CHAPTER 9Cellular Reproduction

RATIO OF SURFACE AREA TO VOLUME

CELLULAR GROWTH As the cell grows, its volume

increases much more rapidly than the surface area.

The cell might have difficulty supplying nutrients and expelling enough waste products.

TRANSPORT OF SUBSTANCES Substances move by diffusion or by

motor proteins. Diffusion over large distances is slow

and inefficient. Small cells maintain more efficient

transport systems.

THE CELL CYCLE Cell division prevents the cell from

becoming too large. It also is the way the cell reproduces

so that you grow and heal certain injuries.

Cells reproduce by a cycle of growing and dividing called the cell cycle.

CELLULAR GROWTH Interphase is the stage during which

the cell grows, carries out cellular functions, and replicates.

Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide.

Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell.

STAGES OF INTERPHASE The first stage of interphase, G1

The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.

THE SECOND STAGE OF INTERPHASE, S The cell copies its DNA in preparation

for cell division.

THE THIRD STAGE OF INTERPHASE, G2

The cell prepares for the division of its nucleus.

THE STAGES OF MITOSIS Prophase

The cell’s chromatin tightens.Sister chromatids are attached at

the centromere.Spindle fibers form in the

cytoplasm.

MITOSIS AND CYTOKINESIS The nuclear envelope seems to

disappear. Spindle fibers attach to the sister

chromatids.

METAPHASE Sister chromatids are pulled along

the spindle apparatus toward the center of the cell.

They line up in the middle of the cell.

ANAPHASE The microtubules of the spindle

apparatus begin to shorten. The sister chromatids separate. The chromosomes move toward the

poles of the cell.

TELOPHASE The chromosomes arrive at the poles

and begin to relax. Two new nuclear membranes begin to

form and the nucleoli reappear. The spindle apparatus disassembles.

CYTOKINESIS In animal cells, microfilaments

constrict, or pinch, the cytoplasm. In plant cells, a new structure, called

a cell plate, forms.

http://www.youtube.com/watch?v=JcZQkmooyPk

NORMAL CELL CYCLE Different cyclin/CDK combinations signal

other activities, including DNA replication, protein synthesis, and nuclear division throughout the cell cycle.

QUALITY CONTROL CHECKPOINTS The cell cycle has built-in checkpoints

that monitor the cycle and can stop it if something goes wrong.

Spindle checkpoints also have been identified in mitosis.

ABNORMAL CELL CYCLE: CANCER Cancer is the uncontrolled growth

and division of cells. Cancer cells can kill an organism by

crowding out normal cells, resulting in the loss of tissue function.

CAUSES OF CANCER The changes that occur in the

regulation of cell growth and division of cancer cells are due to mutations.

Various environmental factors can affect the occurrence of cancer cells.

APOPTOSIS Programmed cell death Cells going through apoptosis

actually shrink and shrivel in a controlled process.

STEM CELLS Unspecialized cells that can develop

into specialized cells when under the right conditions

EMBRYONIC STEM CELLS After fertilization, the resulting mass

of cells divides repeatedly until there are about 100–150 cells. These cells have not become specialized.

ADULT STEM CELLS Found in various tissues in the body

and might be used to maintain and repair the same kind of tissue

Less controversial because the adult stem cells can be obtained with the consent of their donor