Cell Structure and Function
Cells are the smallest building unit of living organisms that can carry out all processes required for life. Almost all cells are too small to see without the aid of a Microscope. Although glass lenses used to magnify images for hundreds of years, they were not enough to reveal individual cells. The invention of Compound microscope was in the late 1500s by the Dutch eyeglass maker Zacharias Janssen. In 1665, the English scientist Robert Hooke was the first to identify cells, and named them. After long studies, the accumulated research can be summarized in the cell theory, which is considered as the first unifying concepts in biology. The Major principles of the Cell Theory:
1. All organisms are made of cells.
2. All existing cells are produced by other living cells.
3. The cell is the most basic unit of life.
The variety of cell types found in living things is staggering; the human body alone is made of trillions of cells of many different shapes, sizes and functions. Despite this variety, the cells in the body share many similar characters. All cells are Microscopic in size, Composed of similar building blocks, and are enclosed by a membrane that controls the movement of materials into and out of the cell. Within this membrane the cell is filled with Cytoplasm, and Organelles. Organelles are structures specialized to perform distinct processes; mostly they are surrounded by a membrane, which take us to the first classification of Cells.
Is type of cells that Do not have a nucleus or other membrane-bound Organelles, the Cell’s DNA is suspended in the Cytoplasm. Most prokaryotes are microscopic single-celled organisms. E.g.: Bacteria. Eukaryotic Cells:
Is type of cells that Have a nucleus and other membrane bound Organelles, The nucleus is the largest organelle where it encloses the genetic information (DNA), Eukaryotes may be Multi-cellular or Single-celled organisms.
The origin of the term “Prokaryotes” and “Eukaryotes” is the Greek root “Karuon” which means “ nuts” or “kernel” that refers to the nucleus, where “Eu= true” and “pro= before” , the cell with true nucleus is Eukaryote.
General Questions on the Section:
1. What are the major principles of the cell theory?
2. What characteristics are shared by most cells?
3. How do prokaryotes and eukaryotes differ?
4. In what way are cells similar to atoms?
We mentioned that Eukaryotic cells share many similar structures, these structures include similar organelles involved in processing the cell functions. In this chapter we will discuss each Organelle structure and function.
Cell internal structure:
There are some similar characters in all cells that shapes its body and protects its identity, these characters are: 1. Cell Membrane: Is a double layered membrane that forms a boundary between a cell and the outside environment and controls the passage of materials into and out of the cell.
2. Cytoskeleton: Is a network of proteins that is constantly changing to meet the needs of a cell. It is made of small protein subunits that form long threads, or fibers that crisscross the entire cell. Cytoskeleton prevents the cell from being a random jumble of suspended organelles.
Cytoskeleton is divided into three types:
1) Microtubules: Are long hollow tubes, that gives the cell its shape. 2) Itermediate filaments: Smaller than microtubules, and gives the cell its strength. 3) Microfilaments: The smallest of three, are tiny threads that enable cells to move and divide.
3. Cytoplasm: It is the jelly like substance that contains dissolved molecular building blocks, such as proteins, nucleic acids, minerals and ions. Cytoplasm is the cell matrix that fills the space between the...
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