Structure of DNA

Because the genetic code is nearly universal, organisms share the same codon-to-amino acid rules, making recombinant DNA tech possible.

The terminator is a distinct downstream regulatory sequence that signals RNA polymerase to stop transcription and detach.

Silent mutations alter the codon sequence without changing the translated amino acid, leaving the protein's function uncompromised.

Electrostatic hydrogen bonds form between the partially positive hydrogen atoms and partially negative oxygen or nitrogen atoms of matching bases.

Eukaryotic chromosomes are highly organized nucleoprotein complexes made of a single linear DNA molecule wound around structural histones.

A premature stop codon halts translation early, yielding an incomplete, truncated polypeptide chain that is usually non-functional.

The Watson-Crick model shows DNA as a right-handed double helix, where two complementary strands twist around a central longitudinal axis.

Enhancers are regulatory DNA sequences that bind activator proteins, interacting with the promoter to boost transcription.

Enclosing the genetic bases within the hydrophobic core protects the fragile hereditary codes from reactive molecules in the cytoplasm.

Without a functional promoter sequence, RNA polymerase cannot locate or bind the gene, shutting down transcription entirely.

DNA methyltransferases add a methyl group to the carbon-5 position of cytosine rings, a key modification for silencing gene expression.

The wider, deeper gap on the outside of the helix is the major groove, which provides easy access for sequence-specific DNA-binding proteins.

A cistron is a genetic unit defined by the cis-trans position test, matching the DNA sequence needed to build one polypeptide.

B-DNA is the standard, stable conformation adopted by native DNA molecules inside the aqueous environment of living cells.

Having fewer hydrogen bonds makes A-T rich regions easier to unzip, which is why replication origins and promoters are rich in A-T pairs.

Ribosomes serve as the structural and catalytic factories where tRNA molecules match codons to assemble amino acids into a protein.

RNA polymerase tracks along the DNA template strand to assemble ribonucleoside triphosphates into a complementary RNA molecule.

A gene includes its structural coding sequence alongside the regulatory elements required to turn its expression on or off.

With 61 codons coding for 20 amino acids, most amino acids are specified by more than one triplet codon, making the code degenerate.