Chapter 14 DNA Structure and Replication

Nucleotide Structure

A nucleotide has three parts: a 5-carbon sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base (A, T, C, G).

Chargaff's Rule

In DNA, the amount of Adenine (A) equals Thymine (T), and Guanine (G) equals Cytosine (C). This is due to complementary base pairing.

DNA Double Helix Structure

DNA is a double helix with a sugar-phosphate backbone. Strands are antiparallel and linked by hydrogen bonds between complementary bases (A-T, G-C).

RNA Structure

RNA is typically single-stranded, has a ribose sugar, and uses the base Uracil (U) instead of Thymine.

DNA vs. RNA

DNA is double-stranded, uses deoxyribose and Thymine. RNA is single-stranded, uses ribose and Uracil.

Semiconservative Replication

Each new DNA molecule consists of one original (parental) strand and one newly synthesized (daughter) strand.

Helicase Function

The enzyme that unwinds and "unzips" the DNA double helix by breaking hydrogen bonds.

Primase Function

The enzyme that synthesizes a short RNA primer to provide a starting point for DNA polymerase.

DNA Polymerase Function

The enzyme that builds the new DNA strand by adding complementary nucleotides. It also proofreads and repairs the new strand.

DNA Ligase Function

The enzyme that "glues" together DNA fragments, such as Okazaki fragments on the lagging strand.

Leading Strand Synthesis

The strand that is synthesized continuously in the 5' to 3' direction towards the replication fork.

Lagging Strand Synthesis

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

Okazaki Fragments

Short, newly synthesized DNA fragments on the lagging strand that are later joined by DNA ligase.

Prokaryotic vs. Eukaryotic Replication

Prokaryotes have one circular chromosome with one origin. Eukaryotes have multiple linear chromosomes with multiple origins (replication bubbles).

Beneficial Mutation

A mutation that improves an organism's survival (e.g., white fur in a polar bear).

Detrimental Mutation

A mutation that harms an organism, often by producing a non-functional protein.

Neutral Mutation

A mutation that has little to no effect on the organism's function or survival.

Inheritable Mutations

Only mutations that occur in the DNA of gametes (eggs or sperm) can be passed to the next generation.

Point Mutation (Substitution)

A mutation where one nucleotide is replaced by another. Often less damaging.

Frameshift Mutation

A mutation caused by an insertion or deletion of nucleotides, which shifts the reading frame and is often highly damaging.