Chromosomes | Definition, Structure, Functions & Example

By | October 27, 2019

Chromosomes

Chromosome Definition:

What are chromosomes: The DNA molecules are tightly packaged within a nucleus with the help of the thread-like structure is known as chromosomes. Each chromosome is made by DNA tightly coiled many times around the proteins, known as Histones which help to support its structure. Each chromosome has a constriction point known as the Centromere, which divided the chromosome into two parts or ‘Arms’. The short length arm of the chromosome is named as “p Arm”, while the long length arm is named as “q Arm”. On the chromosome, the location of the centromere gives the chromosome its characteristic shape and used in order to describe the location of particular genes.

A chromosome is invisible in the nucleus cells when the cell is not dividing, even under the microscope. Although, the DNA which makes the chromosome became more tightly packed during the division of cell, and then can be visible under a microscope. A chromosome is the string of the DNA wrapped around composed with proteins that give a base structure to the connected nucleic acid.

During cell cycle interphase, the chromosome convert into the loose structure, and proteins can be translated from DNA to DNA replicated.

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Chromosome Structure:

Chromosomes have a much complex structure. The base of the structure of the chromosome is made by DNA or Deoxyribonucleic acid. Deoxyribonucleic acid is made up of the two strings of nucleic acid-base pairs. The base pairs of DNA are cytosine, thymine, adenine, and guanine. The spiral structure of the chromosomes formed by two strings of DNA, this is because it is must be pairing between every base with its pair on the opposite string. The pairing occurs between Adenine with Thymine, and Guanine with Cytosine. The opposite side of bases from a Phosphate-Deoxyribose backbone keeps the strands intact.

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When the DNA duplicates, the strands separated. A Polymerase molecule forms a new string that corresponds to each side. By this, the DNA perfectly replicates. This can be perfectly done artificially by a Polymerase chain reaction, in which special enzymes and heat used in order to separate and replicates the strings for a number of times to create many copies of the same DNA. This act made it easier to study any string of DNA, even whole genomes or chromosomes.

When the cell has expressed and DNA duplicated, then the division of cells occurs. This action occurs in both eukaryotes and prokaryotes, while just eukaryotes condense their DNA, so it may be separated. The DNA of prokaryotes is no complex, that the few structural proteins are comrade with the chromosome, while many of the structural proteins are used in eukaryotes.

Firstly, these proteins are core histones. Many histone proteins individuals are bind together to create a core histone. DNA can be wrapped around one of these histones to giving in a wound structure. This structure and associated histone are called Nucleosome. The scaffold protein (next type of protein), begin to wind the fiber into a loose structure. More scaffold proteins are activated and structure becomes denser when the chromosomes condense during the cell division. However, chromosomes individuals cannot be discerned near the middle of the cell division cycle, even at the microscopic level, when the chromosomes become very dense.

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Functions of a Chromosome:

  • The chromosome does not hold only the genetic code of an individual, but also many of the proteins help in its expression.
  • It is a complex form and its structure shows which genes are translated and how genes can be translated into the proteins. This process called Gene Expression and the cause of the creating of an organism.
  • The densely packed of the chromosome at a certain point depending determine how a gene gets expressed. The less active genes will be much tightly packed then those genes that undergoing active transcription.
  • The cellular molecules which help to regulate the genes and transcription usually work by activating or deactivating these proteins, which can be contracted or expand the chromosome.
  • During the division of cells, all the proteins are activated and the chromatins become densely packed into the distinct chromosomes. These dense molecules or material have a better chance of withstanding the pulling forces which occur when the chromosomes are divided into the new cells.

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How many Chromosomes do Humans have?

There are trillions of microscopic cells in the human body, contain all the stuff which performs many functions. There is a command center inside a cell known as the nucleus. A chromosome is the entire chain of the DNA with a group of specific proteins. The genome of the human body has 23 pairs of chromosomes, a total of 46 human chromosomes in it. When DNA replicates, the genome has 92 sister chromatids, but still connect with others, having 46 chromosomes. Human gametes have 23 chromosomes and no pair of homologous.

Examples of Chromosomes:

Some examples of the chromosome are given below:

When a single bacteria cell has gained a large size, it may produce asexually. However, there is no membrane that separates the organism organelles in the bacteria. The cell duplicates its DNA itself and uses special chemicals for survival. The DNA composed in a single chromosome; sometimes it called a Genophore that is replicated by individual strands separated and Polymerase builds new strands. The two chromosomes separate into individual cells, and cell carries their functions by creating proteins from the DNA and interact with the environment.

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In eukaryotes, there is a much complex view of chromosome present. The DNA replicates at the end of the interphase in the eukaryotes. The interphase is a part of the cell cycle in which the growth of cell and functions take place. There are multiple chromosomes that lie in the eukaryotes. The new build chromosome still connected at the Centromere, which is a structure that permits microtubules to connect and keep chromosomes together. These are also called “sister chromatids” because they are similar copies. During “meiotic cell division”, these sister chromatids can undergo some of the variation, when recombination takes place.

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During cell division, when these chromosomes separate, they are known as “sister chromosome”. This sister chromosome separates into different gametes, or sperm and the egg cells. When egg and sperm interact, the zygote receives one sister chromosomes from each parent. These sister chromosomes are not identical copies of each other, they are called Homologous Chromosomes.

Humans have 23 Homologous pairs, so humans have 46 chromosomes in each cell. When the DNA replicates, they have 92 sister chromatids but still connected to each other, so there are just 46 chromosomes.