Biology - Chapter 14 - DNA: The Genetic Material

A double stranded, helical molecule.

Components of DNA

A five-carbon sugar.

A component of DNA

A component of DNA; One of four bases: _____ ____ _____ & ______.

Single carbon ring (T and C)

Double carbon ring (G and A)

Watson and Crick used numerous sources of data to build models of DNA. The following features were incorporated into their models: 1. Single-ringed T was hudrogen bonded with double ringed A, and single-ringed C was bonded with double ringed G, along the entire length of the molecule. Thus the basis for copying is ___________. a. the backbone was made of chains of sugar-phosphate linkages. b. the molecule was double stranded; looked like a ladder with a twist to form a double helix. 2. The sequence of base pairs in a nucleotide strand is different from one species to the next.

A specific sequence of nucleotides where replication begins. the two strands of the double helix unwind at one "origin" in viral and bacterial cells or many origins in eukaryotic cells; "initiation site". *semi-conservative - half is old, half is new.

1. Unwinding the Duplex: Initiator proteins bind to the origin to open the helix. 2. Building a Primer: Since DNA polymerase cannot link the first nucleotides in a newly synthesized strand, primase constructs a "temporary" RNA primer to avoid errors. 3. Assembling Complementary Strands: DNA polymerase binds to the replication fork (site where helix is unzipping and growing) and adds nucleotides to the 3' end (the end with an OH- group attached to carbon #3). 4. Direction of Replication: The growing strand proceeds bidirectionally, in the 5' to 3' direction. a. The leading (continuous) strand: Elongates toward the replication fork; built by adding nucleotides continuously to it's growing 3' end. b. The Lagging (discontinuous) strand: Elongates away from the replication fork; synthesized discontinuously as a series of short segments that are later connected by DNA ligase. [loops. ligase pastes pieces together only on lagging side.]

Open and unwind the DNA double helix. protein/enzyme involved in DNA replication.

Synthesize RNA primers. protein/enzyme involved in DNA replication.

Assemble new complementary strands protein/enzyme involved in DNA replication.

Join discontinuous segments protein/enzyme involved in DNA replication.