Mitosis H Biology

What is Mitosis? Mitosis is the process where cells divide to produce new cells Occurs in healing, growth, and day-to-day life Ex: Hair growth, nail growth, wound healing… ALL eukaryotic organisms produce new cells through mitosis

Cell Cycle Consists of 2 main stages: 1. Interphase – the “growing” stage 2. Mitotic Phase – Cell Division

Interphase The majority of the cell cycle (90%) is spent in Interphase prior to Mitosis Interphase is divided into 3 sub sub-phases: G1 Phase S Phase G2 Phase

G1 Phase Cell begins to grow  needs to increase its surface area before dividing Why? Growth continues through S Phase Organelles increase in number and size Chromosomes appear as threadlike coils Made of Chromatin, a combination of DNA and protein molecules In G1, cells accomplish most of their growth; they get bigger in size and make proteins and organelles needed for normal functions of DNA synthesis. Here, proteins and RNAs are synthesized, and, more especially the centromere and the other components of the centrosomes are made. The cells are fully functional

S Phase (Synthesis) “Synthesis” = To Make During the S Phase, DNA is replicated Chromosomes are copied (# doubles) The region where the two chromatids are joined tightly together is called the centromere. Growth continues Each chromosome is single  replication occurs and then the chromosomes are doubled each consisting of two sister chromatids Chromatin doubles

G2 Phase Cell size continues to increase and prepares for cell division At the end of this phase, there is double the amount of DNA, centrioles have replicated, and the cell is big enough for cell division.

Interphase Recap ✔ ✔ ✔ Up Next 

Mitotic Phase After Interphase, comes the Mitotic Phase begins. Two parts: Mitosis Cytokinesis Cytokinesis usually begins before Mitosis is completed.

Mitosis During mitosis, the nucleus and doubled chromosomes divide  create two identical daughter cells 4 sub phases: Prophase Metaphase Anaphase Telophase Prophase (pro- means before) Metaphase (meta- means middle) Anaphase (ana- means without) Telophase (telo- means end) Cytokinesis usually begins before Mitosis is completed.

Prophase First phase of Mitosis: Nuclear envelope breaks down Chromatin fibers condense, becoming the compact structure we call a chromosome. Spindles (made by the centrioles) begins to form in the cytoplasm Centrioles Spindles 92 chromosomes of DNA at this point

Prophase 2. Centrioles move DNA supercoils into chromosomes

Metaphase Second phase of Mitosis: Nuclear membrane disappears Chromosomes attach to the spindle at the centromeres Chromosomes line up in the middle of the cell forming an equator 92 chromosomes at this point

Metaphase

Anaphase Third phase of Mitosis: Spindle pulls apart chromosomes (by an attachment to the centromere) Chromatids separate at the centromere and move towards each end Each chromatid is now considered its own chromosome Still 92 chromosomes….

Anaphase

Telophase Fourth (and final) phase of Mitosis: Chromosomes reach end of spindle Spindle breaks down Cleavage furrow begins to form Nuclear membrane begins to reform NOW each cell has 46 chromosomes (23 pairs)

Telophase Spindle fall apart Cleavage furrow

Cytokinesis Second part of the Mitotic Phase Cleavage furrow pinches all the way through The cytoplasm is divided in two DNA uncoils into chromatin again Result is two new cells Officially 2 new cells with 46 chromosomes EACH

And the Cycle Continues… 2 NEW cells then enter the cycle and Mitosis begins again! YAY! G1, S, G2 (Interphase) PMAT & Cytokinesis Each new cell at the end of mitosis is DIPLOID Has a full set of chromosomes (46)

IPMATC Interphase Prophase Metaphase Anaphase Telophase Cytokinesis I Play Monopoly At Camp

Recap

What is Apoptosis? Apoptosis is controlled, programmed cell death This is how we develop fingers (instead of having a webbed hand) and how women menstruate This is very important for maintaining healthy, functioning cells within our body! However, sometimes apoptosis doesn’t happen  cancer When a cell is compelled to commit suicide proteins called caspases go into action. They break down the cellular components needed for survival, and they spur production of enzymes known as DNases, which destroy the DNA in the nucleus of the cell. It's like roadies breaking down the stage in an arena after a major band has been through town. The cell shrinks and sends out distress signals, which are answered by vacuum cleaners known as macrophages. The macrophages clean away the shrunken cells, leaving no trace, so these cells have no chance to cause the damage that necrotic cells do.

What is Cancer? Disease caused uncontrollable cell division Can spread cancer cells throughout the body METASTASIS Cancer “masses” displaces normal tissue

What are the treatments for cancer? Surgery Radiation Therapy High energy radiation disrupts cell division Chemotherapy Drugs disrupt cell division Anti-mitotic drug freezes spindle fibers