Lesson On Cell Mitosis A eukaryote organism is one whose cells contain complex structures enclosed within its membranes. The process of mitosis in eukararyotic cells is where the cell initiates a division or separation of the chromosomes in its cell nucleus into two identical sets of two nuclei. This process acts by a previous set of coded instructions. Then this part of the process is generally followed by a full separation process in the cell called cytokinesis which pulls apart not only the nuclei, but the cytoplasm, organelles , and even the cell membranes as well. The result: the parent cell has mitosed into two daughter cells .
Lesson On Cell Mitosis Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle —the division of the parent cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 10% of the total cell cycle. Mitosis occurs only in eukaryotic cells and the process varies in different species. Various kinds of cells have different internal molecular chemical codes which starts and stops this process and regulates its steps. For now, just remember that during mitosis the chromosomes divide into two sets within the cell nucleus !
Lesson On Cell Mitosis Two Examples of Mitosis Animal cells undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while some fungi such as Aspergillus nidulans and Saccharomyces cerevisiae ( yeast ) undergo a special "closed" mitosis, where chromosomes divide within an intact cell nucleus . Prokaryotic cells , which lack a true nucleus, divide by a process called binary fusion .
Lesson On Cell Mitosis Saccharomyces cerevisiae
Lesson On Cell Mitosis The process of mitosis is surprisingly fast and involves chemical alterations of large and highly complex protein molecules. The sequence of events is divided into stages corresponding to the ending of one set of activities and the beginning of the next. These stages are interphase , prophase , ( prometaphase ), metaphase , ana-phase , and telophase . During mitosis the pairs of chromatids condense and attach to fibers that pull the sister chromatids to opposite sides of the cell. The cell then divides in cytokinesis, to generate two identical daughter cells .
Lesson On Cell Mitosis Errors in mitosis can either kill a cell through apotosis or cause mutations that may lead to cancer . Because the complex arrangement of amino acids and bases of the protein chains in the nucleus even a slight modification by mutation can cause death or grotesque deformity of a cell. The highly complex information in cells has been compared by some molecular bio-logists to a vast network of supercomputer programs which would suffer immense damage if even one or two files are damaged or garbled. Some scientists (Intelligent design theorists) have argued that cells actually function by highly advanced engineering or design (something to think about !)
Lesson On Cell Mitosis The structure of the DNA “ double helix”: The atoms in the structure are colour - coded to identify each element , the spiralling backbone of the two strands is shown in orange and the detailed structure of two base pairs is shown in the bottom right of the previous picture representation . Deoxyribonucleic Acid , or DNA is a nucleic acid that contains all contains all the genetic information (codes of life) that instructs the cells of all living organisms in their development and functioning (with the exception of what are called RNA viruses ). DNA may be compared to set of elaborate “blueprints” for living things; or, as some scientists have likened them, to a series of interlocking computer “codes” which operate the mechanisms of the living cell.
Lesson On Cell Mitosis DNA contains the instructions needed to construct other components of cells, such as proteins and RNA molecules . The DNA segments that carry this genetic information are called genes , but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. (This is that of which all living things are made and gives them their unique characteristics !) DNA is itself composed of long complex protein chains called polymers . These polymers themselves are composed of smaller units known as nucleotides . These are medium- sized molecules with “backbones” or frameworks made of sugars and phosphate groups joined by ester bonds .
Lesson On Cell Mitosis DNA has two strands that run in opposite directions to each other and are therefore anti – parallel. Attached to each sugar is one of four types of molecules called bases . The primary nucleobases are cytosine, guanine, adenine ( DNA and RNA ), thymine (DNA) and uracil (RNA), abbreviated as C, G, A, T , and U , respectively. These amino acid bases are the foundation for the study of Genetics. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code , which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription .
Lesson On Cell Mitosis Within cells, DNA is organized into long structures called chromosomes . These chromosomes are duplicated before cells divide, in a process called DNA replication . Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles , such as mitochondria or chloroplast s . In contrast, prokaryotes ( bacteria and archaea ) store their DNA only in the cytoplasm . Within the chromosomes, chromatin proteins such as histones compact and organize DNA . These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.
