Encyclopedic Study Notes on General Biology, Genetics, and Parasitology

Foundations of Cytology and the Discovery of the Cell

The scientific exploration of the cell began with several key discoveries in the 19th century that defined the fundamental units of life. In 1831, Robert Brown was the first to identify and define the cell nucleus. Shortly thereafter, in 1839, J. Purkinje identified the cell protoplasm. The structural importance of these findings was synthesized into the Cell Theory in 1839 by German scientists Matthias Schleiden and Theodor Schwann. This theory established that the cell is the essential unit of life, including the cell wall, protoplasm, and nucleus. Following this, R. Virchow significantly contributed to the theory by stating that every cell is formed by the division of an already existing cell. Earlier historical figures, such as Aristotle, also contributed to biological knowledge by studying approximately $510$ animal species, classifying them, and putting forward initial ideas regarding the harmony and development found in nature.

Viral and Bacterial Biology

The study of non-cellular and prokaryotic life forms reveals distinct structural and reproductive characteristics. The virus was first identified by D.I. Ivanovsky in 1892, with the first discovery occurring on tobacco leaves. Viruses are composed of a shell known as a supercapsid, which consists primarily of proteins and lipids. In contrast, bacteria are unicellular organisms that reproduce rapidly; for example, some bacteria can divide every $20\,\text{minutes}$. Bacterial cells are characterized by a cell wall made of murein, while blue-green algae (prokaryotes) possess a cell wall made of cellulose and pectin. Blue-green algae contain a specific blue pigment known as phycocyanin. Examples of parasitic bacteria include the tuberculosis bacillus, which causes a slow-onset disease. Shape classification for bacteria includes cocci (spherical), bacilli (rod-shaped), vibrios (comma-shaped), and spirilla (spiral-shaped).

Structure and Dynamics of the Eukaryotic Cell Membrane

Eukaryotic cells are typically larger than prokaryotes, with most measuring between $10-100\,\mu m$ in diameter. Every eukaryotic cell is surrounded by a plasma membrane, or plasmalemma, which has a thickness of approximately $7-12\,nm$. This membrane performs vital functions, including serving as a protective barrier, facilitating transport transfer, and providing receptor functions. The structural composition is best explained by the "Mosaic" model proposed by Singer and Nicholson in 1972, which describes a lipid double layer where protein globules are unevenly and mobilely distributed. Under electron microscopy, the protein layers appear dark, while the biomolecular phospholipids appear light.

Membrane proteins are classified into three types: integral proteins (completely absorbed into the membrane), semi-integral proteins (partially penetrating), and peripheral proteins (forming a non-continuous layer). The membrane acts as a selective barrier, maintaining electrical and chemical gradients. For instance, the concentration of $Na^+$ is high around red blood cells, while the concentration of $K^+$ ions is high within the cytoplasm. Transport across the membrane occurs through direct transport, motor transport, and changes in membrane shape (conformation). Transport involving carriers is divided into passive and active types. Specific processes like pinocytosis allow for the absorption of water and dissolved substances, while phagocytosis involves the absorption of solid particles.

Compartmentalization and Organelles of the Eukaryote

Organelles in eukaryotes are divided into general organelles (found in most cells) and specific organelles (found in specialized cells). Common organelles include mitochondria, the endoplasmic reticulum (ER), ribosomes, the Golgi complex, lysosomes, the centrosome, and peroxisomes. Specific organelles include myofibrils, tonofibrils, neurofibrils, flagella, and microvilli. The internal environment of the cell is the hyaloplasm, a colorless colloidal system. The cytoskeleton, consisting of microtubules (made of the protein tubulin) and microfibrils, serves as the musculoskeletal system of the cell.

Mitochondria are double-membrane organelles responsible for energy production through oxidative phosphorylation and cellular respiration. The outer membrane is smooth and contains large pores for substances like $ADP$ and pyruvic acid, while the inner membrane forms folds (cristae) where redox enzymes are located. The mitochondrial matrix contains electron-dense granules with cations like calcium and magnesium. Ribosomes, with a diameter of approximately $25\,nm$, are small, round, electron-dense structures responsible for protein synthesis. The endoplasmic reticulum is categorized as granular (developed in the pancreas and liver) or smooth (found in the digestive glands). The Golgi apparatus, identified by Camillo Golgi in 1898, consists of a stack of rolls and tubes with bubbles; it dehydrates and compacts secretions. Lysosomes, which mature in the Golgi complex, contain enzymes for digestion and are classified into primary (inactive) and secondary types.

Cellular Metabolism and Bioenergetics

Metabolism involves two balanced processes: catabolism and assimilation. Catabolism (dissimilation) is an exoergonic process involving the decomposition of proteins, fats, and carbohydrates into $H_2O$ and $CO_2$, releasing energy for cellular activity. Assimilation is an endoergonic process requiring energy intake to synthesize complex molecules. Glycolysis, the anoxic phase of decomposition occurring in the cytoplasm, results in the destruction of $2$ molecules of $ATP$ initially, though it contributes to the overall energy cycle. A cell contains approximately $70$ chemical elements, with macronutrients including carbon ($C$), oxygen ($O$), phosphorus ($P$), and iron ($Fe$), while micronutrients include zinc ($Zn$), cobalt ($Co$), and manganese ($Mn$). The elements $H$, $C$, $O$, and $N$ make up $98\%$ of the total cell mass. Water content varies, with tooth enamel containing $10\%$ and plant cells containing up to $90\%$ water, where the molecules are held by hydrogen bonds.

