Chapter 9 How Cells ReproduceChapter 9 How Cells Reproduce

Start with 3 questions:Start with 3 questions:– What kind of information guides inheritance?What kind of information guides inheritance?– How is the information copied in a parent cell How is the information copied in a parent cell

before being passed to the daughter cell?before being passed to the daughter cell?– What kind of mechanisms actually parcel out info What kind of mechanisms actually parcel out info

to daughter cells?to daughter cells?

9-1 Overview9-1 Overview

Mitosis – nuclear division in somatic cellsMitosis – nuclear division in somatic cells– Growth, replacing cells, tissue repairGrowth, replacing cells, tissue repair– Plants, animals, fungi, protistsPlants, animals, fungi, protists

Meiosis – formation of gametes/sporesMeiosis – formation of gametes/spores– Basis of sexual reproductionBasis of sexual reproduction– Develop from germ cellsDevelop from germ cells

Prokaryotes?Prokaryotes?– Binary fission (p. 336)Binary fission (p. 336)

ChromosomesChromosomes

Characteristic Characteristic numbernumber

Orderly coilingOrderly coiling DNA winds 2x DNA winds 2x

around histones to around histones to make nucleosomesmake nucleosomes

CentromereCentromere Kinetochore Kinetochore

one chromosome(one dispersed DNAmolecule + proteins;

not duplicated)

one chromosome(threadlike and nowduplicated; two DNAmolecules + proteins)

one chromosome(duplicated and also condensed

tightly)p.61

Nuclear DNA

9.2 Cell Cycle9.2 Cell Cycle

Series of events Series of events from one cell from one cell division to the nextdivision to the next

InterphaseInterphase

G1G1– Growth/functionalGrowth/functional

SS– Synthesis of DNASynthesis of DNA

G2G2– Prepare for divisionPrepare for division

Mitosis and Mitosis and C-some #C-some #

DiploidDiploid– 2n2n– 2 of each type2 of each type

9.3 Closer look9.3 Closer look

ProphaseProphase– C-somes visibleC-somes visible– Centrioles duplicateCentrioles duplicate– Nuclear envelopeNuclear envelope– MT docks at MT docks at

kinetochoreskinetochores

MetaphaseMetaphase

Alignment of c-Alignment of c-somes between somes between spindle polesspindle poles

AnaphaseAnaphase

Sister chromatids Sister chromatids move to opposite move to opposite spindle poles by spindle poles by motor proteinsmotor proteins

TelophaseTelophase

C-somes reach polesC-somes reach poles DecondenseDecondense Vesicles reform Vesicles reform

envelopeenvelope

9.4 Cytokinesis9.4 Cytokinesis

AnimalsAnimals– Contractile ringContractile ring– Cleavage furrowCleavage furrow

PlantsPlants– New fibers made before New fibers made before

prophaseprophase

– Vesicles from Golgi fuse and Vesicles from Golgi fuse and deposit materials for cell platedeposit materials for cell plate

Identifying phases of MitosisIdentifying phases of Mitosis

Phase Determination

9.5 When Control is lost9.5 When Control is lost

Cell cycle Cell cycle checkpointscheckpoints– Proteins monitor Proteins monitor

DNA structureDNA structure– Proteins monitor Proteins monitor

proceeding phasesproceeding phases– Favorable Favorable

conditions?conditions?– Kinases Kinases – Growth factorsGrowth factors

Architecture of control systemArchitecture of control system

Growth assessed at G1 checkpointGrowth assessed at G1 checkpoint DNA replication success assessed at G2DNA replication success assessed at G2 Mitosis assessed at M checkpointMitosis assessed at M checkpoint

Molecular MechanismsMolecular Mechanisms

Cyclin dependent protein kinases (Cdks)Cyclin dependent protein kinases (Cdks)– Cyclins – bind to Cdks, allow them to work as Cyclins – bind to Cdks, allow them to work as

enzymesenzymes– G2 - MPFG2 - MPF

Growth factors – stimulateGrowth factors – stimulate– Usually everyone gets equal amountsUsually everyone gets equal amounts– Specific cell surface receptorsSpecific cell surface receptors– Broad or specificBroad or specific

Tumor supressorsTumor supressors

InhibitInhibit Prevent binding of Prevent binding of

cyclins to CdKscyclins to CdKs Recessive Recessive Gene p53 – role in Gene p53 – role in

G1 checkpoint, G1 checkpoint, checks for DNA checks for DNA errorserrors– Repair or notRepair or not

Figure 2: p53 re-enforces G1 and G2 cell cycle arrest after DNA damage through the cyclin-dependent kinase inhibitor p21WAF1/CIPI Mdm2 and Bax are other p53 transcriptional targets, with Mdm2 regulating p53 levels and Bax mediating apoptosis

Proto-oncogenesProto-oncogenes

StimulateStimulate Mutation = oncogeneMutation = oncogene DominantDominant Changes in surface receptorsChanges in surface receptors

Figure 2. A modified receptor. Under normal circumstances membrane-bound receptors require the binding of their ligand to be in an activated state. In contrast, receptors encoded by oncogenes do not require the regulatory step of ligand binding to be active.

CancersCancers

4 characteristics4 characteristics– Grow & divide abnormallyGrow & divide abnormally– Cytoplasm & membrane alteredCytoplasm & membrane altered– Weakened capacity for adhesionWeakened capacity for adhesion– Lethal effectsLethal effects

http://nobelprize.org/educational_games/medicine/2001/

Control of the cell cycle gameControl of the cell cycle game