• CELL NUCLEUS • structure of double-membrane organelles
▶ Continuing with the video on the structure of double-membrane cell organelles—mitochondria and plastids—is a new video on the structure of the nucleus.
• Which cells have a nucleus?
• What does the nucleus of a non-digesting cell contain?
• What are histone and non-histone proteins?
• What is a chromosome, chromatid, or centromere?
• What is a genotype, phenotype, or karyotype?
Answers to biology questions are revealed in this video and other videos on the BEE Biology channel - / @beebiology5574
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Nucleus
The main structural component of the cell, as it Regulates all vital processes in the cell.
The nucleus has two membranes with pores (formed by proteins called nucleoporins).
The space between the two membranes is called the perinuclear (intermembrane) space.
The internal contents of the nucleus are the karyolymph (nucleoplasm, nuclear sap).
The main component of the nucleus is chromatin (consists of DNA – 40%, histone proteins – 40%, and non-histone proteins, RNA, and water – 20%).
Chromatin is subdivided into:
Euchromatin – practically invisible under a microscope because it is not packaged in protein; it is the informative part of DNA.
Heterochromatin – the part of DNA packaged in protein, usually non-informative, appears as clumps, and can sometimes become euchromatin. Chromatin is characteristic of interphase (non-dividing) cells.
During cell division—mitosis, meiosis—chromatin spirals and becomes chromosomes.
Chromosomes:
The most densely coiled part of a chromosome is the centromere, which divides the chromosome into arms.
Depending on the location of the centromere, chromosomes are classified as:
Equal-armed (metacentric)
Unequal-armed (submetacentric)
Acrocentric
Telocentric
Depending on the number of DNA molecules, chromosomes are classified as single- or double-chromatid.
The number of chromosomes is designated by the letter n, and the number of DNA molecules in them is designated by c.
Basic rules of chromosomes:
Rule of pairing: Every biological species that reproduces sexually has a paired (diploid, double) set of chromosomes in its cells, formed during fertilization (50% each from the father and mother);
These chromosomes in somatic cells form pairs and are called homologous. They contain the same set of genetic information and have the same functions and size.
The rule of chromosome number constancy: each biological species has a certain number of chromosomes (humans have 46), but the number of chromosomes may be the same in different species.
The rule of chromosome individuality: each biological species has a certain number of metacentric, submetacentric, acrocentric, and telocentric chromosomes, which are characterized by a certain size.
Based on the chromosome rules, the following concepts are introduced:
Karyotype is the diploid set of chromosomes in a somatic cell (non-reproductive cell), characterized by a certain number, size, and shape.
Karyotyping is the counting of chromosomes and determination of their shape, which is performed in the metaphase of mitosis;
Genotype is the set of genes in a diploid set of chromosomes;
Gene is a section of a DNA molecule encoding a protein;
Gene pool is the set of genes in a population;
Phenotype – the set of characteristics and basic properties of an organism.
Autosomes – chromosomes identical in males and females (44 autosomes).
Heterochromosomes – one pair of sex chromosomes – XX and XY.
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✔ External Independent Assessment (EIA) in biology;
✔ Unified State Exam (USE) in biology;
✔ Admission to medical school;
✔ Credits in medical biology departments;
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