Cell Division and the Cell Cycle

Important terms in eukaryotic cell division Chromosome =

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication =

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication = process whereby DNA is identically copied (before cell division) mitosis =

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication = process whereby DNA is identically copied (before cell division) mitosis = division of the nucleus cytokinesis =

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication = process whereby DNA is identically copied (before cell division) mitosis = division of the nucleus cytokinesis = division of the cytoplasm chromatin =

Important terms in eukaryotic cell division Chromosome = threadlike structures that are composed of DNA + protein replication = process whereby DNA is identically copied (before cell division) mitosis = division of the nucleus cytokinesis = division of the cytoplasm chromatin = DNA + protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

Chromatid = after replication the chromosome consists of 2 sister chromatids joined at the centromere. Centromere = specialized region of the chromosome, where chromatids are joined. Each chromosome has one centromere.

The Cell Cycle

Interphase 90% of cell cycle is spent in this phase G1 = first growth phase S = protein synthesis phase, DNA synthesis (replication) occurs here G2 = second growth phase

G2 phase of Interphase in animal cells: Nuclear envelope is visible One or more nucleoli are present Centrioles are replicated and the 2 pairs are near nucleus aster forms around each pair of centrioles chromosomes are loosely packed into chromatin fiber, not distinguishable

Prophase: In the Nucleus: Nucleoli disappear chromosome fibers condense into discrete chromosomes each chromosome consists of 2 sister chromatids joined at the centromere

In the Cytoplasm: mitotic spindle begins to form spindle consists of microtubules arranged between the centrosomes centrosomes move apart due to lengthening of microtubules

Prometaphase: Nuclear envelope breaks apart each chromatid has specialized structure called kinetochore located at the centromere region knietochore microtubules (km) interact with chromosomes at the kinetochore region The km’s cause the chromosomes to move nonkinetochore microtubules radiate from each pole

Metaphase Chromosomes move to the metaphase plate and line up there the centromeres of the chromosomes are all aligned on the metaphase plate each sister chromatid of one chromosome, has a kinetochore microtubule attached to it from opposite poles kinetochore microtubules + nonkinetochore microtubules = spindle fiber

Anaphase Kinetochore microtubules shorten and non-kinetochore microtubules lengthen Centromeres divide and each chromosome has no sister chromatid component the shape of the cell elongates into an elipse chromosomes are pulled to the opposite poles

Telophase Nonkinetochore microtubules continue to elongate the cell new daughter nuclei form at the two poles new nuclear envelopes are formed around the chromosomes nucleoli reappear chromosomes uncoil into chromatin fiber last phase of mitosis

Apoptosis: When a cell undergoes apoptosis, white blood cells called macrophages consume cell debris.

Checkpoints in the cell cycle: If it passes the G1 checkpoint cell divides if not enters G0 phase and does not divide

Cyclin protein levels fluctuate according to cell cycle stage Cyclin protein levels fluctuate according to cell cycle stage. When cyclin is high the Cdk attaches and phsophorylation leads to breakdown of nuclear envelope. Later MPF initiates cyclin breakdown

Uncontrolled Cell Growth What Is Cancer? Although cancer comprises at least 100 different diseases, all cancer cells share one important characteristic: they are abnormal cells in which the processes regulating normal cell division are disrupted. Cancer results from a series of molecular events that fundamentally alter the normal properties of cells. In cancer cells the normal control systems that prevent cell overgrowth and the invasion of other tissues are disabled. What role does the p53 gene play?

Uncontrolled Cell Growth (cont.) Only a small number of the approximately 35,000 genes in the human genome have been associated with cancer. Alterations in the same gene often are associated with different forms of cancer. These malfunctioning genes can be broadly classified into three groups. The first group, called proto-oncogenes, produces protein products that normally enhance cell division or inhibit normal cell death. The mutated forms of these genes are called oncogenes. The second group, called tumor suppressors, makes proteins that normally prevent cell division or cause cell death. The third group contains DNA repair genes, which help prevent mutations that lead to cancer.

Uncontrolled Cell Growth (cont.) Proto-oncogenes and tumor suppressor genes work much like the accelerator and brakes of a car, respectively. The normal speed of a car can be maintained by controlled use of both the accelerator and the brake. Similarly, controlled cell growth is maintained by regulation of proto-oncogenes, which accelerate growth, and tumor suppressor genes, which slow cell growth. Mutations that produce oncogenes accelerate growth while those that affect tumor suppressors prevent the normal inhibition of growth. In either case, uncontrolled cell growth occurs. See animation… Are Telomeres the Key to Aging and Cancer?

Human Ingenuity Michael Bishop and Harold Varmus Michael Bishop, PhD, and Harold Varmus, PhD. They received the Nobel Prize in 1989 for their discovery that normal cells contain genes capable of becoming cancer genes. University of San Francisco.

Possible Causes Cancer can often be the result of inherited mutations or are induced by environmental factors such as UV light, X-rays, chemicals, tobacco products, and viruses. All evidence suggests that most cancers are not the result of one single event or factor. Rather, around four to seven events are usually required for a normal cell to evolve through a series of premalignant stages into an invasive cancer. Often many years elapse between the initial event and the development of cancer. The development of molecular biological techniques may help in the diagnosis of potential cancers in the early stages, long before tumors are visible.

Cancer cells How does abnormal cell division of cancer cells differ from normal cell division? Cancer cells are not under density dependent inhibition Continue to grow until all nutrients are used up Cancer cells are immortal, do not shorten telomeres.

What will the future of this biotechnology hold? Stem Cells What will the future of this biotechnology hold?