Chromosome Structure

Study Notes

Chromosomes are thread-like, self-replicating genetic structures within the cell nucleus.
They contain organized DNA molecules.
The term "chromosome" comes from the Greek words "chroma" (color) and "soma" (body).
E. Strasburger discovered chromosomes in 1875.
Waldeyer coined the term "chromosome" in 1888.
Human somatic cells have 46 chromosomes (or 23 pairs).
Human sex cells (gametes) have 23 chromosomes.
Chromosomes are made of tightly coiled DNA and proteins called histones.
Chromosomes are best visible during metaphase.
Chromosomes can self-duplicate and mutate.
Chromosomes are composed of DNA, RNA, and proteins
Chromosomes have different shapes

Telomere: Located at the tips of chromosomes.
Centromere: The middle region of a chromosome, where spindle fibers attach.
P arm: The short arm of the chromosome.
Q arm: The long arm of the chromosome.
Chromatid: One of the two identical halves of a chromosome during cell division.
Chromatin: A complex of DNA and protein that packages chromosomes in the eukaryotic nucleus.

Acrocentric: Very small P arm; centromere close to the end of the chromosome.
Telocentric: No P arm; centromere at the very end of the chromosome.
Submetacentric: P arm slightly smaller than Q arm; centromere near the center.
Metacentric: P and Q arms are equal length; centromere in the exact middle.

The cell cycle is an ordered series of events from the formation of a cell to its own division.
The cell cycle has two main parts: Interphase and M phase (mitotic phase).

Interphase is the longest phase of the cell cycle.
Interphase has three stages: G1, S, and G2 phases.
In the G1 phase, the cell grows, and organelles and cytoplasmic components duplicate.
In the S phase, DNA replicates.
In the G2 phase, cell growth continues, and the cell prepares for division.

M phase is where the cell actually divides.
M phase involves two processes : Mitosis (nuclear division) and Cytokinesis (cytoplasmic division).

Cell division is the final step of the cell cycle, resulting in two or more daughter cells.
Two main types of cell division are mitosis and meiosis.

Mitosis is the division of somatic (body) cells to produce two identical daughter cells.
Mitosis has four stages: Prophase, Metaphase, Anaphase, and Telophase.

Cytokinesis is the division of the cytoplasm.
A contractile ring and cleavage furrow form, dividing the cytoplasm into two daughter cells.
Two identical daughter cells result.