A cell without DNA has many limitations that can hasten its demise. Cells require DNA to carry out essential life functions, transmit genetic material, assemble the right proteins and adapt to fluctuating environmental conditions. Some highly specialized cells shed their nucleus to more efficiently perform a specific task such as carrying hemoglobin and carbon dioxide. Anucleated cells like mature red blood cells are more susceptible to environmental toxicity and have a relatively short life span.
What Is DNA?
Deoxyribonucleic acid (DNA) contains the genetic coding instructions of living organisms. DNA is comprised of adenine, cytosine, guanine and thymine bases that pair up and connect through hydrogen bonds. A complementary base pair – like adenine (A) and thymine (T) – attached to sugar and phosphate molecules is called a nucleotide. Long strands of nucleotides form the now-famous double DNA helix discovered in 1952 by James Watson, Francis Crick, Rosalind Franklin and Maurice Wilkins, scientists at King's College in London.
Eukaryotic cells replicate DNA and then share a copy when the cell divides through the process of mitosis or meiosis. Meiosis includes an extra step during cell division where snippets of DNA break off from one chromosome and reattach to the matching chromosome. Divided chromosomes are pulled to opposite ends of the cell, and the nuclear envelopes reform around the chromatin.
DNA in the Nucleus
The nucleus serves as the commander-in-chief that passes along orders to command units. DNA housed in the nucleus provides all the instructions for encoding the proteins needed by the organism. Losing the nucleus would cause mayhem inside the cell. Without a clear set of instructions, the typical somatic cell would have no idea what to do next.
Cells also need a nucleus to help regulate the movement of substances across the cell membrane. Molecules move back and forth by osmosis, filtration, diffusion and active transport. Different types of vesicles also play a role in moving substances in or out of the cell. Without a nucleus running the show, a cell might collapse or swell and burst.
Why Can’t DNA Leave the Nucleus?
The nuclear envelope is a double-membrane structure that corrals DNA (chromatin) inside the nucleus. During interphase, the nucleus procures nutrients and provides an optimal environment for duplication of DNA. Once the cell is ready to start dividing, the nuclear envelope disassembles and releases the chromosomes into the cytoplasm. DNA is protected and guarded in the nucleus because it contains the entire genome of the organism needed for species propagation.
Do All Cells Need DNA?
Can life exist without DNA? Are viruses living? Are tumor cells alive? Answering these questions requires understanding and agreement on the meaning of life, but not in an arcane philosophical sense. According to NASA astrobiologists, “Life is a self-sustaining chemical system capable of Darwinian evolution.” However, definitions of life differ, and that affects how viruses containing only RNA are classified, for instance.
Eukaryotic cells contain DNA in their nucleus, which oversees normal operating procedures. The purpose of cell division is to grow and multiply. Evolution and adaptation result from unique pairings of DNA nucleotides. Cells without DNA would have no genetic material to transmit.
What Does Messenger RNA (mRNA) Do?
Messenger ribonucleic acid (mRNA) molecules act as the go-between for nuclear DNA and the rest of the cell. As the name suggests, mRNA copies (transcribes) parts of DNA and sends readable messages to organelles, signaling when to divide or assemble certain types of proteins. If a cell lost its nucleus and DNA, the cell would eventually weaken and catch the attention of devouring microphages in the immune system.
Basic Parts of a Cell: Eukaryotic Organisms
Eukaryotic cells have a nucleus that contains DNA. By definition, eukaryotic organisms would not come into existence without DNA. In addition to a nucleus, eukaryotic organisms contain many types of organelles that perform on cue:
- The endoplasmic reticulum (ER) is a folded membrane attached to the nucleus. The outer layer is called rough ER because it is covered with bumpy ribosomes. Protein molecules are put together between the rough ER and smooth inner layer of the ER. Vesicles move the newly assembled proteins to the Golgi apparatus for further processing and distribution.
- Ribosomes are tiny but important protein structures. Ribsomes decode the messenger RNA copied from DNA and put together the prescribed amino acids in the correct order. After being formed in the nucleolus, ribosomes float around in the cytoplasm or bind to the rough endoplasmic reticulum.
- The cytoplasm is a semi-fluid liquid within the cell that facilitates chemical reactions. The cytoskeleton – made of fibrous proteins – helps position organelles in the cytoplasm. Chromatids condense in mitosis and line up along the middle of the cell before being pulled apart by the mitotic spindle, which consists of microtubules in the cytoplasm.
- Vacuoles are storage pouches in the cell that temporarily retain food, water and waste. Plants have a large vacuole that stores water, regulates water pressure and reinforces the cell wall.
- Mitochondria are commonly known as the power plant of the cell. Adenosine triphosphate (ATP) energy is produced through cellular respiration. Cells with high energy needs contain large numbers of mitochondria.
Basic Parts of a Cell: Prokaryotic organisms
The DNA of prokaryotic cells is located in a nucleoid region. Prokaryotic DNA and organelles are not surrounded by membranes. Ribosomes that produce protein are the predominant organelle in the cytoplasm. Bacteria exemplify prokaryotic life forms; some have whiplike flagellum that are sensory organelles.
Where Is DNA Located?
