Nucleic acids contain genetic information and enable synthesis of proteins.
Nucleotides are used to make Nucleic Acids.
|Nucleotides are the subunit that is polymerized (connected
into a long chain) to make nucleic acids (DNA and RNA). Nucleotides consist
of three smaller components: a ribose sugar, a nitrogenous base, and phosphate
Generic nucleotide structure.
base" varies in different
|Ribose is the sugar component
of nucleotides. One of the main chemical differences between DNA and RNA
is that in RNA, the sugar is ribose, but in DNA, the sugar is deoxyribose,
in which an oxygen has been removed. (compare the bottom right corners
of the two structures - you'll see that the "OH" side group of ribose has
been replaced with an "H" ).
Nitrogenous Bases are Adenine, Guanine, Cytosine, and Thymine in
DNA. One of the chemical differences between DNA and RNA is that in RNA,
the nitrogenous base Uracil is used instead of Thymine.
Nucleotides may have one, two, or three phosphate groups attached.
|If there is one phosphate, the nucleotide is a monophosphate
|If there are two phosphates, the nucleotide is a diphosphate
|If there are three phosphates, the nucleotide is a triphosphate
If there are NO phosphate groups, the molecule is called a nucleoside,
not a nucleotide.
Naming Nucleotides: Nucleotide names are a three letter abbreviation.
The first letter refers to the nitrogenous base, the third letter refers
to the phosphate, and the second letter refers to the number of phosphates.
NOTE: If you're paying attention, you probably noticed that the nitrogenous
bases have names like Adenine, Thymine, and Guanine. Are you wondering
why the nucleotides are called Adenosine, Thymidine, and Guanosine? "Adenosine"
is the name for a nucleoside of adenine + ribose. Likewise, "thymidine"
and "guanosine" refer to the nucleosides - the combination of ribose sugar
and nitrogenous base.
Nucleotides can be connected to make nucleic acids.
The connection that forms between nucleotides is between the sugar of the
first nucleotide and the phosphate group of the second.
Each connection between nucleotides is a covalent bond, so the nucleic
acids have a covalently attached sugar-phosphate backbone.
In this figure, the nitrogenous
bases are representated as squares labeled T, C, and G, respectively.
Nucleic Acid Synthesis: Connecting nucleotides to make nucleic acids
Specific enzymes - DNA polymerase connects nucleotides to make DNA, and
RNA polymerase connects nucleotides to make RNA.
A pre-existing nucleic acid molecule to serve as a template - a
model or mold that determines the sequence of the strand being made. Nucleotides
are added based on complementary base-pairing (discussed below).
RNA is a long single chain of nucleotides.
Each sugar is ribose.
The nitrogenous bases are Adenine, Cytosine, Guanine, and Uracil.
The process of RNA synthesis is called transcription.
|RNA, like DNA (see below) is a long chain of individual nucleotides.
Unlike DNA, RNA is a single strand of nucleotides. In nature, parts
of an RNA molecule often base-pair with other parts of the same RNA molecule,
as depicted in the diagram (red lines indicating hydrogen bonds between
the base pairs C-G, A-U, and U-A).
To see an enlarged version of this figure, click
DNA is a pair of long chains of nucleotides.
Each sugar is deoxyribose.
The nitrogenous bases are Adenine, Cytosine, Guanine, and Thymine.
The process of DNA synthesis is called replication.
For more on DNA structure, scroll down or click here.
DNA Structure. At left is
an "unfolded" view of a double-stranded DNA molecule, showing the two chains
of nucleotides, connected in the center by a series of hydrogen bonds between
nitrogenous bases. At right, a schematic illustration showing the arrangement
of the two strands in the double-helix configuration. The "backbone" on
the outside is the sugar-phosphate chain, and the nitrogenous bases form
the bridges across the middle. For an enlarged version, click
DNA structure. The two strands
of DNA backbone are visible as red and grey balls; the nitrogenous bases
are the blue and grey regions in the center of the double helix.
Nitrogenous bases can form hydrogen
Adenine, Thymine, and Uracil can form TWO hydrogen bonds
Guanine and Cytosine can form THREE hydrogen bonds.
In nucleic acids (DNA and RNA), nitrogenous bases can bind to each other
by hydrogen bonding.
