Unicellular organisms Cell division = reproduction Reproduces entire organism& increase population Multicellular organisms Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg Also use cell division to repair & renew cells that die from normal wear & tear or accidents
DNA – deoxyribonucleic acid, the hereditary material of the cell. Chromatin – thin twisted strands of DNA wrapped around proteins How DNA is found in a nondividing cell Histones – proteins DNA is wrapped around in chromatin Chromosomes/chromatid – short, thick, condensed DNA/protein structures found in dividing cells Sister chromatids – double chromosome found during cell division Centromere – region that connects sister chromatids and where the spindle attaches to the chromatids
A mnemonic to help remember the stages of mitosis.
Copy of mitosis 2010
MitosisBiology is the onlysubject in whichmultiplication is thesame thing as division…
Where it all began…You started as a cell smaller thana period at the end of a sentence…
And now look at you! How did you get from there to here?
Mitosis! The fertilized egg must divide… and divide…. and divide…. and divide…
Why do cells divide… for reproduction one celled organisms (clones) asexual reproduction amoeba for growth & development from fertilized egg to multi-celled organism for repair starfish replace cells that die from normal wear & tear or from injury
Dividing cells… What has to be copied DNA organelles cell membrane lots of other molecules • enzymes plant cell animal cell
Copying DNA A dividing cell duplicates its DNA creates 2 copies of all DNA sends the 2 copies to opposite ends of the cell splits into 2 daughter cells the DNA startsDNA loosely wound in cell the nucleus If you tried to divide it like that, it could nucleus tangle & break
Organizing & packaging DNA into chromosomes…DNA cell nucleus DNA has been “wound up”DNA in chromosomes ineveryday “working” cell cell nucleus4 chromosomes DNA in chromosomes in cellin this organism getting ready to divide
Important Vocabulary•DNA•Chromatin•Histone•Chromosomes/chromatid•Sister chromatid•Centromere
Copying & packaging DNA When cell is ready to divide… copy DNA first, then… coil up doubled chromosomes like thread on a spool… • now can move DNA around cell without having it tangle & break Coil DNA intoCopying DNA compact chromosomes
Copying DNA… chromosomes in cell DNA in chromosomes cell 4 single-stranded chromosomes duplicated chromosomes nucleus duplicated chromosomes cell4 double-stranded chromosomes nucleus
double-strandedhuman chromosomesready for mitosis
Chromosomes of Human Female 46 chromosomes 23 pairs
Chromosomes of Human Male 46 chromosomes 23 pairs
Mitosis Vocabulary Centrioles – small, cylinder shaped structures found near the nucleus, involved in mitosis Only in animal cells Aster – star like structure made of microtubules that extend from centrioles Spindle – web like structure made up of microtubule fibers. It arranges and moves the chromosomes around.
Interphase DNA found as chromatin Cell grows & produces more molecules & organelles DNA and centrioles replicateDNA Three mini stages: G1 cell S G2 nucleus Interesting things happen!
Prophase Chromosomes become visible DNA is wound into chromosomes Nuclear membrane andduplicated nucleolus breakdownchromosomes Centrioles move to opposite poles Spindle and asters cell begins to form Chromosomes nucleus pair up!
Metaphase Spindle is fully developed Sister chromatids line up at the equator Chromatids are attached to the spindle at the centromere Chromosomes meet in the middle!
Anaphase Sister chromatids separate One complete set of chromosomes goes to each pole Spindle pull chromatids to opposite poles Cytokinesis begins Chromosomes get pulled apart!
Telophase Chromosomes reach opposite poles Nuclear membrane and nucleolus reappear Spindle disappears Chromosomes unravel Cytokinesis is completed Now there are two!
CytokinesisDivision of the cytoplasm &organelles into two cells thatoccurs at the end of mitosis
New “daughter” cells Get 2 exact copies of original cells same DNA “clones”
How does mitosis differ in plants? Plant cells do not have centrioles Plant cells do not pinch in half Cytokinesis is accomplished through the formation of a cell plate between the two daughter cells
Overview of mitosisCopy DNA Wind Up Bye-Bye! Line Up Separate Divide
Cell Turnover – the speed of mitosis The time it takes for a cell to complete one cycle can vary between a couple of minutes to days. Cells that are continuously being worn away have a rapid turnover. E.g. skin, epithelial cells, RBC, etc. Cells which make up organs such as the eye and the brain do not multiply very often if ever once they reach adult size.
Control of the Cell Cycle Growth & division are carefully regulated The protein cyclin regulates the cell cycle. Cyclin is produced during interphase. Once the cyclin reaches a certain level it triggers mitosis. During mitosis most of the cyclin is destroyed. The new daughter cells must produce new cyclin before a second mitosis can occur
How do we know? Scientists found that when cyclin is injected into a nondividing cell, that cell forms a spindle They then found the amount of cyclin increased and decreased in timing with the cell cycle
Other Regulatory Proteins Internal Proteins in the cell respond to events inside the cell • E.g. makes sure cell does not enter mitosis until all chromosomes have been replicated • E.g. No anaphase until all chromosomes are attached to the spindle
Other Regulatory Proteins External Proteins that respond to events outside the cell • May stimulate growth – e.g. wound healing, embryonic development • May slow growth – e.g. prevent excessive growth, keep tissues from disrupting each other
Cancer – cell division gone wild! Cancer – uncontrolled mitosis Don’t respond to normal cellular controls Cells divide excessively Many causes resulting in gene mutations (often in gene p53) • Smoking, radiation, viral infection, heredity
Cancer – cell division gone wild! Tumor – a mass of abnormal cells Benign tumor – abnormal cells remain in original location Malignant tumor – abnormal cells leave the original site and impair the function of one or more organs
Biology is the only subject inwhich multiplication is the same thing as division… 2006-2007