What Barriers Must Be Broken Down to Get to the DNA?

DNA is the genetic material found in living cells. It provides the necessary code for protein production eventually developing into a complex living organism. Each cell has developed barriers to house and protect DNA to prevent loss or accidental changes. Researchers have developed methods for breaking through the protective barriers in an effort to extract purified DNA for further research. Although most cells and non-living virus particles have developed similar barriers to protect genetic content, basic differences do exist.

Barriers to DNA in Viruses

• Viruses are non-living entities that must infect host cells in order to reproduce. The genetic content, DNA or RNA, is injected into the host cell and incorporates into the DNA reproductive mechanism of the host for reproduction. Protein surrounds the viral DNA, forming a protective barrier called a capsid, which also provides shape. The virus may also incorporate the host cell membrane to form a second protective barrier around the virus as it is released into the host organism or environment.

Prokaryotic Cell Barriers

• Bacteria are single-celled organisms belonging to a group called prokaryotes because they lack an internal barrier for DNA called the nucleus. The DNA is a circular molecule protected within gel-like cytoplasm of the cell. A membrane composed of polysaccharide or protein provides a protective barrier around the DNA and other internal components. Bacteria also possess a second barrier protecting DNA, a cell wall composed of peptidoglycan, a molecule made from polysaccharide and protein. The cell wall also helps maintain cell shape.

Eukaryotic Organisms

• Eukaryotic organisms have two separate barriers that house and protect DNA. The first barrier is the cell membrane, a two-layer membrane consisting of lipid molecules bound together. The outer surface is termed hydrophilic because it is soluble in water. The inner layers are hydrophobic hydrocarbon tails. Inside the cell is a second barrier called the nucleus, a compartment that contains the DNA. The nucleus is similar to the cell membrane composed of a bi-layer of lipid molecules. Eukaryotes include all animals, plants and protozoa. Plant cells add an additional barrier called the cell wall, a rigid layer comprised of cellulose surrounding the membrane.

Internal Barriers to DNA

• Eukaryotic organisms contain additional protective barriers for the DNA. DNA molecules are long strands barely visible underneath the microscope. The strands are wound around a specific group of proteins called histones. The combination of DNA and histones may be visualized as a string of beads called the nucleosome. Formation of the nucleosome provides a barrier to help protect the DNA from foreign DNA, viruses, and incidental mistakes. The bond between DNA and histone is strong. Energy is required to shift the histone before DNA can replicate before cell division or be used to transcribe proteins.