In immunology two types of immune response are described depending on whether there is prior contact with the antigen.
• At this first contact, only lymphocytes with receptors specific to the antigen in question are stimulated and lead to the production of antibodies capable of neutralizing it. The lymphocytes capable of recognizing a specific antigen are very few and the production of antibodies - of low intensity and limited duration - is detectable only after a period of latency of several days. This is called the primary response. The specificity of the resulting seropositivity, however, makes it possible to detect contamination (seroconversion).
• Upon re-contact with an antigen that has already triggered a primary response, specific antibody production is found to increase rapidly after a short latency period. The secretion of IgG then reaches levels much higher than those observed during the primary response, while that of IgM is of the same order. This early and intense response, called secondary response, most often results in the destruction of infectious agents before any clinical sign.
• Many centuries before the discovery of microbes, it was noted that people who developed a contagious disease without death were then specifically immunized against the disease, without being protected against others.
• The ability to react appropriately to an already received stimulus supposes the existence of a memory. The immune memory is based on the existence of memory B and T lymphocytes, resulting from the clonal expansion due to the first contact with the antigen. Their lifespan is significantly higher than that of other lymphocytes and their high reactivity gives its rapid and intense character to the secondary response.
Answer:
The correct answer is: semi-conservative.
Explanation:
DNA replication is an important process in which the DNA is duplicated before cell division so each daughter cell can have a copy of genetic material.
DNA replication is <u>semi-conservative because one strand of DNA is new and the other one is the old strand</u>. To replicate itself, the DNA double helix is opened, and then each strand serves as a model for the new strands.
DNA replication is <u>not a one-step process</u>, as it takes several complicated steps in which <u>lots on enzymes participate</u> (like DNA polymerase and DNA helicase).
DNA replication is <u>also carried by prokaryotic cells</u>, though it's a much simpler process.
Carb carccarb carb seb carb
It was developed by scientists throughout history of mankind
