Cell Biology: Chromatin and Cell Cycle Regulation

Vocabulary flashcards covering chromatin structure, DNA compaction, chromosome types, the stages of the cell cycle, and critical checkpoints.

Chromatin

A complex of DNA and protein, approximately $60\%$ protein, that packages eukaryotic genomes into the nucleus as an active workspace.

Electrostatic Attraction in Chromatin

The force driving DNA to wrap around histones, caused by positively charged histones pulling the negatively charged phosphate backbone of DNA.

Nucleosome

The first level of DNA compaction and the base of successive coiling levels that condense chromosomes.

Heterochromatin

Tightly coiled chromatin that is transcriptionally inaccessible; it helps maintain structure and contains viral sequences.

Euchromatin

Loosely coiled chromatin that is actively transcribed.

Homologous Chromosomes

Chromosomes that carry the same genes at the same loci but may possess different alleles.

Banding Pattern

Karyotype markers reflecting similar $GC$-to-$AT$ ratios at corresponding regions to identify homologs.

Haploidy

A viable long-term cellular state found in organisms like Malaria (Plasmodium) and during part of all plant life cycles.

Mitosis Duration

Kept brief because the cell is metabolically inactive during this phase and must return to interphase quickly.

$G_1$ Phase

The stage of the cell cycle dedicated to growth and preparation for DNA replication.

$S$ Phase

The stage of the cell cycle where DNA replication occurs.

$G_2$ Phase

The stage of the cell cycle involving preparations for mitosis and organelle duplication.

Stem Cells

Undifferentiated cells that divide and differentiate into specialized cells like neurons or myoblasts (muscle cells).

Cyclin

Proteins that accumulate gradually and, at threshold concentration, activate enzymes to push the cell into the next phase.

Cyclin-dependent kinases (CDKs)

Enzymes activated by cyclins that push the cell cycle forward before the cyclin degrades.

$G_1$ Checkpoint

A scan for DNA damage occurring before replication; failure to repair results in apoptosis.

Apoptosis

Programmed cell death triggered when DNA damage is detected and cannot be repaired at a checkpoint.