DNA Structure, Replication, and Gene Mutations

Flashcards covering the history of DNA discovery, its molecular structure, the process of semi-conservative replication, and various types of gene mutations.

Frederick Griffith

Scientist who in $1928$ demonstrated bacterial transformation while searching for a pneumonia vaccine using Streptococcus pneumoniae.

S strain

A shiny, deadly colony of Streptococcus pneumoniae characterized by the presence of a mucus coat.

R strain

A rough, non-deadly colony of Streptococcus pneumoniae that lacks a mucus coat.

Alfred Hershey and Martha Chase

Scientists who in $1952$ used bacteriophages and radioactive labeling to determine that nucleotides, not proteins, were the carriers of genetic information.

Radioactive Phosphorus ($P$)

The substance used by Hershey and Chase to label phage DNA in their first experiment, which was later found inside the infected bacteria.

Radioactive Sulfur ($S$)

The substance used by Hershey and Chase to label phage protein capsids in their second experiment, which remained in the liquid outside the bacteria.

Chargaff’s rules

Developed by Erwin Chargaff in the late $1940\text{s}$, stating that the proportion of $C$ to $G$ and $A$ to $T$ is constant across life, though proportions vary by species.

Rosalind Franklin

A scientist who used X-ray diffraction in $1952$ to produce Image 51, revealing the two strands and diameter of the DNA molecule.

Purine bases

A category of nitrogenous bases in DNA that includes Adenine ($A$) and Guanine ($G$).

Pyrimidine bases

A category of nitrogenous bases in DNA that includes Thymine ($T$) and Cytosine ($C$).

Double helix

The spiral staircase shape of DNA consisting of two nucleotide strands with a sugar-phosphate backbone held together by hydrogen bonds.

Complementary base pairing

The specific pairing of nitrogenous bases in DNA where $A$ pairs with $T$ and $G$ pairs with $C$.

Semi-conservative DNA replication

The model of replication supported by Meselson and Stahl where the parent molecule unwinds and each original strand acts as a template for a new daughter strand.

Matthew Meselson and Franklin Stahl

Scientists who confirmed the semiconservative model of DNA replication using heavy and light isotopes of nitrogen.

Helicase

The enzyme that binds to the origin of replication to unwind and open the DNA helix.

Topoisomerase

An enzyme that prevents supercoiling of the DNA strands during the unwinding process.

Single stranded binding proteins

Proteins that keep the separated DNA strands from rejoining so the bases are exposed for replication.

Primase

An enzyme that adds RNA primers to both DNA strands to provide a starting point for DNA Polymerase.

DNA Polymerase

Enzyme that catalyzes covalent bonds between phosphates and sugars and adds nucleotides only to the $3'$ end, running in a $5'$ to $3'$ direction.

DNA ligase

The enzyme responsible for hooking the ends of old and new strands together and connecting Okazaki fragments.

Leading strand

The DNA strand that is built continuously following a single primer.

Lagging strand

The DNA strand that is built in pieces called Okazaki fragments using multiple primers.

Okazaki fragments

The short pieces of DNA synthesized on the lagging strand that are later connected by DNA ligase.

Point Mutations

Genetic mistakes involving base-pair substitutions that may or may prevented a change in the codon or protein.

Frame Shift Mutations

Mutations caused by insertions or deletions that change the way tRNA reads the three-base codons, altering the resulting amino acids.

Average mutation rate

Estimated to be approximately $2.5 \times 10^{-8}$ mutations per nucleotide site, or $175$ mutations per diploid genome per generation.

Transposons

Also known as "jumping genes," these are pieces of DNA such as L1 factors that self-insert into the genome; they make up as much as $17\text{\%}$ of the human genome.

Ionizing radiation

A type of mutagen, such as X-rays, that causes direct damage to the DNA molecule.

Nonionizing radiation

A mutagen, such as UV light, that energizes cells which in turn cause damage to DNA.