Anaphase

Anaphase is the third phase of mitosis, after metaphase and prophase, when chromosomes split and move to opposite poles of the cell. This ensures each daughter cell receives a complete set of chromosomes. The anaphase diagram shows chromosomes reach their highest level of condensation, which helps with chromosome segregation and nucleus re-formation.

Anaphase’s importance lies in its role in ensuring the correct distribution of genetic material, which is essential for organism development and growth. In this article, we will study anaphase, its structure, parts, and functions as well as some interesting facts about anaphase.

What is Anaphase?

Anaphase is an important stage in cell division, specifically in mitosis and meiosis. It’s the third stage of mitosis and the second stage of meiosis. During anaphase, the sister chromatids separate and move towards opposite poles of the cell. In mitosis, anaphase begins when the centromeres of each chromosome split, allowing the spindle fibers attached to the centromeres to pull the sister chromatids apart. These chromatids are then pulled toward opposite poles of the cell, caused by the shortening of microtubules attached to the chromatids.

In meiosis, anaphase II follows anaphase I. Similarly, sister chromatids separate and move towards opposite poles, which results in the formation of haploid daughter cells. Anaphase is a highly regulated process controlled by various proteins and signalling pathways to ensure the accurate distribution of genetic material to daughter cells.

Structures Involved in Anaphase

Different structures involved in Anaphase and their role is explained below:

Chromosomes

• Chromosomes are thread-like structures found inside the nucleus of a cell.
• They contain genetic information in the form of DNA, which carries instructions for cell growth, development, and functioning.
• During anaphase, chromosomes condense further and split into two identical halves called sister chromatids.

Spindle Fibers

• Spindle fibers are tiny structures made of protein called microtubules.
• They form a scaffold-like structure known as the spindle apparatus, which helps in the movement and segregation of chromosomes during cell division.
• During anaphase, spindle fibers attach to the centromeres of sister chromatids and pull them apart towards opposite ends of the cell.

Centrosomes

• Centrosomes are small organelles located near the nucleus of the cell.
• They consist of a pair of centrioles and helps in organizing the spindle fibers during cell division.
• In anaphase, centrosomes move to opposite poles of the cell, directing the movement of chromosomes towards these poles.

Microtubules

• Microtubules are long, tube-like structures made of protein subunits called tubulin.
• They form the main components of spindle fibers and provide structural support to the cell during division.
• During anaphase, microtubules attached to the centromeres of chromosomes shorten, pulling the sister chromatids towards opposite poles of the cell.

Kinetochores

• Kinetochores are protein structures located at the centromeres of chromosomes.
• They serve as attachment sites for spindle fibers and play a key role in chromosome movement and segregation.
• During anaphase, kinetochores interact with microtubules, causing the separation of sister chromatids and ensuring their proper distribution to daughter cells.

What are the Major Parts of Anaphase?

The process of anaphase during mitosis and meiosis is explained as follows:

Mitosis

Anaphase in mitosis involves the separation of sister chromatids, with each chromatid moving to opposite poles of the cell due to the shortening of microtubules attached to kinetochores. The process is explained as follows:

Chromosome Separation

• At the onset of anaphase, the pairs of sister chromatids, which were aligned along the equator of the cell during metaphase, start to separate.
• The enzyme separase cleaves the protein complexes holding the sister chromatids together at the centromere region.

Movement to Opposite Poles

• As enzyme separase cleaves the protein complexes, the sister chromatids become individual chromosomes.
• Microtubules of the spindle apparatus, which are attached to the kinetochores, begin to shorten.
• This shortening pulls the sister chromatids toward opposite poles of the cell.

Formation of Two Groups

• As the sister chromatids move apart, they become visibly separated into two distinct groups.
• Each group contains a complete set of chromosomes identical to the parent cell’s genome.

Cell Elongation

• In animal cells, as the chromosomes are pulled toward opposite poles, the cell may elongate slightly.
• In plant cells, a cell plate begins to form between the two groups of chromosomes, eventually dividing the cell into two daughter cells.

Meiosis

Anaphase II in meiosis involves the separation of sister chromatids (or homologous chromosomes in meiosis I), with each chromatid (or chromosome) moving to opposite poles of the cell due to the shortening of microtubules attached to kinetochores. Anaphase in meiosis occurs in two stages, Anaphase I and Anaphase II.

