Unit 5 : Cell Division CELL CYCLE – MITOSIS - MEIOSIS

Remember….. The Cell Theory Part 1: Part 2: Part 3: All living things are made of cells. Cells are the basic unit of structure and function in an organism. All cells come from pre-existing cells.

Let’s Review…. Why Are Cells Small? ◦Cells need ENERGY to survive ◦SA/V: ◦Larger cells have a lower SA/V ratio ◦This means they are less efficient. ◦Smaller cells diffuse faster. ◦Less time to get nutrients ◦Less time to remove waste ◦Save ENERGY

Let’s Review…. Why Do Cells Divide? ◦Reproduction ◦bacteria, single-celled organisms ◦Growth ◦many-celled organisms ◦Repair ◦Replace damaged cells

Cell Cycle ◦Cells grow, prepare for division, and divide. ◦Somatic Cell : body cell ◦Skin, hair, muscle, etc. ◦Daughter cells are Diploid ◦They have 2 copies of chromosomes ◦The cycle starts over again.

Cell Cycle ◦3 Stages: ◦INTERPHASE ◦Where the cell does its normal job ◦90% of the time is spent here ◦MITOSIS ◦Cell Division ◦Prophase, Metaphase, Anaphase, Telophase ◦CYTOKINESIS ◦Dividing of the Cytoplasm and Cells

Cell Cycle

Chromosom e ◦Threadlike structure in the nucleus ◦Contains Genetic information ◦One of the two identical “sister” parts of a duplicated chromosome Chromatid Centromere ◦Location where chromatids of a chromosome are attached

The duplicated chromosomes are attached to each other at the centromere, and are called sister chromatids

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Interphase ◦Longest phase of cell cycle ◦Cells grow and carry out their regular functions. ◦The cell is just doing its job. ◦Chromosomes are copied (duplicated) ◦Cell prepares for division ◦(duplicates all the organelles) Starting Point

Interphase ◦G1 = Cell Grows ◦Prepares chromosomes for replication ◦S = Synthesis ◦“DNA synthesis” ◦DNA is copied/ replicated ◦G2 = Growth 2 ◦Preparation for Mitosis ◦Make proteins and organelles G1 G2 S

Interphase ◦Is over after the Chromosomes make copies and the condense into Chromatids G1 G2 S

Mitosis ◦Second part of the Cell Cycle ◦Prophase ◦Metaphase ◦Anaphase ◦Telophase ◦2 Identical cells are created. ◦This is how somatic cells divide ◦(about 24 hours for skin cells) G1 G2 S

Mitosis ◦Begins with one somatic cell ◦One Diploid cell  Two IDENTICAL Diploid daughter cells (contains both sets of chromosomes; a set of mom’s chromosomes AND a set of dad’s chromosomes).

Prophase ◦Nucleus begins to disappear ◦Nuclear membrane disappears ◦DNA condenses (coils together) ◦Chromosomes become visible ◦Centrioles move to opposite poles (separate) ◦Spindle Fibers begin to stretch LABEL: centrioles, nuclear membrane, chromosomes, sister chromatids, cell membrane, centromere

Prophase

Metaphase ◦Chromosomes line up in the center on the equatorial plane (middle) ◦Each side of the centromere attaches to a spindle fiber ◦Chromosomes connect to the spindle fibers LABEL: centrioles, centromere, chromosomes, spindle fibers

Metaphase Chromosomes are aligned along the equator of a dividing cell Notice the spindle fibers produced by the centrioles

Anaphase ◦Centromeres divide ◦The 2 strands of the chromosomes (sister chromatids) separate and move to opposite poles LABEL: centrioles, centromere, chromosomes, spindle fibers

Anaphase Spindle fibers pull apart sister chromatids

Telophase ◦Chromosomes reach the opposite ends of the cell ◦Nuclear membrane begins to reform ◦Cell begins to split in half

Telophase Cytokinesis begins You can see the cell membrane developing between the two cells

Cytokinesis ◦Cytoplasm splits in half forming two daughter cells ◦Animals: the cell membrane pinches in dividing the cell and cytoplasm ◦Plants: Since plants have cell walls, a plate is formed in between the two new cells ◦Cell plate becomes a cell wall

Cytokinesis in animal cell

Cytokinesis in a plant cell