Cell Biology: Functions, Types, Reproduction, and Cloning

**Functions of the Cell**

• Nutrition: Through nutrition, cells obtain the energy they need to create and maintain their structures and perform other vital functions. The molecules from which they obtain materials and energy are nutrients such as water, minerals, oxygen, and organic molecules.
• Relationship: By using this function, cells perceive physical and chemical changes that occur in the environment that surrounds them.
• Reproduction: Using this function, cells originate and divide into new cells.

**Types of Cells**

• Prokaryotes: They are characterized by a lower degree of complexity and a smaller number of organelles. These are single-celled organisms.
• Eukaryotes: They are characterized by a complex organization with many different compartments or organelles that are specialized to perform specific functions. These are multicellular organisms.

**DNA**

DNA is the molecule that stores information about all the features inherited from parent to offspring and, therefore, is the hereditary or genetic material. The DNA molecule is formed by the union of several smaller units called nucleotides. The sequence or order in which the nucleotides are arranged in the chain of DNA is the genetic information.

**Chromatin and Chromosomes**

Nuclear DNA is associated with a group of histone proteins to form very long filaments called chromatin fibers. In a cell in interphase, that is, that is not dividing, chromatin fibers are dispersed in the nucleus. A chromosome has a long and narrow shape with a centromere that bisects the chromosome into arms of the same or different lengths.

**Cell Reproduction: Meiosis II**

In organisms that reproduce sexually, two reproductive cells or gametes fuse to give rise to a single cell, the zygote, which develops to form the offspring. Because the fusion of male and female gametes should not generate a zygote, and therefore, an offspring with double the DNA of their parents, gametes are required to carry half the normal DNA content.

**Cell Reproduction: Mitosis**

Cell reproduction through mitosis is a process of cell division. The division of a cell by mitosis leads to two daughter cells with the same genetic information as the progenitor and therefore identical to each other and identical to the parent cell. In single-celled organisms, cell division is equivalent to the reproduction of the individual, as a stem cell is replaced by two daughter cells. Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase.

**Mechanism of Mitosis**

• Prophase: The DNA condenses to form chromosomes. The nuclear membrane begins to disintegrate, and the centrioles are duplicated and move toward opposite poles.
• Metaphase: The chromosomes align themselves with the fibers of the mitotic spindle at the level of the centromeres and are placed in the center of the cell.
• Anaphase: The sister chromatids separate and are directed to opposite poles of the cell.
• Telophase: Once separated into two sets, the chromosomes begin to decondense and are surrounded by a nuclear membrane.

**Cloning**

Depending on the procedure, cloning may be natural or artificial, as it occurs spontaneously (in nature) or through manipulation.

• Molecular Cloning: Consists of obtaining identical copies of a gene or group of genes. The replication of chromosomes during mitosis is in fact an example of natural molecular cloning.
• Cellular Cloning: Obtaining identical copies of another cell. The division of eukaryotic cells by mitosis, or bacteria by bipartition, are examples of natural cellular cloning.
• Cloning of Organisms: The majority of species present, except for single-celled organisms, reproduce sexually. This means that offspring are not identical to either parent, but a mixture of 50% of the genes from the mother and father. Therefore, meiosis and sexuality disappear with the cloning of organisms.