Question

Опишите строение хромосом

Answer 1

Хромосомы животных и растений представляют собой палочковидные структуры разной длины с довольно постоянной толщиной, у большей части хромосом удается легко найти зону первичной перетяжки, которая делит хромосому на два плеча. В области первичной перетяжки находится центромера, где расположен кинетохор. Некоторые хромосомы имеют вторичную перетяжку. В конце интерфазы каждая хромосома состоит из двух сестринских хроматид. Каждая из них, в свою очередь, состоит из двух половинок – полухроматид или хромонем. Хромонемы содержат уплотненные участки – хромомеры, которые в световом микроскопе имеют вид темноокрашенных гранул. Их число, положение и величина в обеих хроматидах одинаковы и для каждой хромосомы относиельно постоянны. Расстояния между хромомерами называются межхромомерными участками.

Answer 2

Structure of Chromosomes

Chromosomes are thread-like structures found in the nucleus of cells. They contain genetic material, which carries the instructions for the development and functioning of living organisms. Here is a detailed description of the structure of chromosomes:

1. DNA Molecule: The main component of chromosomes is deoxyribonucleic acid (DNA). DNA is a double-stranded molecule that consists of nucleotides. Each nucleotide is composed of a sugar molecule, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).

2. Histones: DNA is wrapped around proteins called histones. Histones help in organizing and compacting the DNA molecule. The DNA and histones together form a structure called a nucleosome.

3. Chromatin Fiber: Nucleosomes are further coiled and folded to form a chromatin fiber. Chromatin fibers are long, thin, and thread-like structures that are visible during interphase (the non-dividing phase of the cell cycle).

4. Sister Chromatids: During cell division, the chromatin fibers condense further to form distinct structures called sister chromatids. Sister chromatids are identical copies of each other and are held together at a region called the centromere.

5. Centromere: The centromere is a specialized region of the chromosome that holds the sister chromatids together. It plays a crucial role in the proper alignment and separation of chromosomes during cell division.

6. Telomeres: Telomeres are protective caps located at the ends of chromosomes. They consist of repetitive DNA sequences and help maintain the stability and integrity of chromosomes during replication and cell division.

7. Ploidy: The number of chromosomes present in a cell is referred to as its ploidy. Humans have 46 chromosomes in most cells, organized into 23 pairs. One member of each pair is inherited from the mother, and the other is inherited from the father. The sex chromosomes, X and Y, determine the biological sex of an individual.

In summary, chromosomes are composed of DNA molecules wrapped around histone proteins. They exist as chromatin fibers during interphase and condense into sister chromatids during cell division. The centromere holds the sister chromatids together, and telomeres protect the ends of the chromosomes. The number and structure of chromosomes vary among different organisms and can play a role in genetic inheritance and diversity