DNA Structure, Cell Division, Mutation, and Genetics Lecture Flashcards

Vocabulary flashcards generated from the lectures on DNA structure, cell cycle, DNA replication, DNA repair mechanisms, mutations, and Mendelian/chromosomal genetics.

Griffith Experiment

An experiment using virulent and non-virulent bacterial strains demonstrating that dead virulent bacteria could transform live non-virulent bacteria via a transforming factor.

Avery et al. Experiment

An experiment that systematically destroyed proteins, sugars, RNA, and DNA in virulent bacterial extracts, establishing that DNA is the transforming factor.

Purines

Nitrogenous bases containing two carbon-nitrogen rings, specifically Adenine and Guanine.

Pyrimidines

Nitrogenous bases containing a single carbon-nitrogen ring, specifically Cytosine, Thymine, and Uracil.

Phosphodiester Bond

A strong covalent bond joining the phosphate group of one nucleotide to the sugar of the next within a strand, establishing $5'$ to $3'$ directional polarity.

Base Stacking

Stabilizing hydrophobic interactions occurring between adjacent, flat non-polar nitrogenous bases stacked on top of one another within the same DNA strand.

Supercoiling

The process of compacting prokaryotic circular DNA chromosomes into tight structures to fit inside the cell.

Nucleosome

A basic structural unit of eukaryotic chromatin consisting of DNA wrapped around a histone octamer.

Binary Fission

An asexual division process in prokaryotes where the cell grows, replicates its genome, and divides into two daughter cells.

Interphase

The period of the eukaryotic cell cycle between cell divisions, comprising the $G_1$, $S$, and $G_2$ phases.

Kinetochore

A protein structure on the chromosome where spindle microtubules attach during prometaphase, capable of sensing tension prior to chromatid separation.

Cytokinesis

The stage following mitosis where the cytoplasm divides, using a contractile ring of actin in animal cells or forming a cell plate in plant cells.

Cyclin-Dependent Kinases (CDK)

Enzymes that regulate progression through the cell cycle by phosphorylating target proteins when activated by binding to cyclins.

Semiconservative Replication

The mechanism of DNA replication in which each generated double helix consists of one original parental strand and one newly synthesized strand.

Meselson-Stahl Experiment

An experiment using heavy $^{15}\text{N}$ and light $^{14}\text{N}$ isotopes that confirmed the semiconservative mechanism of DNA replication.

Origin Recognition Complex (ORC)

A protein complex that binds to the origin of replication to initiate strand separation and recruit pre-replication complexes.

Helicase

An enzyme that unwinds and separates parental double-stranded DNA at the replication fork.

Topoisomerase

An enzyme that acts ahead of the replication fork to relieve torsional stress generated by DNA unwinding.

Single-Stranded Binding Proteins (SSBPs)

Proteins that bind to single-stranded DNA exposed at the replication fork to prevent strands from re-annealing before replication.

Primase

An RNA polymerase that synthesizes a short RNA primer to provide the free $3'\text{-OH}$ group required for DNA polymerase synthesis.

Leading Strand

The newly synthesized DNA strand that is produced continuously toward the moving replication fork in the $5' \rightarrow 3'$ direction.

Lagging Strand

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

DNA Ligase

An enzyme that joins DNA fragments by creating phosphodiester bonds to seal remaining nicks in the sugar-phosphate backbone.

Telomerase

An enzyme carrying an internal RNA template used to extend the $3'$ end of linear eukaryotic chromosomes to prevent telomere shortening.

Exonucleases

Enzymes that remove single nucleotides from the free ends of a DNA strand.

Endonucleases

Enzymes that cleave internal phosphodiester bonds within a DNA molecule.

Point Mutation

A genetic mutation caused by the substitution, insertion, or deletion of a single nucleotide in a DNA sequence.

Silent Mutation

A point mutation that changes a codon without changing the specified amino acid, leaving the final protein sequence unaffected.

Missense Mutation

A point mutation that alters a codon, resulting in the substitution of a different amino acid in the translated protein.

Nonsense Mutation

A point mutation that converts an amino-acid-coding codon into a stop codon, causing premature termination of translation.

Frameshift Mutation

An insertion or deletion of nucleotides in numbers not divisible by three, shifting the mRNA reading frame and altering all downstream amino acids.

Neofunctionalization

An evolutionary outcome of gene duplication where one copy acquires mutations that impart a novel biological function.

Subfunctionalization

An evolutionary outcome of gene duplication where the original gene's multiple functions are divided between the two duplicates.

Mismatch Repair

A post-replication DNA repair mechanism active during S phase that cuts out mispaired single bases using endonucleases and exonucleases and resynthesizes the correct sequence.

Excision Repair

A DNA repair pathway independent of replication where endonucleases excise a $10\text{ to }12$ base region containing helical distortions caused by physical or chemical damage.

Homologous Chromosomes

Chromosome pairs derived from common ancestry that contain the same set of gene loci in the same order, though they may carry different alleles.

Homologous Trait

A structural trait shared by species because it was inherited from a common ancestor.

Analogous Trait

A trait with similar form or function shared by organisms that did not inherit it from a common ancestor.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate correctly during meiotic divisions.

Aneuploidy

A state in which a cell or zygote possesses an abnormal chromosome count resulting from fertilization with a gamete produced via nondisjunction.

Principle of Segregation

Mendel's first law stating that the two alleles for a gene separate equally into gametes during gamete formation.

Principle of Independent Assortment

Mendel's second law stating that the alleles of different genes segregate into gametes independently of one another.

Test Cross

A cross performed between an individual with an unknown genotype exhibiting a dominant phenotype and a homozygous recessive individual.

Linked Genes

Genes located close together on the same chromosome that are usually inherited together and fail to sort independently.

Chiasmata

Visible connection points where non-sister chromatids cross over and exchange segments during meiotic prophase I.

Recombination Frequency

A percentage calculated as $\frac{\text{number of recombinant offspring}}{\text{total offspring}} \times 100\%$ reflecting the relative distance between linked genes.