Chapter 15 - DNA, RNA, and DNA Replication

Topoisomerase

________ enzymes create transient nicks in the sugar- phosphate backbone of DNA to alleviate supercoiling and subsequently seal these nicks.

UV radiation

________ can induce the expression of genes involved in the formation of melanin in humans.

RNA

________ is normally single- stranded (in mRNAs and microRNAs), but it may fold to form three- dimensional structures in ribosomal rRNAs and tRNAs.

DNA polymerase

________ reads the original strand in the 3′ to 5′ direction on one strand of the double helix and can add new nucleotides in the 5′ to 3′ direction constantly.

deoxyribose

The 2′ carbon in ________ is bonded by a hydrogen atom, whereas the 2′ carbon in ribose is attached by a hydroxyl- (OH) group.

Purines

________ have a double- ringed structure, but pyrimidines have a single- ringed structure, hence the breadth of the double helix remains constant.

DNA

________ is a double helix with two antiparallel strands.

Phenotypic plasticity

________ refers to the ability of the same genotypes to create distinct phenotypes in response to diverse environmental variables.

Nonnuclear inheritance

________ involves genes that are found in the mitochondria or chloroplasts and can only be transmitted from the mother.

RNA

In living creatures, nucleic acids, such as DNA and ________, are the bearers of genetic information.

purine

A(n) ________ on one strand is always followed by a pyrimidine on the opposing strand.

DNA polymerase

________ adds new nucleotides in the 5′ to 3′ orientation, always attaching the new nucleotide's 5′ phosphate to the 3′ hydroxyl on the developing nucleotide strand.