Cell Cycle: Prokaryotic vs Eukaryotic

• The cell cycle is the sequence of activities from one cell division to the next, enabling asexual reproduction where offspring come from a single parent.

Prokaryotic Cell Cycle

• Consists of growth and DNA replication.
• Followed by binary fission.
• Results in two cells with identical DNA.

Eukaryotic Cell Cycle

• Consists of interphase and cell division.
• Interphase involves cell growth and DNA replication.
• Divided into G1, S, and G2 phases.
• During G1, the cell grows and gathers materials for division.
• DNA synthesis occurs in the S phase.
• Growth completes in the G2 phase.
• Cells can enter the G0 phase instead of the S phase to differentiate.
• During cell division, cells duplicate asexually via mitosis and cytokinesis for tissue maintenance and repair.
• Cells in ovaries and testes duplicate via meiosis to form genetically unique gametes for sexual reproduction.

DNA Organization in Eukaryotic Cells

• Eukaryotic chromosomes are linear DNA molecules bound to proteins, tightly coiled.
• Chromosomes include telomeres for stabilization.
• Include a centromere to join replicated DNA helices.
• Duplicated chromosomes form identical sister chromatids that separate into independent chromosomes.
• Eukaryotic chromosomes typically occur in homologous pairs with similar genetic information.
• Cells with paired chromosomes are diploid.
• Those with single chromosomes are haploid.
• Cell chromosomes include both autosomes and sex chromosomes.

Mitotic Cell Division

• Interphase includes chromosome duplication, forming sister chromatids.
• The four stages of mitosis are prophase, metaphase, anaphase, and telophase, followed by cytokinesis.
• During prophase, chromosomes condense, kinetochores attach to spindle microtubules, and the nuclear membrane breaks down.
• During metaphase, sister chromatids move to the cell's equator.
• During anaphase, sister chromatids separate and are pulled to opposite poles along spindle microtubules.
• During telophase, chromosomes uncoil and nuclear envelopes reform around each nucleus.
• During cytokinesis, cytoplasm divides via microfilaments (animal cells) or vesicle fusion (plant cells).

Cell Cycle Control

• Complex protein interactions drive the cell cycle.
• Major checkpoints: G1 to S, G2 to mitosis, and metaphase to anaphase.

Sexual Reproduction

• Mutations create genetic variability, forming alleles that cause structural and functional differences.
• Sexual reproduction combines parental alleles uniquely to improve survival and reproduction.

Meiotic Cell Division

• Meiosis produces haploid cells by separating homologous chromosomes.
• Interphase includes chromosome duplication, followed by meiosis I and meiosis II, resulting in four haploid cells.
• During prophase I, homologous duplicated chromosomes pair and crossing over occurs.
• During metaphase I, paired homologous chromosomes align along the equator.
• During anaphase I, paired chromosomes separate and move to opposite poles.
• During telophase I, new nuclei form, creating haploid daughter cells.
• Meiosis II includes prophase II where nuclear membranes break down.
• During metaphase II, chromatids move to the equator.
• During anaphase II, chromatids separate and move to opposite poles.
• During telophase II, nuclear membranes reform, producing four haploid nuclei, followed by cytokinesis.

Mitotic and Meiotic Cell Division in Eukaryotic Life Cycles

• Eukaryotic life cycles include fertilization, forming a diploid cell.
• Meiotic cell division, creating haploid cells.
• Growth of multicellular bodies or asexual reproduction.
• Proportion of time in each stage varies by species.
• Haploid life cycles predominantly involve haploid cells.
• Diploid life cycles predominantly involve diploid cells.
• Alternation of generations life cycles include both diploid and haploid multicellular stages.

Meiosis and Sexual Reproduction

• Genetic variability arises from the shuffling of homologous chromosomes during metaphase.
• Crossing over during prophase I.
• And fusion of gametes during fertilization.

Female Cell Division

• In females, the 4 cells from cell division will undergo oogenesis and form eggs (oocytes).