of the instruction for proteins. Organisms inherit this DNA from their parents. Your curly hair or blue eyes come directly from the genes that your parents or their parents passed on to you. The genes are found inside the DNA. As you recall from an earlier lesson, the DNA cannot pass its information directly, it needs RNA. This all happens pretty much in the same way you snail mail (not email) a letter. Your letter, the DNA gets picked up by the mailman (RNA) and eventually gets delivered to its final destination. The DNA is important, but it couldn’t get where it needs to be without the RNA. So, now that you remember how DNA transmits it message, let’s look at what makes it up.

The smallest units (monomers) of nucleic acids are called nucleotides. How would you build a nucleotide? Good question, each one has three parts.

  • Part one: Take one five-carbon sugar
  • Part two: One phosphate group
  • Part Three: One nitrogenous base

Put the five-carbon sugar in the middle. Attach a phosphate group to one end and a nitrogenous base to the other end and you have a nucleotide!

But, you notice that you have two types of nucleic acids. Is the recipe the same for both? Both are composed of nucleotides. These nucleotides are very similar, with a few minor changes. Lets look at the differences.

First, consider the names; Deoxyribonucleic Acid, Ribonucleic Acid.

For part one, the deoxyribose is the five-carbon sugar you would use to form DNA’s nucleotide. Ribose is the five-carbon sugar you would use to build RNA.

For part two, the phosphate groups are the same for both forms of nucleic acids. There are no differences here.

For part three, the nitrogenous bases are very similar for both DNA and RNA. There are four kinds of nitrogenous bases that can be found in DNA.

DNA’s nitrogenous bases are:





These nitrogenous bases pair up to help form the famous double helix you may have heard about with DNA. The A bonds to T and the C bonds to G.
The nitrogenous bases of RNA are very similar except instead of Thymine, RNA contains Uracil (U).

RNA’s nitrogenous bases are:





Remember that these nucleotides are the monomers that make up the nucleic acids. To put a couple of these nucleotides together you have to (you guessed it) take out some water to form a bond, dehydration synthesis. The phosphate group from one nucleotide will bind to the sugar in the next. This forms a sugar-phosphate backbone. The nitrogenous bases protrude into the center.

Video Instruction
*Availability of You Tube video links may vary. eTAP has no control of these materials.

Experiments for Home or Classroom

"Never-fail" science experiments are designed for either home or classroom use and require only grocery store ingredients and kitchen tools. Scroll down to the second experiment, which illustrates basic principles of polymer chemistry by showing students how to make their own Silly Putty™. Then go on to the fourth experiment, "Isolating DNA." The DNA molecule is very, very long to carry all the information it needs to carry. This means it can be extracted as long, stringy, gooey, visible threads. Note: a different version of the wheat DNA experiment was suggested in Instruction 1-4 -- but the other experiments are new for this Instruction. Click: 

Proteins are polymers made up of amino acids. They are the most complex and important group of molecules because of all the different functions they perform to support life. Every cell that makes up a plant or an animal requires proteins for its structure and function. In this classroom activity, students will learn about the sources of proteins and their uses in the food industry. In part I, students will precipitate casein from milk using an acid (this is the method used to make cottage cheese). In Part 2, students will coagulate casein from milk using an enzyme (this is the method used to make cheese). And in Part 3, students will coagulate soy protein from soymilk, using magnesium sulfate (this is the method used to make tofu). Note that the products of these experiments are not to be eaten.  

Molecules are involved in everything -- including in how you smell and taste. Odor and food molecules activate membrane receptors in your nose and mouth. Each substance we smell or taste has a unique chemical signature -- although most substances are made up of a number of different molecules. Humans have hundreds of kinds of odor membrane receptors and perhaps 50 to 100 kinds of taste receptors. Although we typically describe only five categories of taste -- salty, sour, sweet, bitter, and umami (the taste of monosodium glutamate and similar molecules) -- each category probably has more than one type of receptor. In this experiment, students learn how to investigate the senses of taste and smell and also find out how to plan and carry out their own experiments. In the Class Experiment, students find that the ability to identify a flavor depends on the sense of smell as well as the sense of taste. They also learn basic facts about food molecules, sensory receptors, nerve connections and brain centers. Everyone should start with the Teacher's Guide at: 

Then for the actual experiment, click the Student Guide at: 


Reading List
from the California Department of Education
  Trefil, James S. :101 Things You Don't Know About Science and No One Else Does Either


for Students, Parents and Teachers

Now let's do Practice Exercise 1-8  (top).

Next Page: What Determines the Eukaryotic Cell's Shape? (top)