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Cell biology


Also listed as: Transcriptomics
Related terms
Author information
Basic structure
Main types of cells
Cellular reproduction
Stem cells

Related Terms
  • Amniocentesis, bleeding, chorionic villus sampling, DNA, DNA sequencing, Duchenne muscular dystrophy, Fabry disease, hemophilia, inherited genetic disease, muscle degeneration, PCR, polymerase chain reaction, recessive, sex chromosome, X chromosome.

  • An X-linked recessive disorder is an inherited genetic disease caused by a mutation or error in the DNA (deoxyribonucleic acid) on the X chromosome. DNA is located in a compartment of the cell called the nucleus and is packaged in structures called chromosomes. In addition to DNA, chromosomes also contain proteins, such as histones, which help package the DNA in an orderly way. Human cells contain a total of 46 chromosomes (22 pairs of autosomes and one pair of sex chromosomes). Females have two copies of the X chromosome, while males have one X and one Y chromosome. Each chromosome contains hundreds of genes, each of which contain the instructions for making proteins in the body.
  • Individuals have two copies of most genes, one inherited from the father and one from the mother. In a recessive genetic disorder, both copies of a certain gene need to be defective for the condition to appear.
  • For an X-linked recessive disorder to affect a female, the X chromosomes from both parents must carry a certain genetic mutation. If a female receives one mutant and one normal X chromosome, the normal copy is usually able to compensate for the mutant copy. Because males have only one X chromosome, however, only one X-linked genetic mutation needs to be inherited for a male to be affected with an X-linked recessive disorder. Therefore, X-linked recessive disorders are more common in males than in females.
  • Duchenne muscular dystrophy (DMD) is a disease in which patients experience a progressive degeneration of muscle function. DMD is an X-linked recessive disorder caused by mutations in the gene that provides instructions for making dystrophin, a protein that helps maintain the structure and function of muscle cells. Patients with DMD experience a progressive degeneration of muscle function starting during infancy or early childhood. The loss of muscle function usually starts in the pelvis and the legs, but eventually spreads to all parts of the body. Patients with DMD first lose the ability to walk, and eventually lose the ability to move other parts of their body.
  • Because males inherit an X chromosome from their mother and a Y chromosome from their father, males can inherit an X-linked recessive disorder only from their mother. A male has a 100% chance of inheriting a mutant X chromosome and being at risk for developing a recessive X-linked disorder if his mother has a recessive X-linked disorder. However, if a mother is a carrier for an X-linked recessive disorder (meaning she has one mutant X chromosome and one normal X chromosome), then a male son has a 50% chance of inheriting a mutant X chromosome and being at risk for developing the disorder.
  • Because a female inherits one X chromosome from her mother and one X chromosome from her father, she would need to have a father who is affected with the X-linked recessive disorder to develop the disease. If a female has an affected father and an affected mother, there is a 100% chance she will inherit two mutant X chromosomes and be at risk for developing the disorder. If a female has an affected father and a mother who is a carrier for an X-linked recessive disorder, however, she will have a 50% risk of inheriting two mutant X chromosomes and of being at risk for developing the disease. If a female does not have an affected father and mother who is neither affected nor a carrier, she would be a carrier for the disease but would not develop the disease.
  • Many diseases are known to follow an X-linked recessive pattern of inheritance. Two examples of X-linked recessive diseases are hemophilia and Duchenne muscular dystrophy. Hemophilia is a bleeding disorder that affects the ability of blood to clot. It is an X-linked recessive disorder caused by mutations in genes that make clotting factor proteins. Blood clots normally form after injury to the skin and allow the skin to heal normally. In patients with hemophilia, blood clots don't form properly, which leads to bleeding that can range from mild to severe.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  1. Ashton EJ, Yau SC, Deans ZC, et al. Simultaneous mutation scanning for gross deletions, duplications and point mutations in the DMD gene. Eur J Hum Genet. 2008 Jan;16(1):53-61.
  2. Casaña P, Cabrera N, Cid AR, et al. Severe and moderate hemophilia A: identification of 38 new genetic alterations. Haematologica. 2008 Apr 9.
  3. Castaldo G, D'Argenio V, Nardiello P, et al. Haemophilia A: molecular insights. Clin Chem Lab Med. 2007;45(4):450-61.
  4. Children's Hospital Boston. .
  5. Genetics Home Reference. .
  6. Maheshwari M, Vijaya R, Kabra M, et al. Prenatal diagnosis of Duchenne muscular dystrophy. Natl Med J India. 2000 May-Jun;13(3):129-31.
  7. National Library of Medicine. .
  8. Natural Standard: The Authority on Integrative Medicine. .
  9. Rossetti LC, Radic CP, Larripa IB, et al. Genotyping the hemophilia inversion hotspot by use of inverse PCR. Clin Chem. 2005 Jul;51(7):1154-8.

