NOTES FOR BIOLOGY 1201

Section 001

Spring 2005

DR. STEVEN POMARICO

>>>>>>Cell division functions in reproduction, growth, and tissue renewal

---Cell division

---Genome

Some characteristics of cell division

         -Replication of DNA

         -Equal distribution of DNA to opposite ends of the dividing cell

         -separation into two daughter cells

The Eukaryotic Cell Cycle - 8.1.1

>>>>>The genome of a eukaryotic cell is organized into multiple chromosomes

---Chromosomes

-The chromosome is made up of chromatin

---Chromatin

>>>>>Mitosis alternates with interphase during the cell cycle.

---Cell cycle

-The length of time required for a cell cycle varies with cell type and growth conditions

---Interphase

-Interphase makes up about 90% of the cell cycle

Interphase consists of three phases:

         1. G₁ phase (gap one)

                   -first growth phase

         2. S phase (synthesis phase)

                   -DNA is synthesized

         3. G₂ phase (gap two)

                   -second growth phase

>>>After chromosome replication the cell prepares for the sister chromatids to separate and the nucleus to divide.

-The division of the nucleus is usually followed quickly by cytokinesis

---Cytokinesis

Mitosis: An Overview - 8.1.2

>>>The replication of each chromosome results in a pair of chromosomes called sister chromatids.

-A specialized region called the centromere holds this pair of chromatids together

---Chromatids

---Centromere

-The replication of the chromosomes marks the beginning of mitosis.

---Mitosis

Mitosis: The Phases - 8.1.3

The mitotic phase (M-phase) of the cell cycle is divided into five phases

         1. Prophase

                   -nucleoli disappear

                   -chromatin condenses

                   -mitotic spindle forms

                             -spindle consists of microtubules between two centrosomes

         2. Prometaphase

                   -nuclear envelope disappears

                   -kinetochore microtubules attached kinetochore of chromosomes to

                              the mitotic spindle

                   -non-kinetochore microtubules radiate toward the cells equator

         3. Metaphase

                   -centrosomes positioned at opposite ends (poles) of the cell

                   -chromosomes move to and align on the metaphase plate (equator)

         4. Anaphase

                   -sister chromatids divide into separate daughter chromosomes and                                        move toward opposite poles.

                   -movement of the chromosome is accomplished by depolymerization                                        of the microtubules at the kinetochore

                   -cell begins to elongate

         5. Telophase

                   -daughter chromosomes arrive at poles

                   -kinetochore microtubules disappear

                   -non-kinetochore microtubules elongate (pushing out on the ends of the                                  cells) helps causes the formation of the cleavage furrow.

                   -daughter nuclear envelopes form

                   -chromatin begins de-condensing.

By the end of telophase replication of the nucleus is complete and two genetically identical daughter nuclei are present.

Cytokinesis - 8.1.4

>>>>>>Cytokinesis divides the cytoplasm

         Cytokinesis

                             -the cytoplasm divides

The mechanism of division of the cytoplasm differs for plants and animals.

         In animals:

                   -cleavage furrow (shallow grove) forms near the site of the metaphase                                          plate (cell equator)

                   -a contractile ring forms inside the plasma membrane at the cleavage                         furrow and pinches the parent cell into two daughter cells.

         In plants:

                   -cell plate formation

                   -cell wall deposition