Guanine binds to Cytosine, and Cytosine binds to Guanine
In DNA, Adenine binds to Thymine. In RNA, Adenine binds to Uracil.
These hydrogen-bond interactions between nucleotides C-G and A-T or A-U
are referred to as base-pairing or complementary base-pairing.
Base-pairing holds the double-stranded DNA molecule together.
Base-pairing is necessary for DNA synthesis, RNA synthesis, and Protein
synthesis to occur.
Base-pairing can occur between two strands of DNA, between two strands
of RNA, or between one strand of DNA and one strand of RNA.
Some Nucleic Acids are RNA, which stands for ribonucleic acid.
RNA contains the nitrogenous bases Adenine, Cytosine, Guanine, and
All RNA is single-stranded (a single long chain of nucleotides). However,
one section of the RNA molecule can base-pair with another section.
This molecule, called tRNA
base-pairs with itself to form a cloveleaf structure. Each circle represents
a single nucleotide (A, U, c, or G). Lines that connect different nucleotides
represent the hydrogen bonds
In nature, the cloverleaf
folds up into a "L" shape. This is the same molecule represented in the
figure at left. The inset is another kind of depiction of the structure
of tRNA, called a space-filling model.
There are three kinds of RNA; the main purpose
of all of these is protein
rRNA = ribosomal RNA - part of the ribosome.
Ribosomes are large complexes consisting of multiple different RNA molecules
and many different protein molecules.
mRNA = messenger RNA - This long RNA molecule is an RNA copy of
a gene (a region of DNA that contains the instructions for synthesis of
a particular kind of protein).
tRNA = transfer RNA - during protein synthesis, carries amino acids
to the ribosome, where the amino acids are attached in a growing chain
that becomes the new protein. tRNA binds to mRNA by complementary base-pairing,
so tRNA also serves as a "bridge" between the information code of DNA and
RNA (the order of the nucleotides) and the code of protein (the order of
amino acids). To learn more about this process, read about protein synthesis.
Some Nucleic Acids are DNA, which stands for deoxyribonucleic
acid. Nitrogenous bases in DNA are Adenine, Cytosine, Guanine, and
All DNA is double-stranded. The two strands are antiparallel (pointing
in opposite directions). The backbone of each strand is the chain of sugars
and phosphates. The nitrogenous bases of each strand are in the center,
pointing toward the other strand. Each nitrogenous base forms hydrogen
bonds with the complementary base pair on the opposite strand. Because
the double-stranded DNA molecule twists around, it actually looks more
like a spiral staircase than like a ladder. DNA is referred to as the "double-helix"
because of this twist.
DNA is the genetic material in cells - the essential
part of the chromosomes.
Chromosomes are very long double-helixes of DNA - a long pair of
chains of nucleotides. The number of nucleotides in each strand is different
for each chromosome, but is generally MILLIONS of nucleotides long.
More on chromosomes.
Chromosomes in eukaryotic
cells are linear - they have two ends. Chromosomes in bacteria are
- the two ends are attached.
Genes are regions of the DNA on chromosomes. DNA is simply a long
chain of A, T, C, and G nucleotides in a particular order. Genes are particular
regions of DNA (A, T, C, and G nucleotides in a particular order) that
contain the instructions for making RNA and protein molecules. For example,
human genes contain thousands of genes, including the gene for beta-globin
(part of the hemoglobin protein, which transports oxygen in the blood)
and the gene for insulin (a hormone involved in regulation of glucose levels).
On a specific part of one human chromosome, the gene for beta-globin is
found: a specific sequence of A, T, C, and G nucleotides that contains
the information required for the cell to make beta-globin. On another chromosome
is a specific site where the sequence of nucleotides that encodes insulin
If you want to know more about DNA, chromosomes,
one link to try is:
I. The Chemistry of Life
A. The Basic Chemistry of Biology
II. The Cell
B. The Molecules of Biology
1. Water - Structure and properties,
hydrogen bonding, hydrophilic and hydrophobic, diffusion, osmosis
2. Amino Acids and Proteins;
Protein structure and conformation (and allosteric modification
3. Sugars and Polysaccharides
4. Nucleotides and Nucleic Acids (you are here)
5. Lipids and Membranes (general
information; more detail on membranes)