are the smallest unit of life other than viruses,
which technically aren’t alive. Often they
are the building blocks for larger, multicellular
organisms. In animals, each cell contains
a nucleus. Nuclei (more than one nucleus)
are the “brains” of the cell. Cells also contain
other organelles, or parts, such as mitochondria
(the “stomachs”) and ribosomes (the “factory”
of the cell which makes chemicals the cell
needs to live). Inside the nucleus is all
the genetic information the cell needs to
exists and to reproduce.
most types of cells, genetic information is
organized into structures called chromosomes.
Under electron microscopes, chromosomes have
the shape of the letter X. Sometimes, though,
they look like the letter Y (as in human males).
The general rule is that the more chromosomes
a species has, the more developed it is. Fruit
flies, for example, only have four chromosomes
while humans have 46. Chromosomes work in
pairs; therefore, each human cell has 23 pairs
of chromosomes. In each pair, one comes from
the male parent and one from the female. Each
chromosome contains hundreds, sometimes thousands,
of smaller pieces of information called genes.
determine the unique characteristics or traits
an organism will have. Animals with the gene
for shaggy fur will have shaggy fur, and humans
with the gene for blue eyes will have blue
eyes. Each human being has thousands of traits
determined by his/her genes. Chemically speaking,
each gene is the blueprint for a specific
type of protein in the body. Proteins are
important because they do so many functions
in cells and in the human body. Proteins are
made of smaller units called amino acids.
4. There are
20 types of amino acids. Different combinations
and numbers of these amino acids make different
types of proteins. That means that one protein may
only have four amino acids while another has 20;
or two proteins may both have 20 amino acids but
they’re in a different order in each protein. Each
amino acid is made up of three nucleotide bases
found in DNA.
5. DNA is shaped
like a coiled ladder called a double helix. DNA,
or deoxyribonucleic acid, is made up of four nitrogen
bases called nucleotides, and a “backbone” made
of deoxyribose sugar. The four bases are adenine
(A), guanine (G), cytosine (C), and thymine (T).
These four bases bond to make the rungs of the spiral
ladder, but there are rules: T always bonds with
A (and visa versa) and C always bonds with G (and
vice versa). T will never bond with C or G, nor
will A. When three of these bases are “read” in
order, they form an mRNA codon through transcription.
Like their name suggests, codons are a special code
to make an amino acid. There are 64 possible codons.
Since there are only 20 amino acids, many codons
code for the same amino acids. Some codons are also
used to mark the beginning and end of a protein.
The codon that codes for the amino acid methionine
also functions as an initiator codon or beginner
of a protein sequence. The codons at the end of
the sequence are called terminators.