AP BIOLOGY

Detailed explanation-1: -Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between G-C and A-T base pairs. Duplication of the genetic information occurs by the use of one DNA strand as a template for formation of a complementary strand.

Detailed explanation-2: -The double helix describes the appearance of double-stranded DNA, which is composed of two linear strands that run opposite to each other, or anti-parallel, and twist together. Each DNA strand within the double helix is a long, linear molecule made of smaller units called nucleotides that form a chain.

Detailed explanation-3: -Watson and Crick correctly proposed that DNA is made up of two strands that are twisted around each other to form a right-handed helix. Two strands of nucleotides are held together by hydrogen bonds that form between pairs of nitrogenous bases. The sugar and phosphate “backbone” forms the outside of the helix.

Detailed explanation-4: -The double-helix shape allows for DNA replication and protein synthesis to occur. In these processes, the twisted DNA unwinds and opens to allow a copy of the DNA to be made. In DNA replication, the double helix unwinds and each separated strand is used to synthesize a new strand.

Detailed explanation-5: -RNA nucleotides contain the nitrogenous bases adenine, cytosine, and guanine. However, they do not contain thymine, which is instead replaced by uracil, symbolized by a “U.” RNA exists as a single-stranded molecule rather than a double-stranded helix.