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Mammalian Cell Cycle
Abiola Nelson 1014800Ramzee Small 1012412
Mammalian Cell Cycle
Abiola Nelson 1014800Ramzee Small 1012412
With an introduction to Radiobiology
OutlineDefinition of Mammalian Cell Cycle
Cellular Review
Explanation of Mammalian Cell Cycle
Discussion of Stages of the Mammalian Cell Cycle
Radiobiology
Mammalian Cell CycleWhat is the Mammalian cell cycle?
Mammalian ------- Cell--------Cycle
A series of events that take place in a cell leading to its division and duplication (replication) that produces two daughter cells.
Cellular Review
DefinitionCells are the smallest living subunits of a multicellular organism
Refer to as “Building Block of Life”
They are composed of protoplasm which contains 75% water, electrolytes, proteins, lipids and carbohydrates
Composition of Cell The cell has three (3) major parts
Cell Membrane Semi-permeable structureBarrier between cell and its environment
NucleusHouses DNA which contains chromosomesControl Cell activities
Composition of Cell
Cytoplasm Surround the nucleusSupport, protect and house organelles
RibosomesEndoplasmic ReticulumGolgi Apparatus/ComplexMitochondriaLysosomesMicrotubulesFilaments
Fun Facts About cellYour body contains around 1013 to 1014 cells
The ovum is the largest cell in the body, and can be seen without a microscope
Nerve cell in our arms and legs are at least 2 feet (60 cm) long.
Macrophage has more than one nucleus while a mature red blood cell has NONE
Cells come only from the replication of existing cells.
Mammalian Cell Cycle
Definition
The series of events that take place in a cell leading to its division and duplication (replication) that produces two daughter cells.
The cell cycle has two major portions;Interphase Mitotic Phase
InterphaseCell carries on its regular activities
It also gets ready to divide if stimulated to complete the cell cycle
Interphase encompass three phases;G1 PhaseS PhaseG2 Phase
InterphaseG1 Phase
The cell doubles its organelles
And synthesizes the necessary proteins for DNA replication
What part of the cell is this ?
InterphaseS PhaseSo-called because DNA is Synthesized in this phase
Each chromosome is composed of one DNA double helix, which is equal to a chromatid.
S phase result in each chromosome having two identical DNA double helix molecules.
InterphaseS Phase (Overview of DNA Synthesis)
The DNA double helix splits down the middle and becomes two single strands (serving as templates)
DNA polymerase adds an A base wherever there is a T, a C where there is a G, and so on until all of the bases once again have partners.
Each DNA molecule formed consists of one old strand and one newly assembled strand and constitutes a chromatid of a chromosome.
Summary of DNA Replication
InterphaseG2 PhaseThe cell synthesizes proteins that will assist cell division
At the end of G2 phase a major check-point exist that controls the entry of the cell into M-phase
Mitotic PhaseAlso called the Cell division phase
Mitotic phase includes; Mitosis (division of the nucleus) Cytokinesis (division of the cytoplasm)
Mitotic PhaseMitosis
Divided into distinct steps that were originally identified and characterized through light microscopic observations of dividing cell.
These are termed;Prophase MetaphaseAnaphasetelophase
Mitotic PhaseMitosis
ProphaseThe duplicated chromosomes condense while the nuclear membrane breaks away
The centrioles move toward opposite poles of the cell and organize the spindle fibers, which extend across the equator of the cell
Mitotic PhaseProphase
Mitotic PhaseMitosis
MetaphasePairs of chromatids line up along the equator of the cell, with the sister chromatids attached to opposite poles of the spindle.
The centromere of each pair is attached to a spindle fiber
Mitotic PhaseMitosis
Anaphase At this phase, the sister
chromatids separate to form the two sets of daughter chromosomes.
The spindle fibers contract and slowly pulled each sister chromatid towards the spindle pole it faces
Mitotic PhaseMitosis
TelophaseThe two daughter chromosomes arrive at the spindle poles and decondense
A new nuclear envelope forms around each set of chromosomes which forms the two new nuclei
Cytokinesis
The cytoplasm divides and a new cell membrane is formed.
Summary of Mitotic Phase
Mammalian Cell CycleMost of the cells in our body are NOT replicating at any given point of time
Instead, most cells in our body remain in the G1/G2 phase for their entire lifetime
Specialized cell (muscle and nerve cells) rarely, if ever, go through the cell cycle
Stem cells, are always immature and go through the cell cycle repeatedly
List two of these cells
Mammalian Cell CycleThe cell cycle is controlled by internal and external signals
Name 3 Stimulus that can trigger this cycle
This process must be highly regulated so as to ensure that the resulting cells are viable
Mammalian Cell CycleControl of progression through the cell cycle is exerted at checkpoints.
The two most critical checkpoint are those that occur near the end of G1 prior to S-phase and those near the end of G2 prior to mitosis.
Any cell that did not successfully complete mitosis undergo apoptosis at the restriction checkpoint.
Radiobiology
Definition
A branch of science concerned with the action of ionizing radiation on biological tissues and living organisms.
Ionizing radiation is any type of particle or electromagnetic wave that carries enough energy to ionize or remove electrons from an atom.
History
Research on the biological effects of ionizing radiation started almost immediately after the discovery by Wilhelm Roentgen in 1895.
By 1910 several hundred cases of severe x-ray burns (radiodermatitis), many leading to death, had been reported.
Charles T. Dally, Thomas case
Radio sensitivity
The probability of a cell, tissue, or organ suffering an effect per unit dose of radiation.
Radio sensitivity is highest in cells which are highly mitotic or undifferentiated.
Name cells that are radiosensitive?Name cells that are not radiosensitive?
Cell Irradiation
When exposed to ionizing radiation, large molecules such as nucleic acid and proteins in the cells will be ionized or excited
This may cause changes in the molecular structures which then affect the function and metabolism of the cells
Cell Irradiation
The damage to the cell may occur in one of two ways; Direct Indirect
Cell IrradiationDirect action in cell damage by radiation
In direct action the radiation interacts directly with the critical target in the cell
Which may be ionize or excited, leading to the chain of events that produce the biological damage
Cell IrradiationIndirect action in cell damage by radiation
Radiation indirectly interact with other molecules and atoms (mainly water) within the cell to produce free radicals
Free radicals are highly reactive molecules that break chemical bonds and produce chemical changes that lead to biological damage
Cell Irradiation
Cell before and after Damage due to Ionizing Radiation
Radiobiology Significance
Ionizing radiation is potentially lethal in living organism, but can have health benefits in radiation therapy for treatment for cancer.
Understanding the effects of radiation on cells provide useful information for the development of radiation protection measures
References • Valerie C. Scanlon, Tina Sanders, Essentials of Anatomy and
Physiology, Fifth Edition, Copyright © 2007 by F. A. Davis, pg. 46-66• https://en.wikipedia.org/wiki/History_of_radiation_therapy• Sylvia S. Mader, Understanding human anatomy and physiology, Fifth
Edition, © The McGraw−Hill Companies, 2004, pg. 46• Frederic H. Martini, Ph.D., Judi L. Nath, Ph.D., Edwin F. Bartholomew,
M.S, Fundamental of Anatomy and physiology, Ninth Edition, pg. 63• Philip W. Ballinger, Eugene D. Frank, Merrill’s Atlas of Radiographic
Positions & Radiologic Procedures, Volume One, Tenth Edition, Copyright © 2003. Mosby. Inc., pg. 51• https://en.wikipedia.org/wiki/DNA_damage_(naturally_occurring) • Michael W King, The medical biochemistry page.org