Eukaryotic Cell Reproduction: Mitosis, Cytokinesis, and Nutrition

Eukaryotic Cell Reproduction:

Mitosis Phases:

1) Prophase:

Key occurrences:

• Disappearance of the nucleolus. The genes that synthesize 45S ribosomal RNA (rRNA) are located on chromosomes 13, 14, 15, 21, and 22 (in humans).
• The nuclear envelope disappears due to water entering the cytosol.
• The mitotic spindle forms from the centriolar microtubule organizing center.
• Duplication of the centrosome.

2) Metaphase:

Key occurrences:

• The spindle is completely formed.
• Chromosomes, which appeared as filaments in prophase, are now fully compacted and consist of two chromatids (each containing a DNA molecule).
• Kinetochore microtubules form and push the kinetochores on the chromosomes to align them in the equatorial plane of the cell.

3) Anaphase:

Key occurrences:

• Shortening of kinetochore microtubules separates the sister chromatids, each moving to opposite poles of the cell.
• In late anaphase, cytokinesis begins, distributing cytoplasmic content between the two forming daughter cells.

4) Telophase:

Key occurrences:

• Maximum shortening of kinetochore fibers and total separation of sister chromatids.
• Maximum elongation of the polar spindle fibers.
• Reconstruction of the nuclear envelope from the rough endoplasmic reticulum (RER).
• Decondensation of chromatin into chromosomes.

Cytokinesis in Animal and Plant Cells:

Cytokinesis is the division of the cytoplasm.

1) Animals:

Strangulation of the cell at its equatorial plane occurs due to the formation of a contractile ring of actin and myosin filaments between the spindle fibers.

2) Plants:

In plant cells, cytokinesis is produced by Golgi vesicles that fuse together to form a structure called the phragmoplast, which changes its composition to give rise to the middle lamella (cell plate).

Eukaryotic Functions of Nutrition:

Concept of Nutrition: The function by which organisms obtain material and energy from their environment. Organisms can be classified based on their source material:

• Heterotrophs: Obtain organic matter in a pre-formed state.
• Autotrophs: Obtain inorganic matter (CO₂, mineral salts).

According to the energy source, organisms can be classified as:

• Photosynthetic: Use solar energy for synthesis.
• Chemosynthetic: Obtain energy by oxidation of molecules.

Two small groups:

1. Chemolithotrophs: Use reduced inorganic molecules (NH₃, SH₂). These are bacteria.
2. Chemoorganotrophs: Use small organic molecules and are heterotrophic.

Heterotrophic Nutrition Phases:

1) Ingestion:

Endocytosis, phagocytosis, and pinocytosis.

2) Digestion:

Primary lysosome + endocytic vesicles.

3) Excretion:

Release of waste products by exocytosis.