VIII. CELL REPRODUCTION

VIII. CELL REPRODUCTION Overview: Why Reproduce?

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

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

VIII. 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                

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 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.

VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase a. G1 b. S Chromosome duplication (including DNA synthesis) Centromere Sister chromatids

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

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'

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

5' 3' 3' 5' - 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 Initiation Replication at the fork So, into each 'replication fork',there is "continuous synthesis" on one strand 5' "FORK" "FORK" 3' 3' 5'

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

5' 5' What about the other strands? PROBLEM!!! VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication Initiation 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'

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

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

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

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

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

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

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

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

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

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

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

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

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

Final linkage between DNA frag's made by LIGASE 3' 5' VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication Initiation Replication at the fork DNA Repair Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3' 5' 3' H2O

Final linkage between DNA frag's made by LIGASE 3' 5' VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication Initiation Replication at the fork DNA Repair Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3' REPLICATION COMPLETE H2O

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

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

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

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

VIII. 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.

Cleavage of an animal cell (SEM) Cleavage furrow Contractile ring of microfilaments Daughter cells Cleavage of an animal cell (SEM)

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