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What is a Macromolecule?

All matter is made of small particles called atoms. Atoms are far too small to be seen with the naked eye or even with a microscope. In fact, more than a trillion atoms could fit over the period at the end of a sentence. There are about 90 different kinds of atom found in nature. Matter made up of all one kind of atom is called an element.

What is a Macromolecule?

All matter is made of small particles called atoms. Atoms are far too small to be seen with the naked eye or even with a microscope. In fact, more than a trillion atoms could fit over the period at the end of a sentence. There are about 90 different kinds of atom found in nature. Matter made up of all one kind of atom is called an element.

Clearly, however, there are more than 90 different kinds of matter in our world. This is because atoms can combine in chemical reactions to produce a myriad of new substances. For example, when one atom of sodium (which by itself is a soft metal) and one atom of chlorine (which by itself is a poison green gas) combine, the result is a compound called sodium chloride, more commonly known as table salt. A compound is made up of two or more elements that are chemically bonded.

A molecule is the smallest particle of a compound that has all the properties of that compound. We write the molecular formula of salt as NaCl to indicate it has one atom of sodium and one atom of chlorine.

Atoms may be compared to a variety of differently sized and shaped lego building blocks which can be fitted together in a variety of ways to form a multitude of different creations. The atoms of each element are distinguished by their mass and by the number of connections they can make with other atoms. There is virtually an infinite variety of compounds possible.

Some molecules are small, such as water, H₂O, which has only three atoms and table salt NaCl which has two. Others are larger such as a molecule of table sugar, C₁₂H₂₂O₁₁ (sucrose) which has 45 atoms. Still other molecules, such as proteins and nucleic acids (DNA), are gigantic. They are made up of repeating subunits called monomers. They can contain tens of thousands of atoms.

These gigantic molecules are called macromolecules.

Even individual macromolecules are too small to be seen with the naked eye.

Writing Molecular Formulae

A molecular formula shows the kind and number of atoms in a molecule. For some molecules, the formula provides a hint of how the atoms are arranged.

In spite of the fact that molecules are far too small to be seen, we have several ways of drawing pictures of them. Scientistis frequently draw diagrams called structural formulae to illustrate how the atoms are arranged in a molecule. This can be helpful when trying to visualize how different molecules will react when they are combined.

Drawing Pictures of Molecules

Some structural formulae of famliar molecules

Three Dimensional Molecular Models

The structural formulae of macromolecules are often so complex that they can’t be drawn in two dimensions. Early pioneers of molecular biology built models from wood, wire and other materials. The image to the left is a photograph of the original DNA model built by James Watson and Frances Crick in 1953. It is now on display in the National Science Museum of London.

Often molecular models take the form of stick and ball models in which atoms of different kinds are represented by colored balls with the bonds connecting them represented by sticks.

Such models are very useful in understanding the functions and interactions of the large molecules found in living cells (as long as you don't think this is really what they look like).

The advance of computer graphics has facilitated the construction of three dimensional models of complex molecules that simplify and illustrate their structure and shape.

There can be many ways to represent the same molecule. The first two models in the top row below represent the molecular structure of adenosine triphosphate, a crucial molecule for energy transfer that is found in all living things. The third molecule in that row is a 3D rendering of an alanine peptide. (Alanine is one of the amino acid monomer that makes up proteins.) It is been enhanced by the addition of a cloud to represent the region of the molecule that is hydrophobic (water repelling).

The model on the upper right is a large, unidentified protein. Each ball's color represents a different type of atoms.

Computer animation has added another way to understand the structure of very large molecules in three dimensions such as the revolving DNA model in the lower row right and the animated testosterone molecule next to it.

Some molecules are so large and so complex that only virtual computer models are possible and even those models have a cartoonish look to them.

These models may not look simple to the student new to the idea of macromolecules but they are a boon to high school and college students who have advanced to organic and biolchemistry courses. Many students own their own ball and stick kits to help them understand the shapes and interactions of organic molecules (far right). These kits are available from scientific supply companies and often college and university book stores.

A basic ball and stick model of ATP

By Fuse809 (QuteMol) [Public domain], via Wikimedia Commons
A different rendering of the ATP molecule

By Jynto [CC0], via Wikimedia Commons
A model of a polyalanine molecule showing its hydrophobic region.

By derivative work: Dhatfield (talk) MM_PEF.svg: Edboas (MM_PEF.svg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
A ball and stick model of a large, complex protein
An Animated molecular model of DNA

Zephyris at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
An animated model of testosterone

D Dinneen at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
A computer generated model of a protein molecule that seeks only to illustrates the active functional aspect of the molecule.

Courtesy of Commons http://www.ebi.ac.uk/
Student assembling a molecular model from a ball and stick kit.

By Ariana Rose Taylor-Stanley from Bainbridge Island, United States (Creation) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

A basic ball and stick model of ATP

By Fuse809 (QuteMol) [Public domain], via Wikimedia Commons

A different rendering of the ATP molecule

By Jynto [CC0], via Wikimedia Commons

A model of a polyalanine molecule showing its hydrophobic region.

By derivative work: Dhatfield (talk) MM_PEF.svg: Edboas (MM_PEF.svg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

A large, complex ball & stick protein model

A ball and stick model of a large, complex protein

An Animated molecular model of DNA

Zephyris at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

An animated model of testosterone

D Dinneen at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

A computer generated model of a protein molecule that seeks only to illustrates the active functional aspect of the molecule.

Courtesy of Commons http://www.ebi.ac.uk/

Student assembling a molecular model from a ball and stick kit.

By Ariana Rose Taylor-Stanley from Bainbridge Island, United States (Creation) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Some Very Basic Chemistry

Some Very Basic Chemistry

Writing Molecular Formulae

Drawing Pictures of Molecules

Three Dimensional Molecular Models

How Atoms Bond

What is the Shape of a Molecule?

Meet the Elements

Where Can I Go From Here?

Where Can I Go From Here?