Unit ThreeUnit Three“Cell Proliferation and Genetics”“Cell Proliferation and Genetics”

““Mitosis”Mitosis”

Prokaryotic Cell CycleProkaryotic Cell Cycle

Prokaryotic cell division occurs in two Prokaryotic cell division occurs in two stages, which together comprise a “Simple stages, which together comprise a “Simple Cell Cycle”Cell Cycle”– A) DNA ReplicationA) DNA Replication– B) Cell divides in process known as “Binary B) Cell divides in process known as “Binary

Fission”Fission”

*** Each new cell contains one chromosome and *** Each new cell contains one chromosome and is a complete prokaryotic organism is a complete prokaryotic organism

Eukaryotic Cell CycleEukaryotic Cell Cycle

The eukaryotic cell cycle is much more The eukaryotic cell cycle is much more complex than that of prokaryotes due to the complex than that of prokaryotes due to the following factors:following factors:– 1. cells are larger1. cells are larger– 2. many more organelles2. many more organelles– 3. much more DNA arranged in linear segments 3. much more DNA arranged in linear segments

known as “Chromosomes”known as “Chromosomes”– 4. cell division is more complex due to above 4. cell division is more complex due to above

factorsfactors

Eukaryotic Cell CycleEukaryotic Cell Cycle

Eukaryotic Cell DivisionEukaryotic Cell Division Division of nonreproductive cells is called Division of nonreproductive cells is called

“Mitosis”“Mitosis” Nonreproductive cells are referred to as Nonreproductive cells are referred to as

“Somatic Cells”“Somatic Cells” Mitosis involves the even division of Mitosis involves the even division of

chromosomes and organelles between two cells chromosomes and organelles between two cells that are not part of the reproductive systemthat are not part of the reproductive system

The parent cell undergoing Mitosis has a Diploid The parent cell undergoing Mitosis has a Diploid number (2n) of chromosomesnumber (2n) of chromosomes

The two daughter cells that result from Mitosis The two daughter cells that result from Mitosis have a Diploid number(2n) of chromosomes have a Diploid number(2n) of chromosomes

Eukaryotic Cell DivisionEukaryotic Cell Division Division of reproductive cells is called “Meiosis”Division of reproductive cells is called “Meiosis” Reproductive cells are referred to as “Germ Reproductive cells are referred to as “Germ

Cells”, and upon completion of Meiosis those Cells”, and upon completion of Meiosis those cells are called “Gametes”cells are called “Gametes”

Meiosis is often referred to as “Reduction Meiosis is often referred to as “Reduction Division” because the number of chromosomes Division” because the number of chromosomes is reduced from the Diploid number (2n) to the is reduced from the Diploid number (2n) to the Haploid number (n)Haploid number (n)

One parent cell with a Diploid number results in One parent cell with a Diploid number results in four daughter cells with a Haploid numberfour daughter cells with a Haploid number

ChromosomesChromosomes

First observed by German Embryologist Walther First observed by German Embryologist Walther Fleming 1882Fleming 1882

What he saw under his primitive microscope What he saw under his primitive microscope were thread-like structures of salamander larval were thread-like structures of salamander larval cells appearing to separate lengthwisecells appearing to separate lengthwise

He called the division “Mitosis” based on the He called the division “Mitosis” based on the Greek word “Mitos”, meaning threadGreek word “Mitos”, meaning thread

Number of chromosomes vary greatly by species: Number of chromosomes vary greatly by species: Humans (46), House Cat (18), Plants (100’s)Humans (46), House Cat (18), Plants (100’s)

ChromosomesChromosomes In Somatic Cells, Chromosomes group In Somatic Cells, Chromosomes group

together in pairs based on size and genetic together in pairs based on size and genetic information; they are called “Homologous information; they are called “Homologous Chromosomes” or “Homologues”Chromosomes” or “Homologues”

Before cell division, each Homologous Before cell division, each Homologous Chromosome replicates resulting in two Chromosome replicates resulting in two identical copies called “Sister Chromatids”identical copies called “Sister Chromatids”

The “Sister Chromatids” remain joined after The “Sister Chromatids” remain joined after duplication and prior to cell division at the duplication and prior to cell division at the center or their structures; this area is called the center or their structures; this area is called the “Centromere”“Centromere”

ChromatinChromatin During Interphase, the macromolecular complex During Interphase, the macromolecular complex

of DNA and Protein is referred to as of DNA and Protein is referred to as “Chromatin”, as stated previously“Chromatin”, as stated previously

Chromatin is 40% DNA and 60% ProteinChromatin is 40% DNA and 60% Protein The reason there is a large proportion of protein The reason there is a large proportion of protein

associated with the DNA structure is chemical in associated with the DNA structure is chemical in naturenature

The proteins allow the DNA to thicken and coil The proteins allow the DNA to thicken and coil in preparation for cell division; if there were no in preparation for cell division; if there were no proteins present, this would not happenproteins present, this would not happen

ChromosomesChromosomes Often in discussion, the long strands of DNA are Often in discussion, the long strands of DNA are

called “Chromosomes”called “Chromosomes” However, DNA strands are actually referred to as However, DNA strands are actually referred to as

“Chromosomes” only during cell division (whether it “Chromosomes” only during cell division (whether it is mitosis or meiosis)is mitosis or meiosis)

The above is the case because it is just prior to cell The above is the case because it is just prior to cell division that the DNA strands thicken and coil division that the DNA strands thicken and coil taking on a unique appearance, that of a taking on a unique appearance, that of a “Chromosome”“Chromosome”

