Cell Cycle: Interphase and Mitosis

• The cell cycle consists of two phases: interphase and mitosis.
• Human cells take approximately 30 hours to complete the cell cycle.
• Cancer cells only take about 10 hours to complete the cell cycle, skipping phases and checkpoints, leading to a higher accumulation of mutations, and older cells accumulate more mutations.

Interphase

• The longest stage of the cell cycle, making up 90% of the cycle.
• Interphase includes the G1, S, and G2 phases.
• During G1 (Growth 1), the cell grows and prepares to replicate DNA.
• G0 phase is a dormant, non-dividing state where the cell does not expend much energy; it is a hibernation state, but cells can come back from G0.
• During the S phase, DNA replication occurs.
• During the G2 phase, the cell continues to grow, and there is a checkpoint where cells make final preparations for cell division.
• Checkpoints occur at the end of G1 and G2.

Cell Division (Mitosis)

• Makes up 10% of the cell cycle.
• One copy of replicated DNA is delivered to each of the two daughter cells.
• Cell division occurs in eukaryotes.

Binary Fission

• Occurs in prokaryotes (bacteria).
• Involves one loop of DNA and asexual reproduction.
• Prokaryotes undergo asexual reproduction through binary fission.
• Prokaryotic DNA is loosely packed.

Mitosis

• Eukaryotic cells undergo two types of division.
• Mitosis is a form of asexual reproduction involving one parent.
• Meiosis is sexual reproduction, producing sperm and eggs, and involves 46 chromosomes.

Meiosis (Sexual)

• Occurs in eukaryotes.
• Is sexual reproduction.
• Involves egg cells and sperm cells, each with 23 chromosomes.

Mitosis Process

• Prophase involves sister chromatids where one chromosome after the S phase becomes two identical chromosomes.
• Mitotic spindles connect to sister chromatids at the centromeres, and the nuclear envelope breaks down.
• Metaphase: all sister chromatids line up in the middle connected by mitotic spindles.
• Anaphase: chromosomes within sister chromatids are pulled apart by the contraction of mitotic spindles.
• Telophase: two new daughter cells form, chromosomes reach opposite poles, and the nuclear envelope reforms.
• Cytokinesis: the creation of new cells, completing the cell cycle.
• Two basic reasons for cell division are to make more cells and to grow and repair areas of injury.
• Chromosomes need to be tightly packed.
• Different energy expenditure affects different processes in the cell.

Cell Division Types

• Includes binary fission, mitosis, and meiosis.

Meiosis

• Production of gametes, which are haploid cells.
• Haploid cells include egg cells and sperm cells, each with 23 chromosomes.
• Two haploids result in a zygote.
• A zygote uses mitosis to grow.
• Diploid: a cell or nucleus containing two complete sets of chromosomes, one from each parent.
• Haploid refers to a cell containing a single set of chromosomes.
• Meiosis occurs in two stages after interphase: Meiosis I and Meiosis II.
• Each stage involves one round of cell division followed by cytokinesis.
• Meiosis involves a total of two cell divisions.
• Homologous chromosomes consist of one chromosome from each parent.
• Crossing over is the physical exchange between nonsister chromatids in each duplicated homologous pair.