Structure of Cells and Types of Cells

Cruz, Tiffany Grace V.Humarang, Jelain A.

Era, Emil D.

IntroductionCells were first described by Robert Hooke in his book Micrographia, published in 1665. Using a microscope, he described the structure of cork as closely resembling prison chambers or monks’ quarters (there is some debate about this). He used the term “cell” to describe these hollow chambers. The Cell Theory was first described in 1839. While the Cell Theory has been altered and revised, most biologists today list three or four general characteristics shared by all cells:

1. The cell is the basic unit of life. Anything smaller than a cell is not alive by definition.2. All organisms are composed of one or more cells.3. Cells arise from pre-existing cells.4. All cells, at some point in their life cycle, contain the genetic material for the entire organism.

Cell Structure and FunctionCell wall: It helps in protecting the plasma membrane and plays a vital role in supporting and protecting the cells. It is a thick outer layer made of cellulose. Cell membrane: It is a double layered, thin barrier, surrounding the cell to control the entry and exit of certain substances.Cytoplasm: It is a membrane, which protects the cell by keeping the cell organelles separate from each other. This helps to keep a cell in stable. Cytoplasm is the site, where many vital biochemical reactions take place.Nucleus: They are the membrane bound organelles, which are found in all eukaryotic cells. It is the very important organelle of a cell as it controls the complete activity of a cell and also plays a vital role in reproduction.Nuclear membrane: The bilayer membrane, which protects the nucleus by surrounding around it and acts as a barrier between the cell nucleus and other organs of a cell.Nucleolus: It is an important membrane found inside the nucleus. It plays a vital role in the production of cell's ribosome.Chromosomes: It is made up of DNA and stored in the nucleus, which contains the instructions for traits and characteristics.

Endoplasmic reticulum: It helps in the movement of materials around the cell. It contains an enzyme that helps in building molecules and in manufacturing of proteins. The main function of this organelle is storage and secretion. Ribosome: It plays a vital role in protein synthesis.Mitochondria: They are double membrane, filamentous organelles, which play a vital role in generating and transforming the energy. Mitochondria play a vital role in various functions of the cell metabolisms including oxidative phosphorylation.Golgi Bodies: It helps in the movement of materials within the cell.Lysosomes: It is also called as suicidal bags as it helps in cell renewal and break down old cell parts.Vacuoles: It helps plants in maintaining its shape and it also stores water, food, wastes, etc.Chloroplast: They are the site of photosynthesis, which are present in chlorophyll bacteria, blue-green algae, etc.

Two Basic Types of Cells

Cells come in two basic types. Prokaryotic cells are found in bacteria, including both Archaebacteria and Eubacteria, and including the blue-green algae. Eukaryotic cells are found in animals, plants, Fungi and protists.

Characteristics of Prokaryotic Cells

• Prokaryotes lack an organized nucleus and other membrane-bound organelles.• Prokaryotic DNA is found in a central part of the cell called the nucleoid.• The cell wall of a prokaryote acts as an extra layer of protection, helps

maintain cell shape, and prevents dehydration.• Prokaryotic cell size ranges from 0.1 to 5.0 μm in diameter.• The small size of prokaryotes allows quick entry and diffusion of ions and

molecules to other parts of the cell while also allowing fast removal of waste products out of the cell.

Components of Prokaryotic Cells

All cells share four common components:• a plasma membrane: an outer covering that separates the cell's

interior from its surrounding environment.• cytoplasm: a jelly-like cytosol within the cell in which other cellular

components are found• DNA: the genetic material of the cell• ribosomes: where protein synthesis occurs

Characteristics of Eukaryotic Cells• Eukaryotic cells are larger than prokaryotic cells and have a "true" nucleus, membrane-

bound organelles, and rod-shaped chromosomes.• The nucleus houses the cell's DNA and directs the synthesis of proteins and ribosomes.• Mitochondria are responsible for ATP production; the endoplasmic reticulum modifies

proteins and synthesizes lipids; and the golgi apparatus is where the sorting of lipids and proteins takes place.

• Perixisomes carry out oxidation reactions that break down fatty acids and amino acids and detoxify poisons; vesicles and vacuoles function in storage and transport.

• Animal cells have a centrosome and lysosomes while plant cells do not.• Plant cells have a cell wall, a large central vacuole, chloroplasts, and other specialized

plastids, whereas animal cells do not.

Eukaryotic Cell Structure

Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes. However, unlike prokaryotic cells, eukaryotic cells have:• a membrane-bound nucleus• numerous membrane-bound organelles (including the endoplasmic reticulum,

Golgi apparatus, chloroplasts, and mitochondria)• several rod-shaped chromosomesBecause a eukaryotic cell's nucleus is surrounded by a membrane, it is often said to have a "true nucleus. " Organelles (meaning "little organ") have specialized cellular roles, just as the organs of your body have specialized roles. They allow different functions to be compartmentalized in different areas of the cell.

References

https://www.wyzant.com/resources/lessons/science/biology/cellshttp://staff.jccc.net/pdecell/cells/basiccell.html#typeshttps://www.boundless.com/biology/textbooks/boundless-biology-textbook/cell-structure-4/