DNA’s structure depends on the way its small building blocks are assembled and paired. This lesson introduces nucleotides, the bonds that link them, and the features of the double helix.
A nucleotide consists of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. The sugar in DNA is deoxyribose; RNA contains ribose. A nucleoside is just a base attached to a sugar, without phosphate. Adding phosphate group(s) to a nucleoside produces a nucleotide.
All flashcards
What is the difference between a nucleotide and a nucleoside?
A nucleoside is a nitrogenous base attached to a sugar. A nucleotide is a nucleoside with one or more phosphate groups attached.
What does it mean for DNA strands to be antiparallel?
The two strands run in opposite directions: one runs 5′ to 3′, while the other runs 3′ to 5′.
How are adjacent nucleotides joined in a DNA strand?
A phosphodiester bond links the 5′ phosphate of one nucleotide to the 3′ hydroxyl of the next nucleotide’s sugar.
How does a ddNTP stop DNA-chain extension?
It lacks the free 3′ hydroxyl needed to attach the next nucleotide.
What is a nucleosome?
A unit of chromatin consisting of DNA wrapped around a core of histone proteins.
Quiz questions
What components make up a DNA nucleotide?Answer: A nitrogenous base, deoxyribose, and one or more phosphate groups.
In Sanger sequencing, what does reading terminated fragments from shortest to longest reveal?Answer: The base order of the newly synthesized DNA strand.
During gel electrophoresis, which direction does negatively charged DNA move?Answer: Toward the positive electrode.
What did comparisons of Neanderthal and present-day human genomes support?Answer: Interbreeding between Neanderthals and early modern humans outside Africa.
How does supercoiling help organize prokaryotic DNA?Answer: It compacts DNA in the cytoplasmic nucleoid region.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.