Lesson On Cell Mitosis Detailed Overview of Mitosis Essentially, mitosis results in the transferring of the whole of the parent cell’s genetic information (e.g., its genome ) into two daughter cells. These new cells are identical to the parent cell. The genome itself is made from the total number of chromosomes – complexes of tightly coiled DNA strands – which, as we have said, contain all the informational or programming codes (i.e., genetic information) which are necessary for the cell to grow and function. Yet, for this important biological process to work right, the parent cell must make an identical copy of each chromosome previous to mitosis process. Technically, this is sometimes referred to as the S-phase of the interphase .
Lesson On Cell Mitosis The Interphase An illustration of interphase in Gray’s Anatomy. The old and new chromatin has not yet condensed, and the cell is still undergoing its normal functions.
Lesson On Cell Mitosis Each chromosome now has an identical copy of itself, and together the two are called homologus pairs. The homologus pairs are held together by a specialized region of the chromosome known as the centromere . Each homologus pair is not considered a chromosome in itself, and a chromosome always contains 2 chromatids .
Lesson On Cell Mitosis In most eukaryotes , the nuclear envelope which segregates the DNA from the cytoplasm disassembles. The chromosomes align themselves in a line spanning the cell. Microtubles , essentially miniature strings, splay out from opposite ends of the cell and shorten, pulling apart the sister chromatids of each chromosome. As a matter of convention, each sister chromatid is now considered a chromosome, so they are renamed to sister chromosomes . As the cell elongates, corresponding sister chromosomes are pulled toward opposite ends. A new nuclear envelope forms around the separated sister chromosomes.
Lesson On Cell Mitosis Phases of cell cycle and mitosis ( Interphase and the Larger Cell Cycle) Compared to the much longer cell cycle, the interphase is a rel- atively short period of time. But despite its brevity the Interphase is point where the cell prepares itself for mitosis . Thus, interphase is actually distinct from mitosis itself. Interphase itself is defined by scientists as having three sub-phases or aspects: 1. G1 (the first Gap); 2. S (Synthesis); and 3. G2 (the second Gap). It is to be observed that in all three phases, the cell grows because it produces proteins and cytoplasmic organelles . Only in the syn-thesis phase, however, are chromosomes replicated. Mitosis then falls as a short intermission in this larger cell cycle (see the next chart >>>> ).
Lesson On Cell Mitosis All these phases in the interphase are highly regulated, mainly via proteins. The phases follow one another in strict order and there are "checkpoints" that gives the cell, the cues to proceed from one phase to another.
Lesson On Cell Mitosis Preprophase In plant cells only, prophase is preceded by a pre-prophase stage. Plant cells have many vacuoles, the nucleus has to migrate into the center of the cell before mitosis can begin. This is achieved through the formation of a phragmosome , a transverse sheet of cytoplasm that bisects the cell along the future plane of cell division. In addition to phragmosome formation, preprophase is characterized by the formation of a ring of microtubules and actin filaments (called preprophase band ) underneath the plasma membrane around the equatorial plane of the future mitotic spindle . This band marks the position where the cell will eventually divide. The cells of higher plants (such as the flowering plants ) lack centrioles ; instead, microtubules form a spindle on the surface of the nucleus and are then being organized into a spindle by the chromosomes themselves, after the nuclear membrane breaks down. The preprophase band disappears during nuclear envelope disassembly and spindle formation in prometaphase.
Lesson On Cell Mitosis Chart of Mitosis Prophase Prometaphase Metaphase * Early Anaphase Telophase
Lesson On Cell Mitosis Prophase : The two round objects above the nucleus are the centresomes . The chromatin has already condensed. Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes . The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.
Lesson On Cell Mitosis Prometaphase : At this stage the nuclear membrane has degraded, and microtubules have invaded the nuclear space. These microtubules can attach to kinetochores or they can interact with opposing microtubules . Proteins attach to the centromeres creating the kinetochores . Microtubules attach at the kinetochores and the chromosomes begin moving.
Lesson On Cell Mitosis Metaphase : Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.
Lesson On Cell Mitosis Anaphase The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules .
Lesson On Cell Mitosis Telophase Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei . The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.
Lesson On Cell Mitosis Cytokinesis In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.
Lesson On Cell Mitosis The Cell Cycle & Mitosis Review
Lesson On Cell Mitosis Prokaryotic cells undergo a process similar to mitosis called binary fission . However, the process of binary fission is very much different from the process of mitosis, because of the non-involvement of nuclear dynamics and lack of linear chromosomes. Mitosis occurs only in __________ cells and the process varies in different species.(? Fill in the blank). End of Mitosis Slideshow