Understanding Infectious Diseases and DNA Structure
Phases of Infectious Diseases
Every disease can be divided into three phases:
- Incubation Period: The time elapsed between the entry of bacteria and the onset of the first symptoms.
- Prodromal Period: Characterized by the appearance of nonspecific, general signs that occur in a large number of processes. The pathogen has not yet acted on the body in a way that will cause specific infection.
- Clinical Period: The onset of symptoms and signs indicating the disease. These, along with analytical data, allow for an accurate diagnosis.
Prevention of Infectious Diseases
There are two ways to prevent infectious diseases: acting on the reservoir and source of infection, or on the susceptible host. In the first case, early diagnosis and treatment are important. We also need to monitor the distribution of disease in the community, find carriers, implement isolation, and provide health education.
Defenses Against Infection
Immunity is the resistance of organisms against infections caused by pathogens or foreign substances. The immune system’s response against an antigen is called the immune response.
There are two types of immunity:
- Innate (Nonspecific) Immunity: Present before the body is exposed to pathogens for the first time. It can destroy many pathogens during the first contact. The inflammatory reaction is an example of a nonspecific immune response.
- Adaptive (Acquired or Specific) Immunity: Acquired after contact with the pathogen. Lymphocytes and certain molecules released by them, such as antibodies, provide this type of immunity.
Fighting Infectious Diseases
- Sera: Artificially prepared solutions containing specific antibodies against a pathogen. They are obtained from the blood of a person or animal. Sera provide immediate, passive immunity, but it is short-lived, disappearing when the administered antibodies are removed from the body.
- Vaccines: Preparations that contain the pathogen that causes the disease, but in a weakened, dead, or fragmented form, so it cannot cause harm. The vaccine produces a response similar to that of a natural infection, but without its characteristic virulence and without risk to the vaccinated individual. When administered, vaccines trigger an immune response without causing disease. The individual is protected against the pathogen in future contacts due to the formation of memory cells.
- Drugs: Chemotherapy is the control of infectious diseases through drug products. The most important are antibiotics.
Antibiotics are substances produced and secreted by microorganisms that inhibit the growth of bacteria in very small quantities. They are used prophylactically or therapeutically against bacterial infections.
Structure of DNA
A DNA strand consists of numerous nucleotides linked together linearly. Thus, each DNA strand contains information. Similar to how a sequence of letters provides information in a written language, the sequence of nucleotide bases in DNA has meaning: genetic information. Therefore, some authors have called it “the book of life.”
The Watson and Crick model of DNA allows us to explain the reproduction of this information very clearly: DNA is a double helix, a shape resembling a spiral staircase consisting of two parallel chains or strands linked by bases via hydrogen bonds. The bases would be the steps, and the railings would be the deoxyribose-phosphate chains.
Genetic Expression
The amount of research that resulted in the discovery of the double helix was such that, once discovered, the mechanisms by which the information contained in DNA is transferred or expressed in the characteristics of organisms were also discovered. These mechanisms are summarized in the so-called central dogma of molecular biology, which states:
Genetic information flows from DNA to protein with the intermediation of RNA: mRNA, rRNA, and tRNA.
Reactions are carried out only if there are proteins that direct and control them. And these are only found in individuals bearing the corresponding gene in their cells.
The transfer of information, or protein synthesis, occurs in two stages: transcription and translation.