The structure of double-stranded DNA is universal in all living cells, but differences occur in the methods for extracting genomic DNA from animal and plant cells. Genomic DNA is found in the nucleus of cells. The amount and purity of extracted DNA depends on the type and size of the cell, as certain cells contain more DNA and impurities than others.
General DNA Extraction
Plant and animal cells treated with a soapy substance will degrade the lipids in the cell and nuclear membranes. The DNA mixture will then separate from the cell membranes and proteins. The DNA in solution can be precipitated using alcohol. Depending on the amount in the sample, DNA may be visible by the naked eye. Such a simple procedure does not necessarily produce DNA of high purity.
Plant and Animal Cells
Plant cells are distinguishable from animal cells by their rigid cell wall and organelles like the chloroplast. They also contain proteins and enzymes that play a role in photosynthesis. Some plant cells are polyploidy, meaning they have more than one copy of each chromosome per cell. Cellular processes occurring in plants such as photosynthesis produce a range of secondary metabolites. Animal cells do not have a cell wall, but still need to be treated with chemicals like sodium dodecyl sulphate (SDS) to disrupt the cell membrane to release genomic DNA.
Plant DNA extraction
Plant genomic DNA is more difficult to extract because of the plant’s cell wall, which is removed by homogenization, or by adding cellulase to degrade the cellulose that makes up the cell wall. Also, the metabolites present in the plant cell may interfere with genomic DNA extraction by contaminating the DNA sample during the precipitation process.
Animal DNA Extraction
Peripheral blood leukocytes are a main source of animal genomic DNA, but sample collection is difficult as blood must be withdrawn from the animal. Blood contains a range of compounds like proteins, lipids, white blood cells, red blood cells, platelets, and plasma, which can contaminate the DNA sample. The primary contaminant of animal DNA extracted from blood samples is heme, the non-protein component of hemoglobin.
The differences between plant and animal DNA lie in the sequence of bases in the helix. Compounds found in plant cells are absent in animal cells, and DNA base sequences reflect this, as the genomic plant DNA is often larger than animal DNA. These differences affect extraction methods, as it impacts on yield and purity of DNA.