Chromosomes and Cellular Reproduction Chapter 6

Prokaryotic Cell Reproduction Prokaryotes reproduce via Binary Fission, occurs in two stages: DNA is replicated and prokaryote adds a new cell membrane between the two copies (FtsZ ring). "Filamenting temperature-sensitive mutant Z”

Prokaryotic Cell Reproduction Prokaryotes reproduce via Binary Fission, occurs in two stages: DNA is replicated and prokaryote adds a new cell membrane between the two copies (FtsZ ring). "Filamenting temperature-sensitive mutant Z” FtsZ ring pinches cell into two independent identical cells.

Eukaryotic Cell Reproduction Large amounts of information are encoded in DNA, and they are organized into individual units called genes. A gene is a segment of DNA that codes for a protein or RNA molecule (Traits).

Eukaryotic Cell Reproduction As the eukaryotic cell prepares to divide, the chromosomes-(the DNA and its associated proteins)-become visible, a process called DNA condensation Before this happens, however, the DNA has already been copied. HeLa cells stained for DNA with the Blue Hoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left a cell is going through mitosis and its DNA has condensed ready for division.

Eukaryotic Cell Reproduction DNA condensation The linear DNA strand “super coils” around histone proteins. Exact copies are called chromatids, which are attached at the centromere.

1. First Growth Phase (G₁-Gap Phase) A cell grows rapidly, and carries out routine functions. Cells that are not dividing or in the process of remain in this phase

2. Synthesis Phase (S phase) The cells DNA is Copied, at the end of this phase, each chromosome consists of two sister chromatids joined together at the centromere

3. Second Growth Phase (G₂ phase) Preparations are made for the nucleus to divide. Microtubules are rearranged during this phase in preparation for mitosis

4. Mitosis The Nucleus of the cell is divided into two Nuclei, each nucleus end up with the same number and kinds of chromosomes as the original cell.

5. Cytokinesis The cytoplasm divides and two daughter cells arise from a single parent cell.

Control of the Cell Cycle Three Major Checkpoints: 1. Cell Growth (G₁) checkpoint This checkpoint is to determine if conditions are favorable for a cell to divide (size, health, etc…) 2. DNA Synthesis (G₂) checkpoint DNA replication is checked by DNA repair enzymes, if this checkpoint is passed proteins trigger mitosis 3. Mitosis Checkpoint Triggers the exit from mitosis, signals beginning of the G₁ phase.

What happens when Control of the Cell Cycle is Lost?

The Cell Cycle A cell spends 90% of its time in the first three phases, collectively called interphase. Total, there are 5 phases of the cell cycle

Mitosis and Cytokinesis Chapter 6 Section 3

1. First Growth Phase (G₁-Gap Phase) A cell grows rapidly, and carries out routine functions. Cells that are not dividing or in the process of remain in this phase

2. Synthesis Phase (S phase) The cells DNA is Copied, at the end of this phase, each chromosome consists of two sister chromatids joined together at the centromere

3. Second Growth Phase (G₂ phase) Preparations are made for the nucleus to divide. Microtubules are rearranged during this phase in preparation for mitosis

4. Mitosis The Nucleus of the cell is divided into two Nuclei, each nucleus end up with the same number and kinds of chromosomes as the original cell.

5. Cytokinesis The cytoplasm divides and two daughter cells arise from a single parent cell.

4. Mitosis The Nucleus of the cell is divided into two Nuclei, each nucleus end up with the same number and kinds of chromosomes as the original cell.

Forming the Spindle Spindles are structures made up of both centrioles and microtubule fibers. Involved in moving chromosomes during cell division The Centrosome is a organelle that organizes the assembly of the spindle. Two centrioles in each centrosome.

The Centriole Each spindle fiber is made of an individual microtubule Each centriole is made up of nine triplets of microtubules arranged in a circle. Unlike animal cells, plant cells do not have centrioles, but they do form a spindle that is almost identical to that of animal cells.

Separation of Chromatids by Attaching Spindle Fibers Two sets of microtubules attach on each side of the centromere and extend towards opposite poles. Once attached to the centrosome apparatus, the chromatids will move along the fibers to opposite ends of the cell. As soon as the chromatids separate from one another they are called chromosomes.

Phases of Mitosis Prophase Metaphase Anaphase Telophase

Prophase Chromosomes coil up and become visible (condensation) Nuclear envelope dissolves Spindle fibers form

Metaphase Chromosomes move to center of the cell. Line up along the equator. Spindle fibers link the chromatids to opposite poles.

Anaphase Centromeres divide during anaphase. The two chromosomes move toward opposite poles as the spindle fibers attached shorten

Telophase A nuclear envelope forms around the chromosomes at each pole. Chromosomes now at opposite poles uncoil and the spindle dissolves. Mitosis is complete

5. Cytokinesis The cytoplasm divides and two daughter cells arise from a single parent cell.

Cytokinesis Animal Cells Plant Cells Cytoplasm is divided in half, cell membrane grows to enclose each cell. Cell is pinched in half by belts of proteins (microfilaments) called a cleavage furrow. Forms two identical cells. Vesicles formed by the Golgi Apparatus fuse at the midline and form a cell plate. Cell plate is a membrane bound cell wall that forms across middle of plant cell. A new cell wall then forms on each side of the cell plate, forming two new cells.

Cytokinesis