4 DNA Structure and Replication Free Online FlashCards

What are DNA nucleotides made of, and how do they connect?

Each nucleotide contains deoxyribose sugar, a phosphate group, and one base. Nucleotides connect through phosphodiester bonds to form the sugar–phosphate backbone.

Which bases pair in DNA?

Adenine pairs with thymine, and guanine pairs with cytosine. These specific pairings are held together by hydrogen bonds.

What does it mean that DNA strands are antiparallel?

The strands run in opposite orientations: one is 5′ to 3′ and the other is 3′ to 5′.

How is DNA commonly organized in bacteria and archaea?

Bacteria and archaea keep DNA in a nucleoid, not a membrane-bound nucleus. Many have a main circular chromosome and may also carry plasmids.

What is a nucleosome?

Eukaryotic DNA wraps around histone proteins to form nucleosomes, the basic units of chromatin. A nucleosome core contains about 147 base pairs of DNA.

What does semiconservative DNA replication produce?

Each daughter DNA double helix contains one original strand and one newly synthesized strand.

What forms when DNA opens at a replication origin?

Replication begins at origins, where DNA opens into a bubble with two forks that typically move in opposite directions. Eukaryotic chromosomes use many origins.

What does helicase do at a replication fork?

Helicase separates the DNA strands by disrupting the interactions between paired bases.

What is the role of single-strand DNA-binding proteins?

Single-strand DNA-binding proteins bind exposed DNA strands and keep them from re-pairing.

How do topoisomerases help replication proceed?

Topoisomerases temporarily cut and rejoin DNA to relieve the twisting strain that builds up ahead of a replication fork.

Why does DNA synthesis need a primer?

DNA polymerase extends DNA only in the 5′ to 3′ direction and needs a primer. Primase makes RNA primers to provide a starting point.

How do leading- and lagging-strand synthesis differ?

The leading strand is synthesized continuously in the direction the fork advances. The lagging strand is synthesized discontinuously away from the advancing fork.