CHROMOSOMES : chromosomes are thread like structure that appear inside the nucleus at the time of cell division. Chromosomes have been found in the cells of all eukaryotes.
DISCOVERY : They were first observed by the German embryologist Walther Fleming in 1882, in the rapidly dividing cells of salamander larvae.
Karyotype : The particular array of chromosomes that an individual possesses is called its karyotype. Karyotypes show marked differences among species and sometimes even among individuals of the same species.
Number of Chromosomes : Their number varies from species to species. For example: Penicilium has only one pair of chromosomes, while some ferns have more than 500 pairs.
Human cells have 46 chromosomes, consisting of 23 pairs. Each of these 46 chromosomes contains hundreds or thousands of genes that play important roles in determining how a person’s body develops and functions. The possession of all these chromosomes is therefore essential for survival. Missing of a part or whole of chromosome leads to serious consequences, usually death occurs.
Structure of chromosomes : A chromosomes is made of :
- Centromere (primary constriction)
- A secondary constriction.
Chromosomes may widely differ in appearance. They are varied in size, staining properties, the location of centromere, the relative length of the two arms on either side of centromere, and the position of constricted regions along the arms.
Types of chromosomes : Depending upon the location of centromere between the middle and tip of the chromosomes, the chromosomes are called :
These chromosomes acquire different shapes at the time of anaphase during cell division. The usual shapes I, j and v.
Composition of Chromosomes : chemically, the chromosomes are composed of :
- 40% Deoxyribonucleic acid (DNA)
- 60% PROTEIN
DEOXYRIBONUCLEIC ACID (DNA)
The DNA of a chromosome is one very long, double stranded fiber that extends unbroken through the entire length of the chromosomes. A typical human body contains concerning a hundred and forty million nucleotides in its deoxyribonucleic acid.
Amount of information :The amount of information one chromosome contains would fill about 280 printed books of 1000 pages each, if each nucleotide corresponds to a word and each page had about 500 words on it.
Size : If the strand of DNA from a single chromosome were laid out in a straight line, it would be about 5 centimeters long. Fitting such a strand into a small space of nucleus is nature’s marvel and that’s only 1 to 46 chromosomes. In the cell, however, the deoxyribonucleic acid is curled up permitting it to suit into a far smaller area than would well be potential. In the cell, however, the deoxyribonucleic acid is curled up permitting it to suit into a far smaller area than would well be potential.
Structure of DNA : DNA resembles a string of beads. Every two hundred nucleotids, the DNA duplex is in volute around a core of eight simple protein proteins forming a posh referred to as a nucleosome.
Proteins : Histones are positively charged proteins due to an abundance of the basic amino acids, arginine and lysine. They are thus strongly attracted to the negatively charged phosphate groups of the DNA. The histone cores thus act as magnetic forms that promotes and guide the coiling of the DNA. Further whorled happens once the string of nucleosomes wraps up into higher order coils known as super coils.
Heterochromatin :Highly condensed portions of the chromatids are called hetero chromatin. Some of these portions remain permanently condensed, so that their DNA is never expressed.
Euchromatin : The remainder of the chromosomes, known as euchromatin, is condensed solely throughout biological process, once compact packaging facilitates the movement of the chromosomes. In the least alternative times, euchromatin is gift in associate open configuration and its genes may be expressed. The manner chromatin granule is prepackaged once the cell isn’t dividing isn’t well understood on the far side the amount of nucleosomes and could be a topic of intensive analysis.