Number of Human Chromosomes
Human chromosomes bear more than a passing resemblance to twirls of black thread. These tiny structures are found inside the cell nucleus and consist of DNA and proteins. There are 46 human chromosomes inside most cells. 44 are autosomes, that is non-sex chromosomes and two are the sex chromosomes – X and Y.
The chromosomes are all of different sizes and contain varying number of genes. The structure of human chromosomes change during the life cycle of the cell as it grows and divides. This article is a simple guide to some of the most important chromosomal structures.
Structure of Human Chromosomes
Sister Chromatids – these are two identical copies of the chromosome. During cell division all the DNA of each chromosome is replicated. They eventually separate to become a full chromosome.
Centromere – the central region of the chromosomal structure. It’s where the two sister chromatids are joined to each other.
DNA – dubbed the molecule of life. Each chromosome contains a long linear molecule of DNA and there’s more than two metres of it in each one. So for it to be able to fit it’s tightly wound around histone proteins.
Telomeres – repetitive DNA sequences that are situated at the tips of chromosomes (the repeated sequence reads – TTAGGG). They are vital to the survival and life of the chromosome. Telomeres protect the ends of the chromosomes from damage and stop them from becoming attached to each other. They shrink after every cell division and there has been a great deal of research interest into the relationship between telomere length and cellular senescence and theories about the possibilities of increasing life spans if telomere length can be maintained.
Short Arm – all human chromosomes possess two arms – a short arm and a long arm. It is termed the ‘p’ arm.
Long Arm – is termed the ‘q’ arm.
DNA Structure – How is DNA Packed into a Nucleus?