Basic structure
  • Cell membrane: The cell membrane, also called the plasma membrane, is the outer boundary of the cell. This structure surrounds the cell and helps control what substances enter or exit the cell. The membrane is made up of two flexible layers of fats and proteins.
  • Chloroplast: A chloroplast is a small, organ-like structure inside the cell. Chloroplasts are only found in plant cells. They help plants convert sunlight energy into energy that allows the plant to produce food (carbohydrates). This process is called photosynthesis.
  • Cilia: Cilia are short, hair-like structures on the outside of cells. They act like a propeller for some cells, allowing them to move. Cilia may also help some cells take in food. In humans, the cells that produce mucus in the nose and throat also have cilia. These cilia trap airborne irritants and carry them toward the esophagus where they are swallowed. This helps prevent infections from developing inside the lungs.
  • Cytoplasm: The cytoplasm is the jelly-like substance that surrounds the nucleus of the cell and contains the organelles. The organelles are small, organ-like structures inside the cell, including the mitochondria, ribosome, and golgi apparatus.
  • Flagella: A flagellum is a whip-like structure located on the outside of some cells, such as bacteria. Flagella help cells move and/or take in food.
  • Golgi apparatus: A golgi apparatus, also called golgi complex, is a small, organ-like structure inside of cells. All living organisms except viruses, bacteria, and blue-green algae have a golgi apparatus inside each of their cells. The golgi apparatus is involved in processing and exporting proteins from the cell. For instance, some of these proteins are secreted by the cells, while others are incorporated into the cell membrane.
  • Mitochondria: The mitochondria are rod-shaped organelles that are often called the powerhouse of the cell. Mitochondria convert nutrients into energy for the cell. All organisms except viruses, bacteria, and blue-green algae have mitochondria inside their cells.
  • Nucleus: The nucleus is a round, organ-like structure inside cells. It contains the cell's genetic makeup. This genetic material is needed in order for the cell to multiply because it provides the instructions for cellular division.
  • Ribosome: A ribosome is a small, organ-like structure inside cells. It contains ribonucleic acid (RNA), which translates the genetic information to produce proteins for the cell. Each protein has a specific structure and function in the cell.

Main types of cells
  • Eukaryote: If a cell has a membrane surrounding its nucleus and organelles, it is a eukaryote. All organisms except viruses, bacteria, and blue-green algae are considered eukaryotes. These cells are more complex than prokaryote cells. The organism's genetic information is contained inside the membrane-bound nucleus.
  • Prokaryote: If a cell does not have a membrane surrounding its nucleus and organelles, it is called a prokaryote. Single-celled organisms, including bacteria, viruses, and blue-green algae, are called prokaryotes.

Cellular reproduction
  • General: Cell division occurs when the parent cell divides into two cells, called daughter cells. When a single-celled organism, such as the Amoeba, divides, it forms an entirely new organism. Cell division allows multi-cellular organisms, such as humans, to continually repair and renew of cells. For instance, when the skin is scraped, cells divide to form new skin cells. As a result, the wound heals. There are two types of cellular reproduction: meiosis and mitosis.
  • Meiosis: Meiosis, also called sexual reproduction, leads to the production of sperm or egg cells. Meiosis is a two-part cell division process in organisms, including humans, which sexually reproduce. Meiosis produces gametes (sperm or eggs cells) that contain half the number of chromosomes as the parent cell. Chromosomes contain all of the genetic information of an organism.
  • The parent cell contains 46 chromosomes. During the first phase of meiosis, the parent cell divides into two cells. Each of these new cells contains 23 chromosomes. During the second phase, each of these two cells produces a clone cell that also contains 23 chromosomes. A total of four gametes are now present.
  • Mitosis: Mitosis, also called asexual reproduction, occurs when one cell divides and creates an identical cell. There are five main phases of mitosis: interphase, prophase, metaphase, anaphase, and telophase.
  • During interphase, the cell prepares for division by enlarging and making a copy of its genetic material. During prophase, the genetic material condenses into structures called chromosomes. The membrane that contains the nucleus breaks down and tiny fibers called spindles form at opposite ends of the cell and meet at the equator. During metaphase, the chromosomes move so that they are aligned in the middle of the cell. During anaphase, the paired chromosomes (called chromatids) move to opposite ends of the cell. During telophase, the cell begins to split in half. Two new nuclei emerge at either end of the cell, and one-half of the chromosomes line up near each nucleus. The two cells then split apart completely, forming two new cells that are identical.

