Chapters
In this article, we will discuss the structure of chromosomes and the importance of mitosis in the production of genetically identical daughter cells during the growth of multicellular organisms, replacement of damaged or dead cells, repair of tissues by cell replacement, and asexual reproduction. So, let us get started.
Structure of Chromosome
Before discussing the chromosome structure, let us see what are chromosomes.
The term chromosome is made up of the Greek words chroma and soma. Chroma means colour and soma means body. This name was given to chromosomes by the scientists because chromosomes are bodies or cell structures, that are stained using a few colourful dyes.
Chromosomes refer to the thread-like structures that are present inside the nucleus of animal and plant cells. Each chromosome is composed of protein and one molecule of DNA (deoxyribonucleic acid). DNA is transferred from parents to the offspring, and it contains certain instructions due to which every living organism is unique.
In the next section of the article, we will discuss the structure of chromosomes in detail.
Structure of Chromosomes
- Chromosomes are composed of a single, extremely long, condensed DNA molecule related to proteins in eukaryotic cells
- The primary proteins found are large positively charged globular proteins known as histones. Their function is to organize and condense the DNA tightly so that it can fit into the nucleus.
- The remaining proteins are enzymes that are employed in replicating and repairing DNA
- Chromatin refers to the combination of tightly coiled DNA and proteins. Chromatids and chromosomes are composed of chromatin.
- Two similar strands of DNA are formed when DNA replicates during the interphase (S phase). These identical strands of DNA are known as chromatids and a narrow region called centromere joins them together.
- The interphase or S phase is the second phase in the normal mitotic cell cycle. The S phase is also referred to as a synthetic phase. During this stage, the cell undergoes DNA replication which means that the two copies of DNA are created during this phase. As a result, the number of chromosomes doubles.
- The two chromatids that form a double structure of chromosomes are referred to as sister chromatids.
- The sister chromatids must be similar, i.e, they should have the same genes because it is important for cell division. This is because one chromatid goes into a single daughter cell and the other chromatid goes into the other daughter cell during mitosis to ensure that the daughter cells are genetically identical.
- Each chromatid is composed of a single extremely long, condensed DNA molecule, which is composed of a series of genes
- The protective structures known as telomeres seal the ends of the chromatids in chromosomes.
In the next section of the article, we will discuss the types of chromosomes.
Types of Chromosomes
Chromosomes are divided into two components (p and q arms) along with a constriction point known as a centromere in the middle. The centromere can be found in various positions, and it creates the basis for four different chromosome classes:
- Metacentric: They are chromosomes in the middle which means that p and q are of a comparable length. For example, chromosomes 1, 3, 16, 19, 20.
- Submetacentric: They refer to the chromosomes off-centre that lead to a shorter p arm relative to the q arm. For example, chromosomes 2.4 – 13, 17, 18, X
- Acrocentric: They are centromere severely offset from the centre leading to an extremely shorter arm. For example, chromosomes 13 – 15, 21, 22, Y
- Telocentric: They are centromere present at the end of the chromosome which means that no p arm is present. These chromosomes are not found in humans.
In the next section of the article, we will discuss the importance of mitosis.
What is Mitosis?
Multicellular organisms, for instance, humans are composed of millions of cells. These cells go through several stages during their life, collectively referred to as a cell cycle. The mitotic cycle refers to a type of cell cycle in which the division of cells occurs by the process of mitosis. Mitosis is a process of division of the nucleus which produces two genetically identical nuclei that are also genetically identical to the parent nucleus.
The mitotic cell cycle is critical for creating new daughter cells from the parent cells. The new cells replace the older worn-out cells that are not functioning properly. The process of mitosis represents the reproduction process at a lower level.
In the next section, we will discuss the importance of mitosis in detail.
Importance of Mitosis
The mitosis process is extremely important and is critical to many biological processes such as the growth of multicellular organisms, replacement of cells and repair of tissues, and asexual reproduction.
Growth of multicellular organisms
- The two daughter cells produced are genetically identical to each other, i.e. they are clones. These daughter cells contain the same number of chromosomes as the parent cell.
- This helps unicellular zygotes to grow into multicellular organisms
- Growth may happen across the entire body of the organism or may be limited to specific regions like meristems (growing points) of the plants
Replacement of cells & repair of tissues
- Mitosis and cell division can repair the damaged tissues
- Because cells are dying continuously, hence they need to be replaced continuously by genetically identical cells.
- For example, in humans, cell replacement specifically occurs quickly in the lining of the gut and skin.
- Few animals like zebrafish and axolotls can regenerate body parts. Zebrafish regenerate fins and axolotls regenerate legs and tails along with the other parts.
Asexual reproduction
- Asexual reproduction refers to the production of a new individual of species through one parent organism. In asexual reproduction, the offspring produced is genetically identical to the parent.
- Cell division in the unicellular organism (organism made up of one cell only) like Amoeba results in the reproduction of offspring that is genetically identical.
- New individuals in multicellular organisms (as observed in several species of plants) grow from the parent organism through cell division and then detach, i.e. bud off from the parent in different ways. The examples include budding in Hydra and yeast and runners from strawberries.
Did you like this article? Rate it!
Loading...
Keep on teaching us,you are excellent teachers
This is great
Thanks a lot for this book,it really helped me a lot
It’s useful to me
Thanks a lot for your Better book!
It’s a perfect article, go ahead