13 topics with concise reviews: definitions, key facts, and class questions.
This section focuses on the main «command center»—the cell nucleus, as well as the processes of cell division and cell death. Here we examine how the genetic material is organized, the structure of the nuclear envelope and nucleolus, and their functions.
You will study the levels of chromatin compaction, characteristics of sex chromatin, and the human karyotype. A dedicated module covers the dynamics of cellular life: we examine the cell cycle in detail, the complex mechanisms of its regulation, the phases of mitosis, and the phenomena of polyploidy and cell death (apoptosis and necrosis).
Practical classes and exams most frequently test the levels of DNA packing, morphological differences of mitotic phases under a microscope, and the diagnostics of sex chromatin (Barr bodies). Pay special attention to the regulation of cell cycle—this is the fundamental basis you will need in the future to understand the mechanisms of tumor development during your pathological anatomy course.
What is the difference between a chromosome and a chromatid?
A chromatid is a single DNA molecule with associated proteins. A chromosome is the highest structural unit, which may consist of one or two chromatids depending on the stage of the cell's life cycle.
UTP cannot enter the cell due to the phosphate groups, so the nucleoside uridine is used instead. Thymidine is used to track DNA replication, while uridine is specifically incorporated only into RNA during transcription.
UTP cannot enter the cell due to the phosphate groups, so the nucleoside uridine is used instead. Thymidine is used to track DNA replication, while uridine is specifically incorporated only into RNA during transcription.
Can euchromatin be visualized under a conventional light microscope?
No, decondensed regions (euchromatin) are completely indistinguishable at the light-microscope level. All dark nuclear regions visible under a light microscope are heterochromatin.
Can a Barr body be found in the somatic cells of a healthy male?
No. In males with an XY karyotype, the single X chromosome and the Y chromosome are in a decondensed state (as euchromatin). They lack an additional X chromosome that could condense.
How do histones bind to DNA?
The bond is maintained by electrostatic attraction. Positively charged amino acid residues of histones (arginine, lysine) interact with the negatively charged phosphate groups of DNA.
Why is it standard practice to describe the karyotype specifically during metaphase?
By the beginning of metaphase, chromosomes reach their maximum degree of condensation. They acquire a distinct X-shape and become best visible under microscopy.
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