Chromosome Organization and Molecular Structure – Vocabulary Flashcards

A comprehensive set of vocabulary flashcards covering key terms from the lecture on chromosome organization and molecular structure.

Chromosome

A DNA–protein complex structure that carries genetic material in cells.

Genome

The complete set of genetic material of an organism; one circular chromosome in bacteria, a full set of nuclear chromosomes in eukaryotes.

Nucleoid

Non-membrane-bound region in bacteria where the chromosomal DNA is located and contacts the cytoplasm.

Capsid

Protein coat that encloses the nucleic acid of a virus.

Viral Genome

Genetic material of a virus; may be DNA or RNA, single- or double-stranded, circular or linear.

Bacteriophage

A virus that infects bacteria; may possess sheath, base plate and tail fibers.

Loop Domain

Segment of bacterial chromosomal DNA folded into a loop, aiding ~10-fold compaction.

DNA Supercoiling

Additional twisting of the DNA double helix that further compacts bacterial chromosomes.

DNA Gyrase (Topoisomerase II)

Bacterial enzyme that introduces negative supercoils and relaxes positive supercoils using ATP.

DNA Topoisomerase I

Bacterial enzyme that relaxes negative supercoils, counteracting DNA gyrase.

Chromatin

DNA-protein complex in eukaryotic nuclei; must be highly compacted to fit in the nucleus.

Histone

Basic, positively charged protein that binds DNA; core types are H2A, H2B, H3, H4, and linker H1.

Nucleosome

146 bp of DNA wrapped 1.65 turns around a histone octamer; “bead” of chromatin.

30 nm Fiber

Higher-order structure formed by association of nucleosomes, shortened DNA another seven-fold.

Solenoid Model

Proposed regular spiral arrangement of nucleosomes in the 30 nm fiber (six per turn).

Three-Dimensional Zigzag Model

Proposed irregular 30 nm fiber with little face-to-face nucleosome contact.

Nuclear Matrix

Fibrous network inside the nucleus composed of nuclear lamina and internal matrix proteins.

Radial Loop Domain

DNA loop (25,000–200,000 bp) anchored to the nuclear matrix at SAR/MAR sites for additional compaction.

Scaffold-Attachment Region (SAR/MAR)

DNA sequence that binds the nuclear matrix, forming radial loops and influencing gene regulation.

Chromosome Territory

Discrete, non-overlapping nuclear region occupied by each interphase chromosome.

Euchromatin

Less condensed, transcriptionally active chromatin where 30 nm fibers form radial loops.

Heterochromatin

Highly compacted, transcriptionally inactive chromatin; radial loops compacted further.

Constitutive Heterochromatin

Regions always heterochromatic and permanently transcriptionally inactive (e.g., centromeres).

Facultative Heterochromatin

Regions that can switch between euchromatin and heterochromatin (e.g., Barr body).

Origin of Replication

DNA sequence where replication begins; eukaryotic chromosomes have many (≈ every 100 kb).

Centromere

Chromosomal region forming the kinetochore; essential for proper segregation during mitosis/meiosis.

Telomere

Specialized DNA sequence at each end of a linear chromosome that protects ends from degradation.

Condensin

SMC-containing protein complex that drives chromosome condensation in prophase/metaphase.

Cohesin

SMC-containing protein complex that holds sister chromatids together until anaphase.

SMC Proteins

Structural Maintenance of Chromosomes proteins that use ATP to change chromosome structure.

Repetitive Sequence

DNA sequence present in multiple copies; may be unique, moderately, or highly repetitive.

Unique (Non-repetitive) Sequence

DNA sequence occurring once or a few times per genome; includes most structural genes.

Moderately Repetitive Sequence

Sequence present hundreds to thousands of times (e.g., rRNA, histone genes, transposable elements).

Highly Repetitive Sequence

Short sequence present tens of thousands to millions of times, often in tandem arrays.

Alu Family

Primate-specific highly repetitive SINE elements dispersed throughout the human genome (~1 million copies).

Introns

Non-coding regions within eukaryotic genes; numerous and long in higher eukaryotes, rare in lower ones.

Metaphase Chromosome

Fully condensed chromosome during M phase; ~1,400 nm diameter, mostly heterochromatic.

Loop Scaffold

Protein framework (modified nuclear matrix) that retains highly compacted radial loops in metaphase.

Base Pair (bp)

Unit of length for double-stranded DNA corresponding to one paired nucleotide on each strand.