Unit: The Cell Cycle 1

Phases of the Cell Cycle Interphase G1: cell grows and prepares for DNA duplication S: Synthesis DNA duplicates G2: More growth M Phase (Division) Mitosis Nucleus divides Cytokinesis Cytoplasm divides

What is the difference between: DNA: chain of nucleotides Chromatin: uncoiled DNA Chromosomes: tightly packaged chromatin (DNA)

Chromosomes Each chromosome contain 100s-1000s of genes A gene is a section of DNA that codes for a protein (which determine our physical traits) In eukaryotes, chromosomes exist in homologous pairs, inheriting 1 from each parent Homologous pairs carry genes for the same traits

How many chromosomes? Example: Humans have 23 pairs of chromosomes, or 46 total chromosomes, in all body cells (somatic cells) 46 = 2n = diploid (TWO SETS of chromosomes, 1 from mom & 1 from dad) The exception to the rule are sperm and egg (gametes), which have only 1 copy of each chromosome 23 = n = haploid (1 set of chromosomes)

Copying the chromosomes All DNA in a cell must be copied completely before dividing (Remember chromosomes are in pairs) Single copies look like an “I” Replicated copies look like an “X” Known as sister chromatids Attached at the centromere Both of these pictures represent 2 chromosomes (not 4!)

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Mitosis Cell division to produce two cells that are identical to the parent cell and each other When: Growth Repair Asexual Reproduction

Phases of Mitosis The four phases of mitosis describe how the chromosomes and nucleus divide Prophase Metaphase Anaphase Telophase Cytokinesis is the division of the entire cell (cytoplasm); this occurs directly after telophase

Interphase (not mitosis!)

Interphase (not mitosis!) Nuclear envelope Chromatin Centrioles Not seen: cell grows and replicates DNA to prepare for division

Prophase

Prophase Centrioles move to opposite sides of cell Spindle fibers form Organelles have replicated Nuclear envelope breaks down Chromosomes condense; sister chromatids join

Metaphase

Metaphase Sister chromatids line up in middle, and are attached to the spindle

Anaphase

Anaphase Sister chromatids are pulled apart to opposite poles; Each side will have the identical DNA

Telophase

Telophase Spindle breaks down Nuclear envelope reforms Chromosomes uncoil

Cytokinesis (following mitosis!)

Cytokinesis (following mitosis!) Notice the cell will be in Interphase again Animal cells - cell membrane pinches off (cleavage furrow) Plant cells - cell wall forms between (cell plate)

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