Structure of DNA

An N-glycosidic bond connects the 1' carbon of the pentose sugar to the nitrogen atom at position 1 in pyrimidines or position 9 in purines.

Exons are the coding segments of a gene that remain in the mature mRNA transcript after splicing, carrying the blueprint for translation.

The B-DNA helix has a pitch of 3.4 nm and a base-pair step of 0.34 nm, accommodating roughly 10 base pairs per full turn.

By convention, the coding strand is written 5' to 3' because the ribosome reads mRNA 5' to 3' to build a protein from its N- to C-terminus.

Each phosphate group in the backbone retains a negative charge at physiological pH by releasing a hydrogen ion (H+), acting as an acid.

Inserting or deleting a base shifts the triplet reading frame downstream, completely altering the remaining amino acid sequence.

The nucleosome is the primary structural unit of chromatin, packing a 147-base-pair segment of DNA around a histone octamer core.

The non-template strand matches the mRNA transcript sequence exactly (except that DNA has T where RNA has U), earning it the name "coding strand."

The flat base pairs stack horizontally inside the core of the helix, resembling the sequential steps of a spiral staircase.

A nonsense mutation introduces a premature stop signal (UAA, UAG, or UGA), halting translation and yielding a truncated protein.

Placing the charged, polar groups on the outside allows DNA to interact favorably with the watery environment of the nucleoplasm.

The promoter is a specific upstream nucleotide sequence that signals the transcription machinery where to start making RNA.

A missense mutation alters a single nucleotide, changing a codon so that it incorporates a different amino acid into the protein.

Hydrogen bonds are weak non-covalent interactions, allowing the twin strands to unzip easily when driven by specialized enzymes.

Pleiotropy happens when a single gene codes for a protein used in multiple tissues, meaning a mutation can cause widespread symptoms.

If A=30%, then T=30%, totaling 60%. The remaining 40% is split equally between Guanine (20%) and Cytosine (20%).

The glycosidic bonds do not project directly opposite one another, making the spaces between the backbones unequal around the cylinder.

Refined by Beadle and Tatum, and later updated to "one gene-one polypeptide," this concept binds a genetic locus to a single protein product.

The hydrophilic sugar-phosphate backbones face the aqueous exterior, while the nitrogenous bases point inward to hide from water and form pairs.