Understanding Chromosomes: Structure, Facts and Differences

Chromosome is a structure found in cells that stores genetic information. Chromosomes consist of DNA that functions as “instructions” to produce the proteins needed by the cell. Each organism has a specific number of chromosomes found in each cell.

For example, humans have 46 chromosomes in each cell, consisting of 23 pairs. Genetic information contained in chromosomes can provide instructions for determining individual characteristics, such as hair color, height, and susceptibility to certain diseases.

Chromosomes have a quite unique structure that makes DNA wrap around proteins to form a coil. The structure is also called histone. Without the twist, the DNA molecule would be too long to enter the cell. There are some other facts about chromosomes and the structure of chromosomes. Read more about the meaning of chromosomes in the following article.

Meaning of Chromosomes

Chromosome comes from two Greek words, namely chroma which means color and soma which means body. The scientists gave this name because this molecule is a cell or body structure that appears to have certain colors when viewed under a microscope.

Chromosomal molecules were first observed in the late 1800s, but the nature and function of the cellular structure of chromosomes at that time was still unclear. Then, in the early 1900s, Thomas Hunt Morgan re-examined parts of chromosomes and found the relationship between chromosomes and the inherent characteristics of living beings.

So, in general it can be concluded that chromosomes are groups of DNA that are tightly bound together and are located in the nucleus (cell nucleus) of almost every cell in the body. This group of DNA is a molecule that has a shape similar to a thread that carries hereditary information (descendants) such as body height, skin color, to eye color.

Chromosome molecules are made of proteins and a DNA molecule that contains the genetic instructions of an organism passed down from parent to child. In humans, animals, and plants, most chromosome molecules are arranged in pairs in the cell nucleus.

Chromosome can also be interpreted as a structure in a cell that contains long DNA that contains part or all of the genetic information of an organism. Most chromosomes in eukaryotes have packaging proteins called histones that, along with chaperone proteins, bind and compact DNA molecules to maintain their integrity.

This chromosome has a quite complex three-dimensional structure and has an important role in the regulation of transcription. Chromosomes are usually only visible under a light microscope during metaphase of cell division (when all the chromosomes are lined up in the middle of the cell in a condensed or condensed form).

Before that happens, each chromosome is duplicated (S phase) and the two copies are joined by the centromere to form an X-shaped structure (if the centromere is located at the equator) or a two-armed structure (if the centromere is located at the edge). These joined copies are now called sister chromatids. During metaphase, X-shaped structures called metaphase chromosomes are very compact, so they are easy to distinguish and study. In animal cells, chromosomes reach their highest level of compaction during anaphase during the process of chromosome separation.

Chromosomal recombination that occurs during meiosis and sexual reproduction plays an important role in increasing genetic diversity. If there is an incorrect manipulation of chromosomes, through a process known as chromosome instability and translocation, cells can experience problems in the mitosis process.

Normally, this will trigger the cell to initiate apoptosis which causes its own death, but sometimes mutations in the cell can inhibit this process and cause the development of cancer. There are some who use the term chromosome in a broader sense, that is to refer to the individual parts of chromatin in a cell, both visible and invisible under a light microscope.

There are also people who use the concept of chromosome in a narrower sense, that is to refer to the individual parts of the chromatin during cell division, which are visible under the light microscope due to the high degree of condensation.

Chromosomal Structure

Chromosomes consist of 44 or 22 pairs of body chromosomes (autosomes) and a pair of sex chromosomes (gonosomes), namely XX in women and XY in men. In haploid cells such as egg cells or sperm cells, there are 23 chromosomes consisting of 22 autosomes and one gonosome.

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Egg cells have approximately 22 autosomes and 1 X, while sperm cells have 22 autosomes and 1 X or 1 Y. The function of chromosomes is to store genetic information that will be passed down from parent to child and form traits and characteristics. special individual.

Chromosomes also play an important role in the process of cell division and determine the sex of an individual. The structure of the chromosomes among them are:

1. Centromere

The centromere is the structural part of the chromosome located in the middle, which connects sister chromatids. Centromeres help divide sister chromatids correctly during cell division.

The centromere consists of two parts, namely the near centromere and the far centromere. Proximal centromeres are located closer to the ends of sister chromatids, while distant centromeres are located farther from the ends of sister chromatids.

The two parts of the centromere are connected by a structure called a kinetochore. During cell division, the kinetochores will elongate and help pull sister chromatids in opposite directions so that correct division occurs. If there is a problem with the centromere, for example the centromere is too long or too short, then cell division will not occur correctly and can cause problems for the cell.

2. Chromatids 

The next part of the chromosome structure is the chromatid which consists of DNA molecules bound to proteins. Chromatids are formed during a process of cell division called DNA synthesis or DNA replication. During this process, the DNA molecule will be divided into two exactly the same parts, which will then form two chromatids.

Chromatids are located side by side with other identical chromatids called sister chromatids. Sister chromatids are bound to each other in the middle by structures called centromeres. At the time of cell division, the chromatid will be divided into two exactly the same parts and form two new cells that have exactly the same chromosomes as the original cell.

If there is a problem in the chromatid division process, for example there is an error in the division of sister chromatids or an error in DNA division, then it can cause problems in the cell.

3. Telomeres

The structural part of the chromosome that is at the end of the chromosome is called a telomere. Telomeres consist of a group of nucleotides that are repeated many times, that is about 6-20 times.

