Chemistry of CarbohydratesName______

Prd.___Date______

Part A: Carbohydrates

Biologists today depend upon chemists for much of their understanding of life and life processes. Therefore, an understanding of some chemical concepts important to living things is necessary. Organic compounds are those which contain the element ______. Most are made by living things, but some can be made in a laboratory.

Why is carbon such an important element in living things? Carbon atoms have ____ valence electrons so they can form covalent bonds with as many as _____other atoms. Carbon atoms can bond with each other to form ______or ______. The carbon atoms in these chains and rings can also connect with atoms of other elements to form the basic units of most biomolecules. Most biomolecules are polymers (“poly”=many; “mer”=unit) of smaller, repeating units called ______(“mono”=single or 1; “mer”=unit). There are 4 main kinds of biomolecules: Carbohydrates, Lipids, Proteins, and ______.

Carbohydrates are molecules that may also be called ______. They are composed of only 3 elements: ______, ______, and ______. The individual monomer units that make up all carbohydrates are called ______(“mono”=single or 1; “saccharis”= sugar).

Carbohydrates are important molecules for providing ______for living organisms. In addition, they play important structural roles for certain organisms. For example, ______is a complex carbohydrate (polysaccharide) that helps build the cell walls of plant cells.

Part B: Monosaccharides or Single Sugars

The many different types of carbohydrates (or sugars) are grouped into 3 categories: monosaccharides, disaccharides (“di”=2) or polysaccharides.

Examine the structural formulas and the corresponding models for the three monosaccharides. The models do not show the exact 3-dimensional shape of the molecules but illustrate how they differ from each other as well as how they join together.

  1. What 3 elements are present in monosaccharides? ______
  1. How many atoms of carbon are there in each of the monosaccharides?

a)Glucose ______

b)Galactose______

c)Fructose______

  1. Write the molecular formulas for glucose, fructose and galactose by adding the proper subscripts to each of the following:

a)Glucose C____H____O_____

b)Galactose C____H____O_____

c)Fructose C____H____O_____

  1. Compare the number of hydrogen atoms to the number of oxygen atoms in each sugar. What is the ratio of hydrogen to oxygen? (that is, how many hydrogen atoms are there for each oxygen atom). ______
  1. How do the ratios of hydrogen to oxygen compare in glucose, galactose, and fructose?______
  1. How do they compare to the ratio in water? ______
  1. Molecules may have the same molecular formula with identical numbers of atoms, yet differ in their 3-dimensional shape. This is called ______. Describe an example of isomerism in monosaccharides: ______

Part C: Disaccharides or Double Sugars

Two monosaccharide sugar molecules can join together chemically to form a larger carbohydrate molecule called a ______, or double sugar.

By chemically joining a glucose molecule to another glucose molecule, a double sugar called maltose is formed. By joining a glucose molecule with a fructose molecule, a double sugar called sucrose is formed. By joining a glucose molecule with a galactose molecule, a double sugar called lactose is formed.

Glucose + Glucose  ______(disaccharide)

Glucose + ______ Sucrose (disaccharide)

Glucose + Galactose  ______(disaccharide)

  1. Attempt to join 2 paper models of glucose to form maltose. What must be removed from each model in order to join them? ______. Models should fit together but will not join unless an OH end and an H end are removed.
  1. What common molecule does an H atom combined with an OH group form? ______
  1. This type of chemical reaction is called a ______reaction. (It may also be called a condensation reaction). (“dehydrate”=to lose water; “synthesis”=to build something). Why is this a good name for this type of reaction?
    ______

Withyour models, construct the following disaccharides:Maltose, Sucrose, and Lactose.

  1. Carbohydrate molecules store energy in the bonds between the C, H, and O’s. Why is there more stored energy in a Sucrose molecule than in a Glucose molecule? ______
  1. Write the molecular formulas for each of the 3 disaccharides you built. Fill in the correct subscripts for each: (Remember you lost a water molecule in order to join them)

Maltose C_____H_____O_____

Sucrose C_____H_____O_____

Lactose C_____H_____O_____

  1. What is the H:O ratio of each of the disaccharides? ______:______
  1. Does isomerism exist in disaccharides? (Compare your paper models of the 3 disaccharides): ______
  1. How many monosaccharide molecules are needed to construct one disaccharide molecule? ______

Part D: Polysaccharides or Complex Carbohydrates

Just as double sugars were formed from two monosaccharide molecules, complex sugars or ______are formed when many monosaccharides are joined together. Starch and cellulose are two of the most common polysaccharides in biology. They consist of long chains of glucose molecules bonded together.

Construct a starch molecule by joining three glucose molecules. Note: this will only represent a small part of a starch molecule because starch actually consists of hundreds of glucose molecules bonded together.

1. What must be removed from the glucose molecules in order to join them?

______What common molecule does this form? ______

2. What type of chemical reaction joins these glucose molecules to each other? ______

3. Determine the molecular formula of this small segment of starch. Fill in the proper subscripts:

Starch: C_____H_____O_____

4. What is the H:O ratio in starch? ______:______

5. How does this compare the ratios in the other carbohydrates we have studied? ______

Part E: Final Analysis

1. What 3 elements make up all carbohydrates?

______

2. What is the ratio between Hydrogen and Oxygen in all carbohydrates?
______

3. What is the name of the monomer units that make up all carbohydrates? ______

4. What common molecule is always formed when monosaccharide molecules are joined? ______

5. What kind of chemical reaction builds the larger carbohydrate polymers? ______

6. “Mono” means 1, “di” means 2, and “poly” means many. Why are these terms used to describe the three types of carbohydrates? ______

7. What is the primary function of carbohydrates in living organisms? ______