Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells III. Cellular Respiration IV. Photosynthesis V. Protein Synthesis VI. Cellular Reproduction

VII. CELL REPRODUCTION Overview: Why Reproduce?

Overview: Why Reproduce? VII. CELL REPRODUCTION Overview: Why Reproduce? Reproduction is selected for, by definition. X X X X

- WHY?? Bigger is better…. So selection favors growth… But as cells increase in size, they decrease in efficiency.

- WHY?? Bigger is better…. So selection favors growth… But as cells increase in size, they decrease in efficiency. So, to get bigger, most organisms increase cell number, not cell size….

- WHY?? And with many cells, cell specialization can increase efficiency at the organismal level.

Overview: Why Reproduce? A. The Cell Cycle VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle G1 G2 S (DNA synthesis) INTERPHASE Cytokinesis MITOTIC (M) PHASE Mitosis

Overview: Why Reproduce? A. The Cell Cycle VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase:       a.  G1: high metabolic activity (protein synthesis) chromosomes diffuse; one DNA double helix per chromosome                

LE 12-15 G0 G1 checkpoint G1 G1 If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle. If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.

Overview: Why Reproduce? A. The Cell Cycle 1. Interphase a. G1 b. S VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase a. G1 b. S Chromosome duplication (including DNA synthesis) Centromere Sister chromatids A C G T G C A C G T G C A C G T G C Two identical double-helices, each composed of an ‘old’ and ‘new’ strand. Creating two chromatids in each chromosome

VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase a. G1 b. S c. G2

VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase 2. Mitosis

INTERPHASE PROPHASE PROMETAPHASE LE 12-6aa Centrosomes (with centriole pairs Chromatin (duplicated) Early mitotic spindle Aster Fragments of nuclear envelope Kinetochore Nonkinetochore microtubules Centromere Nucleus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule

METAPHASE ANAPHASE TELOPHASE LE 12-6ba Metaphase plate Cleavage furrow Nucleolus forming Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Spindle

Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis G2 OF INTERPHASE PROPHASE PROMETAPHASE

Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication LE 12-6da VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis   TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE

Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis   10 µm Nucleus Chromatin condensing Chromosomes Nucleolus Cell plate Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelope will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro- tubules shorten. Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is starting to form. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.