These repeating nucleotides usually consist of guanine and thiamin. Telomeres are responsible for protecting the ends of chromosomes from damage that may occur during the DNA replication process.

In addition, telomeres also play an important role in the aging process of cells and can indicate an individual’s health condition. Telomeres that are too short or too long can cause problems in cells, such as genetic mutations or abnormal cell aging.

4. Chromomer 

Chromomeres are structures from chromosomes that have a bead-like shape. Chromomeres are accumulations of chromatin material that are sometimes visible during interphase.

This part of the structure of one chromosome will be seen very clearly on polytenous chromosomes or chromosomes with DNA that has been replicated repeatedly without separation and is side by side until a chromosome cell is formed that resembles a wire.

5. Satellite 

A satellite is a structural part of a chromosome that consists of DNA molecules bound to proteins. Satellites are located near the centromere of the chromosome and form a structure called a kinetochore.

Satellites usually consist of several hundred to thousands of nucleotides repeated many times, consisting of guanine and thiamin. Satellites usually do not carry genetic information that is useful for organisms, but play an important role in the process of cell division.

Satellites help pull sister chromatids in opposite directions during cell division, so that correct division occurs. If there is a problem with the satellite, such as the satellite being too long or too short, it can cause problems in the cell division process.

Facts About Chromosomes

As explained earlier, chromosomes are groups of DNA cells that have a circular and close shape and are located in the nucleus or core of the cell and are present in almost every cell in the body of living beings, both human and animal.

Chromosomes have some unique facts such as their function, and their mode of inheritance. See the following explanation:

1. Chromosome Function

The unique structure of chromosomes keeps DNA wrapped around coil-like proteins called histones. Without the coil, the DNA molecule would be too long to enter the cell.

As an illustration, if the entire DNA molecule in a human cell was stripped of its histones, it would have a length of about 6 feet or the equivalent of 1.8 meters.

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In order for an organism or living being to grow and function properly, cells must continue to divide. The purpose is to be able to replace old damaged cells with new cells. During the process of cell division, it is important that the DNA remains intact and evenly distributed among the other cells.

Chromosomes play an important role in the process of cell division. This molecule is responsible for ensuring that DNA is copied and distributed accurately in most cell divisions.

However, there is still a possibility that this group of DNA can make mistakes in the process of cell division. Changes in the amount or structure of DNA groups in new cells can cause serious problems, such as certain types of leukemia and some types of cancer.

In addition, it is also important that the egg and sperm cells contain the correct number of chromosomes with the correct structure. If not, then the offspring produced may not be able to develop well.

2. The chromosomes of every living being are not the same

In number and shape, this group of DNA varies greatly in every living being. Most bacteria have one or even two circular chromosomes. Meanwhile, humans, animals, and plants have linear chromosomes that are arranged in pairs in the cell nucleus or nucleus.

The only human cell that does not contain a pair of chromosomes is the reproductive cell or gamete. This reproductive cell can only carry one copy of each chromosome.

When two reproductive cells unite, the cells will become a single cell containing two copies of each chromosome. This cell then divides again to produce a complete adult individual with a complete set of paired chromosomes in almost every cell.

Groups of DNA with a circular shape can also be found in mitochondria. Mitochondria is where cells breathe. This part will later have the task of being able to burn glucose and produce the energy needed by the body.

In mitochondria, DNA groups have a smaller size. The group of circular DNA or chromosomes is outside the nucleus of the cell in the mitochondria and has a function as the cell’s energy generator.

3. Mode of Chromosome Inheritance

Chromosomes in humans and most other living things, one copy of each group of DNA is inherited by the female and male parents.

Because of that, every child that is born will definitely inherit part of the nature of the mother and father. However, the pattern of chromosomal inheritance is different for the small group of DNA found in the mitochondria. Mitochondrial DNA is always inherited from the female parent or egg cell and not from the male.

4. Men and Women Have Different Chromosomes

In addition to having physical differences, men and women also have different sets of DNA called sex chromosomes. Females have two X chromosome cells (XX) while males have one X chromosome and one Y chromosome (XY).

If a person has an unbalanced number of sex chromosomes, this can cause serious health problems. Women who have three X chromosomes (XXX) can experience mental retardation. Men who have two X chromosomes (XXY) will experience Klinefelter syndrome characterized by small testicles, enlarged breasts (gynecomastia), low muscle mass, and larger hips like women.

Another syndrome caused by an imbalance in the number of sex chromosomes is Turner syndrome. Girls who suffer from Turner syndrome have only one X chromosome and usually have a short body, flat chest, and kidney or heart problems.

Chromosomal abnormalities

Abnormalities that occur in chromosomes can usually be grouped into two large groups, among which are numerical abnormalities and structural abnormalities.

1. Numerical Differences

Numerical abnormalities will occur if the number of chromosomes is less or even more than it should be, namely two. If a person loses one of them, then the condition is called monosomy.

Whereas if a person has more than two chromosomes, then the condition is called trisomy. One of the problems caused by chromosomal numerical abnormalities is Down syndrome.

Down syndrome is characterized by mental retardation in the sufferer, a different and distinctive facial shape and weak or poor muscle strength.

2. Structural Abnormalities

Structural abnormalities generally occur due to several things, namely deletions, duplications, translocations, inversions and rings. In general, most of the structural abnormalities occur due to problems in the egg and sperm cells.

That is the explanation of the meaning of chromosomes. Hope all the discussion above is useful for you, Reader.