Cell Cycle

The DNA Gene Theory The Cell Theory “Central Dogma of Biology” “Cell Doctrine” 1. DNA is the molecule of inheritance. Ø DNA molecules are synthesized as precise replicas of 1. All organisms are constructed of one or more previous DNA molecules cells. Ø These precise replicas are passed to new generations 2. The cell is the basic unit of life.

2. A chromosome is one long dsDNA. 3. All cells arise from previous cells. Ø In eukaryotes, the dsDNA molecule is wrapped with histones & other proteins to form chromatin. “Omnis cellula e cellula!”

3. A gene (a discrete unit of heredity) is a specific \ cellular reproduction must include copying & region of DNA on a chromosome. transmitting DNA Ø Specific gene: instructions for a specific protein

4. Each chromosome = 100s–1000s of genes.

Eukaryotic Cells Have Multiple Cellula e Cellula Chromosomes

✶ Growth & Development – New cells produced – Need the right number of cells ✶ In division, each new in the right location • Either too few or too many is bad. cell needs the correct number and kind of ✶ Cell Replacement – Lost or damaged cells chromosomes replaced –Replicate and divide chromosomes in ✶ Asexual Reproduction nucleus – New organism formed Sea star regenerating –Distribution of organelles

Chromosomes Must Duplicate Before The Cell Cycle Division ✶ Ordered sequence of events in a cell’s life [Semiconservative Replication] ✶ Interphase (G1/S/G2): 90% of cell cycle – Most cellular activity

✶ Mitotic phase (M) – Mitosis = nucleus divides – Cytokinesis = cytoplasm & plasma Human duplicated chromosome Chromosome duplication membrane divides The eukaryotic cell cycle and separation

Heyer 1 Cell Cycle

All cell reproduction requires Duplicated chromosomes DNA duplication One chromatid Sister chromatid ✶ Each cell must have its own copy of Centromere genetic material ✶ Duplicated chromosome: two sister – DNA replication in S Stage of Interphase chromatids ✶ Sister chromatids contain identical DNA ✶ Then DNA must be separated (segregation) so that each cell has a ✶ Sister chromatids are held together by complete copy the centromere – Mitosis of Mitotic Phase

chromatin condenses into Mitosis distinct ✶ Sister chromatids separate, move to chromosomes opposite poles ✶ Sister chromatids are now “unduplicated chromosomes” Chromatin ✶ Cell elongates Chromosomes

Late Mitosis

✶ New nuclear envelopes form ✶ Chromosomes de-condense ✶ Cytokinesis begins

Heyer 2