Access Keys:
Skip to content (Access Key - 0)

Carbon and Life

Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.
Comment: Migration of unmigrated content due to installation of a new plugin

...

Section
Column
width60%

 

Multimedia
height320
width480
namecondensation_hydrolysis.swf
width480

Column
width40%
 
Section
Column
width70%

This animation also depicts a hydrolysis reaction (a type of catabolism whereby a polymer is broken down by the addition of water).  Hit the "home" icon to return to the beginning; select condensation and hit play.

Column
width30%
 

...

Section
Column
width70%

Carbohydrate biomolecules generally have a basic structural formula that is written as C(H2O)n. For example, glucose has the structural formula C6H12O6. The carbohydrates have many functions in cells. They can be used for energy storage (e.g., starch) and as structural molecules (e.g., cellulose). And as we will see, they also play a role in information storage in nucleic acids (organic compounds that make up RNA and DNA).

The basic monomeric units of carbohydrates are the simple sugars (monosaccharides). Monosaccharides include glucose (also known as dextrose), fructose, ribose, galactose, and ribulose. Note, the -ose suffix is used by chemists to describe all carbohydrates.

A disaccharide is a sugar formed by a condensation reaction between two monosaccharides. Condensation synthesis of maltose (glucose + glucose), a common disaccharide, is illustrated in the following animation. Other disaccharides include sucrose (glucose + fructose) and lactose (glucose + galactose); sucrose is common table sugar, and lactose is milk sugar.

This animation shows the formation of disaccharides

Multimedia
height320
width480
namedisaccharide_formation.swf
width480

 
More complex forms of carbohydrates can be synthesized by cells via additional condensation reactions. Polysaccharide polymers can consist of up to several thousand monomers of simple sugars. The type of polysaccharide is determined by the number, type, and arrangement of its monomers. Starch is a polymer of glucose monomers. It is used by plants to store surplus sugar and when we and other animals eat a starchy plant (such as a potato) we use the starch for energy and nutrients. Animals store surplus sugar in their livers in the form of a molecule known as glycogen.

Column
width30%
 

...

Section
bordertrue
Column
width40%


Figure 7.  Triacylglycerols. (Click to enlarge) Fats and oils have three fatty acid molecules (only one strand is shown here) and one glycerol molecule (not shown). Double bonds determine whether a fat is saturated or unsaturated.

Column
width60%

Lipids are an assortment of molecules so diverse that it may seem odd to group them together. However, they do share one common trait; they are all (to some extent) hydrophobic. Also, in contrast to the other groups of macromolecules, the lipids are not polymers. The lipids main biological functions include energy storage (e.g., fats), main structural components of cell membranes (e.g., phospholipids and cholesterol), and hormones and other cell signaling molecules (e.g., estrogen and testosterone). The lipids include dietary fats (also known as triacylglycerols), phospholipids (which are an important component of cell membranes), and steroids (e.g., cholesterol, estrogen and testosterone).

Fats and oils are triacylglycerols, which are formed when three fatty acid molecules and one glycerol molecule join via condensation synthesis. This animation depicts the synthesis of a triacylglycerol molecule.

This animation shows synthesis of a fat:

Multimedia
height320
width480
namefat_synthesis.swf
width480

 

Section
Column
width70%

Fats can be saturated or unsaturated. Saturated fats do not have double bonds in their hydrocarbon chains because their carbon is bound to two other carbons and two hydrogens. Unsaturated fats have double bonds along their lengths (monounsaturated = one double bond, polyunsaturated = more than one double bond). Saturated fats have straight chains that organize into more tightly packed arrangements. In contrast, unsaturated fats have kinks caused by the double bonds, which do not permit tight packing. Thus, saturated fats tend to be solids at room temperature, whereas unsaturated fats are usually liquid. A liquid unsaturated fat can be converted to a solid saturated fat by a process called hydrogenation (e.g., margarine).

Fats are used in energy storage, protection, and insulation. Aquatic and polar mammals counteract heat loss by having extra fat for insulation. Compare the Arctic polar bear and subtropical gazelle. Clearly, they don't have a similar need for extra insulation.

Column
width30%
 

...

Section
Column
width60%

Polypeptides are a polymer (chain) of amino acids. Proteins consist of one or more polypeptide chains arranged in a specific conformation. The order of amino acids in a particular polypeptide chain is determined by the specific gene for that chain. In other words, every polypeptide chain has a corresponding gene.

The animation shown here illustrates the formation of a polypeptide. Do not simply think of proteins as linear strings of amino acids. In reality, they fold into a three-dimensional structure and take on complex shapes (basic protein structure is discussed in the case study below).

Multimedia
height320
width480
namepeptide_formation.swf
width480

 

Column
width40%
 

Nucleic Acids

...