Chromosome in detail



Chromosome, the microscopic threadlike part of the cell that carries hereditary information in the form of genes. A defining feature of any chromosome is its compactness. For instance, the 46 chromosomes found in human cells have a combined length of 200 nm (1 nm = 10− 9 metre); if the chromosomes were to be unraveled, the genetic material they contain would measure roughly 2 metres (about 6.5 feet) in length. The compactness of chromosomes plays an important role in helping to organize genetic material during cell division and enabling it to fit inside structures such as the nucleus of a cell, the average diameter of which is about 5 to 10 μm (1 μm = 0.00l mm, or 0.000039 inch), or the polygonal head of a virus particle, which may be in the range of just 20 to 30 nm in diameter.

Chromosome Definition

A chromosome is a string of DNA wrapped around associated proteins that give the connected nucleic acid bases a structure. During interphase of the cell cycle, the chromosome exists in a loose structure, so proteins can be translated from the DNA and the DNA can be replicated. During mitosis and meiosis, the chromosome becomes condensed, to be organized and separated. The substance consisting of all the chromosomes in a cell and all their associated proteins is known as chromatin. In prokaryotes, there is usually only a single chromosome, which exists in a ring-like or linear shape. The chromatin of most eukaryotic organisms consists of multiple chromosomes, as described later in the article. Each chromosome carries part of the genetic code necessary to produce an organism.

Function of a Chromosome

Chromosomes are the thread-like structure found in the nuclei of both animal and plant cells. They are made of protein and one molecule of deoxyribonucleic acid (DNA).

As the genetic material passes from parents to child, the chromosomes are responsible for containing the instructions that make the offspring unique while still carrying traits from the parent. In most organisms, one chromosome is inherited from the mother and the other is inherited from the father; to ensure that offspring carry traits from both parents. It’s crucial that certain cells, like reproductive cells, have the correct number of chromosomes in order to function properly.

The structure of chromosomes helps ensure the DNA remains tightly wrapped around the proteins;otherwise, DNA molecules would be too large for the inside of the cells.

Organisms grow by undergoing cell division to produce new cells and replace older, wornout cells. During this cell division, DNA must remain intact and keep its even distribution throughout the cells. Chromosomes are important to this process to ensure the DNA is accurately replicated.

Examples of Chromosome

Prokaryote Replication

When a single bacteria cell has reached a large enough size, it can reproduce asexually. Although there are no membranes that separate individual organelles in bacteria, the cell will duplicate its DNA and and special chemicals it needs to survive. The DNA exists in a single chromosome, sometimes called a genophore, which is replicated by the individual strands being separated and polymerase building new, corresponding strands. The two chromosomes are separated into individual cells, and the cells carry on their functions by creating proteins from the DNA and interacting with the environment.

Eukaryote Replication

A much more complicated view of chromosomes is present in eukaryotes. In eukaryotes, the DNA is replicated at the end of interphase, the part of the cell cycle in which the cell grows and functions. Much like in the prokaryotes, the DNA strands are separated and new strands are created by enzymes. However, in eukaryotes, there are multiple chromosomes. The new chromosomes remain connected at the centromere, a structure that allows microtubules to connect and holds chromosomes together. These are now known as sister chromatids because they are identical copies. These chromatids can undergo some variation during meiotic cell division, when recombination can occur.

When they separate during cell division, they are known as sister chromosomes. The sister chromosomes are separated into different gametes, or sperm and egg cells. When a sperm and egg unite, the zygote receives one sister chromosome from each parent, but because they are not identical copies of each other they are known as homologous chromosomes. In human, there are 23 homologous pairs, so humans have 46 chromosomes in each cell. When the DNA is replicated, they have 92 sister chromatids, but they are still connected so there are still only 46 chromosomes. Human gametes only have 23 chromosomes, and no homologous pairs.

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