According to Dr. Charles Mallory, a biology professor at The University of Miami, the principles of cell theory include: 1. All organisms are made up of cells. 2. Cells are the basic units that form the structure and carry out the functions of all organisms. 3. Cells are formed only from other cells. 4. Cells contain the genetic instructions of organisms. 5. Cells control the metabolism and biochemistry of organisms.
Complex organisms are made up of billions of tiny cells. The structure of an organism depends on the way its cells are arranged. The variety of ways that cells are put together accounts for the biodiversity of organisms. Cells are involved in all the processes in an organism’s body and carry out the fundamental activities that make life possible.
According to The National Science Teachers Association, these vital activities include absorption of nutrients and water, digestion, growth, production of biological molecules, secretion, respiration, excretion of wastes, generation of a membrane potential or voltage, response to stimuli and reproduction.
So we can say that life presents to have a great variety of organization. Atoms are organized into molecules, molecules into organelles, and organelles into cells, and so on.
According to the Cell Theory, all living things are composed of one or more cells, and the functions of a multi-cellular organism are a consequence of the types of cells it has. From what we have read cells fall into two broad groups: prokaryotes and eukaryotes cells. Prokaryotic cells are smaller and lack much of the internal compartmentalization and complexity of eukaryotic cells. Cells do have certain features in common, such as a cell membrane, DNA and RNA, cytoplasm, and ribosomes. The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell (Cell Organization, 2013).
Eukaryotic cells have a great variety of organelles and functions. The cytoplasm of a eukaryotic cell consists of various organelles suspended in the liquid cytosol (Simon, Dickey, Reese, 2012). Organelles that Eukaryotic cells include are:
- Plasma Membrane
Description: Phospholipid bilayer with embedded proteins
Function:Regulates what passes into and out of cell; cell-to-cell recognition; connection and adhesion; cell communication. I would imagine this like the walls in your home.
Description: Structure (usually spherical) that contains chromosomes and is surrounded by double membrane
Function: Instructions for protein synthesis and cell reproduction; contains genetic information
Description: Long threads of DNA that form a complex with protein
Function: Contain hereditary information used to direct synthesis of proteins
Description: Site of genes for rRNA synthesis
Function: Synthesis of rRNA and ribosome assembly
Description: Small, complex assemblies of protein and RNA, often bound to ER
Function: Sites of protein synthesis
- Endoplasmic Reticulum (ER)
Description: Network of internal membranes. “Endo” means “inside”, “plasmic” refers to the cytoplasm, and “reticulum” means means “network.”
Function: Intracellular compartment forms transport vesicles; participates in lipid synthesis and synthesis of membrane or secreted proteins
- Golgi Apparatus
Description: Stacks of flattened vesicles. “Golgi” is the name of the person who first described these structures. Golgi are like stack of hollow membrane pancakes.
Function: Packages proteins for export from cell; forms secretory vesicles
Description: Vesicles derived from Golgi apparatus that contain hydrolytic digestive enzymes. “Lysos” means “breakage” and “some” means “body.” They contain digestive enzymes which, if released into the cell, would digest the vital components of the cell and kill it. “Break” it, in other words.
Function: Digest worn-out organelles and cell debris; digest material taken up by endocytosis. These are not waste product. They are chemicals intentionally manufactured by the cell for export, like hormones and pheromones.
Description: Vesicles that are formed from incorporation of lipids and proteins and that contain oxidative and other enzymes
Function: Isolate particular chemical activities form the rest of cell
Description: Bacteria-like elements with double membrane. They are very complex.
Function: “Power plants” of the cell; sites of oxidative metabolism, the essential energy-producing process of the cell. Mitochondria contain their own naked, circular DNA and their own ribosomes.
Description: Bacteria-like elements with double membrane surrounding a third, thylakoid membrane containing chlorophyll, a photosynthetic pigment
Function: Sites of photosynthesis. Chloroplasts capture light energy from the sun to produce the free energy stored in ATP through a process call photosynthesis. The photosynthetic mechanism also produces food for the organism in the form of sugar.
Description: Network of protein filaments
Function: Structural support; cell movement; movement of vesicles within cells
- Flagella (cilia)
Description: Cellular extensions with 9+2 arrangement of pairs of microtubules
Function: Motility or moving fluids over surfaces
- Cell wall
Description: Outer layer of cellulose or chitin; or absent
Function: Protection, support.
Each of these organelles performs a specific function critical to the cells survival. Organelles serve specific functions within eukaryotes, such as energy production, photosynthesis, and membrane construction. Most are membrane-bound structures that are the sites of specific types of biochemical reactions. The nucleus is particularly important among eukaryotic organelles because it is the location of a cell’s DNA. Two other critical organelles are mitochondria and chloroplasts, which play important roles in energy conversion and are thought to have their evolutionary origins as simple single-celled organisms.
In conclusion we can see that cells accomplish a lot of their functions in a very tiny, crowded little package.
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