Genetics, Heredity, and Molecular Biology

Genetics, founded by Gregor Mendel in 1866 and confirmed by De Vries, Correns, and Tschermak (Cermak) in 1900, studies the laws of heredity. Friedrich Miescher discovered nucleic acids in 1869, and Richard Altmann introduced the term in 1889, identifying purine and pyrimidine bases. In 1950, Erwin Chargaff determined the rules of complementarity: the amount of adenine ($A$) equals thymine ($T$), and guanine ($G$) equals cytosine ($C$). The double-helix structure of DNA was discovered by Watson and Crick in 1953. Genetic information is stored in genes, which consist of smaller units: the cistron (functional unit), muton (smallest part capable of mutation), and recon (unit of recombination), according to S. Benzer.

Protein biosynthesis involves several stages: increased amino acid activity, initiation (starting the chain), elongation (lengthening the polypeptide chain), and termination (the end of formation). This process is regulated by repression and inhibition. Chromosomal theory, developed by T. Morgan and his students, explains the transmission of genes on chromosomes. Chromosomes are classified by their centromere location: metacentric (equal arms), submetacentric (unequal arms), and acrocentric (one arm very short/rod-shaped). The human karyotype includes $46$ chromosomes, which can be grouped using Patau's classification (7 groups, A-G) based on size and centromere location. Somatic cells contain diploid sets, while gametes contain haploid sets.

Cellular Reproduction and Lifecycle

Mitosis is the primary form of eukaryotic cell division, ensuring even distribution of genetic material (2n4c to 2n2c). It consists of several phases: Prophase ($10-100\,\min$), where chromosomes spiralize and the nuclear envelope dissolves; Metaphase ($6-40\,\min$), where chromosomes align at the equator; Anaphase ($4-25\,\min$), where centromeres divide and chromatids move to poles; and Telophase ($9-30\,\min$), where the nuclei reform. Meiosis involves two divisions, including Prophase I with substages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Crossing over occurrs during Prophase I. Other reproductive methods include conjugation (found in bacteria and ciliates), parthenogenesis (development from an unfertilized egg, used by silkworms), and schizogony (multiple division used by malarial plasmodium).

Principles of Evolution

Biological evolution is an irreversible process, a term introduced by C. Bonnet in 1762. Microevolution leads to diversification within populations and species, while macroevolution involves the formation of higher systematic units (genera, families). Natural selection is the driving factor, appearing in forms like stabilizing selection (preserving traits in constant environments) and driving (directional) selection. Jean-Baptiste Lamarck published "Philosophy of Zoology" in 1809, proposing early evolutionary ideas, though Charles Darwin’s "Origin of Species" (1859) provided the mechanism of natural selection after his voyage on the Beagle ($1831-1836$). Key evolutionary directions include aromorphosis (morphophysiological progress), idioadaptation (specific niche adaptation), and degeneration (simplification). Isolation, geographic or biological, is essential for the emergence of new species.

Ecology and the Biosphere

Ecology studies organisms and their environments, categorized into abiotic, biotic, and anthropogenic factors. Organisms have environmental valency, with eurytopes having broad tolerance and stenotopes having narrow tolerance. Ecosystems function through periodic metabolism and energy flow, governed by the ecological pyramid rule stating that energy and biomass decrease approximately $10$ times at each successive trophic level. Vladimir Vernadsky developed the theory of the biosphere, the layer of Earth where life exists, comprising the atmosphere, hydrosphere ($71\%$ of the planet), and lithosphere. Living matter performs gas exchange, concentration (accumulating elements), and redox functions. Human ecology studies adaptive types, such as the Arctic adaptive type (high hemoglobin, large chest) and the Tropical adaptive type (elongated limbs, increased sweating), which reflect genetic adaptations to specific climates.

Medical Parasitology and Interspecies Interaction

Interspecies relationships include antibiosis (competition) and symbiosis (living together). Symbiosis is further divided into mutualism (mutually beneficial), commensalism (one benefits, the other unaffected), and synocism (using a host for shelter, like living in rodent nests). Antagonism includes predation and parasitism. Medical parasitology, advanced by scientists like V.A. Dogel and E.N. Pavlovsky, focuses on parasites affecting humans. Parasites can be ectoparasites (outer surface) or endoparasites (internal). Transmission occurs through inoculation (e.g., malaria transmitted by mosquito saliva) or contamination (fecal-oral). Vector-borne diseases involve blood-sucking arthropods, such as the tse-tse fly (Trypanosoma gambiense/sleeping sickness) and triatome bugs (Trypanosoma cruzi/Chagas disease). Leishmaniasis, discovered by P.F. Borovsky in 1898, is transmitted by sandflies and occurs in cutaneous (Ashgabat ulcer) or visceral forms.

Questions & Discussion

The text provided consists of a comprehensive set of examination questions covering cell history, molecular genetics, evolutionary biology, and medical parasitology. The questions address specific details such as the diameter of a centriole ($150\,nm$), the discovery of DNA polymerase by A. Kornberg in 1956, and the classification of chromosomal diseases like Down syndrome (Trisomy 21), Shershevsky-Turner ($45$ chromosomes), and Klinefelter syndrome. Evolutionary concepts like those from Aristotle's "History of Animals" and Darwin's observations of unique South American animals (llama, tapir, sloth) are highlighted to test the breadth of biological knowledge.