CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION Copyright © 2009 Pearson Education, Inc.

◦ Living organisms reproduce by two methods –Asexual reproduction –Offspring are identical to the original cell or organism –Involves inheritance of all genes from one parent –Sexual reproduction –Offspring are similar to parents, but show variations in traits –Involves inheritance of unique sets of genes from two parents ◦ What drives reproduction??? Cell division Copyright © 2009 Pearson Education, Inc.

◦ Binary fission- “dividing in half” –Two identical cells arise from one cell Copyright © 2009 Pearson Education, Inc. Prokaryotic chromosome Duplication of chromosome and separation of copies Cell wall Plasma membrane 1 Continued elongation of the cell and movement of copies 2 Division into two daughter cells 3

Two options: –Mitosis: two genetically identical cells, with the same chromosome number as the original cell –Meiosis: four genetically different cells, with half the chromosome number of the original cell Eukaryotic cell division Copyright © 2009 Pearson Education, Inc.

Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells ◦ Eukaryotic chromosomes are composed of chromatin –Chromatin = DNA + proteins –Early in the division process, chromosomes duplicate (sister chromatids) –Sister chromatids are joined at centromere Eukaryotic chromosomes

MITOSIS: CELL “CLONING”

◦ The cell cycle is an ordered sequence of events for cell division ◦ It consists of two stages –Interphase: duplication of cell contents –G 1 —growth, increase in cytoplasm –S—duplication of chromosomes –G 2 —growth, preparation for division –Mitotic phase: division –Mitosis—division of the nucleus –Cytokinesis—division of cytoplasm Copyright © 2009 Pearson Education, Inc.

S (DNA synthesis) G1G1 G2G2 Cytokinesis Mitosis I NTERPHASE M ITOTIC PHASE (M)

◦ Mitosis progresses through a series of stages 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase (Cytokinesis overlaps) Copyright © 2009 Pearson Education, Inc.

◦ A mitotic spindle is required to divide the chromosomes –The mitotic spindle is composed of ____________ –It is produced by centrosomes Copyright © 2009 Pearson Education, Inc.

Centrosomes (with centriole pairs) Kinetochore Early mitotic spindle Chromatin INTERPHASE PROMETAPHASEPROPHASE Centrosome Fragments of nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Nuclear envelope Spindle microtubules Nucleolus Centromere

Metaphase plate Nucleolus forming METAPHASETELOPHASE AND CYTOKINESISANAPHASE Cleavage furrow Daughter chromosomes Nuclear envelope forming Spindle

◦ Cytokinesis –Cytoplasm is divided into separate cells ***Applying Your Knowledge By the end of cytokinesis –How many chromosomes are present in one human cell? –How many chromatids are present in one human cell? The final mitosis: Cytokinesis Copyright © 2009 Pearson Education, Inc.

TELOPHASE AND CYTOKINESIS

Let’s review mitosis Copyright © 2009 Pearson Education, Inc. ◦ Mitosis produces genetically identical cells for –Growth –Replacement –Asexual reproduction

◦ Factors that control cell division –Presence of essential nutrients –Growth factors, proteins that stimulate division –Presence of other cells causes density-dependent inhibition –Contact with a solid surface; most cells show anchorage dependence Copyright © 2009 Pearson Education, Inc.

Culture of cells Addition of growth factor

Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density- dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).

◦ Cell cycle control system –A set of molecules, including growth factors, that triggers and coordinates events of the cell cycle ◦ Checkpoints –Control points where signals regulate the cell cycle –G 1 checkpoint allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G 0 phase –G 2 checkpoint –M checkpoint Copyright © 2009 Pearson Education, Inc.

G 1 checkpoint Control system M S G2G2 G1G1 M checkpoint G 2 checkpoint G0G0

What happens when cells don’t obey the checkpoints and control system? Why do we need to control cell division?

–All cancers are genetic at their origin –They divide rapidly, often in the absence of growth factors –They often do not have density-dependent inhibition –They are “immortal” Copyright © 2009 Pearson Education, Inc.

◦ Classification of cancer by origin –Carcinomas arise in external or internal body coverings –Sarcomas arise in supportive and connective tissue –Leukemias and lymphomas arise from blood- forming tissues Copyright © 2009 Pearson Education, Inc.

Classification of cancer by origin –Carcinomas arise in external or internal body coverings (ex. Basal cell carcinoma) Copyright © 2009 Pearson Education, Inc.

Classification of cancer by origin –Sarcomas arise in supportive and connective tissue (ex. Kaposi’s sarcoma) Copyright © 2009 Pearson Education, Inc.

Classification of cancer by origin –Leukemias and lymphomas arise from blood- forming tissues Copyright © 2009 Pearson Education, Inc.

◦ Types –Benign tumors remain at the original site –Malignant tumors spread to other locations by metastasis Cancer terminology A tumor grows from a single cancer cell. Cancer cells spread through lymph and blood vessels to other parts of the body. Cancer cells invade neighboring tissue. Tumor Glandular tissue Lymph vessels Blood vessel