Chromosomes
What are chromosomes?
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece
of coiled DNA containing many genes, regulatory elements and other nucleotide sequences.
Chromosomes also contain DNA-bound proteins, which serve to package the DNA and
control its functions.
Chromosomes vary widely between different organisms. The DNA molecule may be circular
or linear, and can be composed of 100,000 to 10,000,000,000 nucleotides in a long chain.
Typically, eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic
cells (cells without defined nuclei) have smaller circular chromosomes, although there are
many exceptions to this rule. Also, cells may contain more than one type of chromosome;
for example, mitochondria in most eukaryotes and chloroplasts in plants have their own
small chromosomes.
Information on chromosomes
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the
cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly
packed during cell division and is then visible under a microscope. Most of what researchers
know about chromosomes was learned by observing chromosomes during cell division.
Each chromosome has a constriction point called the centromere, which divides the
chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the
“p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the
centromere on each chromosome gives the chromosome its characteristic shape, and can be
used to help describe the location of specific genes.
Function of chromosomes
In the broadest sense, chromosomes function is to control all the activities of a living cell.
Chromosomes are essential for the process of cell division and are responsible for the
replication, division and creation of daughter cells, that contain correct sequences of DNA
and proteins. Proteins make up one of the most important components of the human body,
they are responsible for building muscles and tissues, growth and repair, as well as the
synthesis of the thousands of enzymes like DNA replication enzymes, produced by the body.
Protein synthesis steps, and their successful completion is the responsibility of genes, that
are contained in chromosomes. Chromosome functions include holding genes, the units of
heredity.
Genes are located at a particular point on a chromosome, known as its locus. Each
chromosome contains DNA in a double helix structure, which houses thousands of genes
along the strand, each with their own loci. Genes are the units that hold codes that control
the building and maintenance of cells; they also control the characteristic traits that are
passed on from parents to offspring.
Chromosomes are often referred to as the 'packaging material' that hold DNA and proteins
together in eukaryotic cells (cells that have a nucleus). Cell division is a continuous process
that must occur for an organism to function, whether for growth, repair or reproduction.
During cell division stages, it is the chromosome that is responsible for the replication and
distribution of DNA amongst new cells. Strangely enough, the function of chromosomes in
plant cells are the same as the function of chromosomes in animal cells. In fact,
chromosomes differ structurally more between prokaryotes and eukaryotes, as opposed to
different species.