The Reproduction of Cells

Reading assignment: Campbell Chapters 11, 12; pp. 204-229
 
 

I. Requirements for cell division

Three general stages are required for cell division:
 

1. A cell must first copy all of its genes

2. The two copies of the genetic code must be partitioned to opposite ends of the cell.

3. The organelles of the cell must increase in number and be partitioned into the two "daughter cells" as the original cell divides.

Bacterial cells divide by the process of binary fission (="division in half")

Binary fission = the process by which prokaryotic organisms (e.g., bacteria) divide to form two daughter cells from one parent cell.

(Figure 11.2)
 

A. Definitions
 
1. Genome
 

2. Chromosome
 

3. Somatic cells
 

4. chromatin
 

5. chromatids
 

6. centromere
 

7. mitosis
 

8. cytokinesis

 

B. Phases of cell cycle.
 

(Figure 11.5)

1. Interphase
 

a. G1

b. S

c. G2

2. Mitosis
 
a. prophase

b. metaphase

c. anaphase

d. telophase
 

3. Cytokinesis

 

IV. The details of mitosis

(figure 11.6)
 

A. Interphase = chromosome duplication

B. Prophase = the duplicated chromosomes condense; centrosomes move to the cell poles and microtubules (protein fibers) extend from the centrosome.

C. Prometaphase = the nuclear membrane disintegrates; microtubule fibers connect to the centromere region of the chromosomes (the specialized region of the centromere that allows for fiber linkage is called the kinetochore). Microtubules from one pole attach to the kinetochore on one chromatid, those from the other pole attach to the kinetochore of the other chromatid.

D. Metaphase = the microtubule fibers begin to move the chromosomes such that they line up on the metaphase plate (the central region of the cell).

E. Anaphase = the paired centromeres divide allowing each sister chromatid to separate and move to opposite poles of the cell: the movement occurs as the kinetochore "climbs" the microtubule fibers that make up the mitotic spindle. During anaphase, the kinetochore almost "walks" up the microtubule fiber

F. telophase and cytokinesis = other microtubules (non-kinetochore fibers) in the middle of the cell begin to elongate, causing the cell to also elongate; new nuclear membranes are formed; the sides of the cell begin to pinch inward forming the cleavage furrow.
 

A. Animals: (figure 11.9)
 
1. Cleavage furrow
B. Plants
 
1. Cell plate

A. Definitions
 
1. restriction point 

 

2. density-dependent inhibition
 

VII. Cancer cells
 

Loss of control over division

(figure 11.14)
 

A. Definitions
 
1. Life cycle = the sequence of stages through which an organism passes in going from conception to reproduction.

2. Diploid phase = phase in which cells contain two copies of each chromosome (with possible exception of sex chromosomes which we will discuss in a later lecture). The chromosomes that make up a pair are called homologous chromosomes. One chromosome of each homologous pair is inherited from an organism's paternal parent. The other chromosome of each homologous pair is inherited from the maternal parent.

3. Haploid phase = phase in which cells contain one copy of each chromosome.

4. Meiosis = a form of cell division in which diploid cells undergo a reduction in chromosome number to form haploid cells.

5. Fertilization = the union of two haploid gametes to form a diploid zygote.

B. Three types of life cycles in organisms
 

1. The animal life cycle
 
(figures 12.3 and 12.4(a))

2. life cycle of some fungi and algae
 

(figure 12.4(b))

3. Plant life cycle
 

(figure 12.4(c)