DNA Replication Process and Cellular Differences

DNA replication occurs during the S phase of interphase through a semiconservative process. This mechanism preserves part of the original strand while creating a new complementary strand.

Definition: The replication fork is the point where two DNA strands are separated by helicase, allowing for new strand synthesis.

Highlight: Key enzymes in replication include topoisomerase for uncoiling, helicase for strand separation, and DNA polymerases for nucleotide addition.

The process involves three main stages: initiation at origin points, elongation with leading and lagging strand synthesis, and termination.

Vocabulary: Okazaki fragments are discontinuous DNA segments synthesized on the lagging strand during replication.

Example: Eukaryotic cells utilize multiple origin points for replication, while prokaryotic cells have just one origin point, demonstrating evolutionary adaptation to genome size and complexity.

DNA Structure and Basic Components

The fundamental structure of DNA consists of nucleotides arranged in a double helix formation. Each nucleotide contains three main components: a phosphate group at the 5' end, a deoxyribose sugar at the 3' end, and a nitrogenous base.

Definition: Nucleotides are the monomeric units of DNA, consisting of a phosphate group, deoxyribose sugar, and nitrogenous base.

Vocabulary: Purines (A & G) and Pyrimidines (T & C) are the two types of nitrogenous bases that form specific base pairs in DNA.

Highlight: Three crucial bonds maintain DNA structure: hydrogen bonds between strands, glycosidic bonds connecting bases to sugar, and phosphodiester bonds linking sugar to phosphate groups.

The chromosome structure involves DNA being tightly coiled around histones to form nucleosomes, which further organize into chromatin fibers and ultimately chromosomes.

Example: DNA directionality is determined by the deoxyribose sugar - when a strand begins with sugar, it runs from 3' to 5'.