Molecular Biology: Chromosome Structure and Function

This set covers the history, morphology, structural components, and types of prokaryotic and eukaryotic chromosomes as discussed in the lecture transcript.

Walther Flemming, Eduard Strasburger and Edouard van Beneden

Scientists who first described chromosomes between $1879-1892$ and first observed them during cell division.

Henrich Wilhelm Gottfried Waldeyer

The individual who first used the term "Chromosomes" in $1888$.

Chroma and Soma

The Greek roots for the word chromosome, where "Chroma" means colour (due to affinity for basic dyes) and "Soma" means body.

Chromatin fibers

Thin threads that compose chromosomes and undergo folding, coiling, and supercoiling during prophase.

Walter Sutton and Theodor Boveri

Scientists who discovered the chromosomal theory of inheritance in $1902$, showing that chromosomes occur in pairs with one from each parent.

Thomas Hunt Morgan

A scientist who used Drosophila (fruit flies) to suggest that genes reside inside chromosomes.

Nucleoid

The region in a prokaryote where the single circular chromosome is complexed with histone-like proteins and lacks a nuclear membrane.

Plasmids

Independent, circular, autonomously self-replicating extra-chromosomal DNA that often carries non-essential but desirable traits like antibiotic resistance.

Chromosomal Domains

The $50$ or so loops in the bacterial nucleoid that are bound to a central protein scaffold and attached to the cell membrane.

DNA gyrase (Topoisomerase II)

An enzyme necessary for unwinding coils to the right; it cuts and subsequently reconnects the DNA to facilitate protein synthesis and reproduction.

Negative supercoiling

The most common type of DNA supercoiling, which occurs to the left.

Metaphase

The phase of cell division where chromosomes are most easily observed, being very thick, short, and lined up on the equatorial plate.

Euchromatin

A type of chromatin consisting of DNA that is loose and transcriptionally active.

Heterochromatin

A type of chromatin consisting of mostly compact and inactive DNA.

Histones

Small proteins containing a high proportion of basic amino acids (arginine and lysine) that facilitate binding to negatively charged DNA molecules.

Telomere

Repetitive sequences of non-coding DNA at the ends of chromosomes that provide stability and protection, much like the plastic tip on shoe laces.

Centromere

Also called the primary constriction, it is the region where two sister chromatids are joined and where microtubules attach during metaphase.

p arm and q arm

The two sections of a chromosome divided by the centromere; "p" stands for petit (small) and "q" follows it in the alphabet.

Metacentric Chromosome

A chromosome where the centromere is located exactly at the center, resulting in arms of equal size.

Submetacentric Chromosome

A chromosome where the centromere is located off-center, creating one longer arm and often appearing "J" or "L" shaped at anaphase.

Acrocentric Chromosome

A chromosome where the centromere is close to one end, resulting in one very short arm and one very long arm.

Telocentric Chromosome

A chromosome where the centromere is at one end, resulting in only one arm and an "I" shape.

Kinetochore

The specific location within the centromere, composed of DNA and protein, where spindle fibers bind during anaphase.

Diploid

The state of having $46$ chromosomes, characteristic of human somatic (body) cells.

Haploid

The state of having $23$ chromosomes, characteristic of human sex cells.

Karyotype

A test used to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.

Idiogram

A diagrammatic representation of a karyotype where chromosomes are ordered in a series of decreasing size.

Giemsa

A chemical dye used to treat chromosomes, producing dark G-bands (G-positive) and light bands (G-negative) for identification.