Biology Chapter 2 summary

Cell Types and Cycle

• Diploid (2n) cells contain two copies of each chromosome; haploid (n) cells have one copy.
• The cell cycle comprises five stages: G1, S, G2, M, and G0.
• G1 stage involves cell growth and organelle production, preparing for DNA synthesis.
• S stage is where DNA replication occurs, forming sister chromatids held at the centromere.
• G2 stage includes further cell growth and organelle replication, with quality control before mitosis.
• M stage encompasses mitosis and cytokinesis, resulting in two identical diploid daughter cells.
• G0 stage is a non-dividing phase where cells perform regular functions.
• p53 plays a critical role in cell cycle checkpoints, particularly G1 to S and G2 to M.
• Cyclins and cyclin-dependent kinases (CDKs) regulate progression through the cell cycle.

Mitosis

• Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase.
• In prophase, chromosomes condense, the nuclear membrane dissolves, and centriole migration occurs.
• Metaphase features chromosomes aligning along the metaphase plate.
• Anaphase involves separation of sister chromatids to opposite poles.
• Telophase sees the reformation of the nuclear membrane and division of cytosol and organelles during cytokinesis.

Meiosis

• Meiosis occurs in gametocytes and results in four haploid gametes.
• It involves one round of replication followed by two divisions: meiosis I and II.
• Prophase I features synapsis, where homologues intertwine, forming tetrads.
• Crossing over during prophase I provides genetic diversity, following Mendel’s second law.
• In metaphase I, homologous chromosomes align on the metaphase plate; in anaphase I, they are pulled apart.
• Meiosis II resembles mitosis, separating sister chromatids.

Reproductive System

• Human biological sex is determined by the 23rd chromosome pair: XX for females, XY for males.
• X-linked mutations can lead to sex-linked disorders, more commonly affecting males due to hemizygosity.
• The Y chromosome contains the SRY gene, which differentiates gonads into testes.
• Sperm develop in the seminiferous tubules of the testes, nourished by Sertoli cells.
• Leydig cells produce testosterone, essential for male secondary sex characteristics.
• Sperm mature in the epididymis and are transported through the reproductive tract during ejaculation.
• Seminal vesicles and the prostate gland contribute fluids that nourish and alkalinize semen during ejaculation.

Spermatogenesis

• In spermatogenesis, a spermatogonium yields four haploid sperm.
• Germ cells transition from primary spermatocytes to secondary spermatocytes after meiosis I, and to spermatids after meiosis II.
• After maturation, spermatozoa have a head (containing genetic material and acrosome), midpiece (ATP generation), and flagellum (motility).

Oogenesis

• Oogenesis occurs in the ovaries, producing one ovum and polar bodies from an oogonium.
• At birth, primary oocytes are arrested in prophase I and later mature into secondary oocytes, halted at metaphase II until fertilization.
• Zona pellucida and corona radiata protect and support the oocyte during fertilization.
• Hormones regulating the reproductive cycle include GnRH, FSH, and LH, influencing both male and female reproductive functions.

Menstrual Cycle

• The menstrual cycle involves a periodic endometrial lining growth and shedding.
• Follicular phase stimulated by GnRH leads to FSH and LH secretion, promoting follicle development.
• Ovulation occurs due to an LH surge triggered by elevated estrogen levels.
• In the luteal phase, the corpus luteum secretes progesterone, sustaining the uterine lining.
• Menstruation happens if fertilization does not occur, leading to a drop in estrogen and progesterone.

Menopause

• Menopause typically occurs between ages 45 and 55, signifying the end of reproductive capability.
• Ovarian hormone production ceases, leading to an increase in FSH and LH levels.
• Accompanying changes include hot flashes, bloating, headaches, and mood swings.

Explore the fundamental concepts of the cell cycle, including diploid and haploid cells, interphase stages such as G1, S, and G2, and the crucial processes that take place during each phase. Understand how cells prepare for division and the importance of the restriction point in maintaining DNA integrity.