Bacterial cell division (binary fission) Fig

Cell Cycle (Fig. 12.4)

Levels of chromatin packing (Fig. 19.1) nucleosomes (“beads on a string”) chromatin fiber (30-nm) looped domains metaphase chromosome (replicated)

Testing hypothesis for chromosome migration during anaphase (Fig. 12.7)

Mitosis in Allium root tip (long. section)— Steven P. Lynch

Hypothesis for the evolution of mitosis (Fig )

Importance of regulating cell cycle Survival of unicellular organisms depends on appropriate timing and changing rates of cell division in response to changing environmental conditions. Normal growth, development, and maintenance of multicellular organisms depends on appropriate timing and rates of cell division.

Mechanical analogy for the cell-cycle control system (Fig )

Molecular basis of cell- cycle control system at G2 checkpoint (Fig )

Internal signals regulating mitosis M phase checkpoint prevents the beginning of anaphase until all chromosomes are properly attached to spindle at equator. Unattached kinetochore proteins trigger a signaling pathway that keeps anaphase- promoting complex (APC) inactive. Active APC breaks down cyclin and proteins holding sister chromatids together.

External signals regulating mitosis Lack of specific nutrients. Presence of specific growth factors (proteins produced by cells which stimulate other cells to divide) –Release of PDGF by platelets promotes division of fibroblasts for wound healing. –Crowded cells stop dividing (density-dependent inhibition).

Communication between mating yeast cells (Fig. 11.1)

Local and distant cell communication in animals (Fig. 11.3)

Communication by direct contact between cells (Fig. 11.4)

Epinephrine and glycogen (animal starch) depolymerization ( Observations of Earl W. Sutherland) 1.Epinephrine + intact cells containing glycogen and glycogen phosphorylase  glucose (product of depolymerization) 2.Epinephrine + glycogen and glycogen phosphorylase  no reaction 3.Conclusion: epinephrine must interact with cell membrane (Nobel Prize in 1971)

Overview of cell signaling (Fig. 11.5)

External signals regulating cell division 1.Missing essential nutrient  no division 2.Growth factor (secreted by certain body cells)  cell division 3.Anchorage dependence = loose cells not attached to a substratum  no division 4.Density-dependent inhibition (see next figure)

Density- dependent inhibition of cell division (Fig )

Characteristics of cancer cells 1.Do not respond to normal signals regulating the cell cycle. 2.Immortal (normal cells stop dividing after times) 3.Form malignant tumor which impairs functioning of one or more organs. 4.Metastasis = spread of cancer cells to other healthy tissues.

Growth and metastasis of a malignant breast tumor (Fig )