Mechanisms of Genetic Inheritance: DNA Structure and Synthesis

Nucleotide

The basic building block of nucleic acids, consisting of a phosphate group, pentose sugar, and nitrogenous base.

Phosphate Group

Part of a nucleotide that is negatively charged and attached to the 5' carbon of the sugar.

Deoxyribose

The 5-carbon sugar found in DNA, which lacks an oxygen atom at the 2' position.

Ribose

The 5-carbon sugar found in RNA, which has an -OH group on the 2' position.

Purines

Nitrogenous bases with a double-ring structure, including adenine (A) and guanine (G).

Pyrimidines

Nitrogenous bases with a single-ring structure, including cytosine (C), thymine (T), and uracil (U).

Antiparallel

Describes the two strands of DNA running in opposite directions, one 5' to 3' and the other 3' to 5'.

Covalent Bonds

Strong chemical bonds that form the backbone of the DNA strand, connecting the sugar of one nucleotide to the phosphate of the next.

Hydrogen Bonds

Weak interactions between nitrogenous bases that hold the two strands of DNA together.

Chargaff's Rules

States that in any DNA sample, the amount of adenine equals thymine, and guanine equals cytosine (i.e., %A = %T and %G = %C).

Semiconservative Replication

The process by which DNA is replicated, producing two molecules with one original strand and one newly synthesized strand.

Topoisomerase

An enzyme that relaxes supercoiling ahead of the replication fork during DNA replication.

Helicase

An enzyme that unzips the double helix by breaking hydrogen bonds between bases during DNA replication.

Primase

An enzyme that synthesizes a short RNA primer to provide a 3' starting point for DNA polymerase.

DNA Polymerase III

The main enzyme responsible for adding nucleotides to the 3' end of a growing DNA strand.

DNA Polymerase I

An enzyme that removes RNA primers and replaces them with DNA nucleotides during DNA replication.

Ligase

An enzyme that joins the sugar-phosphate backbones of Okazaki fragments to create a continuous DNA strand.

Leading Strand

The strand of DNA that is synthesized continuously toward the replication fork during DNA replication.

Lagging Strand

The strand of DNA that is synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.

Origins of Replication

Specific sequences where DNA replication begins, leading to the formation of replication bubbles.

Prokaryotes

Organisms with a single, circular chromosome and typically one origin of replication.

Eukaryotes

Organisms with multiple linear chromosomes and multiple origins of replication per chromosome.

Telomeres

Protective caps of repetitive DNA at the ends of linear chromosomes that prevent loss of essential information during replication.

Okazaki Fragments

Short segments of DNA newly synthesized on the lagging strand during replication, each requiring a separate RNA primer.

Directionality in DNA Synthesis

DNA Polymerase can only add nucleotides to the 3' end of a growing DNA strand, leading to synthesis in a 5' to 3' direction.

Uracil (U)

A nitrogenous base found in RNA, replacing thymine (T) from DNA; important in the formation of RNA primers during replication.