Cell division & heredity · Topic 14 of 17

DNA & RNA: Structure and Replication

Tap any line to see why it matters

Biology · nucleic acids

DNA is a double helix of nucleotides paired A–T and C–G; RNA is single-stranded with ribose and uracil; replication is semiconservative.

01 · Base pairingA–T · C–G (RNA: A–U)

02 · DNA vs RNARNA: ribose · single strand · U for T

03 · ReplicationNew DNA = 1 old + 1 new strand

DNA stores the genetic code; RNA carries out its instructions

Nucleotide = 5-carbon sugar + phosphate + nitrogenous base must know

Double helix: sugar–phosphate sides, base-pair rungs must know

Hydrogen bonds between bases hold the two strands together

The two strands run in opposite directions (antiparallel)

Semiconservative: each new DNA = 1 old strand + 1 new strand

Step by step

Helicase unzips the helix (breaks the hydrogen bonds)

DNA polymerase builds a new strand on each old template strand

Ligase seals gaps → 2 identical DNA molecules (in S phase)

DNA bases: A, T, C, G · RNA bases: A, U, C, G

DNA base pairs: A–T and C–G (complementary) must know

Chargaff's rule: in DNA, %A = %T and %C = %G

Strand TACGGATC → partner strand ATGCCTAG (swap A↔T, C↔G)

A = 30% → T = 30%; G + C = 40% → G = 20%, C = 20%

RNA: ribose sugar, single strand, U instead of T must know

Commonly confused

	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Two (double helix)	One
Bases	A, T, C, G	A, U, C, G
Job	Stores the genetic code	Carries out the code to make proteins

Show 3 more facts

Leading strand = continuous · lagging strand = Okazaki fragments

Purines A, G (2 rings) pair with pyrimidines C, T, U (1 ring)

Polymerase proofreads; an uncorrected error becomes a mutation

Pearl

A pairs with T, C pairs with G — and in RNA, U stands in for T.

Practice this topic, then test the whole section.

HESI and HESI A2 are registered trademarks of Elsevier. NurseSavvy is not affiliated with or endorsed by Elsevier.