The Cell Cycle

Cell Theory

• All Cellular life is made of one or more cells

• Basic organizational and functional units of all organisms

• All cells came from other cells

Multicellular vs Unicellular Organisms

Multicellular:

• Reproduction

• Growth and development

• Tissue Renewal

Unicellular only has reproduction

During Cell Division…

All parts of the cell are divided into new cells

Genetic Material

Distributed into daughter cell during cell division

Prokaryote vs Eukaryote DNA

• Prokaryotes usually have 1 circular DNA molecule

• Eukaryotes usually have more than 1 linear DNA molecule

Chromosomes

• Molecule of DNA in a cell

• DNA wrapped around proteins 

• Highly organized, high density

• Only present during cell division

Chromatin

• DNA/protein complex in dispersed state. Thread/fiber-like

• DNA is in this state when a cell is not actively dividing

Ploidy

• The number of sets of chromosomes in the nucleus of a cell

• NEVER CHANGES in the cell cycle

Haploid vs Diploid

Haploid:

• Having one of each chromosome

Diploid:

• Having a homologous pair of chromosomes

Both can undergo Mitosis

Cells can divide to form…

2 identical daughter cells

Prokaryotes undergo…

Binary Fission

Interphase

• Time in between cell divisions

• Not a resting stage; Cells are still highly active

• About 90% of the cell cycle

• DNA is chromatin here

Interphase 1: G1 (Gap 1 phase)

• Growth and normal development and functions

• Prep for S phase

• Most time is spent here

Interphase 2: S (Synthesis)

• Chromosomes are duplicated (DNA and chromosomal)

• Protein synthesis (Does not change ploidy)

• Centrosome Duplication

After Chromosomes are Replicated in Synthesis…

• 2 sister chromatids (identical copies)

• They are connected to centromere

• DNA is still chromatin

Interphase 3: G2 (Gap 2)

• Usually shorter than G1 or S

• DNA is still chromatin

• High metabolic activities

• Prepares for Mitosis

M Phase

• Mitosis and cytokinesis 

• Shortest part of the cell cycle (<10%)

Mitosis

• Nuclear division of somatic cells

• Continuous process

• Divided into 4 stages: PMAT

M Phase 1: Prophase

• Chromosomes condense

• Nucleus breaks down

• Mitotic spindle forms 

  • Fibers within cell oriented from pole to pole of cell

  • Guide chromosome movement during mitosis

• Kinetochores form

M Phase 2: Metaphase

Chromosomes align at meta phase plate

M Phase 3: Anaphase

• Sister chromatids separate, move to opposite poles

• Pulled by kinetochores (proteins attached to centromeres)

• After separation, each chromatid considered to be a chromosome

M Phase 4: Telophase

• Opposite of prophase

• Chromosomes start to de-condense

• Nuclear Envelope reforms

• (New nuclei identical to parent nucleus)

M Phase: Cytokinesis

• Cytoplasmic division (2 cells, each with 1 nucleus)

• Distinct process from Mitosis, but overlaps with telophase

Cytokinesis in animal cells is called…

Cleavage furrow

Cytokinesis in Plant Cells

• Cell Plate forms (New Membrane at location of metaphase plate)

• Fuses with plasma membrane, divides daughter cells