In every cell of ours, we have nearly two meters of DNA which are packed into a nucleus. It is almost ten times smaller than the width of human hair. DNA wraps around proteins referred to as histones that aids in compressing the long thread into a manageable and dense shape – the chromosomes. This setup and packaging are highly organized and not random. These structures are significant in the regulation of the expression of genes for cells to properly function.
Situated in the nucleus of animal and plant cells, each of the chromosomes comprises a protein and a molecule of DNA (deoxyribonucleic acid). This thread-like chromosome structure is passed from the parents to the offspring, wherein the DNA it accommodates has special instructions which cause each type of living individual to be unique.
Role of Chromosomes
The unique chromosome structure causes DNA to be tightly wound around the histones. In the absence of these packagings, the molecules of DNA would be longer to fit in the cells. For instance, if all the molecules of DNA in a single human cell were unwound from its histones and put end-to-end, it would extend for 6 feet.
For an entity to function and grow properly, cells should divide constantly producing new cells replacing worn-out and old cells. At the time of cell division, it is vital for DNA to stay intact and evenly distributed in the cells. Chromosomes form a vital part of the process ensuring DNA is copied accurately and spread in the huge majority of cell divisions. On rare occasions, mistakes occur.Modifications in the structure and number of chromosomes in new cells can cause serious issues. For instance, one type of leukaemia in humans and other cancers can be a result of defective chromosomes composed of joint fragments of broken chromosomes.It is imperative that the eggs and sperms (reproductive cells) contain the right number of chromosomes and such chromosomes have an accurate structure. In the event that this does not happen, the offspring as a result can fail to properly develop. For instance, individuals with Down syndrome, instead of two copies, show three copies of chromosome 21.
Chromosomes In Different Individuals
The number and shape of chromosomes are not the same in all living individuals, it varies. Most bacteria have 1 or 2 circular chromosomes. Along with other plants and animals, humans show linear chromosomes which are organized in pairs in the nucleus of cells. It is only the gametes or the reproductive cells in humans which do not contain a pair of chromosomes. It just carries one copy of each chromosome. In the event of the fusion of two reproductive cells, it becomes a single cell that contains two copies of each chromosome. Such a cell then divides and their successors divide several times ultimately producing a mature individual which has a complete set of paired chromosomes in all of their cells. Apart from the linear chromosomes seen in the nucleus, the cells of the humans and even in the other complex entities, it is seen that they carry an even smaller type of chromosomes like that seen in bacteria. Such a circular chromosome is seen in mitochondria – located exterior to the nucleus which serves as the powerhouse of cells. This was brief on chromosomes. Next up we have discussed epithelial tissue and neural tissue. Explore this topic the visual way by subscribing to BYJU’S YouTube Channel.
Chromosomal abnormalities are of different types. An individual can have an abnormal number of chromosomes or can have unusual regions on one or more than one chromosome. Several of these abnormalities can be diagnosed even before birth.
An unusual number of nonsex chromosomes typically lead to many abnormalities. For instance, receiving extra nonsex chromosomes can be deadly to a fetus or can result in abnormalities (Down Syndrome for instance) that usually is a result of a person who has three copies of chromosome 21. To the fetus, the absence of a nonsex chromosome is fatal.
Abnormality is also the presence of a large area on the chromosomes that typically is as a whole section was missed out or by mistake placed in a different chromosome (translocation). For instance, myelogenous leukaemia at times is a result of translocation of part of chromosome 9 onto chromosome 22. This abnormality could be inherited or could be a result of a new mutation.
In the cells, mitochondria synthesize molecules that are used up for energy. As opposed to other structures found in the cell, each of the mitochondria has its own circular chromosome which comprises its DNA (mitochondrial DNA). It codes for a few, not all of the proteins which make up the mitochondrion. The mitochondrial DNA typically is from the individual’s mother as generally when the egg is fertilized, only the mitochondria from the egg form the section of the developing embryo.