CHAPTER 8 The Cellular Basis of Reproduction and Inheritance

Biology is the only subject in which multiplication is the same thing as division… 2006-2007

CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION Cell division is at the heart of the reproduction of cells and organisms Organisms can reproduce sexually or asexually

Like begets like, more or less Some organisms make exact copies of themselves, asexual reproduction Other organisms make similar copies of themselves in a more complex process,sexual reproduction

Prokaryotes reproduce by binary fission Prokaryotic cells divide asexually These cells possess a single chromosome, containing genes The chromosome is replicated The cell then divides into two cells, a process called binary fission Duplication of chromosome and separation of copies Continued growth of the cell and movement of copies Division into two cells

THE EUKARYOTIC CELL CYCLE AND MITOSIS A eukaryotic cell has many more genes than a prokaryotic cell The genes are grouped into multiple chromosomes, found in the nucleus The chromosomes of this plant cell are stained dark purple

The large, complex chromosomes of eukaryotes duplicate with each cell division Sister chromatids Chromosomes contain a very long DNA molecule with thousands of genes Individual chromosomes are only visible during cell division They are packaged as chromatin Before a cell starts dividing, the chromosomes are duplicated This process produces sister chromatids Centromere

double-stranded human chromosomes ready for mitosis

The large, complex chromosomes of eukaryotes duplicate with each cell division When the cell divides, the sister chromatids separate Two daughter cells are produced Each has a complete and identical set of chromosomes Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

The Cell Cycle The cell cycle is the sequence of growth and division of a cell. Duration varies with cell type The cell cycle consists of two major phases: Interphase, where chromosomes duplicate and cell parts are made The mitotic phase, when cell division occurs Interphase

Interphase: A Busy Time Interphase, the busiest phase of the cell cycle, is divided into three parts. Interphase DNA synthesis and replication Rapid growth and metabolic activity cell prepares for division

Cell division is a continuum of dynamic changes Eukaryotic cell division consists of two stages: Mitosis~ process during which duplicated chromosomes are separated into 2 nuclei Cytokinesis ~ entire cell divides into 2 daughter cells

MITOSIS: Making New Cells Making New DNA

Where it all began… You started as a cell smaller than a period at the end of a sentence…

Getting from there to here… Going from egg to baby…. the original fertilized egg has to divide… and divide…

Why do cells divide… One-celled organisms Multi-celled organisms for reproduction asexual reproduction (clones) Multi-celled organisms for growth & development from fertilized egg to adult for repair & replacement replace cells that die from normal wear & tear or from injury amoeba starfish Unicellular organisms Cell division = reproduction Reproduces entire organism& increase population Multicellular organisms Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg Also use cell division to repair & renew cells that die from normal wear & tear or accidents

Mitosis

Mitosis

Mitosis in whitefish blastula

Mitosis in plant cell

onion root tip

8.7 Cytokinesis differs for plant and animal cells In animals, cytokinesis occurs by cleavage This process pinches the cell apart In plants, a membranous cell plate splits the cell in two

Overview of mitosis Please Make Another Two Cells I.P.M.A.T.C. interphase prophase Please Make Another Two Cells cytokinesis metaphase anaphase telophase

New “daughter” cells Get 2 exact copies of original cells same DNA “clones”

8.8 Anchorage, cell density, and chemical growth factors affect cell division In laboratory cultures, most normal cells divide only when attached to a surface They are anchorage dependent Cells continue dividing until they touch one another This is called density-dependent inhibition Growth factors are proteins secreted by cells that stimulate other cells to divide

8.9 Growth factors signal the cell cycle control system Proteins called cyclins within the cell control the cell cycle Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division

8.10 Connection: Growing out of control, cancer cells produce malignant tumors Cancer cells have abnormal cell cycles They divide excessively and can form abnormal masses called tumors Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

Cancer: breast cancer cell & mammogram

Traditional treatments for cancers Treatments target rapidly dividing cells high-energy radiation kills rapidly dividing cells chemotherapy stop DNA replication stop mitosis & cytokinesis stop blood vessel growth

New “miracle drugs” Drugs targeting proteins (enzymes) found only in cancer cells Gleevec treatment for adult leukemia (CML) & stomach cancer (GIST) 1st successful drug targeting only cancer cells Proof of Principle: you can treat cancer by targeting cancer-specific proteins. GIST = gastrointestinal stromal tumors, which affect as many as 5,000 people in the United States CML = chronic myelogenous leukemia, adult leukemia, which affect as many as 8,000 people in the United States Fastest FDA approval — 2.5 months without Gleevec with Gleevec Novartes

Cancer: A mistake in the Cell Cycle Currently, scientists consider cancer to be a result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle. Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients

Cancer: A mistake in the Cell Cycle In later stages, cancer cells enter the circulatory system and spread throughout the body, a process called metastasis, forming new tumors that disrupt the function of organs, organ systems, and ultimately, the organism.

The causes of cancer The causes of cancer are difficult to pinpoint because both genetic and environmental factors are involved. Environmental factors, such as cigarette smoke, air and water pollution, and exposure to ultraviolet radiation from the sun, are all known to damage the genes that control the cell cycle. Cancer may also be caused by viral infections that damage the genes.

Cancer prevention Physicians and dietary experts agree that diets low in fat and high in fiber content can reduce the risk of many kinds of cancer. Vitamins and minerals may also help prevent cancer. In addition to diet, other healthy choices such as daily exercise and not using tobacco also are known to reduce the risk of cancer.