Structure and types of the eukaryotic chromosomes

Chromosome = DNA molecule + proteins; in interphase decondensed in tiny fibers, during mitosis condensed in visible particles (methaphase chromosomes in light microscope)


 * Chromosome condensation (multilevel spiralisation)
 * interaction with different types of proteins
 * shortening of chromosome 50 000x in mitosis
 * nucleosome fiber („beads on a string“, 11 nm in diameter) - nucleosome core of 8 histone molecules (2xH2A, 2xH2B, 2xH3, 2xH4), DNA turns around in one and ¾ loops and is fixed by histone H1
 * solenoid – 6 nucleosomes per one turn; solenoid loops form chromatine fiber (diameter 30 nm)
 * chromatin fiber loops are attached to the protein scaffold (300 nm in diameter) and the whole structure is again spiralised (700 nm in diameter) with different density along the chromosome
 * metaphase chromosome consists of two sister chromatids (total diameter 1400 nm)


 * Structure of eukaryotic chromosomes


 * Chromosome types:
 * metacentric (mediocentric) – centromere in the middle of the chromosome lenght
 * submetacentric – centromere divides chromosome into short (p) and long arms (q)
 * acrocentric – very short p-arms, secondary constriction (NOR - nucleolar organizing region with many copies of rRNA genes) and terminal structure of satellites
 * telocentric – only centromere and long arms; not in human beings, typical for example for mice and rats
 * holocentric – multiple sites of attachment to the spindle along the chromosome; in insects or worms.

Related articles

 * Eukaryotic Chromosomes