DNA Structure & Function Flashcards

Vocabulary practice flashcards generated from lecture notes on DNA structure, historical experiments, chromosome packaging, and DNA replication mechanisms.

Friedrich Miescher

Swiss scientist who isolated phosphate-rich acidic compounds from the nuclei of leukocytes in hospital bandages in 1869, naming the material "nuclein" (later known as DNA).

Frederick Griffith

Scientist who performed experiments in 1928 providing the first demonstration of bacterial transformation using pathogenic S cells and nonpathogenic R cells of Streptococcus pneumoniae.

Transforming Principle

The molecular substance responsible for bacterial transformation, confirmed in 1944 by Oswald Avery, Colin MacLeod, and Maclyn McCarty to be nucleic acids (DNA).

Chargaff's Rules

Rules established by Erwin Chargaff in 1950 stating that in double-stranded DNA, the percentage of adenine equals thymine ($\% A = \% T$) and the percentage of cytosine equals guanine ($\% C = \% G$).

Hershey-Chase Experiment

A 1952 experiment conducted by Alfred Hershey and Martha Chase using T2 bacteriophages labeled with ${}^{32}\text{P}$ (DNA) and ${}^{35}\text{S}$ (protein) to confirm that DNA is the genetic material.

Nucleotide

The repeating monomer building block of nucleic acids, consisting of a pentose sugar (deoxyribose in DNA or ribose in RNA), a nitrogenous base, and a phosphate group.

Rosalind Franklin and Maurice Wilkins

Researchers who utilized X-ray crystallography to capture X-ray diffraction photographs of DNA, revealing key structural dimensions and helical symmetry.

James Watson and Francis Crick

Scientists who deduced and constructed the elegant double-helical structural model of DNA in 1953.

Antiparallel

The structural orientation of the two strands in a DNA double helix, running parallel to each other but in opposite directions ($5' \rightarrow 3'$ and $3' \rightarrow 5'$).

Phosphodiester Bond

The covalent bond that links adjacent nucleotides together along the sugar-phosphate backbone of a nucleic acid strand.

Nucleosome

The fundamental unit of eukaryotic chromatin, consisting of an octet of 8 histone proteins wrapped by 146 or 147 nucleotide base pairs of DNA.

Euchromatin

Loosely packed chromatin structure prevalent during interphase, making genetic information accessible for gene expression.

Heterochromatin

Highly condensed regions of chromatin during interphase (such as centromeres and telomeres) that prevent easy access to genetic information.

Semiconservative Replication

The model of DNA replication where each generated daughter DNA molecule contains one original parental strand and one newly synthesized strand.

Meselson and Stahl Experiment

An experiment using heavy (${}^{15}\text{N}$) and light (${}^{14}\text{N}$) nitrogen isotopes in E. coli to demonstrate that DNA replicates semiconservatively.

Sanger Dideoxynucleotide Sequencing

A DNA sequencing technique developed by Frederick Sanger using dye-labeled dideoxynucleotides (ddNTPs) to produce chain-terminated fragments separated by capillary electrophoresis.

Polymerase Chain Reaction (PCR)

A molecular laboratory technique used to rapidly amplify a specific DNA segment into billions of copies across repeated cycles of denaturation, annealing, and elongation.

Gel Electrophoresis

A technique that uses an electric current to separate negatively charged DNA fragments by size as they pass through a porous gel matrix toward a positive pole.

Helicase

The enzyme that opens and unwinds the parental DNA double helix at the replication fork by breaking hydrogen bonds between nitrogenous bases.

Single-Strand Binding Proteins (SSB)

Proteins that bind to single-stranded template DNA to stabilize unwound strands and prevent them from rewinding into a double helix.

Topoisomerase

An enzyme that relieves torsional strain ahead of the unwinding replication fork by causing transient breaks in the DNA and resealing them.

Primase

The enzyme that synthesizes a short RNA primer ($5\text{--}10$ nucleotides long) to provide a free $3'-OH$ starting group for DNA polymerase.

DNA Polymerase III

The main prokaryotic enzyme that adds dNTPs to elongate a growing DNA strand in the $5' \rightarrow 3'$ direction.

DNA Polymerase I

The enzyme that removes RNA primers from synthesized DNA strands and replaces them with DNA nucleotides.

DNA Ligase

An enzyme that seals gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds.

Leading Strand

The new DNA strand synthesized continuously by DNA polymerase III toward the replication fork in the $5' \rightarrow 3'$ direction.

Lagging Strand

The new DNA strand synthesized discontinuously away from the replication fork as a series of Okazaki fragments in an overall $3' \rightarrow 5'$ direction.

Okazaki Fragments

Short, newly synthesized DNA segments formed on the lagging strand template during replication.

Sliding Clamp

A ring-shaped protein structure that attaches DNA polymerase to the template strand and prevents it from dissociating during synthesis.

Thymine Dimer

A specific type of DNA damage caused by ultraviolet (UV) light where adjacent thymine bases covalently bond to one another, disrupting proper replication.

Nucleotide Excision Repair

A DNA repair pathway in which a nuclease removes damaged single-stranded DNA, DNA polymerase synthesizes replacement DNA, and DNA ligase seals the backbone.

Telomeres

Repetitive, non-coding nucleotide sequences ($5'\text{--TTAGGG--}3'$ in humans) located at the ends of eukaryotic chromosomes that postpone gene erosion.

Telomerase

An enzyme containing its own RNA template that catalyzes the lengthening of telomeres in eukaryotic germ cells to prevent gene loss across generations.

Elizabeth Blackburn

Scientist awarded the 2009 Nobel Prize for Medicine and Physiology for discovering telomerase and elucidating its role in chromosome protection.