Polymers that contain sugars…

A. May store hereditary information

B. May store energy

C. May protect cells

D. All of the above

The correct answer is D. all of the above.

Sugars are biological molecules that occur in carbohydrates and also form part of nucleic acids. Monomers are the basic units of all biological macromolecules, and these can link together to form larger molecules known as polymers.

Cellulose, a linear polymer of D-glucose units (two are shown) linked by β(1→4)-glycosidic bonds.

The simplest sugar is one molecule in size and is known as a monosaccharide. There are many types of these sugars that bond in various ways to form complex carbohydrates.

Glucose is a six carbon, hexose sugar that is formed during photosynthesis and is broken down during cellular respiration to produce energy in the form of ATP.

The ATP molecule is one of the three nucleic acids that occur, and this molecule contains ribose sugar as part of the structure.

Energy is also stored in carbohydrates such as starch and glycogen. The glycogen is how animals are able to store sugar in the liver, while starch is the way in which plants are able to store sugar.

Sugars also help in the protection of the cell by providing structural support. For example, cellulose is a complex carbohydrate that is a part of the plant cell wall.

Chitin is another complex carb that forms fungal cell walls and also forms the tough exoskeleton of animals such as crustaceans and insects.

Sugars are found forming the backbone of DNA and RNA molecules where they bond to phosphates and nitrogen bases. The DNA carries the genetic code (hereditary information) for the cell and the RNA is involved in protein synthesis in which the code is expressed.

Sugars

When we think of sugars we think mostly of carbohydrates since these molecules are generally made of one or more types of sugar molecules. The basic unit of any biological molecule is called a monomer, and when several monomers bond together they form a polymer.

Polymers are formed by dehydration synthesis in which a water molecule is removed from two or more monomers. The reverse reaction called hydrolysis is when a water molecule is added causing bonds between polymers to break so that it is broken down into monomers.

In the case of carbohydrates, the monomer is a single sugar that is called a monosaccharide. These sugars can be categorized according to how many atoms of carbon are present.

Six carbon sugars include familiar molecules like glucose, which has the formula C6H12O6. This molecule is formed during photosynthesis in photoautotrophic organisms such as plants and green algae.

The glucose is a source of energy that is broken down during cellular respiration to produce energy in the form of ATP.

Glucose also links together to form bigger molecules and can combine with other monosaccharides to form different types of carbohydrate polymers.

When two alpha-D-glucose monomers bond together they form maltose, a disaccharide. Other examples of disaccharides include sucrose (table sugar), and lactose (milk sugar).

Larger and even more complex carbohydrates can be formed from glucose.  For instance, starch or glycogen molecules can be made when several of the alpha-D-glucose monomers link together.

Energy storage

Various types of sugar molecules are important in energy. Some of the smaller molecules such as glucose provide a quick burst of energy, while other larger complex carbohydrates can be stored for later energy production.

Starch is the way in which plants store sugars over the long term. Glycogen is how animals store sugar. These are both sources of long term energy storage for these organisms.

When animals eat food containing starch they are able to digest this molecule by various amylase enzymes that are produced from glands in the digestive system.

Glycogen is formed by a process known as glycogenesis which involves a series of reactions in which the glucose monomers are linked together and arranged to form the glycogen molecule.

During times when blood sugar drops too low the glycogen can be broken down by hydrolysis in a process known as glycogenolysis.

Glucose is broken down during cell respiration to produce ATP, which is used as energy to catalyze many cellular reactions.

The ATP molecule contains a ribose sugar which bonds to one of three phosphate groups and to a nitrogenous base. It is the breaking of phosphate bonds that enable the release of some energy.

Protection of the cell

Sugars play an important role in protecting cells. In fact, the plant cell wall is comprised partly of the carbohydrate cellulose.

Cellulose is formed when several thousand monomers of beta-D-glucose attach to each other to form a chain that has high tensile strength.

The cellulose also combines with other substances such as hemicellulose, pectin and sometimes lignin, to form plant cell walls. The cell wall of plants is thus very strong and provides a great deal of structural support for the plant body.

Chitin is an aminopolysaccharide molecule that is very abundant in living organisms and also functions in structural support. This is a substance that forms the exoskeleton that is present in arthropods such as insects, crabs, and shrimp. It is also a component of the cell walls of the fungi.

The structure of chitin is very similar to that of cellulose but an acetamido group is present at carbon 2 instead of a hydroxyl group.

Genetic material

Some familiar five carbon sugars (pentoses) include the ribose that is present in RNA and the deoxyribose that is found in DNA.

Thus, sugar molecules are not only found in carbohydrates, but also in nucleic acids such as ATP. The sugars form part of the backbone that makes up the polynucleotide strands in each case.

The sugar molecule bonds to a phosphate group by phosphodiester bonds. The nitrogen bases bond to the sugar as well. It is this sequence of bases that is our genetic code.

The DNA is the molecule which stores our genetic material, which is transcribed and translated into proteins by means of different molecules of RNA.

References

  1. S Eggling (2003). Disaccharides and polysaccharides. Retrieved from clackamas.edu.
  2. EA Davidson (2018). Carbohydrate. Retrieved from Encyclopedia Britannica.
  3. Editors of Encyclopedia Britannica (2018). Monosaccharide. Retrieved from Encyclopedia Britannica.
  4. Editors of Encyclopedia Britannica (2018). Cellulose. Retrieved from Encyclopedia Britannica.
  5. D Elieh-Ali-Komi, MR Hamblin (2016). Chitin and chitosan: production and application of versatile biomedical nanomaterials. International Journal of Advanced Research.

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