Difference Between Karyokinesis And Cytokinesis

very organism’s life begins with a single cell called a zygote. This zygote passes through numerous cell divisions, or mitosis, to develop into a multicellular organism. A cell divides into two stages: karyokinesis, which involves the division of the nucleus and cytokinesis- a division of the cytoplasm. This only means that during cell division, the chromosome-containing nucleus will split into two daughter cells before the cytoplasm and organelles are divided equally. The four stages of karyokinesis are prophase, metaphase, anaphase, and telophase. Cytokinesis denotes the division of the cytoplasm that occurs after these steps are finished. Animal and plant cells experience cytokinesis in diverse ways. The present article aims to take you through all the processes of karyokinesis and cytokinesis in a stepwise manner. Let’s start.

Differences Between Karyokinesis and Cytokinesis

S.No	Characteristics	Karyokinesis	Cytokinesis
1.	Definition	It refers to the division of the nucleus containing.  chromosomes equally into two daughter cells.	It refers to the division of cytoplasm and organelles.  the equally into two daughter cells.
2.	Sequence	The first step of cell division or mitosis	The first step of cell division or mitosis
3.	Complexity	More complex as it consists of 4 stages	Simpler
4.	Dependency	Independent	Dependant on karyokinesis
5.	Distribution	It distributes chromosomal material in daughter cells	It distributes cytoplasm and organelles in daughter cells
6.	Events	Spindle formation and movement of chromosomes	Formation of cell plate or cleavage furrow
7.	Speed	Slower	Faster
8.	Constriction	Nuclear membrane constricts	The cell membrane forms a cleavage furrow  that splits into daughter cells
9.	Types	Two types (symmetric and asymmetric)	No such types

What is Karyokinesis?

It is the first step in mitosis. It is made up of two words- ‘Karyon‘ means nucleus and ‘kinesis’ means division. Thus, karyokinesis refers to the division of the nucleus containing chromosomes into two daughter cells equally. It involves four stages.

(a) Prophase (Longest phase)
(b) Metaphase
(c) Anaphase (Shortest phase)
(d) Telophase

Let’s explore all the events that take place in these stages.

(a) Prophase: 

It is the first and longest phase and is divided into two phases:
●   Early prophase
●   Late prophase

Early Prophase:  

1. It is the first stage of mitosis that follows the S and G2 phases of interphase.
2. Astral rays are tiny, radiating protein microtubules that form in the centriole.
3. DNA molecules are linked together. 
4. Chromosomes take the form of long, slender threads after nuclear chromatin condenses. The centromere connects the two sister chromatids that make up each chromosome. 
5. Each centromere has two kinetochores, which resemble discs and are where spindle fibers join the centromere.

Late Prophase: 

1. There is the complete disintegration of Golgi complexes, ER, nucleolus, and nuclear envelope. 
2. Shows the formation of spindle fibers. 

(b) Metaphase:

1. The nuclear envelope entirely breaks down during prophase. The chromosomes are now in metaphase and dispersed throughout the cell’s cytoplasm. This phase is referred to as the Metaphase Transition.
2. The chromosomes have finished condensing, and a microscope can now plainly see them. At this point, it is easiest to study the shape of chromosomes.
3. The centromere holds the two sister chromatids that make up the metaphase chromosome together. The kinetochores, or little disc-shaped structures, are found on the surface of the centromeres. They are the attachment points for spindle fibers.
4. The chromatids of each chromosome are attached to spindle fibers from one pole by their kinetochores, while their sister chromatids are connected to spindle fibers from the other pole. Chromosomes are located at the equator. The term “metaphase plate” refers to the chromosomes’ alignment plane during metaphase.

(c) Anaphase (Shortest Duration):

1. The chromosome that is positioned at the metaphase plate splits simultaneously, and the two daughter chromatids start moving in opposite directions.
2. Each chromosome’s centromere is oriented towards the pole, and its arms are positioned such that they trail behind.
3. Spindle fibers may run continuously (from the pole to the kinetochore) or intermittently (pole to pole).

