DNA Structure and Analysis

Comprehensive vocabulary flashcards covering the chemical discovery, physical structure, conformations, RNA types, and analytical techniques of DNA and RNA from Chapter 10 lectures.

Genetic Material

The molecular substance responsible for inheritance that controls the form and characteristics of an individual when physically passed to offspring.

Central Dogma

The core principle of molecular genetics stating that DNA makes RNA through transcription, which then makes proteins through translation.

Friedrich Miescher

The Swiss chemist and biologist who in 1869 isolated an acidic, phosphorus-rich substance from the nuclei of white blood cells in pus, naming it nuclein.

Nuclein

The phosphorus-containing substance extracted from white blood cell nuclei by Friedrich Miescher in 1869, later recognized as nucleic acid.

Transforming Principle

The term coined during Frederick Griffith's 1928 experiment for the substance from heat-killed pathogenic bacteria that stably transforms non-pathogenic bacteria into virulent ones.

Avery, MacLeod, and McCarty Experiment

The 1944 study using enzymatic destruction (DNase, RNase, and protease) of IIIS bacterial filtrate to demonstrate that DNA is the active transforming factor.

Hershey-Chase Experiment

The 1952 study using radioactive isotopes $^{32}\text{P}$ to label DNA and $^{35}\text{S}$ to label protein, proving that T2 bacteriophage injects DNA into Escherichia coli during infection.

Endosymbiont Theory Evidence for DNA

The indirect evidence for DNA as genetic material based on the presence of DNA in mitochondria and chloroplasts, which perform genetic functions.

Tetranucleotide Theory

An early hypothesis proposed by Phoebus Aaron Levene asserting that DNA consisted of repeating four-base units in a fixed sequence, leading scientists to falsely believe DNA was too simple to store genetic information.

Chargaff's Rules

The biochemical findings by Erwin Chargaff stating that DNA base composition varies between species, and that within a species, the amount of Adenine equals Thymine ($A = T$) and Guanine equals Cytosine ($G = C$).

Primary Structure of Nucleic Acids

The linear sequence of nucleotides linked together by covalent bonds in a single polynucleotide chain.

Nucleotide

The basic repeating subunit of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups attached at the $C\text{-}5'$ position.

Nucleoside

A molecule composed solely of a nitrogenous base covalently bound to a pentose sugar, lacking a phosphate group.

Purines

A class of nitrogenous bases containing a double-ring structure, which includes Adenine (A) and Guanine (G).

Pyrimidines

A class of nitrogenous bases containing a single-ring structure, which includes Cytosine (C), Thymine (T in DNA), and Uracil (U in RNA).

Ribose

The five-carbon pentose sugar found in RNA, characterized by having a hydroxyl group ($\text{-OH}$) attached to its $2'$ carbon atom.

2-Deoxyribose

The five-carbon pentose sugar found in DNA, characterized by having a hydrogen atom ($\text{-H}$) instead of a hydroxyl group on its $2'$ carbon atom.

Phosphodiester Bond

The covalent linkage that joins the $C\text{-}5'$ phosphate group of one nucleotide to the $C\text{-}3'$ hydroxyl group of the adjacent sugar in a polynucleotide chain.

5' to 3' Directionality

The chemical polarity of a nucleic acid strand determined by a free phosphate group at the $5'$ end and a free hydroxyl group at the $3'$ end, along which new nucleotides are added.

Rosalind Franklin

The scientist who conducted X-ray crystallography on DNA in 1952, producing X-ray diffraction images that revealed a helical structure with a $3.4\,\text{\AA}$ periodicity.

Watson-Crick Model

The secondary structure model of DNA proposed in 1953, describing it as a right-handed double helix with antiparallel sugar-phosphate backbones and complementary base pairs.

Antiparallel Strands

The arrangement of the two polynucleotide chains in a DNA double helix, running in opposite $5' \rightarrow 3'$ directions relative to one another.

Major Groove

The larger of the two alternating spiral spaces along the DNA double helix, where base pairs are more exposed and accessible for sequence-specific protein binding such as transcription factors.

Minor Groove

The smaller alternating spiral space along the DNA double helix, primarily involved in sequence-independent protein interactions such as histone binding.

B-DNA

The standard right-handed double-helical conformation of DNA observed under aqueous, low-salt conditions, considered the biologically prevalent form.

A-DNA

A right-handed double helix conformation of DNA that is more compact than B-DNA, occurring under high-salt or dehydration conditions.

Z-DNA

A left-handed double helix conformation of DNA characterized by a zig-zag sugar-phosphate backbone, formed transiently during biological activity or under negative supercoiling.

Messenger RNA (mRNA)

The class of single-stranded RNA that serves as a short-lived template carrying genetic code from DNA to ribosomes for protein synthesis.

Ribosomal RNA (rRNA)

The most abundant class of RNA (comprising approximately $80\%$ of total cellular RNA) that serves as structural and catalytic components of ribosomes.

Transfer RNA (tRNA)

The class of RNA (comprising about $15\%$ of cellular RNA) that adapts genetic code into amino acids by delivering specific amino acids to the ribosome during translation.

Svedberg Coefficient (S)

A unit measuring sedimentation rate during centrifugation, influenced by a molecule's mass, shape, and density rather than linear molecular weight alone.

Reverse Transcriptase

An RNA-dependent DNA polymerase enzyme used by retroviruses to synthesize complementary single-stranded DNA from an RNA template.

Retrovirus

A class of RNA viruses, such as HIV, that replicates by converting its single-stranded RNA genome into a DNA intermediate using reverse transcriptase.

Hyperchromic Shift

The increase in UV light absorption at $260\,\text{nm}$ that occurs when double-stranded DNA denatures into single strands upon heating.

Melting Temperature (T_m)

The specific temperature at which $50\%$ of double-stranded DNA molecules in a sample become denatured into single strands.

Molecular Hybridization

The analytical technique of reannealing single-stranded nucleic acids from the same or different sources based on complementary base pairing.

Fluorescent In Situ Hybridization (FISH)

A molecular technique using fluorescently labeled single-stranded nucleic acid probes to locate specific complementary DNA or RNA sequences directly within fixed tissue or chromosomal samples.

Gel Electrophoresis

A laboratory technique that uses an electric field to separate negatively charged nucleic acid fragments through a gel matrix based on their size.

DNA Ladder

A reference standard consisting of a solution of DNA fragments of known lengths, used in gel electrophoresis to estimate the size and mass of unknown DNA samples.

Hairpin Structure

An RNA or DNA secondary structure formed when a single strand folds back on itself, creating a complementary base-paired stem and an unpaired single-stranded loop.