1. Polymers are the most important chemicals in living things. 2. The polymers that are of most interest to molecular biologists fall into two classes: informational and operational. 3. There are three polymers in these classes: proteins, DNA and RNA.Proteins are operational; DNA is informational; and RNA is both.
2. The polymers that are of most interest to molecular biologists fall into two classes: informational and operational.
3. There are three polymers in these classes: proteins, DNA and RNA.Proteins are operational; DNA is informational; and RNA is both.
DNA is an informational polymer; proteins are operational; and RNA can act in either capacity. We'll discuss each of these three polymers in turn, emphasizing what kinds of small molecules each is composed of; what kind of bonds are used to knit these small molecules together; and what the structure of the final products look like. Along the way, I'll say a little about what these three do, but a more thorough discussion of their role in living cells will be left for later sessions.
Proteins are a diverse lot. They come in all sizes and shapes, and they fulfill many functions. They are the workhorses, the machines, and the blue collar laborers of biology. They also act as girders, glue, bricks and facings. They help keep unwanted substances out of cells and bring needed material in. Proteins make cells move, muscles contract, and nerves conduct. And much more.
Proteins are polymers composed of a class of small molecules called amino acids. The structure of a typical amino acid (leucine) is shown at the right. The figure on the right is a "Chime" image, identifiable via the "MDL Information Systems" logo in the lower right corner. These images can only be seen if the appropriate plug-in has been installed in your browser. If you don't see a three-dimensional figure slowly turning, then you probably don't have the "Chime" plug-in. The plug-in can be obtained for both Macintosh and Windows computers by clicking here, however, only the Netscape browser will work properly with Macintosh computers (Windows computers may use either Internet Explorer or Netscape Navigator). You can manipulate "Chime" images. If you click and hold on the figure, a popup menu will appear indicating some of the possible ways you can change the way the molecule is represented. You can also zoom in and out (by dragging with the "shift" key down) and turn the molecule with the mouse. Try clicking, dragging, and dragging with the control key depressed, and see what happens. Change some of the settings. Have fun! As their name suggests, amino acids are substances that bear two different features on the same molecule. One face, the acid side, carries a group of atoms -- the acid group -- that has a tendency to lose a positively charged hydrogen atom (one that has lost an electron -- a hydrogen ion) leaving behind a negative charge on the amino acid. The other face carries an amino group that has the opposite tendency: it picks up loose hydrogen ions floating in solution. When it does so, it becomes positively charged. Dissolved in water, amino acids bear opposite charges on their two sides, one negative and the other positive. Both the acid and amino groups are attached to a central carbon atom, to which is also attached a hydrogen atom and a side chain. Side chains There are 20 different amino acids that are found in proteins. All have acid and amino groups, and a central carbon atom. The 20 are distinguished from one another by the presence of a side chain. It is the side chain that imparts distinctive properties to each amino acid. In the picture above, the side chain is a single hydrogen atom, but most side chains are more complex. One of the most important properties of the side chains is their tendency to dissolve in water. Some amino acids, like phenylalanine pictured below, bear an oily side chain composed of just carbons and hydrogen atoms. Since oils don't dissolve readily in water, these amino acids are not very soluble. Other amino acids have acidic side chains -- ones that tend to lose hydrogen ions in solution (aspartic acid, pictured below, has an acidic side chain). Others, like arginine, have amino groups in their side chains. Amino acids with either acid or amino groups in their side chains tend to be quite soluble in water. Still other amino acids have side chains containing sulfur. Yet others bear bulky groups, while some have very small side chains All in all then, there is a great diversity in structure in the twenty amino acids, which in turn contributes to the great diversity of proteins. Animals, plants, bacteria, and viruses -- virtually all living things -- use the same set of 20 amino acids to form proteins, although, as far as we can tell, other similar amino acids could have as easily been employed. The near universality of this set of 20 suggests that its choice may date back to very near the origin of all living earthly beings. Each amino acid has a long name, as well as a three and one letter identifier. If you'd like to learn the names of the various amino acids, take a look at the protein tutorial.
Proteins are polymers composed of a class of small molecules called amino acids. The structure of a typical amino acid (leucine) is shown at the right.
The figure on the right is a "Chime" image, identifiable via the "MDL Information Systems" logo in the lower right corner. These images can only be seen if the appropriate plug-in has been installed in your browser. If you don't see a three-dimensional figure slowly turning, then you probably don't have the "Chime" plug-in. The plug-in can be obtained for both Macintosh and Windows computers by clicking here, however, only the Netscape browser will work properly with Macintosh computers (Windows computers may use either Internet Explorer or Netscape Navigator). You can manipulate "Chime" images. If you click and hold on the figure, a popup menu will appear indicating some of the possible ways you can change the way the molecule is represented. You can also zoom in and out (by dragging with the "shift" key down) and turn the molecule with the mouse. Try clicking, dragging, and dragging with the control key depressed, and see what happens. Change some of the settings. Have fun!
You can manipulate "Chime" images. If you click and hold on the figure, a popup menu will appear indicating some of the possible ways you can change the way the molecule is represented. You can also zoom in and out (by dragging with the "shift" key down) and turn the molecule with the mouse. Try clicking, dragging, and dragging with the control key depressed, and see what happens. Change some of the settings. Have fun!
As their name suggests, amino acids are substances that bear two different features on the same molecule. One face, the acid side, carries a group of atoms -- the acid group -- that has a tendency to lose a positively charged hydrogen atom (one that has lost an electron -- a hydrogen ion) leaving behind a negative charge on the amino acid.
The other face carries an amino group that has the opposite tendency: it picks up loose hydrogen ions floating in solution. When it does so, it becomes positively charged. Dissolved in water, amino acids bear opposite charges on their two sides, one negative and the other positive.
Both the acid and amino groups are attached to a central carbon atom, to which is also attached a hydrogen atom and a side chain.
There are 20 different amino acids that are found in proteins. All have acid and amino groups, and a central carbon atom. The 20 are distinguished from one another by the presence of a side chain. It is the side chain that imparts distinctive properties to each amino acid. In the picture above, the side chain is a single hydrogen atom, but most side chains are more complex. One of the most important properties of the side chains is their tendency to dissolve in water. Some amino acids, like phenylalanine pictured below,
bear an oily side chain composed of just carbons and hydrogen atoms. Since oils don't dissolve readily in water, these amino acids are not very soluble.
Other amino acids have acidic side chains -- ones that tend to lose hydrogen ions in solution (aspartic acid, pictured below, has an acidic side chain). Others, like arginine, have amino groups in their side chains. Amino acids with either acid or amino groups in their side chains tend to be quite soluble in water.
Still other amino acids have side chains containing sulfur. Yet others bear bulky groups, while some have very small side chains All in all then, there is a great diversity in structure in the twenty amino acids, which in turn contributes to the great diversity of proteins.
Animals, plants, bacteria, and viruses -- virtually all living things -- use the same set of 20 amino acids to form proteins, although, as far as we can tell, other similar amino acids could have as easily been employed. The near universality of this set of 20 suggests that its choice may date back to very near the origin of all living earthly beings.
Each amino acid has a long name, as well as a three and one letter identifier. If you'd like to learn the names of the various amino acids, take a look at the protein tutorial.
