Bell Work

• What is the difference between mitosis and meiosis?

Lecture 35

Mitosis

Mitosis

• Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei.

Mitosis

• It is followed immediately by cytokinesis.

Cytokinesis

• Divides the nuclei, cytoplasm, organelles, and cell membrane into two separate cells containing roughly equal parts of these cellular components.

Mitosis

• Mitosis occurs only in eukaryotic cells.• Prokaryotic cells, which lack a nucleus, divide

by a process called binary fission.

Significance of Mitosis

• Development and growth • Cell replacement • Regeneration • Asexual reproduction

A Short Summary of Mitosis

• During mitosis the pairs of chromatids condense and attach to fibers that pull the sister chromatids to opposite sides of the cell.

• The cell then divides in cytokinesis, to produce two identical daughter cells which are still diploid cells.

The Result of Mitosis

• The primary result of mitosis is the transferring of the parent cell's genome into two daughter cells.

• These two cells are identical and do not differ in any way from the original parent cell.

Mitosis Copies Chromosomes

• The genome is composed of a number of chromosomes.

• Because each daughter cell is genetically identical to the parent cell, the parent cell must make a copy of each chromosome before mitosis.

What are Chromosomes?

• Tightly-coiled DNA that contain genetic information vital for proper cell function.

The Copying of Chromosomes

• Occurs during the S phase of interphase

Once Copying Occurs

• Each chromosome now has an identical copy of itself, and together the two are called sister chromatids.

The Centromere

• The sister chromatids are held together by a specialized region of the chromosome: a DNA sequence called the centromere.

The Stages of Mitosis

• These stages are prophase, metaphase, anaphase and telophase.

Interphase

• Three phases: G1 (first gap), S (synthesis), and G2 (second gap).

• A cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2).

• Chromosomes are replicated only during the S phase.

Interphase

• Not part of mitosis• In the S phase, DNA is copied

Prophase

• At the onset of prophase, chromatin fibers become tightly coiled, condensing into discrete chromosomes.

• Since the genetic material has already been duplicated earlier in S phase, the replicated chromosomes have two sister chromatids, bound together at the centromere.

Also During Prophase

• Centrosomes (consisting of a pair of centrioles, and actin, and a halo of microtubule fragments) are pushed to opposite sides of the cell.

• Microtubules act as cellular ropes or poles

Prophase

• Chromatin condenses

Metaphase

• The two centrosomes start pulling the chromosomes through their attached centromeres towards the two ends of the cell.

• The centromeres of the chromosomes line up along the metaphase plate or equatorial plane, an imaginary line that is right in between the two centrosome poles.

• This line is called the spindle equator.

Metaphase

• Chromosomes line up in the middle

Anaphase

• The proteins that bind sister chromatids together are cleaved.

• These sister chromatids now become separate daughter chromosomes, and are pulled apart by shortening the microtubules and move toward the respective centrosomes to which they are attached.

• The cleaved centromeres go first while the chromatids trail behind.

Anaphase

• Chromosomes pull apart (two sister chromotids each containing information)

Telophase

• Corresponding daughter chromosomes attach at opposite ends of the cell.

• A new nuclear membrane, using the membrane vesicles of the parent cell's old nuclear membrane, forms around each set of separated daughter chromosomes (though the membrane does not enclose the centrosomes)

• Both sets of chromosomes, now surrounded by new nuclei, begin to "relax" or decondense back into chromatin.

• Mitosis is complete, but cell division is not.

Telophase

• Two new nuclei form

Cytokinesis

• Cytokinesis is a separate process that begins at the same time as telophase.

• Cytokinesis is technically not even a phase of mitosis, but rather a separate process, necessary for completing cell division.

Digital Mitosis Flip Book