Download Structure of DNA and RNA

Structure of DNA Lab
Introduction:
Deoxyribonucleic acid (DNA) is one of the two types of nucleic acids found in organisms and viruses. The
structure of DNA determines which proteins particular cells will make. The general structure of DNA
was determined in 1953 by James Watson and Francis Crick. The model of DNA that they constructed
was made of two chains now referred to as the double helix. Each chain consists of linked deoxyribose
sugars and phosphates units. The chains are complementary to each other. One of four nitrogencontaining bases connects the chains together like the rungs of a ladder. The bases are cytosine,
guanine, thymine, and adenine. The DNA molecule looks like a spiral staircase. The structure of DNA is
illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn.
DNA is a polymer. The monomer units of DNA are nucleotides. Each nucleotide consists of a 5-carbon
sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group.
(See Table 1.) There are four different types of nucleotides found in DNA, differing only in the
nitrogenous base. Adenine and guanine are purines. Purines are the larger of the two types of bases
found in DNA. They have two rings of carbons & nitrogens. Cytosine and thymine are pyrimidines and
have a single carbon-nitrogen ring.
The sequence of these bases encodes hereditary instructions for making proteins—which are long chains
of amino acids. These proteins help build an organism, act as enzymes, and do much of the work inside
cells.
Table 1
DNA Nucleotide
(Sugar + Phosphate + Base)
Procedure:
1. Use the section of DNA (Human hemoglobin or Chicken Hemoglobin), and figure out the sequence
of bases present on the complementary strand of this molecule.
Human Hemoglobin
Left Strand
Complementary Strand
Chicken Hemoglobin
Left Strand
TAA
GTT
TGT
TGT
CGA
CCG
CCG
CCG
CTG
CGA
GTC
GTC
CAA
TAT
GTC
CGA
CTT
TTG
TGA
AGG
Questions& Observations:
1. What 2 molecules make up the sides of the DNA molecule?
2. What nitrogen bases form the rungs of the DNA double helix?
3. What is meant by the complementary strand of DNA?
4. What sugar makes up DNA nucleotides?
5. How are nucleotides named?
6. DNA is the instructions for building what molecule in our cells?
7. What would happen if one or more bases on the DNA strand were changed?
8. What is the base pairing rule that nitrogen bases must follow?
9. How many differences did you find between the human and the chicken?
Complementary Strand
Messenger RNA
So, now, we know the nucleus controls the cell's activities through the chemical DNA, but
how? It is the sequence of bases that determine which protein is to be made. The sequence is like a
code that we can now interpret. The sequence determines which proteins are made and the proteins
determine which activities will be performed. This is how the nucleus is the control center of the
cell. The only problem is that the DNA is too big to go through the nuclear pores so a chemical is used
to read the DNA in the nucleus. That chemical is messenger RNA (mRNA). The messenger RNA (mRNA)
is small enough to go through the nuclear pores. It takes the "message" of the DNA to the ribosomes
and "tells them" what proteins are to be made. Recall that proteins are the body's building blocks.
Imagine that the code taken to the ribosomes is telling the ribosome what is needed - like a recipe.
Messenger RNA is similar to DNA, except that it is a single strand, and it has NO thymine.
Instead of thymine, mRNA contains the base Uracil. In addition to that difference, mRNA has the
sugar ribose instead of deoxyribose. RNA stands for Ribonucleic Acid.
10. How does the base pairing for RNA differ from DNA?
11. Complete the data table for the RNA sequence of the DNA strand for Human Hemoglobin
12. What sugar is found in DNA? In RNA?
Human Hemoglobin
Left Strand
TAA
TGT
CGA
CCG
CTG
GTC
CAA
GTC
CTT
TGA
RNA Sequence