Anaphase I

1. Homologous Chromosome Separation
   • In Anaphase I of meiosis, homologous chromosomes, each consisting of two sister chromatids, are separated.
   • This separation results in the segregation of homologous chromosomes into two groups, each containing one chromosome from each homologous pair.
2. Movement to Opposite Poles
   • Microtubules of the spindle apparatus attached to the kinetochores of homologous chromosomes begin to shorten, pulling them toward opposite poles of the cell.
3. Formation of Two Groups
   • As homologous chromosomes move toward opposite poles, they become visibly separated into two groups.
   • Each group contains a haploid set of chromosomes, with each chromosome consisting of two sister chromatids.

Anaphase II

1. Sister Chromatid Separation
   • In Anaphase II, sister chromatids of each chromosome are separated.
   • This separation results in the formation of individual chromosomes, each consisting of a single chromatid.
2. Movement to Opposite Poles
   • Microtubules attached to the centromeres of sister chromatids shorten, pulling them toward opposite poles of the cell.
3. Formation of Two Groups
   • As sister chromatids move toward opposite poles, they become visibly separated into two groups.
   • Each group contains a haploid set of chromosomes, with each chromosome consisting of a single chromatid.

Functions of Anaphase

Some of the functions of the anaphase are:

• Anaphase ensures the accurate distribution of genetic material by separating sister chromatids (in mitosis) or homologous chromosomes (in meiosis II) to opposite poles of the cell.
• Each daughter cell receives the correct number and type of chromosomes, maintaining genetic integrity.
• Anaphase involves changes in the spindle apparatus which help in the movement of chromosomes towards opposite poles, ensuring efficient segregation.
• During anaphase, centrosomes move to opposite poles, guiding the orientation of the spindle apparatus for proper chromosome segregation.
• Anaphase marks the beginning of cytokinesis, the process of cytoplasmic division.
• Proper chromosome segregation during anaphase is important for maintaining genomic stability.

What are the Important Facts About Anaphase?

Some interesting facts about Anaphase are:

• Anaphase is the stage in both mitosis and meiosis where chromosomes separate and move towards opposite poles of the cell.
• It ensures that each daughter cell receives the correct number of chromosomes.
• During anaphase, the sister chromatids, which are identical copies of each chromosome, are pulled apart by spindle fibers towards opposite poles of the cell.
• Anaphase is facilitated by the mitotic spindle, a structure made of microtubules that form between the centrosomes.
• Anaphase is regulated by various cell cycle checkpoints to ensure that all chromosomes are properly attached to the spindle fibers before they separate. This helps prevent errors in chromosome distribution.
• Anaphase is relatively short compared to other stages of the cell cycle. It typically lasts only a few minutes.
• Anaphase is followed by cytokinesis, where the cytoplasm of the cell is divided into two separate daughter cells.
• Cytokinesis usually begins during late anaphase and continues through telophase.
• While the general process of anaphase is similar in both mitosis and meiosis, there are variations between the two processes. For example, in meiosis, there are two rounds of division, resulting in four daughter cells with half the number of chromosomes as the parent cell.
• Anaphase is important for maintaining the correct chromosome number in daughter cells, which is essential for the proper functioning and development of organisms.
• Errors in anaphase can lead to genetic disorders or cell death.

Conclusion: Anaphase

During anaphase, chromosomes split and move to opposite ends of the cell. This separation is guided by the spindle fibers. It ensures that each new cell receives the correct number of chromosomes. Anaphase acts as a checkpoint to prevent errors in chromosome distribution. Without anaphase, cells might end up with the wrong genetic information. This could lead to serious issues like genetic disorders or cell death. Therefore, anaphase is essential for maintaining the integrity of the genetic material and ensuring the proper functioning of cells.

FAQs on Anaphase

What are the Key Facts About Anaphase?

Anaphase is a stage of cell division where chromosomes separate and move to opposite ends of the cell.

What are the Parts of the Anaphase?

The key parts of anaphase include chromosomes, spindle fibers, and centrosomes.

What are the Main Activity in Anaphase?

Anaphase is primarily characterized by the separation of duplicated chromosomes into individual chromatids, guided by spindle fibers, ensuring each daughter cell receives the correct genetic material.

Does Anaphase Have DNA?

Anaphase involves the movement of DNA-containing chromatids towards opposite poles of the cell.

How Many Cells are Involved in Anaphase?

Anaphase involves one cell undergoing division into two daughter cells.

What is Anaphase and Cytokinesis?

Anaphase is the stage of cell division where sister chromatids separate and move towards opposite poles of the cell. Cytokinesis is the process of cytoplasmic division, occurring after nuclear division, resulting in the formation of two daughter cells.