Lab 5 – Biomolecules – Part 1 Purpose To investigate carbohydrates, lipids, and

Question

Lab 5 – Biomolecules – Part 1

Purpose                            

To investigate carbohydrates, lipids, and proteins

To perform colorimetric tests to identify specific biomolecules

To analyze data and identify features of the scientific method

Introduction

Humans are omnivores in that they consume a variety of food types from several different ecosystem levels. The biomolecules we consume - carbohydrates, lipids, and proteins - provide us with energy and building blocks for our bodies to function. Vitamins and minerals are important dietary components required in small amounts. Water is not a nutrient or a source of calories but is critical to life.

                                   

Carbohydrates

Carbohydrates include sugars and starches and are composed of monosaccharide building blocks. Glucose is a simple sugar, a monosaccharide. Fructose is a monosaccharide found in honey, tree fruits, berries, and many vegetables. It is the sweetest naturally occurring sugar.

Two simple sugars joined together form a disaccharide. An example of a disaccharide is sucrose (table sugar) which is formed by glucose + fructose. Lactose, also known as milk sugar, is a disaccharide composed of a galactose and a glucose molecule. The enzyme, lactase is required to break down lactose into its two monosaccharide sugars. Lactase is normally secreted by intestinal cells. In many people, the production of lactase diminishes with age and they become lactose intolerant.

Starches are polysaccharides which contain many linked sugar molecules.     

Experiment 1 – Testing for Reducing Sugars

Many of the foods that we eat contain carbohydrates. Monosaccharides and short chains such a disaccharides taste sweet due to certain aspects of their chemical structure. A structural characteristics of some sugars can be identified using a chemical solution called Beneditc’s reagent. When heated, the copper ions in Benedicts solution react with the free end of any reducing sugar such as glucose, Copper ions are reduced by the sugars producing orange and red precipitates. Benedict's. Benedict's reagent is blue, but when heated in the presence of a reducing sugar, changes color. Green, yellow (+sugar), orange (++ sugar), or red (+++ sugar).

Materials

Benedict’s solution

Unknown solution

1% glucose solution

5 test tubes

Test tube rack

10 ml graduated cylinder

Pipette

Ruler

Wax pencil

Thermometer

Stopwatch/timer

* water

* knife

* fork

* potato

* cutting board

* onion

* hot water bath / microwaved or heated water

* you must provide

Procedure

Label 5 test tubes 1 – 5.

Prepare your testing samples as follows:

Cut a raw potato into 1 cm x 1 cm cube. Cut only this block into smaller pieces and finally mash with a fork adding a small amount of water. Place half of the mashed potato into test tube 1. Add 5 mil of water to test tube 1 (Do no discard the rest of the potato)

Cut a raw onion potato into 1 cm x 1 cm cube. Cut only this block into smaller pieces and finally mash with a fork adding a small amount of water. Place half of the mashed onion into test tube 2. Add 5 mil of water to test tube 2 (Do no discard the rest of the onion)

Place 5 ml 1% glucose solution into test tube 3

Place 5 ml of water into test tube 4

Place 5 ml unknown solution into test tube 5.

Record initial color of each sample in Table 1.

To prepare a hot water bath: Using an stove/ or microwave safe container, heat water to a temperature between 85 – 95 degrees Celsius, using the thermometer in you lab kit to confirm the temperature just prior to step #8. The hot water bath must be the appropriate shape to accommodate the 5 test tube.

Add 10 drops of Benedict’s solution to each test tube. Swirl each tube gently to mix.

Place the five test tubes into the hot water bath and let sit for 10 minutes.

Record any color change in Table #1. NOTE: If a red, yellow, or green precipitate forms, a reducing sugar is present in the sample.

NOTE: Wash your test tube immediately after recording results to prevent permanent staining from the reaction products

Table 1: Experimental Results for Reducing Sugars

Sample

Initial Color

Final Color

Positive for reducing sugar (yes or no)

1 – potato

2 – onion

3 – glucose

4 – water

5 – unknown

Table 1: Experimental Results for Reducing Sugars

Sample

Initial Color

Final Color

Positive for reducing sugar (yes or no)

1 – potato

2 – onion

3 – glucose

4 – water

5 – unknown

Explanation / Answer

Table 1: Experimental Results for Reducing Sugars

Sample

Initial Color

Final Color

Positive for reducing sugar (yes or no)

1 – potato

2 – onion

3 – glucose

4 – water

The Potato Juice after heating turned to green, which indicates that Potato Juice has small amount of sugar in it. potato mainy contains starch. Starch gives negative test to Benedict's reagents. Onion Juice turned an orange color. it idicates Onion Juice high sugar content. Glucose turned red color which indicates that there is a high sugar content in the solution. Water works as negative control. there is no sugar in it so its give blue color due to Benedict's reagent.

Sample

Initial Color

Final Color

Positive for reducing sugar (yes or no)

1 – potato

milky white green yes

2 – onion

colorless orange yes

3 – glucose

colorless red yes

4 – water

colorless blue no

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