Most DNA is located in the nucleus (nuclear DNA), but small quantities are also present in the mitochondria (mitochondrial DNA). Nuclear DNA regulates cell metabolism and transmits genetic material from one dividing cell to the next. Mitochondrial DNA synthesizes proteins, makes enzymes and replicates itself. Prokaryotic cells also contain DNA, but there is no nuclear membrane or envelope.
Why Can’t a Cell Survive Without a Nucleus?
A cell requires a nucleus for some of the same reasons that a body needs a heart and a brain. The nucleus manages the daily operations of the cell. Organelles need instructions from the nucleus. Without a nucleus, the cell cannot get what it needs to survive and thrive.
A cell without DNA lacks the capacity to do much of anything other than its one given task. Living organisms depend on genes in DNA to guide proteins and enzymes. Even primitive life forms have DNA or RNA. Within the 46 chromosomes of the human body, there are approximately 20,500 genes in DNA that are responsible for the trillions of cells in human tissue, according to Genetics Digest.
DNA and Cell Differentiation
All organisms start with a little ball of cells that specialize into many different types of cells like neurons, white blood cells and muscle cells. In the beginning, all cells need a nucleus to tell it what to do. Instructions can even include programmed death. For example, hair, skin and nails are dead cells filled with keratin.
Reproductive or therapeutic cloning involves removing the nucleus of an egg cell and replacing it with the nucleus of a somatic donor cell. Then the cell is electrically or chemically jump-started. Under carefully controlled conditions, the cells will grow and differentiate into a new organ, tissue or organism possessing the DNA of the donor.
Susceptibility of Cells Without Nuclei
Mature red blood cells and epithelial cells of the skin and gut are prone to wear and tear, injury, and mutation due to ferrying wastes or coming into contact with environmental toxins. Not surprisingly, cells that do not have a nucleus die off faster than other types of cells. Absence of a nucleus in such cells offers a protective factor. If these cells had a nucleus, the odds of chromosomal damage would be higher and possibly fatal to the organism if allowed to divide and pass along life-threatening mutations, causing diseases and tumors.
Sperm and Egg: Nucleus Function (Meiosis)
Without DNA, cells could not reproduce, which would mean extinction of the species. Normally, the nucleus makes copies of chromosomal DNA, then segments of DNA recombine, and next the chromosomes divide twice, forming four haploid egg or sperm cells. Mistakes in meiosis can result in cells with missing DNA and inheritable diseases.
Why Plant Cells Need DNA
Like animal cells, plant cells have a membrane-enclosed nucleus containing DNA. In addition, plants contain chlorophyll, which captures sun energy for use in photosynthesis and harvesting food energy. In turn, plants produce food for the rest of the food web. Plants also enhance the environment by releasing oxygen and sinking atmospheric carbon dioxide.
The presence of a nucleus enables plants to reproduce and maintain population stability. If plants did not have a nucleus directing the activities of the cell, they would not be able manufacture food. Consequently, plants would die out. In turn, herbivores would be in jeopardy if their food source was eliminated.
Plant Cell DNA and Biodiversity
Biodiversity is the key to species survival for multicellular organisms. Plant species cannot migrate to a new home if climate changes or disease vectors suddenly threaten the survival of a species isolated in a particular area. Through gene recombination in meiosis, genetic variation exists within populations that makes certain plants hardier and more resistant, thanks to their unique genome. Although plants of the same type may all look alike at first glance, there are typically small but significant differences observable to the trained eye.
For instance, two seemingly identical plants growing side by side may have slight variations in average leaf size, venation and root structure owing to their unique genotype. Such subtle differences can be helpful or harmful if environmental conditions change. For example, during periods of drought, plants face higher rates of water evaporation. Plants with heavily veined, small leaves may be better fit to survive and reproduce in arid conditions, for instance.
Viral Hijacking of Cellular DNA
Viruses may pose a serious threat the DNA of the host cell. A virus infects its host by injecting molecules of viral DNA or RNA into a host cell. Viral DNA commands the cell to produce copies of viral proteins rather than the cell's own, to create more viruses that continue to replicate. Eventually, the cell can burst and die, spreading viruses that will divide over and over again. Common diseases such as chicken pox and influenza are caused by viruses, which do not respond to antibiotics.
DNA Test Questions
Students studying cellular and molecular biology must have a firm grasp on the role and importance of DNA in all phases of the cell cycle. Without DNA, living organisms could not grow. Further, plants could not divide by mitosis, and animals could not exchange genes through meiosis. Most cells simply wouldn't be cells without DNA.
Sample test questions:
If its nucleus and DNA were missing, a plant cell would be unable to which of the following?
- Complete the cell cycle.
- Grow larger.
- Divide by mitosis.
- All of the above.
If its nucleus and DNA were missing, an animal cell would be unable to do which of the following?
- Complete the cell cycle.
- Grow larger.
- Divide by meiosis.
- All of the above.
- Astrobiology at NASA: About Life Detection
- U.S. National Library of Medicine: Genetics Home Reference: What Is DNA?
- Medical News Today: Viruses: What Are They and What Do They Do?
- NCBI Bookshelf: StatPearls: Genetics, Meiosis
- Genetics Digest: How Many Genes Do Humans Have?
- National Cancer Institute: Cell Function
- Florida State University: Molecular Expressions: Plant Cell Structure
- The National Wildlife Federation: Biodiversity
- PBS:The Discovery of DNA's Structure