The basic structural, functional and biological units of all known living organisms are the cells that are often termed as the building blocks of the body. A cell consists of protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as unicellular or multicellular and while the number of cells in plants and animals varies from species to species, humans contain about 100 trillion (1014) cells. Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometers. The feature presents various animations which illustrate the basics of cell biology.
Anatomy of Cells
Basically there are two types of cells which are as follows:
– Prokaryotic Cells
Image Courtesy: estrellamountain.edu
Prokaryotic cells are thought to be the first form of life on Earth since they have signaling and self-sustaining processes. The DNA of a prokaryotic cell consists of a single chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid. Most of the prokaryotes are smallest of all organisms and usually range from 0.5 to 2.0 µm in diameter. The animation shows the cell division in a prokaryotic cell.
– Eukaryotic Cells
Image Courtesy: clccharter.org
Image Courtesy: en.wikipedia.org
The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound compartments in which specific metabolic activities take place. Most important among these is a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell’s DNA. This nucleus gives the eukaryote its name, which means “true nucleus”. Plants, animals, fungi, slime molds, protozoa, and algae are all eukaryotic. The cells are about fifteen times wider than a typical prokaryote and can be thousand times greater in volume. The animations show the membrane targeting and elongation stages of the eukaryotic cell.
Both the type of cells, whether prokaryotic or eukaryotic contain some basic components which are common in both of them.
– Cell Membrane
Image Courtesy: dctf.uniroma1.it
Image Courtesy: classhelp.info
The membrane surrounds the cytoplasm of a cell but in animals, the plasma membrane is the outer most boundary of the cell whereas in case of plants and prokaryotes, it is covered by a cell wall. The membrane serves to protect a cell from its surrounding environment and is mostly made from a double layer of phospholipids. Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones. The animation shows osmosis of particles through plasma membrane.
– Genetic Material
Image Courtesy: en.wikipedia.org
Image Courtesy: geneticsrus.org
The genetic material in a cell is of two types: namely DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). The biological information contained in an organism is encoded in its DNA sequence whereas RNA is used for information transport and enzymatic functions. Prokaryotic genetic material is organized in a simple circular DNA molecule in the nucleoid region whereas the Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus. The first animation shows the structure of a part of the DNA double helix. The second animation shows how RNA polymerase unwinds the DNA strands and hence transports the information.
– Metabolism and Growth
Image Courtesy: theworldofbiochemistry.wordpress.com
The cells grow during the division through the process of metabolism and it is by this mechanism through which individual cells process nutrient molecules. There are two division of metabolism:
Catabolism: The division in which cell breaks down complex molecules to produce energy and reducing power. The animation shows how complex molecules are broken down in a cellular process.
Anabolism: A process in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.
– Cell Replication
Image Courtesy: water.me.vccs.edu
Image Courtesy: esu7.org
Cell division involves a single cell dividing into two daughter cells. This leads to growth in multicellular organisms and to procreation (vegetative reproduction) in unicellular organisms. Prokaryotic cells divide by binary fission, while eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis. The animation shows how cell division occurs in prokaryotic cell. The second animation shows how replication occurs in eukaryotic cells found in multicellular organisms.
– Cell Movement
Image Courtesy: reddit.com
In multicellular organisms, cells can move during processes such as wound healing, the immune response and cancer metastasis whereas unicellular organisms can move in order to find food or escape predators. Common mechanisms of motion include flagella and cilia. The animation shows the movement of a white blood cell as it moves to kill the bacteria.