The Chemists View of Carbohydrates

To understand the structure of carbohydrates, look at the units of which they are made. The sugars most important in nutrition are the 6-carbon monosaccharides known as hexoses. Each contains 6 carbon atoms, 12 hydrogens, and 6 oxygens (written in shorthand as C6H12O6).

Each atom can form a certain number of chemical bonds with other atoms:

  • Carbon atoms can form four bonds.
  • Nitrogen atoms, three.
  • Oxygen atoms, two.
  • Hydrogen atoms, only one.

Chemists represent the bonds as lines between the chemical symbols (such as C, N, O, and H) that stand for the atoms (see Figure 4-1).

Atoms form molecules in ways that satisfy the bonding requirements of each atom. Figure 4-1 shows the structure of ethyl alcohol, the active ingredient of carbohydrates: compounds composed of carbon, oxygen, and hydrogen arranged as monosaccharides or multiples of monosaccharides. Most, but not all, carbohydrates have a ratio of one carbon molecule to one water molecule: (CH2O)n.

  • carbo = carbon (C)
  • hydrate = with water (H2O)

simple carbohydrates (sugars): monosaccharides and disaccharides.

complex carbohydrates (starches and fibers): polysaccharides composed of straight or branched chains of monosaccharides.

Figure 4-1

Atoms and Their Bonds

The four main types of atoms found in nutrients are hydrogen (H), oxygen (O), nitrogen (N), and carbon (C). Appendix B presents basic chemistry terms and relationships.

H-

-O-

1 1

1

2

3

4

Each atom has a characteristic number of bonds it can form with other atoms.

Each atom has a characteristic number of bonds it can form with other atoms.

Ethyl alcohol, a simple molecule showing bonding.

Figure 4-2

Chemical Structure of Glucose

On paper, the structure of glucose has to be drawn flat, but in nature the five carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and below the plane.

On paper, the structure of glucose has to be drawn flat, but in nature the five carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and below the plane.

Fructose is shown as a pentagon, but it does have 6 carbon atoms. The ring contains 4 carbons and an oxygen; 2 carbons stick out from the ring (see Figure 4-4).

Galactose occurs only as a part of lactose.

monosaccharide (mon-oh-SACK-uh-ride): a carbohydrate of the general formula CnH2nOn that consists of a single ring.

  • mono = one
  • saccharide = sugar

See Appendix C for the complex chemical structures of the monosaccharides.

glucose (GLOO-kose): a monosaccharide; sometimes known as blood sugar or dextrose.

  • ose = carbohydrate
  • glucose

Figure 4-3

Simplified Diagrams of Glucose alcoholic beverages, as an example. The two carbons each have four bonds represented by lines; the oxygen has two; and each hydrogen has one bond connecting it to other atoms. An accurate drawing of a chemical structure must obey these rules because the laws of nature demand it.

T~R SUMMARY

The carbohydrates are made of carbon (C), oxygen (O), and hydrogen ^ (H). Each of these atoms can form a specified number of chemical bonds: carbon forms four, oxygen forms two, and hydrogen forms one.

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  • Michael
    How Do chemists determine % Carbohydrates?
    4 years ago

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