(CSF) Mitosis Lesson

Mitosis Lesson

You have probably seen pictures of yourself when you were a baby or infant. Maybe a relative you haven't seen in a long time commented on how much you have grown. The cells inside your body have been dividing and growing since you were a baby. A single cell will divide to make two identical cells. Then the two new cells will divide to make four additional cells.

Cell Division Image, a single cell will divide into two cells. The two cells grow and divide to create 4 new cells.

 

Lifespan of Cells

The lifespan of some common cells are:

Red Blood Cells: 4 months

Stomach Cells: 2 days

Epidermal Cells: 2 weeks

Liver Cells: 300-500 days

Muscle Cells: 15 years

Bone Cells:25-30 years

Nerve Cells: A Lifetime

 

The sequence of events that involves the growth, DNA replication, and cell division of a cell during its lifespan is called the cell cycle. The cell cycle consists of three main parts: Interphase, mitosis, and cytokinesis. A cell spends most of its time during interphase. There are three stages in interphase. The first phase is called G1. During this phase, the cell is carrying out its normal functions and activities. Cardiac muscle cells are found only in the heart and they are responsible for heart beats. Skeletal muscle cells attach to bones and assist with movement. Red blood cells carry oxygen from the lungs to various parts of the body. The second phase of interphase is the S phase. DNA is capable of self-replication.  An exact copy of the DNA is made so that the cell has two sets of DNA in its nucleus. This process is called DNA replication. DNA is a nucleic acid that carries the genetic information that is necessary for the development and function of all biological activities within the cell. It is necessary that the new cell contains the same genetic as the original cell.  For example, we would want all of our salvia cells to have the same information so they can perform the same function.  Saliva contains enzymes that are very helpful to moisten food so that chewing and breaking down food is easier.

The third phase of interphase is called G2.The cell is getting ready for the next stage, mitosis. The cell may continue to grow and carry out essential functions necessary for life. Many nerve cells, such as brain cells, will remain in interphase.

The majority of cells will get their organelles used in mitosis prepared for cell division.

Phases image, see description below

See description of diagram Links to an external site.

 

The second stage of the cell cycle is mitosis. During this stage, the nucleus of the cell divides into two new nuclei with the same number of chromosomes. The four phases of mitosis are prophase, metaphase, anaphase, and telophase. In prophase, the chromatin unfolds and condenses to form double rod-shaped chromosomes. The two chromosomes are held together at their midsection by a structure called the centromere. Each end of the chromosome is now called a chromatid, one of two identical halves of a chromosome. The two chromatids on one end of the centromere are called sister chromatids because they are the exact copy of each other. Therefore at the end of mitosis, each cell will have the same genetic information.  Also during prophase, the nuclear membrane starts to break down or disappear. In animal cells, the pair of centrioles begins to move towards opposite ends of the cell.

Scheme of a Chromosome.

(1) Chromatid. One of the two identical parts of the chromosome after S phase.

(2) Centromere. The point where the two chromatids touch, and where the microtubules attach.

(3) Short arm

(4) Long arm. In accordance with the display rules in Cytogenetics, the short arm is on top.

 

 

 

Prophase

Prophase eukaryotic mitosis Image

 

  • Nucleolus disappears
  • Chromatin condenses into chromosomes
  • Separation of entrosomes
  • Formation of the miotic spindle

 

 

 

 

Metaphase

During metaphase, the chromosomes line up along the metaphase plate in the middle of the cell. The centrioles have made their way to the opposite end of the cell. The centrioles will attach spindle fibers, long protein fibers made up of microtubules, to the centromere.

 

Metaphase eukaryotic mitosis Image

 

 

  • Chromosomes align in the metaphase plate

 

 

 

 

 

 

Anaphase

During anaphase, the sister chromatids are pulled and separated to opposite sides of the cell. Each sister chromatid becomes a new chromosome with a copy of the genetic information that was in the original cell.

Anaphase eukaryotic mitosis Image

 

  • Chromatids separate towards opposite poles

 

 

 

 

 

 

Telophase

During telophase, a new nuclear membrane begins to form around each of the new set of chromosomes. The nuclei and other organelles begin to reassemble. The spindle fibers begin to disappear. The chromosomes begin to uncoil and lose their rod-shaped appearance.

Telophase eukaryotic mitosis Image

  • New nuclear envelope forms
  • Chromosomes unfold back into chromatin
  • Nucleoli reappear
  • Cell continues to elongate

 

 

 

 

 

 

 

 

Cytokinesis

Cytokinesis Image as described in text The last stage of the cell cycle is cytokinesis. During this final process of cell division, the cytoplasm splits and organelles are distributed into each of the two new daughter cells. The daughter cells will have the same number of chromosomes as the original cell. A human body cell has 46 chromosomes. In animal cells, the cell membrane pinches in along the equator of the cell to form a structure called a cleavage furrow. The cell membrane separates into two new daughter cells along the cleavage furrow. Recall that plant cells have a rigid cell wall. Their cell wall prevents the cell membrane from squeezing towards the middle of the cell. A plant cell sends vesicles filled with cellulose to line up along the equatorial plate (center) of the cell to form a structure called the cell plate. The accumulation of cellulose will eventually lead to the cell splitting into two new daughter cells.

 

 

Mitosis

Mitosis image, description below

See description of diagram Links to an external site.

 

Watch the video below. Take notes as you review the stages of the cell cycle.

Recognizing Cancer

Cancer: Uncontrolled Mitosis

In a perfect world, the cells in living things would maintain a healthy rate of mitosis for growth and repair.   The DNA (genetic material) inside of cells controls which cells move through the cell cycle and when.

Cancer is a disease where cells grow uncontrollably, repeating mitosis over and over again without stopping.   This is caused by mutations (or errors) in the genetic material, or DNA.   Rapidly dividing cancer cells can crowd important tissues in the body, preventing their function and stealing their blood supply.   When these cancer cells accumulate in large amounts we call them tumors.

 

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