Receptor mediated endocytosis is the ingestion of molecules
bound to the surface receptors of the cell into endosomes. This is how
antigens bound to the receptors of B lymphocytes, for example, succeed
in entering the cell.
Receptors: The expression
of receptors for antigens on the cell surface is the defining property
of lymphocytes. Every lymphocyte bears a receptor with a unique structure.
The gene for this receptor is created by the rearrangement of receptor
segments during the lymphocyte maturation.
Rejection reaction: The destruction of foreign
transplanted tissue by aggressive lymphocytes is called a rejection
reaction. A distinction is made between the initial (primary) rejection
reaction and the following (secondary) rejection reactions against transplants
from the same donor or from a person related to the first donor. Secondary
rejection reactions are generally much more pronounced than primary
reactions.
Retroviruses are widespread. HIV, for example,
is one of the retroviruses. The genetic information is stored in the
form of single-strand RNA.
Reverse transcriptase is an essential
enzyme of retroviruses. It transcribes the RNA genome of these viruses
into DNA which is then integrated into the genome of the host cell.
Reverse transcriptase is also an important tool in molecular biology.
It can be used to transcribe RNA into cDNA for cloning.
Rhesus blood type antigens: The Rhesus blood type antigens (RH
antigens) are antigens in the membrane of the red blood cells which
are also present in Rhesus monkeys.
Rheumatoid arthritis: Rheumatoid arthritis is a very common
inflammatory disease of the joints which probably results from an autoimmune
reaction. It goes hand in hand with the production of the so-called
rheumatoid factor, an IgM anti-IgG antibody which can also be produced
as part of normal immune responses.
RNA (Ribonucleic acid) is also
a carrier of genetic information. In contrast to DNA, RNA is generally
single strand.
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