CHEMISTRY IN CONTEXT
LAB 28: CHEMICALS OF LIFE, PAGE 1
MARCH 29, 2007
NAME
Chemicals of Life
INTRODUCTION/PRE-LAB:
The fundamental chemical components of cells and ALL living things can be grouped into four
basic categories: carbohydrates, proteins, lipids, and nucleic acids. Other chemicals such as
water, salts, minerals, and vitamins are also present and vital to living cells. Test have been
derived by biologists and chemists for determining the presence of many of the key chemicals.
Today, you will take several substances and conduct the tests to determine if they contain one
OR MORE of the four major types of biochemicals.
Before beginning and as a pre-lab question, list TWO examples from EACH of the four
categories of chemicals below:
++ Carbohydrates:
++ Lipids:
++ Proteins:
++ Nucleic Acids:
Some important safety reminders for today’s lab:
1) You will be using several chemical dyes and reagents today that are only significantly
toxic if ingested or exposed to open wounds. Therefore, be CAREFUL not to ingest,
inhale, or expose these chemicals to open wounds.
2) You will need to create a HOT WATER BATH. Keep all combustibles away from the
hot plate (i.e. paper and clothing). And, handle the beakers with beaker tongs. You will
observe STANDARD PRECAUTIONS for today’s lab.
CHEMISTRY IN CONTEXT
LAB 28: CHEMICALS OF LIFE, PAGE 2
MARCH 29, 2007
NAME
APPARATUS/MATERIALS:
Indicators:
Iodine solution (2-4 drops) – tests for carbohydrates
(turns from yellow-brown to dark purple if carbohydrate is present)
Biuret solution (5-10 drops) – tests for proteins
(turns from light blue to purple if protein is present)
Sudan III (5 drops) – tests for lipids
(mix vigorously, turns to pale yellow if NO lipid is present, forms two layers with
a pale pink-orange layer if lipid is present)
diphenylamine (12 drops)
(place in a hot water bath for 10 minutes, turns purple if DNA is present and
green if RNA is present)
Other Materials:
Unknown A (12 drops)
Unknown B (12 drops)
Unknown C (12 drops)
Unknown D (12 drops)
5 centrifuge tubes OR 5 small test tubes
Hot water bath set-up (with a 150 OR 250mL beaker)
250mL beaker (to set your test tubes OR centrifuge tubes in)
PROCEDURE:
1) Label 5 centrifuge tubes OR 5 small test tubes A-E.
2) Add 12 drops of unknown A to tube A, 12 drops of unknown B to tube B, 12 drops of
unknown C to tube C, 12 drops of unknown D to tube D, and 12 drops of unknown E to
tube E.
3) Add 2-4 drops of iodine solution to each of the tubes and record a + (for starch is present)
or – (for starch is not present) in the table in the Data/Observations section.
4) Rinse ALL tubes THOROUGHLY and repeat procedure steps 2-3 for one of the other
indicator tests described in the Apparatus/Materials section.
5) Rinse out ALL materials thoroughly at the end of lab.
6) Design and conduct a lab to test for the presence of carbohydrates, proteins, lipids, and
DNA in a plant sample. Before beginning, predict WHICH chemicals of life the plant
sample (navy beans) will contain. (NOTE: The plant sample is the slurry provided at the
main lab bench.)
CHEMISTRY IN CONTEXT
LAB 28: CHEMICALS OF LIFE, PAGE 3
MARCH 29, 2007
NAME
DATA/OBSERVATIONS:
Record + or – below:
UNKNOWN
Carbohydrate?
Protein?
Lipid?
Nucleic
Acid?
A
B
C
D
E
Plant
ANALYSIS:
1) Do you recall what the monomer is for each of the following polymer units?
a) Starch
b) Nucleic Acids
c) Proteins
d) Cellulose
2) It has been said that the DNA molecule (the blueprint of life) takes on a spiral staircase or
double helix appearance. Use the internet to locate a picture of DNA that fits this
description. Then, print it out and attach it to your lab. (Remember to print for your lab
partner, too!)