12BIC - Unit 8: Mitosis

Diploid (2n)

A eukaryotic cell or organism containing two complete sets of chromosomes (two copies of each homologous chromosome), such as a human somatic body cell.

Haploid (n)

A eukaryotic cell or organism containing only one complete set of chromosomes, such as human gametes (sperm or oocytes).

Cell cycle

The ordered sequence of events that takes place between one cell division and the next, structurally divided into interphase, nuclear division (mitosis), and cell division (cytokinesis).

Interphase characteristics

A period of intense metabolic activity where the cell grows to normal size, produces organelles, synthesizes proteins, and replicates its DNA; chromosomes are not visible because chromatin is dispersed.

G1 phase (Gap 1)

The first stage of interphase where the cell undergoes growth and actively produces RNA, proteins, and enzymes to prepare for DNA synthesis.

S phase (Synthesis)

The phase of interphase during which DNA replication occurs, doubling the amount of DNA so that each chromosome consists of two identical sister chromatids.

G2 phase (Gap 2)

The final stage of interphase where the cell continues growing and double-checks the newly replicated DNA for any copy errors before division begins.

Chromosome structure components

A structure composed of a linear DNA molecule tightly wound around small basic proteins called histones, forming a complex called chromatin.

Chromatid

One of the two identical, parallel copies of DNA that make up a replicated chromosome, which are joined together at the centromere.

Centromere

The specialized region of a chromosome that holds two sister chromatids together and provides the site of attachment for spindle fibres.

Telomere

A protective end cap of non-coding DNA found at the tips of chromosomes that prevents the loss of vital genes during successive rounds of replication.

Karyotype autosomes vs sex chromosomes

Autosomes are chromosomes that control general metabolism and bodily characteristics, whereas sex chromosomes (X and Y) specifically control genetic gender.

Importance of mitosis

Ensures genetic stability by producing two genetically identical cells, which is essential for growth, cell replacement, tissue repair, and asexual reproduction.

Prophase structural changes

The longest stage of mitosis where chromosomes condense (become shorter and thicker), centrioles divide and move to opposite poles, spindle microtubules develop, nucleoli disappear, and the nuclear membrane disintegrates.

Metaphase structural changes

A relatively short stage where chromosomes migrate toward the equator of the cell and attach securely to the developed spindle fibres.

Kinetochores

Protein structures made on the centromere (one for each chromatid) before nuclear division that physically connect the centromere to the spindle fibres.

Anaphase structural changes

A rapid stage where centromeres split and contracting spindle fibres shorten, pulling the separated sister chromatids (now called individual chromosomes) toward opposite poles via their kinetochores.

Telophase structural changes

The final stage where chromatids reach opposite poles, uncoil and lengthen back into chromatin, spindle fibres break down, centrioles replicate, nucleoli reappear, and the nuclear membrane reforms.

Cytokinesis

The process of cell division following mitosis where the cytoplasm divides; in animal cells, the cell membrane constricts (furrows), while in plant cells, a cell plate forms.

Telomere replication problem

The DNA copying enzyme cannot run fully to the end of a linear DNA strand, meaning a small piece of non-coding telomere DNA is lost with every single cell division.

Telomerase

An enzyme that actively adds non-coding bases back onto the ends of chromosomes to keep the DNA longer and prevent loss of vital genetic data.

Cellular aging and telomeres

Fully differentiated somatic cells do not top up their telomeres; once telomeres are completely lost, cell division stops entirely and the cell enters permanent aging (senescence) or cell death.

Stem cells

Unspecialized cells capable of dividing an unlimited number of times that can either remain as stem cells or differentiate into specialized cells to replace cells and repair damaged tissues.

Potency

The biological measure of a stem cell's capacity to differentiate into other distinct specialized cell types.

Totipotent stem cells

Early embryonic stem cells (from the zygote up to the 16-cell stage) capable of producing absolutely any cell type, including placental tissues.

Pluripotent stem cells

Embryonic stem cells (from after the 16-cell stage up to day 14/15) that can differentiate into any body cell type required for embryonic development, but can no longer form the placenta.

Multipotent stem cells

Adult stem cells found in small numbers within fully developed tissues (like bone marrow, skin, and gut lining) that are limited to producing only a few specific cell types.

Hematopoietic stem cells

Multipotent adult stem cells located in the bone marrow that divide daily to generate hundreds of billions of functioning red and white blood cells.

Induced pluripotent stem cells

Differentiated adult somatic cells that are genetically altered and reprogrammed in a laboratory to behave like embryonic stem cells.

Oncogene

A mutated gene that accelerates and drives uncontrolled mitosis and cell division, ultimately leading to the formation of cancer.

Tumour

An irregular, abnormal mass of cells formed as a direct result of continuous, uncontrolled cell division.

Carcinogen

Any environmental agent (such as asbestos, tobacco smoke, heavy metals, or ionizing radiation) that damages DNA, causing mutations that increase the chances of cancerous growth.

Benign tumour

An irregular mass of cells resulting from uncontrolled division that remains confined to its original location and does not spread to other tissues.

Malignant tumour

A cancerous mass of cells that actively invades, disrupts, and destroys surrounding healthy tissues.

Metastasis

The dangerous process where cancer cells break away from a primary malignant tumour, travel through blood or lymph vessels, and establish secondary tumor growths in other parts of the body.