Chromosomes, The Condensed Form of the Code of Life
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).
Nivedita Dar30 May, 2024
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Chromosomes are the most condensed form of our genetic material, the DNA helix. DNA is essentially a sequence of nitrogenous bases in a specific pattern, which is recognized by the cellular machinery and translated (yes, just like a language it is translated) into a sequence of proteins required by cellular life to survive.
Why Condense DNA?
DNA needs to be condensed to be transferred to the progeny. It would be impossible for a cell to uncoil 2 meters of DNA and then transfer pieces of this thread into a new nucleus, which is micron-sized. By condensing DNA into chromosomes, this process becomes very efficient.Why Uncoil DNA Again?
DNA needs to be uncoiled because it must be translated, which is not possible in its condensed form as nuclear machinery cannot access it.Structure of Chromosomes
The Gross Structure
The gross structure of chromosomes can be seen under a light microscope. Each chromosome has two symmetrical structures during mitotic metaphase. These structures are termed chromatids. Each chromatid comprises a single molecule of DNA. The two chromatids are joined at the centromere. The centromere divides the chromosome into two parts: the short arm, called the p arm, and the longer arm, called the q arm. This highly condensed structure of the chromosome is seen at metaphase.The Ultrastructure
The condensation of DNA happens with the help of proteins called histones. These positively charged proteins bind negatively charged DNA molecules. About 147 base pairs of DNA coil around the histone, leading to a “beads on a string” appearance. At the advent of cell division, both meiosis and mitosis, the chromosomes need to be segregated and transferred into the progeny. Spindle fibers are formed at the equator of the cell by a structure called the centrosome. The spindle attaches to the central constriction of the chromosome. Due to the contraction of these spindle fibers, chromosomes move into adjacent cells.Autosomes and Sex Chromosomes
Humans have 23 pairs of chromosomes, totaling 46 chromosomes. Of these, 22 pairs are autosomes, which are non-sex chromosomes that carry the bulk of genetic information, including genes responsible for various bodily functions and characteristics. The 23rd pair consists of sex chromosomes, which determine an individual’s sex. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The sex chromosomes carry genes that are crucial for the development of sexual characteristics and reproduction. Mutations or abnormalities in either autosomes or sex chromosomes can lead to genetic disorders, underscoring the importance of proper chromosomal function and structure.Chromosomes FAQs
What is non dysfunction of chromosomes?
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division(mitosis/meiosis). This can lead to congenital defects in children.
What is Down's syndrome?
Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.
What is karyotype?
Karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes.
What are autosomes and sex chromosomes?
Autosomes are the chromosomes that determine somatic characters such as body weight, length, etc. of an organism.
Sex Chromosomes are the chromosomes that determine sex and sex-related hormonal traits.
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