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Mammalian Cell CycleAbiola Nelson 1014800Ramzee Small 1012412

Mammalian Cell CycleAbiola Nelson 1014800Ramzee Small 1012412

With an introduction to Radiobiology


Definition of Mammalian Cell Cycle

Cellular Review

Explanation of Mammalian Cell Cycle

Discussion of Stages of the Mammalian Cell Cycle


Mammalian Cell Cycle

What 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


Cells 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 organellesRibosomesEndoplasmic 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


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


Cell 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 Phase

Also 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


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.



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.


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


Valerie C. Scanlon, Tina Sanders, Essentials of Anatomy and Physiology, Fifth Edition, Copyright 2007 by F. A. Davis, pg. 46-66 S. Mader, Understanding human anatomy and physiology, Fifth Edition, The McGrawHill Companies, 2004, pg. 46Frederic H. Martini, Ph.D., Judi L. Nath, Ph.D., Edwin F. Bartholomew, M.S, Fundamental of Anatomy and physiology, Ninth Edition, pg. 63Philip W. Ballinger, Eugene D. Frank, Merrills Atlas of Radiographic Positions & Radiologic Procedures, Volume One, Tenth Edition, Copyright 2003. Mosby. Inc., pg. 51 Michael W King, The medical biochemistry