2.5: CELL DIVISION

2.5.1: Cell Cycle: Outline the stages of the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis Cytokinesis starting

*During its life, a cell passes through a well-ordered series of events known as the cell division cycle. *The cell division cycle involves three basic stages: interphase, mitosis and cytokinesis. *Interphase is much longer than mitosis and it begins as soon as a daughter cell is formed. It is an active period during which: the cell grows; DNA transcription and DNA replication occur; and biochemical reactions are performed. Interphase is broken up into three stages: *G1 Stage (first growth stage) The cell performs its normal differentiated function. Protein synthesis mitochondria replication/ chloroplast replication. *S Stage DNA replication. At this point the mass of DNA in the cell has doubled. *G2 Stage (second growth stage) Preparation for cell division *Mitosis is a continuous process but it is useful to divide it into four stages: prophase, metaphase, anaphase, and telophase. During mitosis the nucleus divides into two daughter nuclei each with same the number of chromosomes as the parent nucleus. *Cytokinesis the cell separates its cytoplasm, organelles and DNA equally and pinching in of the plasma membrane to divide the cell into two equal daughter cells. Cytokinesis commences towards the end of mitosis.

2.5.2: STATE: Tumours (cancer) cells are the result of uncontrolled cell division and these can occur in any organ or tissue

2.5.3: STATE: Interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and / or chloroplasts

Mitosis is division of the nucleus in which one parent nucleus divides into two daughter nuclei each having the same number of chromosomes as the parent nucleus and genetticaly identical to the parent nucleus.

2.5.4 and 2.5.5: Mitosis Supercoiling of chromosomes Nuclear membrane breaks down Spindle microtubles extend from pole to equator Microtubules attach to centromere Chromosomes line along equator of cell Centromere splits and sister Chromatids (now chromosomes) move to opposite poles Reformation of nuclear membrane around chromosomes Chromosomes uncoil

STATE: Growth, embryonic development, tissue repair and asexual reproduction (of eukaryotic cells) involve mitosis

IB Question: Describe the events that occur during mitosis. [9]

IB Question: Describe the events that occur during mitosis. [9] sequence of stages is prophase metaphase anaphase telophase; chromosomes condense/supercoil/become shorter and fatter in prophase; spindle microtubules grow (from poles to equator) in prophase/metaphase; nuclear membrane breaks down in prophase/metaphase; spindle microtubules attach to the centromeres/chromosomes in metaphase; chromosomes line up at equator in metaphase; centromeres divide / (paired) chromatids separate / chromosomes separate into two chromatids in metaphase/anaphase; (sister) chromatids/chromosomes pulled to opposite poles in anaphase; spindle microtubules disappear in telophase; nuclear membrane reforms around chromosomes/chromatids in telophase; chromosomes/chromatids decondense in telophase; [9 max]

IB Question: Before cell division in unicellular and multicellular organisms, the nucleus must divide to produce two genetically identical nuclei. Explain the events that occur in cells that result in the production of genetically identical nuclei. [8]

IB Question: Before cell division in unicellular and multicellular organisms, the nucleus must divide to produce two genetically identical nuclei. Explain the events that occur in cells that result in the production of genetically identical nuclei. [8] mitosis; DNA replication; each chromosome consists of two sister / identical chromatids; chromosomes condense / supercoiling; nuclear membrane breaks down; chromosomes align (at equatorial plate); spindle fibres / microtubules attach to centromeres of chromosomes on opposite sides; centromeres split; chromatids become chromosomes; sister / identical chromosomes pulled to opposite poles; nuclear membranes reform; events correctly assigned to interphase, prophase, metaphase, anaphase, and telophase; [8 max]

Mitosis is division of the nucleus in which one parent nucleus divides into two daughter nuclei each genetically identical as the parent nucleus. The cell below shows the sequence of events which leads to the production of two genetically identical nuclei. Cell is in interphase of the cell cycle. Two pairs of chromosomes are shown. One pair contains the A gene while the second pair contains the B gene During the S-phase of interphase, each chromosome makes an identical copy of itself. Each chromosome is composed of two identical sister chromatids

Prophase: The cell enters the first stage of mitosis called prophase in which the following events occur: *Supercoiling of chromosomes *Nuclear membrane breaks down *Spindle microtubles extend from pole to equator and will attach to the centromere of each duplicated chromosome. Metaphase: The second stage of mitosis is metaphase. During this stage the spindle microtubles have aligned the duplicated chromosomes along the equator of the cell

Anaphase: During anaphase of mitosis the centromeres split and the sister chromatids of each duplicated chromosome are pulled to opposite poles of the cell Telophase: In the final stage of mitosis, telophase, the following events occur *Reformation of nuclear membrane around chromosomes *Chromosomes uncoil *cytokinesis also occurs which is division of the cytoplasm The end result of mitosis is two daughter nuclei have been produced which are identical to each other and identical to the parent nucleus.

IB QUESTION: Describe the events that occur in the four phases of mitosis in animals. [6] May 11 TZ2

(a) anaphase [1] (b) growth (through increasing cell number); embryonic development; tissue production/repair; (asexual) reproduction; [2 max] (c) uncontrolled mitosis/cell division [1]