Throughout the majority of the cell cycle Throughout the majority of the cell cycle (Interphase), the DNA strands are called (Interphase), the DNA strands are called “Chromatin”“Chromatin”

Cell DivisionCell Division Cell Division takes approximately 1 hour of the Cell Division takes approximately 1 hour of the

24 hour Cell Cycle24 hour Cell Cycle Cell Division has four distinct phasesCell Division has four distinct phases Some scientists further subdivide those phases Some scientists further subdivide those phases

into five or moreinto five or more The four phases in order are:The four phases in order are:

– A) ProphaseA) Prophase– B) MetaphaseB) Metaphase– C) AnaphaseC) Anaphase– D) TelophaseD) Telophase

ProphaseProphase

1. Chromosomes begin to migrate to the 1. Chromosomes begin to migrate to the center of the cellcenter of the cell

2. Chromosomes also pair up with their 2. Chromosomes also pair up with their homologuehomologue

3. The Nuclear membrane degrades3. The Nuclear membrane degrades 4. The Centrioles appear, migrate to 4. The Centrioles appear, migrate to

opposite ends of the cell, and project their opposite ends of the cell, and project their Spindle Fibers outward toward the Spindle Fibers outward toward the Centromeres of the ChromosomesCentromeres of the Chromosomes

ProphaseProphase

MetaphaseMetaphase

1. The Chromosomes are lined up in the 1. The Chromosomes are lined up in the middle of the cellmiddle of the cell

2. The Nuclear Membrane has completely 2. The Nuclear Membrane has completely disintegrateddisintegrated

3. The Centrioles’ Spindle Fibers attach to 3. The Centrioles’ Spindle Fibers attach to the centers of the Chromosomes, the the centers of the Chromosomes, the Centromeres, in preparation to pull the Centromeres, in preparation to pull the Chromosomes apartChromosomes apart

MetaphaseMetaphase

AnaphaseAnaphase

1. Spindle Fibers from the Centrioles pull the 1. Spindle Fibers from the Centrioles pull the Chromosomes apart toward opposite ends Chromosomes apart toward opposite ends of the cellof the cell

2. Once the Chromosomes separate they 2. Once the Chromosomes separate they are referred to as “Sister Chromatids”are referred to as “Sister Chromatids”

AnaphaseAnaphase

TelophaseTelophase 1. Each set of Sister Chromatids has been pulled to 1. Each set of Sister Chromatids has been pulled to

opposite ends of the parent cellopposite ends of the parent cell 2. The Nuclear Membrane begins to reform around two 2. The Nuclear Membrane begins to reform around two

new nuclei (the locations of the sister chromatids)new nuclei (the locations of the sister chromatids) 3. The Sister Chromatids begin to uncoil and loosen, 3. The Sister Chromatids begin to uncoil and loosen,

and now are designated as Chromosomesand now are designated as Chromosomes 4. The Plasma Membrane of the parent cell begins to 4. The Plasma Membrane of the parent cell begins to

“pinch off” into two new membranes via “Cytokinesis” “pinch off” into two new membranes via “Cytokinesis” 5. The Centrioles deactivate and “disappear” into the 5. The Centrioles deactivate and “disappear” into the

cytoplasmcytoplasm

TelophaseTelophase

Miscellaneous Cell Cycle InformationMiscellaneous Cell Cycle Information

Cytokinesis – the division of the cytoplasm at the end of Cytokinesis – the division of the cytoplasm at the end of cellular divisioncellular division

Cleavage Furrow – the physical action of the parent Cleavage Furrow – the physical action of the parent cell’s cytoplasm being pinched apart during Cytokinesiscell’s cytoplasm being pinched apart during Cytokinesis

Mitosis is sometimes referred to as “Karyokinesis”Mitosis is sometimes referred to as “Karyokinesis” Plant cells use a “Cell Plate” (wall in the center of the Plant cells use a “Cell Plate” (wall in the center of the

parent cell) to divide the cytoplasm instead of a parent cell) to divide the cytoplasm instead of a “Cleavage Furrow”“Cleavage Furrow”

It is important to understand that a cell does not It is important to understand that a cell does not necessarily divide every 24 hours: it can enter a “stasis” necessarily divide every 24 hours: it can enter a “stasis” until environmental conditions are more favorableuntil environmental conditions are more favorable

CancerCancer

Old/malfunctioning cells do not die and Old/malfunctioning cells do not die and continue to reproduce improperly functioning continue to reproduce improperly functioning cellscells

Bundles of cells that are malformed are Bundles of cells that are malformed are called “Tumors”called “Tumors”

Some of the cells in the tumor can then Some of the cells in the tumor can then migrate to other parts of the body, thereby migrate to other parts of the body, thereby enabling the proliferation of more cancerous enabling the proliferation of more cancerous cells/tumors in other locations: “Metastases”cells/tumors in other locations: “Metastases”

Cancer TreatmentCancer Treatment The conventional approach to treating, and hopefully The conventional approach to treating, and hopefully

curing cancer, is Chemotherapy and Radiationcuring cancer, is Chemotherapy and Radiation Chemotherapy – a chemical that is delivered to the Chemotherapy – a chemical that is delivered to the

person usually intravenously; the drug targets and person usually intravenously; the drug targets and kills cancer cellskills cancer cells

Radiation – high frequency energy delivered to a Radiation – high frequency energy delivered to a person’s body via a machine in an effort to target person’s body via a machine in an effort to target and kill cancer cellsand kill cancer cells

There are many forms of cancer each with a unique There are many forms of cancer each with a unique set of treatment optionsset of treatment options