Stem cells
  • General: Stem cells are unspecialized cells that can potentially develop into different types of specialized cells. Researchers are interested in studying these cells because they may help treat diseases that are currently incurable, such as, Alzheimer's disease, Parkinson's disease, or multiple sclerosis (MS).
  • Adult stem cells (somatic stem cell): Adult stem cells are present in many human body tissues and organs. These cells allow the person to repair damaged cells or produce new cells in a tissue or organ. Researchers have discovered stem cells in more tissues and organs than they once thought possible. Stem cells have been identified in the brain, bone marrow, bloodstream, blood vessels, skeletal muscle, skin, and liver.
  • Today, adult stem cells are commonly used in patients who need bone marrow transplants. Researchers have been transplanting blood-forming stem cells from the bone marrow for more than 30 years.
  • Scientists have been studying these cells in laboratories to determine whether adult stem cells can be manipulated to produce specific types of cells. If scientists can find ways to make the adult stem cells produce specialized cells, they may be able to treat diseases. For instance, these specialized cells might be able to replace insulin-producing cells in patients with diabetes or dopamine-producing cells in patients with Parkinson's disease.
  • One potential advantage of adult stem cells is that they could be taken out of the patient and grown on a petri dish under specific conditions to make specialized cells. Then, the cells could be reintroduced into the same patient. Since the cells originally came from the same patient, there is no chance of rejection.
  • Unlike embryonic stem cell research, adult stem cell research is widely accepted. This is because the process does not require the destruction of an embryo.
  • Embryonic stem cells: Embryonic stem cells are present in organisms during the very early stages of development. In an embryo that is three to five days old, these stem cells produce specialized cells that make up the heart, liver, lungs, and other tissues.
  • Scientists are capable of removing stem cells from a human embryo for research. They are removed from eggs that have been fertilized in a laboratory and then donated for research purposes. Scientists want to learn more about the functions of these cells and how they are different from specialized cells. Researchers have suggested that these cells may be an effective cure for diseases, such as multiple sclerosis (MS). These cells may be able to replace the dead or defective cells that cause such diseases.
  • Embryonic stem cell research is controversial. Some individuals believe it is unethical to isolate stem cells from an embryo because embryos have the potential to develop into human beings.
  • In 2001, President George W. Bush approved federal funding for research of more than 60 pre-existing stem cell lines that have already been isolated from embryos. The embryos from which the existing stem cell lines were created had already been destroyed.
  • Federal funds are not available to isolate stem cells from additional embryos that have been fertilized in a laboratory and then donated for research purposes. Because the government does not currently support using embryos for research, it may only be conducted with private funds.
  • Umbilical cord stem cells: The umbilical cord, which carries blood, oxygen, and nutrients from the placenta to the baby during pregnancy, also contains stem cells. These cells can be removed from the placenta after the baby is born, and the umbilical cord is not longer needed.
  • Researchers are studying umbilical cord stem cells as possible treatments for diseases. One potential benefit of these cells is that they are less likely to cause transplant rejection than donated bone marrow or blood stem cells. Transplant rejection occurs when the transplant recipient recognizes the donated cells as foreign invaders and attacks them. Transplant rejection is less likely to occur because umbilical cord stem cells have not developed the features that the recipient's immune system can recognize and attack.
  • In addition, patients who receive umbilical cord blood have a decreased risk of developing graft-versus host disease (GVHD). This disease occurs when the donated cells attack the recipient's cells because they are identified as foreign. GVHD is less likely to occur because the umbilical cord blood does not contain well-developed immune cells needed to launch an attack.

Copyright © 2011 Natural Standard (

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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