The Cell Cycle: Cell Growth, Cell Division

Where it all began… You started as a cell smaller than a period at the end of a sentence…

How did you get from there to here? And now look at you…

Reproduction –asexual reproduction one-celled organisms Growth and Development –from fertilized egg to multi-celled organism Repair and Replacement –replace cells that die from normal wear & tear or from injury Why do cells divide? amoeba

Cell Cycle

Cell cycle Cell has a “life cycle” cell is formed from a mitotic division cell grows & matures to divide again cell grows & matures to never divide again G 1, S, G 2, M G1G0G1G0 epithelial cells, blood cells, stem cells liver cells brain / nerve cells muscle cells

Interphase 90% of cell life cycle –cell doing its “everyday job” produce RNA, synthesize proteins/enzymes –prepares for duplication if triggered I’m working here! Time to divide & multiply!

Interphase Divided into 3 phases: –G1 = 1 st Gap cell doing its “everyday job” cell grows A few hours to indefinitely –S = DNA Synthesis copies chromosomes 3-6 hours –G2 = 2 nd Gap prepares for division cell grows (more) produces organelles, proteins, membranes 2-5 hours G0G0 signal to divide

Interphase Longest phase of the cell cycle –Consists of G1, S, G2 Cell prepares for mitosis –replicates chromosome DNA & proteins –produces proteins & organelles green = key features

Organizing DNA DNA is organized in Nucleosomes –double helix DNA molecule –wrapped around Histones like thread on spools –DNA-protein complex = Chromatin organized into long thin fiber –condensed further during mitosis DNA histones chromatin duplicated mitotic chromosome ACTGGTCAGGCAATGTC double stranded chromosome

Copying DNA & packaging it… After DNA duplication, chromatin condenses –coiling & folding to make a smaller package DNA chromatin mitotic chromosome

double- stranded mitotic human chromosomes

Mitotic Chromosome Duplicated chromosome –2 chromatids –narrow at centromere –contain identical copies of original DNA homologous chromosomes homologous chromosomes sister chromatids homologous = “same information” single-stranded double-stranded

Mitosis Dividing cell’s DNA between 2 daughter nuclei –“dance of the chromosomes” 4 phases –Prophase –Metaphase –Anaphase –Telophase

Mitosis

Overview of mitosis interphaseprophase(pro-metaphase) metaphaseanaphasetelophase cytokinesis I.P.M.A.T.

Prophase Chromatin condenses –Becomes 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 green = key features

Transition to Metaphase Prometaphase –Special proteins attach to the centromeres creating kinetochores –microtubules attach at kinetochores connect centromeres to centrioles –Nuclear envelope fragments green = key features

Anaphase Sister chromatids separate –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 green = key features

Telophase Chromosomes arrive at opposite poles –Nuclear envelop starts to reappear –nucleoli form –Chromosomes uncoil no longer visible under light microscope Spindle fibers disperse Cytokinesis –cell division green = key features

Cytokinesis Animals –constriction belt of actin microfilaments around equator of cell cleavage furrow forms splits cell in two like tightening a draw string

Mitosis in whitefish blastula

Cytokinesis in Plants Plants –Cell Plate 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

onion root tip

G 1 /S checkpoint G 1 /S checkpoint is most critical –primary decision point “Go Ahead signal” –if cell receives “GO” signal, it divides internal signals: cell growth (size), cell nutrition external signals: “growth factors” –if cell does not receive signal, it exits cycle & switches to G 0 phase non-dividing, working state

What about Stem cells? What are stem cells? How can they be used? What are concerns about using stem cells? What are the types of stem cells?

Multicellular organisms depend on interactions among different cell types. Tissues are groups of cells that perform a similar function. Organs are groups of tissues that perform a specific or related function. Organ systems are groups of organs that carry out similar functions. CELLTISSUEORGAN vascular tissue leaf stem lateral roots primary root SYSTEMS root system shoot system

Specialized cells perform specific functions. Cells develop into their mature forms through the process of cell differentiation. Cells differ because different combinations of genes are expressed. A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines

Stem cells can develop into different cell types. Stem cells have the ability to –divide and renew themselves –remain undifferentiated in form –develop into a variety of specialized cell types

Stem cells are classified into three types. –totipotent, or growing into any other cell type –pluripotent, or growing into any cell type but a totipotent cell –multipotent, or growing into cells of a closely related cell family

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules. Stem cells come from adults and embryos. –Adult stem cells can be hard to isolate and grow. –The use of adult stem cells may prevent transplant rejection. –The use of embryonic stem cells raises ethical issues. –Embryonic stem cells are pluripotent and can be grown indefinitely in culture.

The use of stem cells offers many current and potential benefits. –Stem cells are used to treat leukemia and lymphoma. –Stem cells may cure disease or replace damaged organs. –Stem cells & BlindnessStem cells & Blindness –Stem cells may revolutionize the drug development process.

Cell cycle s ignals Cell cycle controls –Cyclin regulatory proteins levels cycle in the cell –CDK cyclin-dependent kinases phosphorylates cellular proteins –activates or inactivates proteins –MPF triggers passage through different stages of cell cycle activated Cdk inactivated Cdk