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Carbohydrates are the third major component of plasma membranes. They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids) ( [link] ). These carbohydrate chains may consist of 2–60 monosaccharide units and can be either straight or branched. Along with peripheral proteins, carbohydrates form specialized sites on the cell surface that allow cells to recognize each other. These sites have unique patterns that allow the cell to be recognized, much the way that the facial features unique to each person allow him or her to be recognized. This recognition function is very important to cells, as it allows the immune system to differentiate between body cells (called “self”) and foreign cells or tissues (called “non-self”). Similar types of glycoproteins and glycolipids are found on the surfaces of viruses and may change frequently, preventing immune cells from recognizing and attacking them.

These carbohydrates on the exterior surface of the cell—the carbohydrate components of both glycoproteins and glycolipids—are collectively referred to as the glycocalyx (meaning “sugar coating”). The glycocalyx is highly hydrophilic and attracts large amounts of water to the surface of the cell. This aids in the interaction of the cell with its watery environment and in the cell’s ability to obtain substances dissolved in the water. As discussed above, the glycocalyx is also important for cell identification, self/non-self determination, and embryonic development, and is used in cell-cell attachments to form tissues.

Evolution connection

How viruses infect specific organs

Glycoprotein and glycolipid patterns on the surfaces of cells give many viruses an opportunity for infection. HIV and hepatitis viruses infect only specific organs or cells in the human body. HIV is able to penetrate the plasma membranes of a subtype of lymphocytes called T-helper cells, as well as some monocytes and central nervous system cells. The hepatitis virus attacks liver cells.

These viruses are able to invade these cells, because the cells have binding sites on their surfaces that are specific to and compatible with certain viruses ( [link] ). Other recognition sites on the virus’s surface interact with the human immune system, prompting the body to produce antibodies. Antibodies are made in response to the antigens or proteins associated with invasive pathogens, or in response to foreign cells, such as might occur with an organ transplant. These same sites serve as places for antibodies to attach and either destroy or inhibit the activity of the virus. Unfortunately, these recognition sites on HIV change at a rapid rate because of mutations, making the production of an effective vaccine against the virus very difficult, as the virus evolves and adapts. A person infected with HIV will quickly develop different populations, or variants, of the virus that are distinguished by differences in these recognition sites. This rapid change of surface markers decreases the effectiveness of the person’s immune system in attacking the virus, because the antibodies will not recognize the new variations of the surface patterns. In the case of HIV, the problem is compounded by the fact that the virus specifically infects and destroys cells involved in the immune response, further incapacitating the host.

This illustration shows the plasma membrane of a T cell. CD4 receptors extend from the membrane into the extracellular space. The HIV virus recognizes part of the CD4 receptor and attaches to it.
HIV binds to the CD4 receptor, a glycoprotein on the surfaces of T cells. (credit: modification of work by NIH, NIAID)

Questions & Answers

what is biomolecules
Lawerence Reply
This is a group of molecules produced by a living organism
thank alot,I had a hard time getting the answer
wat is the meaning of Mr.niger. d
It Reply
Now Mr. Niger Dac M;movement R;respiration N;nutrition G;growth E;excretion R;reproduction D;death A;adaptation C;competition
Sorry.... I;irritability
Mesumbe Reply
Emmanuel Daniel
what is the meaning of Mr Niger?
state all the elements and their symbols
Taiwo Reply
what types of muscles are found in the heart
Diamond Reply
Cardiac muscle
cardiac or myocardia muscle
cardiac muscles
cardiac muscle
Cardiac muscle
Thank you dear!
please can you tell me the meaning of Mr Niger?
It is an initial to represent life processes of organisms. M means movement, R for reproduction, N stands for nutrition, I for irritability or sensitivity,G means growth , E for excretion and R stands for respiration.
cardiac muscle
what is digestion
Dolla Reply
it is the chemical break down of insoluble food substances such as fatty acid to soluble substances which are then used for body processes
does human being sperm performed in the ovary of goat
sadeeq Reply
levels of ecological study
human sperms contains acid
what is an artery
It is one of the organs of the circulatory system that carries oxygenated blood from the heart to other parts of the body.
artery is type of blood vessel which carries blood away from heart...
how liver destroy red blood cells?
big bang theory was discovered by
Sweety Reply
Georges Lemaître
the meaning of nucleus
Spring Reply
nucleus Is also known as the cell's headquarters
what is pathology?
Azi Reply
is the study of diseases, it's cause and development of a disease
State the law of segregation
Theolla Reply
what is a cell
Bunmi Reply
A cell is a basic structural unit of an organism
what are molecules?
molecule:a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
cell is basic structural and functional unit of life which can perform all the metabolic activities
which organ function as modulator & effector in homeostasis glucose level ( Liver & islet of Langerhans ) & How ?
a cell is the basic unit of life
A cell is the basic unit of life
basic structural and functional unit of any living organism
comapare and contrast food chain
Chengo Reply
what are the classes of biology
Oluebube Reply
Microbiology Biochemistry Botany Zoology Horticulture
what is translocation
James Reply

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