Chapter 12 The Cell Cycle: Cell Growth, Cell Division 2007-2008
Where it all began You started as a cell smaller than a period at the end of a sentence
And now look at you How did you get from there to here?
Getting from there to here Going from egg to baby. the original fertilized egg has to divide and divide and divide and divide
Why do cells divide? Metabolic requirements also set an upper limit to the size of a single cell. As a cell increases in size its volume increases faster (X3)than its surface area (X2). Smaller objects have a greater ratio of surface area to volume. Cell membrane cannot keep up with the nutrient supply needed by an enlarging cytoplasm. The solution to the problem is to split into two cells. Fig. 7.5 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Why do cells divide? Fig. 7.5 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What are the benefits of Cell Division? For reproduction asexual reproduction one-celled organisms For growth from fertilized egg to multi-celled organism For repair & renewal replace cells that die from normal wear & tear or from injury amoeba
Making new cells Nucleus chromosomes DNA Cytoskeleton centrioles in animals microtubule spindle fibers
Function protects DNA Structure Nucleus nuclear envelope double membrane DNA histone protein membrane fused in spots to create pores allows large macromolecules to pass through chromosome What kind of molecules need to pass through? nuclear pores nucleolus nuclear pore nuclear envelope
Cytoskeleton Function structural support maintains shape of cell provides anchorage for organelles protein fibers microfilaments, intermediate filaments, microtubules motility cell locomotion cilia, flagella, etc. regulation organizes structures & activities of cell
Cytoskeleton actin microtubule nuclei
Centrioles Cell division in animal cells, pair of centrioles organize microtubules spindle fibers guide chromosomes in mitosis
Getting the right stuff What is passed on to daughter cells? exact copy of genetic material = DNA mitosis organelles, cytoplasm, cell membrane, enzymes cytokinesis chromosomes (stained orange) in kangaroo rat epithelial cell notice cytoskeleton fibers
Overview of mitosis I.P.M.A.T. interphase prophase (pro-metaphase) cytokinesis metaphase anaphase telophase
Interphase 90% of cell life cycle cell doing its everyday job produce RNA, synthesize proteins/enzymes prepares for duplication if triggered Checkpoints I m working here! Time to divide & multiply!
The distinct events of the cell cycle are directed by a distinct cell cycle control system. These molecules trigger and coordinate key events in the cell cycle. The control cycle has a built-in clock, but it is also regulated by external adjustments and internal controls. Chromatids Attached? Than activate the APC! Password please! Fig. 12.13 MPF please! Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
A checkpoint in the cell cycle is a critical control point where stop and go signals regulate the cycle. Three major checkpoints are found in the: G 1, G 2, and M phases. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
For many cells, the G 1 checkpoint, the restriction point in mammalian cells, is the most important. If the cells receives a go-ahead signal, it usually completes the cell cycle and divides. If it does not receive a go-ahead signal, the cell exits the cycle and switches to a nondividing state, the G 0 phase. Most human cells are in this phase. Read the ppt Regulation of the Cell Cycle for details! Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Cell cycle Cell has a life cycle G2 Gap 2 M Mitosis G1 Gap 1 cell is formed from a mitotic division S Synthesis G0 Resting cell grows & matures to divide again cell grows & matures to never divide again G 1, S, G 2, M liver cells G 1 G 0 epithelial cells, blood cells, stem cells brain / nerve cells muscle cells
Interphase Divided into 3 phases: G 1 = 1 st Gap (Growth) cell doing its everyday job cell grows S = DNA Synthesis copies chromosomes G 2 = 2 nd Gap (Growth) prepares for division cell grows (more) produces organelles, proteins, membranes G 0
green = key features Interphase Nucleus well-defined DNA loosely packed in long chromatin fibers Prepares for mitosis replicates chromosome DNA & proteins produces proteins & organelles
S phase: Copying / Replicating DNA Synthesis phase of Interphase dividing cell replicates DNA must separate DNA copies correctly to 2 daughter cells human cell duplicates ~3 meters DNA each daughter cell gets complete identical copy error rate = ~1 per 100 million bases 3 billion base pairs in mammalian genome ~30 errors per cell cycle mutations (to somatic (body) cells)
