DNA Structure, Replication and Recombination: every key term you need (+ practice quiz)
25 flashcard terms for Genetics Topic 3, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The demonstration that heritable change could be transferred by material from dead cells, which identified nucleic acid rather than protein as the genetic substance.
Chargaff's rules
The observations that adenine equals thymine and guanine equals cytosine in a genome, which the double helix immediately explained.
Double helix
Two antiparallel strands wound about a common axis with bases paired inside and the sugar-phosphate backbone outside.
Semiconservative replication
Each daughter duplex keeps one parental strand, demonstrated by following the density of labelled molecules across successive generations.
Origin of replication
A defined sequence where strand separation begins. Bacteria typically use one per chromosome while eukaryotes use many to finish in time.
Replication fork
The moving junction where the parental duplex is unwound and both new strands are made, with the two strands synthesized by different logic.
Helicase
Unwinds the duplex ahead of the fork, using nucleotide hydrolysis and generating torsional strain that must be relieved further along.
Single-strand binding protein
Coats separated strands to keep them apart and protect them from folding back or being degraded before copying.
Topoisomerase
Cuts and rejoins the backbone to release supercoiling generated by unwinding, without which the fork would seize.
Primase
Lays down a short nucleic acid primer, needed because the copying enzymes can only extend an existing end and cannot start a chain.
DNA polymerase directionality
New strands grow only in one direction, adding to the free hydroxyl end, which is why one strand is copied continuously and the other in pieces.
Leading and lagging strands
The leading strand is made in one continuous run toward the fork; the lagging strand is made backward in fragments that are later joined.
Okazaki fragment
A short piece of the lagging strand. Each is primed separately, so lagging-strand synthesis needs repeated priming and processing.
Sliding clamp
A ring that encircles the template and tethers the polymerase, greatly increasing how many bases are added before the enzyme falls off.
Proofreading activity
An exonuclease function that removes a newly added mismatched base, lowering the error rate by orders of magnitude before repair systems act.
DNA ligase
Seals the remaining break in the backbone after primers are replaced, completing both replication and many repair pathways.
Telomere
A repetitive cap on a linear chromosome end that buffers the shortening caused by the inability to prime the very end of the lagging strand.
Telomerase
An enzyme carrying its own template that extends chromosome ends. Its activity is high in germ line and stem cells and low in most somatic tissue.
Nucleosome
The basic packing unit in which a stretch of the duplex wraps around a histone core, the first stage of compaction and a barrier to enzyme access.
Chromatin remodelling
Repositioning or evicting nucleosomes using energy, changing which sequences are accessible without altering the sequence itself.
Euchromatin and heterochromatin
Loosely packed, generally accessible regions versus densely packed, generally silent ones, a distinction that can be reset during development.
Homologous recombination
Repairs a double-strand break by copying an intact homologous sequence, making it accurate but dependent on a template being present.
Holliday junction
The four-armed intermediate of strand exchange. How it is resolved decides whether flanking markers are exchanged.
Nonhomologous end joining
Rejoins broken ends directly without a template. It works at any point in the cycle but frequently loses or adds a few bases.
Gene conversion
Nonreciprocal transfer during recombination in which one allele is rewritten by the other, producing ratios that depart from the expected equal segregation.