THE CELL CYCLE “The Circle of Life”

Cells reproduce because: The volume is increasing at a greater rate than the surface area (cell membrane) Agar block experiment

Cells reproduce for Growth Repair Reproduction

THE CELL CYCLE

The Cell Cycle

INTERPHASE THE PERIOD BETWEEN CELL DIVISIONS DIVIDED INTO G1, S, AND G2 SOME CELLS DO NOT COMPLETE THE CYCLE AND ENTER G0

G1 A PERIOD OF GROWTH AND DEVELOPMENT NORMAL ACTIVITIES OF THE CELL OCCUR SYNTHESIS OF PROTEINS, NUCLEIC ACIDS, AND OTHER NECESSARY MOLECULES OCCURS

G0 SOME CELLS REMAIN IN G1 THESE CELLS ARE USUALLY HIGHLY SPECIALIZED NERVE CELLS GENERALLY REMAIN IN G0; THEY ARE UNABLE TO DIVIDE LIVER CELLS WILL REMAIN IN G0 UNLESS DAMAGE OCCURS AND NEW CELLS ARE NEEDED

G1 CHECKPOINT THE RESTRICTION POINT THE “POINT OF NO RETURN” ENZYMES CHECK THAT GROWTH IS SUFFICIENT FOR CELL DIVISION CELLS THAT REACH THE R POINT OF GROWTH AND DEVELOPMENT MUST COMPLETE THE ENTIRE CELL CYCLE SKIN CELLS, CELLS THAT LINE THE DIGESTIVE TRACT, ETC.

S PHASE CELLS CANNOT DIVIDE NORMALLY UNLESS THEY CREATE A NEW SET OF CHROMOSOMES THROUGH THE PROCESS OF DNA REPLICATION THIS STAGE IS CALLED “S” FOR SYNTHESIS OF DNA

DNA REPLICATION

SISTER CHROMATIDS EACH REPLICATED CHROMOSOME CONSISTS OF TWO IDENTICAL CHROMATIDS OR “SISTER CHROMATIDS” CHROMATIDS ARE HELD TOGETHER AT THE CENTROMERE.

G2 PHASE ADDITIONAL MANUFACTURE OF MOLECULES FOR THE TWO NEW CELLS OCCURS THE CELL MUST HAVE SUFFICIENT ORGANELLES, PROTEINS, ETC. FOR TWO CELLS RATHER THAN FOR ONE AT THE END OF G2, THE CELL IS READY TO DIVIDE

Checkpoints G2 Checkpoint DNA polymerase checks for and corrects mistakes in replication Triggers the beginning of mitosis

MITOSIS MITOSIS IS THE DUPLICATION OF THE CELL’S NUCLEUS PRIOR TO CELL DIVISION IT MAINTAINS THE DIPLOID NUMBER OF CHROMOSOMES THE DIPLOID NUMBER IN HUMANS IS 46

PROPHASE THE FIRST STAGE OF MITOSIS THE SISTER CHROMATIDS CONDENSE AND BECOME VISIBLE THE NUCLEAR MEMBRANE DISSOLVES SPINDLE FIBERS DEVELOP FROM THE CENTROSOMES

Prophase

THE MITOTIC SPINDLE THE SPINDLE FIBERS COME FROM THE CENTROSOME MICROTUBULES FORM BETWEEN THE CENTROSOMES TO MAKE THE MITOTIC SPINDLE

MITOTIC SPINDLE CENTRIOLES ARE FOUND IN THE CENTROSOMES OF ANIMAL CELLS. KINETOCHORE FIBERS ATTACH TO CENTROMERES AND PULL CHROMATIDS APART

MITOTIC SPINDLE (cont.) OTHER SPINDLE FIBERS STRETCH FROM CENTROSOME TO CENTROSOME AND PUSH THE CELL OUTWARD TO MAKE IT BIGGER THESE ARE KNOWN AS POLAR FIBERS

METAPHASE SISTER CHROMATIDS ARE ATTACHED TO KINETOCHORE FIBERS AT THE CENTROMERES

METAPHASE THE KINETOCHORE FIBERS PULL THE CHROMOSOMES INTO A RING IN THE CENTER OF THE CELL KNOWN AS THE METAPHASE PLATE

Metaphase

ANAPHASE SISTER CHROMATIDS ARE PULLED APART BY KINETOCHORE FIBERS, BREAKING THE ATTACHMENT AT THE CENTROMERE EACH CHROMATID IS NOW A CHROMOSOME

Anaphase (continued) THE POLAR FIBERS PASS EACH OTHER AT THE EQUATOR TO ELONGATE THE CELL, MAKING IT EASIER TO SPLIT THE CYTOPLASM

ANAPHASE SISTER CHROMATIDS ARE PULLED TO OPPOSITE SIDES OF THE CELL KNOWN AS THE POLES OF THE CELL

TELOPHASE THE CHROMOSOMES BECOME ELONGATED SPINDLE FIBERS DISAPPEAR

TELOPHASE NUCLEAR MEMBRANE RE-FORMS IN EACH DAUGHTER CELL CYTOKINESIS BEGINS TO CUT THE CELL IN TWO

Telophase

Checkpoints Mitosis Checkpoint Triggers the end of mitosis Causes the two new daughter cells to enter G1

CYTOKINESIS A CELL PLATE FORMS IN PLANTS THE CELL MEMBRANE CONSTRICTS IN ANIMALS FORMING A CLEAVAGE FURROW

Plant Cell Cytokinesis A CELL PLATE FORMS IN PLANTS WHEN VESICLES FUSE

Animal Cell Cytokinesis MICROFILAMENTS ALONG THE EQUATOR CONSTRICT IN ANIMALS FORMING A CLEAVAGE FURROW

Cancer Cancer is uncontrolled cell division It occurs because genes that control the manufacture of checkpoint proteins are damaged; OR The cell produces too much of the growth-promoting chemicals in the body

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