Chapter 16

A covalent bond forms between the carbon at the 3' position of a nucleotide and the phosphate group at the 5' position of the next nucleotide.

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Nucleotides are composed of a pentose sugar, a nitrogenous base, and a phosphate group.

It untwists the double helix and separates the two DNA strands. By pulling apart and untwisting the DNA strands, helicase makes them available for replication.

Each new double helix consists of one old and one new strand.

nucleotide excision repair In nucleotide excision repair, a section of DNA containing the damage is removed, and the gap is then filled in and completed by DNA polymerase and DNA ligase.

telomeres Telomeres consist of many copies of a short DNA sequence that is bound by specific proteins.

DNA and proteins Long DNA molecules are associated with proteins that allow DNA to coil and pack.

It exists as chromatin and is unavailable for gene expression. Chromatin is the term for the loosely coiled DNA observed in cells during interphase. Even during interphase, however, parts of the chromosome may still be rather tightly coiled and packed.

DNA polymerase

Primers are short sequences that allow the initiation of DNA synthesis. When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.

Phosphate groups The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis

Primase This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.

They are formed on the lagging strand of DNA. While DNA is synthesized continuously on the leading strand, Okazaki fragments are formed on the lagging strand because DNA synthesis always proceeds in the 5' to 3' direction.