Organizing DNA DNA is organized in chromosomes double helix DNA molecule wrapped around histone proteins like thread on spools DNA-protein complex = chromatin organized into long thin fiber condensed further during mitosis ACTGGTCAGGCAATGTC DNA histones chromatin http://www.dnalc.org/ resources/3d/dnawr apadvanced06.html double stranded chromosome duplicated mitotic chromosome
Copying DNA & packaging it After DNA duplication, chromatin condenses coiling & folding to make a smaller package DNA mitotic chromosome chromatin
double-stranded mitotic human chromosomes
Mitotic Chromosome Duplicated chromosome homologous chromosomes 2 sister chromatids narrow at centromeres contain identical copies of original DNA homologous chromosomes single-stranded sister chromatids double-stranded homologous = same information
Mitosis Dividing cell s DNA between 2 daughter nuclei dance of the chromosomes 4 phases prophase metaphase anaphase telophase
green = key features Prophase Chromatin condenses visible chromosomes chromatids Centrioles move to opposite poles of cell animal cell Protein fibers cross cell to form mitotic spindle microtubules actin, myosin coordinates movement of chromosomes Nucleolus disappears Nuclear membrane breaks down
Transition to Metaphase Prometaphase spindle fibers attach to centromeres creating kinetochores microtubules attach at kinetochores connect centromeres to centrioles chromosomes begin moving Nuclear envelope dissolves green = key features
green = key features Metaphase Chromosomes align along middle of cell metaphase plate meta = middle spindle fibers coordinate movement helps to ensure chromosomes separate properly so each new nucleus receives only 1 copy of each chromosome
green = key features Anaphase Sister chromatids separate at kinetochores move to opposite poles pulled at centromeres pulled by motor proteins walking along microtubules actin, myosin increased production of ATP by mitochondria Poles move farther apart polar microtubules lengthen
Separation of chromatids In anaphase, proteins holding together sister chromatids are inactivated separate to become individual chromosomes 1 chromosome 2 chromatids double-stranded 2 chromosomes single-stranded
Chromosome movement Kinetochores use motor proteins that walk chromosome along attached microtubule microtubule shortens by dismantling at kinetochore (chromosome) end
green = key features Telophase Chromosomes arrive at opposite poles daughter nuclei form nucleoli form chromosomes disperse no longer visible under light microscope Spindle fibers disperse Cytokinesis begins cell division
Cytokinesis Animals constriction belt of actin microfilaments around equator of cell cleavage furrow forms splits cell in two like tightening a draw string
Cytokinesis in Animals The Stages of Mitosis http://www.youtube.com/watch?v=vgv3fv-uzyi
Mitosis in whitefish blastula
Mitosis in animal cells
Cytokinesis in Plants Plants cell plate forms vesicles line up at equator derived from Golgi vesicles fuse to form 2 cell membranes new cell wall laid down between membranes new cell wall fuses with existing cell wall
Cytokinesis in plant cell
Mitosis in plant cell
onion root tip
Evolution of mitosis Mitosis in eukaryotes likely evolved from binary fission in bacteria single circular chromosome no membranebound organelles chromosome: double-stranded DNA Origin of replication replication of DNA elongation of cell ring of proteins cell pinches in two
Evolution of mitosis A possible progression of mechanisms intermediate between binary fission & mitosis seen in modern organisms prokaryotes (bacteria) protists dinoflagellates protists diatoms eukaryotes yeast eukaryotes animals
Dinoflagellates algae red tide bioluminescence
Diatoms microscopic algae marine freshwater
Any Questions?? 2007-2008
Ghosts of Lectures Past (storage) 2007-2008
Control of Cell Cycle
Kinetochore Each chromatid has own kinetochore proteins microtubules attach to kinetochore proteins
Chromosome structure scaffold protein chromatin loop rosettes of chromatin loops chromosome DNA histone nucleosome DNA double helix
Cell Division cycle Phases of a dividing cell s life interphase cell grows replicates chromosomes metaphase prophase G 2 M anaphase telophase interphase (G 1, S, G 2 phases) mitosis (M) S cytokinesis (C) G 1 produces new organelles, enzymes, membranes G 1, S, G 2 mitotic phase cell separates & divides chromosomes mitosis cell divides cytoplasm & organelles cytokinesis C
Substitute Slides for Student Print version (for student note-taking) 2007-2008
And now look at you How did you get from there to here?