Understanding Chromosomes: Structure, Facts and Differences

Written by Nandy

Chromosomes are structures found in cells that store genetic information. Chromosomes consist of DNA which functions as a “guide” to produce the proteins needed by the cell. Every organism has a specific number of chromosomes contained in each cell.

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

Chromosomes have a fairly unique structure that makes DNA wrapped around proteins to form a coil. These structures are also known as histones. Without these coils, the DNA molecule would be too long to enter the cell. There are several other facts about chromosomes and the structure of chromosomes. Check out further understanding of chromosome material in the following article.

Definition of Chromosomes

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

Chromosome molecules were first observed in the late 1800s, but the nature and function of the cell structure of chromosomes at that time were still unclear. Then, in the early 1900s, Thomas Hunt Morgan re-examined the chromosomes and found a relationship between chromosomes and the inherent traits in living things.

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

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

Chromosomes can also be interpreted as structures in cells that contain long DNA that contains part or all of the genetic information of an organism. Most chromosomes in eukaryotes have packaging proteins called histones that, together with companion proteins, bind and condense the DNA molecule to maintain its 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 the metaphase of cell division (when all the chromosomes line up in the center 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 edges). These joined copies are now called sister chromatids. During metaphase, X-shaped structures called metaphase chromosomes are very compact, making them easy to distinguish and study. In animal cells, chromosomes reach their highest degree of condensation during anaphase during the process of splitting chromosomes.

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

Normally, this would trigger the cell to initiate apoptosis leading to its own death, but sometimes mutations within the cell can inhibit this process and lead to the development of cancer. There are some people who use the term chromosome in a broader sense, namely to refer to the individual parts of chromatin in cells, 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 individual sections of chromatin during cell division, which are visible under a light microscope due to the high degree of condensation.

Structure Chromosome

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

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 on from parent to child and form traits and characteristics. individual characteristics.

Chromosomes also play an important role in the process of cell division and determine the sex of an individual. The structure of the chromosome parts include:

1. Centromere

The centromere is the structural part of the chromosome that is located in the middle, which connects sister chromatids. Centromere helps divide sister chromatids properly during cell division.

The centromere consists of two parts, namely the near centromere and the far centromere. The near centromere is located closer to the ends of sister chromatids, while the far centromere is located farther to the ends of sister chromatids.

The two parts of the centromere are connected by a structure known as the kinetochore. During cell division, the kinetochores will elongate and help pull sister chromatids in opposite directions so that proper 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 properly and can cause problems in 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 the process of cell division known as DNA synthesis or DNA replication. During this process, the DNA molecule divides into two identical parts, which form two chromatids.

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Chromatids located side by side with other chromatids that are exactly the same are called sister chromatids. Sister chromatids are attached to each other in the middle by a structure known as the centromere. At the time of cell division, the chromatids will divide into two identical 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 the division of DNA, it can cause problems in the cell.

3. Telomeres

The structural part of the chromosome at the end of the chromosome is called the telomere. Telomeres consist of a bunch of nucleotides repeated many times, i.e. around 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 process of DNA replication.

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. Chromomeres 

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

This part of the structure of chromosome one will be seen very clearly in polytene chromosomes or chromosomes with DNA that has been replicated many times without separation and coexists to form a wire-like chromosome cell.

5. Satellite 

Satellites are the structural parts of the chromosomes which consist of DNA molecules bound to proteins. The satellites are located near the centromere on the chromosome and form a structure known as the kinetochore.

Satellites are usually composed of several hundred to thousands of nucleotides repeated many times, consisting of guanine and thiamin. Satellites usually do not carry useful genetic information to 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 proper division occurs. If there is a problem with the satellite, such as the satellite is too long or too short, it can cause problems in the process of cell division.

Facts About Chromosomes

Source: Pixabay

As previously explained, chromosomes are a collection of DNA cells that have a circular and tight shape and are located in the nucleus or cell nucleus and are present in almost every cell in the bodies of living things, both humans and animals.

Chromosomes have some unique facts such as their function, and how they are inherited. Check out the following explanation:

1. Function of Chromosomes

The unique structure of chromosomes makes DNA wrapped around coil-like proteins called histones. Without these coils, the DNA molecule would be too long to fit into the cell.

As an illustration, if all the DNA molecules in human cells were removed from their histones, they would be about 6 feet long or the equivalent of 1.8 meters.

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

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

However, there is still a possibility that this DNA pool can make mistakes in the process of cell division. Changes in the amount or structure of the DNA pool in a new cell 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 contain the correct number of chromosomes with the correct structure. If not, the resulting offspring may not be able to develop properly.

2. Chromosomes of Every Living Thing Are Not the Same

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

The only human cells that do not contain a chromosome pair are the reproductive cells or gametes. These reproductive cells can carry only one copy of each chromosome.

When two reproductive cells unite, they 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 chromosome cells in almost every cell.

Bundles of DNA with a circular shape can also be found in mitochondria. Mitochondria are where the cell breathes. This section will have the task of being able to burn glucose and produce the energy needed by the body.

In mitochondria, the DNA pool is smaller. This collection of circular DNA or chromosomes is outside the cell nucleus in the mitochondria and has a function as the cell’s powerhouse.

3. How to Inheritance of Chromosomes

Chromosomes present in humans and most other living things, one copy of each set of DNA is inherited by the female as well as the male.

For this reason, every child born will definitely inherit some of the characteristics of his mother and father. However, the pattern of inheritance of chromosomes is different for the small DNA pools found in mitochondria. Mitochondrial DNA is always inherited from the female parent or egg cell and not from the male.

4. Boys and Girls 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 chromosomes (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 have mental disabilities. Men who have two X chromosomes (XXY) will experience Klinefelter’s syndrome which is characterized by small testicle size, 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. Women with Turner syndrome have only one X chromosome and usually have short stature, flat chests, and kidney or heart problems.

Chromosome Abnormalities

Abnormalities that occur in chromosomes can usually be grouped into two major groups, namely numerical abnormalities and structural abnormalities.

1. Numerical Abnormalities

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

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

Down syndrome is characterized by mental retardation in sufferers, facial shapes that look different and distinctive, 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 with the egg and sperm.