VIII CELL REPRODUCTION VIII CELL REPRODUCTION Overview Why

VIII. CELL REPRODUCTION

VIII. CELL REPRODUCTION Overview: Why Reproduce?

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

- WHY? ? Bigger is better…. 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.

SA/V = 6 SA/V = 3 SA/V = 1. 5 The “surface area to volume ratio” decreases as something increases in size….

SA/V = 6 SA/V = 3 SA/V = 1. 5 The “surface area to volume ratio” decreases as something increases in size…. The surface area – the membrane – limits the rate of supply of nutrients to the cell. The volume – where all the enzymes are – represents potential production and ‘demand’ for nutrients.

SA/V = 6 SA/V = 3 SA/V = 1. 5 So, as something gets larger, the volume increases more than the surface area… and the demand for nutrients (to meet peak productivity) grows faster than the rate at which the more slowly increasing SA can supply them. So, supply fails to meet demand, and the cell cannot meet peak productivity… it becomes less efficient.

- 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.

LE 12 -5 VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle INTERPHASE S (DNA synthesis) G 1 is s e Mi MI (M) TOTIC PH ASE to t Cy sis in k o G 2

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

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle 1. Interphase: Some cell types are "stuck" in this stage when they mature. . . it is only "stem cells" that keep dividing. In some tissues, all stem cells eventually mature, so the tissue can't regenerate (neurons)

LE 12 -15 G 0 G 1 checkpoint G 1 If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. G 1 If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state.

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle 1. Interphase a. G 1 b. S Chromosome duplication (including DNA synthesis) Centromere Sister chromatids

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle 1. Interphase a. G 1 b. S c. G 2

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

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation - Replisomes land at "origin" - They have a variety of enzymes that work together, including: HELICASE that unzips the double helix. PRIMASE, an RNA POLYMERASE, that starts replication DNA POLYMERASES that make DNA.

- HELICASE separates strands 5' 3' 3' 5'

- HELICASE separates strands - PRIMASE lays down RNA from 5' 3' (like transcription) 5' 3' 3' 3' 5' 3'

- HELICASE separates strands - PRIMASE lays down RNA from 5' 3' (like transcription) - DNA POLYMERASE - 'knocks' primase off and adds DNA bases to the free 3' OH group. . 5' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork So, into each 'replication fork', there is "continuous synthesis" on one strand 5' 3' "FORK" 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork What about the other strands? 5' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork What about the other strands? PROBLEM!!! Only 5' phosphates available. . . so they can't be extended 5' 5' 3' 3' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork The process must start again. . 5' 5' 3' Primase makes RNA 3' 3' 3' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork The process must start again. . DNA POLY adds DNA 5' 5' 3' 3' DNA POLY adds DNA 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork And what happens when more DNA is opened up? ? 5' 5' 3' 3' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork Continuous synthesis can continue from 3' end of DNA 5' 5' 3' 3' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork But Primase must begin the process on "lagging" strand 5' 5' 3' 3' 5' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork . . . then DNA POLY can add DNA bases to "primer" 5' 5' 3' 3' 5' 5' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork And this happens at the other fork. . . DNA is opened. . . 3' 5' 5' 3' 3' 5' 5' 5' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork Continuous synthesis occurs from the free 3' end 3' 5' 5' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork Discontinuous synthesis on "lagging strand" (Primase, etc) 3' 5' 5' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork So, BOTH STRAND HAVE "OKAZAKI FRAGMENTS. . " 3' 5' 5' 3' 3' 5' 5' 5' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork NOW WHAT? ? ? We have RNA in the DNA double helix 3' 5' 5' 3' 3' 5' 5' 5' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5' 3' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork 3. DNA Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5' 3' 3' 3' 5'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork 3. DNA Repair Final linkage between DNA frag's made by LIGASE 5' 3' 3' 3' 5' H 2 O 3'

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork 3. DNA Repair Final linkage between DNA frag's made by LIGASE 5' 3' 3' 3' 5' 3' H 2 O REPLICATION COMPLETE

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication 1. Initiation 2. Replication at the fork 3. DNA Repair Semi-conservative replication

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis

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

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

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis G 2 OF INTERPHASE PROMETAPHASE

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

LE 12 -10 VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis Nucleus Chromatin condensing 10 µm Chromosomes Nucleolus 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. 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. 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.

LE 12 -9 a 100 µm Cleavage furrow Contractile ring of microfilaments Daughter cells Cleavage of an animal cell (SEM)

LE 12 -9 b Vesicles forming cell plate Wall of parent cell Cell plate 1 µm New cell wall Daughter cells Cell plate formation in a plant cell (TEM)