The Cell cycle A form of cellular reproduction

What is the cell cycle? A series of steps showing the formation of 2 cells from a single cell 3 main steps: 1. Interphase (carrying out the cell’s normal activities) 2. Mitosis (division of the nucleus) 3. Cytokinesis (division of cytoplasm)

Cell cycle

interphase The longest phase of the cell cycle G1 Phase: growth *As the cell grows larger, it must divide or it may die.

Interphase Continued… S-phase: DNA replicates (synthesis) G2 phase: growth & prep for cell division; critical checkpoint

Mitosis: Nuclear Division Mitosis is called nuclear division because the steps refer to the contents of the nucleus. 4 steps: Prophase Metaphase Anaphase Telophase

Present during interphase Carries genetic info Chromatin Present during interphase Carries genetic info Looks like noodles – condenses to form chromosomes Chromosome Present during mitosis Carries genetic info Coiled up so that it looks like an “X” Chromatid Present during mitosis Carries genetic info ½ a chromosome (pulls apart during Anaphase) *All are made of DNA

Vocabulary Chromatin – Chromosome – Chromatid – loose combo of DNA and proteins (condenses to form chromosomes) Chromosome – continuous thread of DNA consisting of numerous genes and regulatory info (X shape) Chromatid – one half of the chromosome

Vocabulary continued… Centromere – Where spindle fibers attach (center) Telomere – Found at the tips of the chromosome - helps prevent loss of genes by not allowing chromosomes to attach to each other. Centrioles – Small cylinder shaped organelles made of protein tubes. Aids in mitosis.

prophase Nuclear membrane disintegrates Nucleolus disappears Chromatin condenses to form chromosomes Spindle fibers begin to form at poles

metaphase Chromosomes attach to spindle fibers and line up along the middle of the cell *Middle

anaphase Chromatid pairs separate and move in opposite directions *Away Chromatid pairs separate and move in opposite directions Spindle fibers contract pulling them toward the poles (away from each other)

Telophase (Nuclear Division) Cell begins to separate Separate nuclei begin to appear Spindle fibers disappear

Cytokinesis (Cytoplasm Division) The process that results in 2 genetically identical daughter cells Plant cells form a cell plate in addition to daughter cells dividing

question If a cell containing 46 chromosomes undergoes mitosis, how many chromosomes does each of its daughter cells contain? 46

National Geographic Article http://www.youtube.com/watch?v=s1ylUTbXyWU