(d) Telophase:

1. As chromosomes condense, they lose their individuality, gather at the opposite spindle poles, and become chromatin.
2. Around the chromosomal clusters, the nuclear membrane can be seen again.
3. Endoplasmic reticulum (ER), Golgi complex, and nucleolus all resurface.
4. Spindle fibers disintegrate.

Symptoms of Karyokinesis:

Symptoms involving the changes that take place during karyokinesis are as follows:

1. It involves the regeneration of cells through cell division. 
2. Genes are equally distributed between daughter cells. 

So, here we come at the end of karyokinesis. Now we will move to the next stage, called cytokinesis. Let’s start.

What is Cytokinesis?

It is followed by karyokinesis. It is the second and final stage of mitosis.  The word “cyto” means “cytoplasm” and “kinesis” means “division”. It refers to the division of cytoplasm into two daughter cells equally. It takes place differently in both plant and animal cells.

Types of Cytokinesis:

Cytokinesis is mainly of two kinds:

a. Symmetrical

It is the process of cell division in which the parent cell splits into two equal daughter cells.  Example: Spermatogenesis. 

b. Asymmetrical

It is the process of cell division in which the parent cell splits into two unequal daughter cells. Example: Oogenesis.

Symptoms of Cytokinesis

Symptoms involving the changes that take place during cytokinesis are as follows:

1. Formation of cell plate in plant cell and cell furrow an in-animal cells.  
2. There will be a formation on of contractile ring.
3. Plasma membrane fuse with each other and later become separated.
4. Equal distribution of cytoplasm with organelles among daughter cells. 

Mechanism of Cytokinesis:

It involves the division of cytoplasm and organelles equally into two daughter cells. It is a dependent phase as it takes place only when karyokinesis has already taken place. It takes place differently in plants as well as animal cells. We will first study animal cells and after that plant cells.

1. Cytokinesis in animal cells:

The contractile ring forms at the metaphase plate, beginning the process of cytokinesis. Actin filaments make up the contractile ring. These filaments create a fissure-like appearance by pulling the equator inward. This cleavage furrow forms as this furrow gradually deepen. The membrane splits when the cleavage approaches its edge, producing two new daughter cells. 

2. Cytokinesis in plant cells:

Plant cells are enclosed by a cell wall that is inextensible. Therefore, it undergoes cytokinesis by a different mechanism. In plant cells, wall formation starts in the center of the cell and grows outward towards the cell wall. The Golgi vesicles accumulate in the center and form the middle lamella or cell plate. Once the cell plate is formed, the plasma membrane begins to develop and finally one plant divides into two daughter plant cells. At the time of cytoplasmic division, organelles like mitochondria and plastids get distributed between the two daughter cells.

Karyokinesis and cytokinesis are two different steps by which the content of the parent cell is distributed into two daughter cells equally. This is necessary for the continuation of species. So, the first step is karyokinesis which involves the distribution of the nucleus and the next step is cytokinesis which involves the distribution of organelles and cytoplasm into two daughter cells equally. Karyokinesis involves different phases-prophase, metaphase, anaphase, and telophase which depict the change in chromosomes present in the nucleus. At the end of telophase, cell membranes form outside the daughter cells and a contractile ring will start appearing. Finally, a parent cell divides into daughter cells.

Frequently Asked Questions (FAQs) on Karyokinesis and Cytokinesis

Question 1. Name the types of Spindle Fibers.

Answer. The spindle fibers are of two types:
(a)  Continuous:  extend from pole to pole
(b) Discontinuous/ chromosomal: extend from pole to kinetochore.

Question 2. Does protein synthesis take place in Prophase?

Answer. No protein synthesis does not take place in prophase.

Question 3. Why do Mitochondria not Disintegrate in Prophase?

Answer. Mitochondria do not disintegrate because further stages need energy, and that energy is provided by mitochondria only.

Question 4. Do always karyokinesis is followed by Cytokinesis?

Answer.  In some organisms, like liquid endosperm in coconut, karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises leading to the formation of the syncytium.

Question 5. What are Kinetochores?

Answer. On the surface of the centromeres are structures in the shape of discs known as kinetochores. They serve as the sites at which spindle fibers are attached.