MITOSIS & CELL CYCLE

THE CELL CYCLE A TYPICAL CELL GOES THROUGH TWO DISTINCT PERIODS: 1.A PERIOD OF GROWTH 2.A PERIOD OF DIVISION

THE CELL CYCLE THE PERIOD OF GROWTH IS INTERPHASE: THE PERIOD OF DIVISION IS MITOSIS MITOSIS IS THE DIVISION OF SOMATIC CELLS

INTERPHASE

The longest and busiest part of a cell’s life 3 STAGES OF INTERPHASE 1.G1-Cell growth; protein synthesis 2.S-Chromosome replication; sister chromatids form 3.G2-Cell prepares for mitosis

A CLOSER LOOK AT MITOSIS WHEN BODY (SOMATIC) CELLS BECOME TOO LARGE, THEY WILL DIVIDE IN A PROCESS KNOWN AS MITOSIS IN WHICH TWO DAUGHTER CELLS ARE FORMED. THERE ARE FOUR DISTINCT PHASES OF MITOSIS:  PROPHASE  METAPHASE  ANAPHASE  TELOPHASE

PROPHASE

Prophase is the first and longest phase of mitosis. During prophase the long stringy chromatin coils up into visible chromosomes. The duplicated chromosomes are made up of two halves called sister chromatids.

METAPHASE

METAPHASE: The doubled chromosomes become attached to the spindle fibers by their centromeres. The chromosomes begin to line up on the midline of the spindle.

ANAPHASE

ANAPHASE: the centromeres split apart and chromatid pairs from each chromosome separate from each other.

TELOPHASE

TELOPHASE (final phase) SISTER CHROMATIDS MOVE TO OPPOSITE ENDS OF THE CELL AND THE CYTOPLASM BEGINS TO DIVIDE

CYTOKINESIS

THE PROCESS IN WHICH THE CYTOPLASM DIVIDES TO FORM TWO NEW CELLS

RESULTS OF MITOSIS MITOSIS RESULTS IN TWO GENETIC DUPLICATES OF THE PARENT CELL.

WHY MEIOSIS? WHEN CELLS DIVIDE BY MITOSIS, THE NEW CELLS ARE IDENTICAL TO THE ORIGINAL CELLS. IF MITOSIS WAS THE ONLY FORM OF CELL DIVISION ALL OFFSPRING PRODUCED WOULD HAVE TWICE AS MANY CHROMOSOMES AS ITS PARENTS.

MEIOSIS MEIOSIS - OCCURS IN THE SPECIALIZED BODY CELLS THAT PRODUCE GAMETES. MEIOSIS CONSISTS OF TWO SEPARATE DIVISIONS.

MEIOSIS MEIOSIS I - BEGINS WITH ONE DIPLOID CELL AND CREATES 2 DIPLOID CELLS. MEIOSIS II – BEGINS WITH 2 DIPLOID CELLS WHICH DIVIDES TO FORM 4 HAPLOID CELLS SEX CELLS. THE HAPLOID CELLS ARE CALLED SEX CELLS - GAMETES.

MEIOSIS MALE GAMETES ARE CALLED SPERM. FEMALE GAMETES ARE CALLED EGGS. WHEN SPERM FERTILIZES AN EGG, THE RESULTING CELL, IS CALLED A ZYGOTE. THE FUSION OF HAPLOID SEX CELLS IS CALLED SEXUAL REPRODUCTION.

PROPHASE I THE CHROMATIN COILS TO FORM VISIBLE CHROMOSOMES AND THE SPINDLES FORMS. EACH PAIR OF HOMOLOGOUS CHROMOSOMES COME TOGETHER TO FORM A FOUR-PART STRUCTURE CALLED TETRAD. CROSSING OVER CROSSING OVER RESULTS IN NEW COMBINATIONS OF GENES ON A CHROMOSOME.

METAPHASE I THE SPINDLE FIBERS PULL THE TETRADS TO THE EQUATOR OF THE CELL.

ANAPHASE I ANAPHASE IS CHARACTERIZED BY CHROMOSOMES MOVING TOWARDS THE POLES OF THE CELL. THE CENTROMERES HOLDING THE SISTER CHROMATIDS TOGETHER DO NOT SPLIT AS THEY DO IN MITOSIS.

TELOPHASE I THE SPINDLES ARE BROKEN DOWN, THE CHROMOSOMES UNCOIL, AND THE CYTOPLASM DIVIDES TO YIELD TWO NEW CELLS.

THE SECOND DIVISION OF MEIOSIS PROPHASE II: SPINDLE FIBERS ATTACH TO THE CHROMOSOMES. METAPHASE II: CHROMOSOMES LINE UP RANDOMLY AT THE EQUATOR ANAPHASE II: CENTROMERES SPLIT, SISTER CHROMATIDS SEPARATE TELOPHASE II: THE NUCLEI RE-FORM, THE SPINDLES BREAK DOWN, THE CYTOPLASM DIVIDES.

MITOSIS V/S MEIOSIS MITOSIS ONLYBOTH MEIOSIS ONLY produces 2 identical daughter cells duplication of chromosomes occurs produces 4 haploid cells chromosome number is maintained chromosome number is halved daughter cells are identical to parent daughter cells are not identical to parent 1 cell division is involved 2 cell divisions are involved associated with asexual reproduction associated with sexual reproduction necessary for growth and maintenance produces gametes genetic variation is a rare occurrence genetic variation is more likely

THE END