Module 9: Cell Division - Mitosis vs. Meiosis Part 1

Terminology and concepts related to eukaryotic cell structures, chromosome types, cell cycle phases, and the regulatory signals governing cell division.

Nucleus

A prominent structure about $5 \mu\text{m}$ in diameter that stores genetic material and governs the characteristics and metabolism of a cell.

Chromatin

A combination of DNA and associated proteins found in the nucleus that undergoes coiling and condenses into chromosomes.

Nuclear envelope

A double membrane that separates the nucleus from the cytoplasm.

Nuclear pores

Openings in the nuclear envelope that permit the transport of protein and ribosomal subunits.

Nucleoplasm

The semifluid medium found within the nucleus.

Nucleolus

The specific region within the nucleus where ribosomal RNA (rRNA) is made.

Histones

An octamer of proteins that DNA wraps around twice to form a nucleosome.

Euchromatin

Areas of chromatin where nucleosomes are less condensed and activity, such as gene transcription, is more active.

Heterochromatin

Areas of chromatin where nucleosomes are more condensed and activity is less active.

Haploid ($1n$)

Cells that have only one of each type of chromosome, which is half the diploid number (e.g., $23$ in human eggs or sperm).

Diploid ($2n$)

Cells that have two (a pair) of each type of chromosome, such as human body cells which have $46$ in $23$ pairs.

Polyploidy

A condition where cells have more than one homologous copy of each chromosome (e.g., strawberry cells are octoploid).

Somatic cells

Body cells that continue to undergo cell division even in an adult, such as blood, skin, and epithelial cells.

Apoptosis

Programmed cell death that removes unwanted tissue during development and plays an important role in preventing cancer.

Cell cycle

The orderly sequence of stages occurring between the time a cell divides and the time the resulting daughter cells also divide.

Interphase

The stage of the cell cycle consisting of $G_1, S$, and $G_2$, which lasts about $20$ hours or $90\%$ of the cycle in mammalian cells.

$G_1$ Phase

The growth stage where the cell doubles its organelles and accumulates material for DNA synthesis.

$G_0$ Phase

A state where cells pause and carry out normal functions but do not prepare to divide, such as nerve and muscle cells.

$S$ Phase

The stage of DNA Replication where each chromosome goes from one DNA molecule (chromatid) to two DNA molecules (sister chromatids).

Mitotic spindle

A structure formed by two centrosomes that coordinates the movement of chromosomes during cell division.

$G_2$ Phase

The Growth and Prep to Divide stage where proteins for cell division are synthesized and centrosome duplication finishes.

Mitosis

The division of the nucleus involving four stages: Prophase, Metaphase, Anaphase, and Telophase.

Cytokinesis

The division of the cytoplasm that follows mitosis, resulting in two identical daughter cells.

Proto-oncogenes

Genes that encode proteins to promote the cell cycle and prevent apoptosis; they are likened to the "gas pedal" of a car.

Oncogenes

Cancer-causing genes that result from the mutation of proto-oncogenes.

Tumor suppressor genes

Genes that encode proteins to stop the cell cycle and promote apoptosis; they act like the "brakes" of a car.

p53

A tumor suppressor gene that stops the cell cycle at the first checkpoint if DNA damage is found.

Growth factors

External signals that set into motion the events associated with entering the cell cycle.