Part IV and Chapter 11

BiologySixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.

Cell division increases the number of somatic (body) cells, and consists of:

•Mitosis (division of nucleus)

•Cytokinesis (division of cytoplasm)

Bacteria reproduce by dividing

A copy of the genetic material must be made so each new cell will have a complete genome.

Once the DNA is copied and moved to opposite sides of the cell, a new cell membrane is built to create two new cells.

Eukaryotic organisms store their hereditary material in chromosomes.

The total number of chromosomes an organism has can range from 1 to over 1,000!

Humans have 46 total chromosomes.

The haploid (n) number of chromosomes = the number of types of chromosomes.

The diploid (2n) number of chromosomes = two chromosomes of each kind.

The haploid number for humans = 23 (23 types)

The diploid number for humans = 46 (2x23)

(There are two copies of each of the 23 types of chromosomes)

Haploid vs. Diploid

23 Types (haploid)

46 Total (diploid)

Homologous chromosomes – both copies of the same type of chromosome.

Sister chromatids – two replicas of a single chromosome

Centromere – the place where sister chromatids are attached

Homologous pair for chromosome #19

Homologous pair for chromosome #21

Because none of these chromosomes are replicated, there are no sister chromatids shown.

Interphase- G1 – cell growth/organelle replication (G0 phase = resting)

- S – synthesis of a replica of the genome

- G2 – cell growth/organelle replication

Mitosis-Prophase

-Metaphase

-Anaphase

-Telophase

Cytokinesis

By the end of Interphase the genome has been replicated, new organelles made, and the cell has grown.

Cleavage Furrow

There are three checkpoints during the cell cycle that ensure the cell divides only when it is supposed to.

When cells enter G0, they are mature and are not actively dividing

Cyclin activates Cdk (cyclin-dependent kinase) by forming the Mitosis-promoting factor (MPF)

Phosphorylation of Cdk controls the activation and inactivation of Cdk. Cdk in turn activates other enzymes responsible for getting the cell through checkpoints.

Multicellular organisms need more control over cell division than single celled organisms

Growth factors are external signals the cell receives that promote cell growth and division

Platelet-derived growth factor (PDGF) is released when blood clots and signals the surrounding cells to begin growing.

Over 50 different proteins have been identified as growth factors – more exist!

Normal P53 either repairs damaged DNA or triggers the destruction of a cell with unrepairable DNA.

Abnormal P53 loses its ability to recognize damaged DNA, so damaged cells may continue to divide.

Cancer – unregulated cell growth.

Proto-oncogenes are involved with stimulating cell division and can undergo mutations to become cancer-causing oncogenes, which are responsible for uncontrolled cell growth.

Tumor-suppressor genes are involved with suppressing cell division and when they mutate, they stop suppressing the cell cycle and it can occur nonstop.

The End.