Bio 150 Chapter 16: Molecular Basis for Inheritance

Vocabulary practice flashcards covering the molecular basis of inheritance, DNA structure and replication, and chromosome organization from Bio 150 Chapter 16.

Chargaff’s rules

The regularity observed in base ratios where complementary base-pairing dictates that the amount of adenine equals thymine ($A=T$) and the amount of guanine equals cytosine ($G=C$).

Antiparallel

The arrangement of the two sugar–phosphate backbones in a DNA molecule running in opposite directions to one another.

Semi-conservative replication

A mechanism of DNA replication in which parental strands separate, each functioning as a template for a complementary strand, yielding new DNA molecules composed of one old strand and one new strand.

Origin of replication

Special sites with specific sequences of nucleotides where the initiation of DNA replication begins.

Helicase

The enzyme that catalyzes unwinding by unscrewing and relaxing the DNA molecule during initiation.

Topoisomerase

The enzyme that corrects overwinding of the DNA molecule during the unwinding stage of replication.

Single strand binding stabilization proteins

Proteins that separate DNA strands and keep them separated to stabilize the replication fork.

Primase

The enzyme that catalyzes priming by adding a short RNA molecule at the beginning of the new DNA strand.

DNA-dependent DNA polymerase III

The enzyme that catalyzes elongation during DNA replication by adding nucleotides exclusively to the $3'$ end.

Leading strand

The new DNA strand that is synthesized continuously and grows in the $5'$ to $3'$ direction.

Lagging strand

The new DNA strand that undergoes discontinuous synthesis because it is antiparallel.

Okazaki’s fragments

The short segments of DNA synthesized discontinuously along the lagging strand during replication.

DNA ligase

The enzyme that links nucleotides together after RNA primers are removed and the resulting gaps are filled by DNA polymerase during termination.

Telomere

Repeats of short non-coding sequences at the end of a linear DNA molecule that delay the erosion of functional DNA after successive rounds of replication.

Telomerase

An enzyme present in animal germ cells (reproductive cells) but absent in somatic cells that functions to elongate telomeres.

Nucleosomes

The basic units of DNA packing, resembling 'beads on a string,' consisting of DNA wound around a protein core made of two copies each of four histone types (H2A, H2B, H3, and H4).

30 nM chromatin fibers

A tightly wound coil containing six nucleosomes per turn, pulled into a $30\text{ nM}$ wide cylinder by molecules of histone H1.

Looped domains

Loops formed by successive chromatin fibers attached to a non-histone protein scaffolding.

Heterochromatin

Chromatin that remains tightly condensed during interphase and is not actively transcribed.

Euchromatin

Chromatin that is less condensed during interphase, is actively transcribed, and only becomes condensed during mitosis.