Mitosis & Mitosis & Asexual Asexual

ReproductionReproduction

What IS Mitosis?

Mitosis is defined as the division of the nucleus into two nuclei with complete sets of chromosomes. However, mitosis is followed by the division of the cell and organelles as well, thus resulting in two new cells, each with complete sets of chromosomes.

Why do we NEED Mitosis?

Growth Repair Maintenance

Development of a zygote

Asexual Reproduction

Phases of Mitosis

• Cell grows• Chromosomes duplicate

• centrioles move apart

• spindle fibers form between centrioles

• chromosomes condense

• nuclear membrane starts to disintegrate

• nuclear membrane is gone

• centrioles are as far apart as possible

• spindle fibers are fully formed

• chromosomes* line up in the Middle**

* Chromatid pairs

** M for middle, M for metaphase!

• chromatid pairs pull apart

• spindle fibers shorten

• cell is elongating

• each half of the centriole copies itself

• nuclear membrane reassembles

• chromosomes relax

• cytokinesis begins

Cytokinesis is the pinching inward of the cell membrane to form two new cells.

How do Plant Cells Differ?Spindle fibers form even though plant cells don’t have centrioles.

An acid secreted by the cell causes the cell wall to weaken so that the cells can elongate.

Because of the cell wall, plant cells can not rely on cytokinesis. Instead, plants form cell plates. These are tiny sections of cell wall that slowly fuse together to form a new cell wall.

Cell Plates

Photos of Mitosis

Just another cool photo of…?

What phases can you find?

To understand the molecular mechanism of cell division, we need to know the life cycle of a cell.  It consists of four phases: G1, S, G2 and M, where "G" stands for

"Gap", "S" represents "Synthesis" and "M" means "Mitosis".  A newly divided cell may either enter into another round of cell division or remain in the resting state for a long period.  In the latter case, the cell is said to be in  the G0 phase.  Upon specific

stimulation, cells in the G0 phase may re-

enter the G1 phase.

                                                          

                                                 Figure 8-A-1.  The cell cycle.  Without counting the G0 phase, a cell cycle takes

12-24 hours for most mammalian cells, and only 20-30 minutes for E. coli cells. 

Cell Cycle

Most mammalian cells complete this cycle in 12-24 hours while bacteria complete the cell cycle in 20-30 minutes! Now you know why you get sick, quick!

Asexual Reproduction:is a type of reproduction in which there is only one parent and all offspring are genetically identical to the parent.

Types of Asexual Reproduction

Binary Fission One cell divides into two complete and equal cells.

Budding Similar to binary fission, but one daughter cell is MUCH smaller.

SporulationSpecial cells called spores released with a protective coat. It will develop when conditions are favorable

Regeneration The ability to replace lost or damaged body parts.

Vegetative Propagation

Various forms of asexual reproduction in plants. There are FIVE we will learn about…..!

Five Types of Vegetative Propagation

Cutting Part of a plant with stem & leaves in water will grow roots.

Bulb Underground stem surrounded by fleshy leaves. New bulbs grow from existing ones.

Tuber An enlarged underground stem surrounded by food. New plants develop from buds on the tuber.

RunnerHorizontal stems run close to the ground. New plant forms when the runner touches the ground and grows roots

Grafting Taking a cut branch from one plant and attaching it to the rooted trunk or branch of another.

Stock: the

rooted plant

Scion: the cut branch

Important!! The scion keeps all of its original characteristics, as does the stock

Aging and Mitosis

As we get older, mitosis slows down. Eventually we reach a critical point where more cells are lost than are being replaced.

Cancer & Mitosis

Most cells have contact inhibition. This means that they will stop reproducing when they get too close to one another.

Cancer cells lose contact inhibition and reproduce uncontrollably.

The cancer cells take all of the nutrients, energy and blood flow away from other organs in order to feed the tumor.