DNA as Genetic Material and Nucleic Acid Structure

Vocabulary flashcards reviewing key terms, landmark experiments, and structural features of DNA and RNA from BIOL2202 Genetics.

Smooth (S) strain of Streptococcus pneumoniae

A bacterial strain that secretes a polysaccharide capsule protecting it from host immune systems, making it invasive and capable of causing pneumonia.

Rough (R) strain of Streptococcus pneumoniae

A bacterial strain that lacks a protective capsule, making it non-invasive and unable to cause pneumonia.

Transformation principle

The substance from dead type IIIS bacteria that converted non-virulent type IIR bacteria into virulent type IIIS bacteria, identified in Griffith's 1928 experiment.

Avery, MacLeod, & McCarty Experiment (1940s)

An experiment demonstrating that only purified DNA extract converted type IIR bacteria into type IIIS, and that treatment with DNase prevented transformation.

Bacteriophage T2

A virus composed of DNA enclosed within a protein capsid head, sheath, base plate, and tail fibers, used by Hershey and Chase to determine the genetic material.

Phosphorus-32 (${}^{32}\text{P}$)

A radioisotope used by Hershey and Chase to specifically label viral DNA, which was shown to remain inside infected E. coli cells.

Sulfur-35 (${}^{35}\text{S}$)

A radioisotope used by Hershey and Chase to specifically label viral coat proteins, which remained outside infected E. coli cells in the supernatant.

RNA Viruses

Viruses that use RNA instead of DNA as their genetic material, such as Tomato bushy stunt virus, Tobacco mosaic virus, Influenza virus, HIV, f2, and QB.

Nucleoside

A molecule consisting of a nitrogenous base covalently linked to a pentose sugar (ribose or deoxyribose) without any phosphate groups.

Nucleotide

The repeating structural subunit of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

Phosphodiester bond

A covalent linkage connecting the 5' carbon of one nucleotide sugar to the 3' carbon of another via a phosphate group, forming the sugar-phosphate backbone.

Purines

Double-ring nitrogenous bases found in nucleic acids, consisting of Adenine (A) and Guanine (G).

Pyrimidines

Single-ring nitrogenous bases found in nucleic acids, consisting of Thymine (T), Cytosine (C), and Uracil (U).

Antiparallel orientation

The arrangement of the two complementary strands of a DNA double helix running in opposite directions (one 5' to 3', the other 3' to 5').

B-DNA

The standard right-handed double helix predominant in living cells, featuring approximately 10 base pairs per complete 360° turn ($3.4\,\text{nm}$).

A-DNA

A right-handed double helix with 11 base pairs per turn that forms under low humidity conditions and helps protect bacterial DNA during severe dehydration.

Z-DNA

A left-handed double helix with 12 base pairs per turn, favored by GC-rich sequences or cytosine methylation, and involved in transcription and recombination.

X-ray diffraction of DNA

An experimental technique performed by Rosalind Franklin and Maurice Wilkins whose X-pattern photograph revealed the helical structure of DNA.

Nucleosome

A structural unit of eukaryotic chromatin consisting of a length of DNA wrapped twice around a core of histone proteins.

Stem-loop (Hairpin) structure

An RNA secondary structure formed when complementary regions fold back and base pair to form a stem, leaving non-complementary bases in an unpaired loop.