BIOL 231 — Exam 2 Study Guide Flashcards

Vocabulary practice flashcards covering core concepts from the BIOL 231 Exam 2 study guide, including DNA replication, gene regulation, membrane biophysics, transport thermodynamics, and electrophysiology.

Nitrogenous base

The specific chemical component of a nucleotide that pairs with another nucleotide across the double helix via hydrogen bonds.

Nucleosome

The fundamental unit of chromatin, composed of DNA wrapped around a histone octamer containing two copies each of H2A, H2B, H3, and H4.

Hershey–Chase experiment

An experiment confirming DNA as the bacteriophage genetic material by labeling viral protein with $^{35}\text{S}$ and viral DNA with $^{32}\text{P}$; $^{32}\text{P}$-labeled DNA entered bacterial cells and directed new phage production.

Transforming principle

The chemical substance responsible for genetic transformation discovered in Streptococcus pneumoniae by Griffith, and subsequently proven to be DNA by Avery, MacLeod, and McCarty.

DNA end-replication problem

The inability of DNA polymerase to fully duplicate linear chromosome ends because removal of the terminal lagging-strand RNA primer leaves no upstream $3'\text{-OH}$ group for synthesis.

Telomerase

An enzyme containing an internal RNA template used to synthesize repetitive telomeric DNA at linear chromosome ends, counteracting end-replication loss.

Coding strand

The DNA strand whose base sequence directly matches the synthesized mRNA (with thymine substituted for uracil), complementary to the template strand read $3' \rightarrow 5'$.

Degeneracy

A feature of the genetic code wherein multiple distinct triplet codons can specify the exact same amino acid.

Nonsense mutation

A base-pair substitution converting an amino acid-specifying codon into a premature stop codon, terminating translation prematurely and yielding a truncated protein.

5′ 7-methylguanosine cap

The chemical modification on the $5'$ end of eukaryotic mRNA that is recognized by the small ribosomal subunit during translation initiation.

Peptidyl transfer

The catalytic reaction executed by ribosomal rRNA that forms a peptide bond, transferring the growing polypeptide chain onto the incoming amino acid situated at the A-site tRNA.

microRNA (miRNA)

A non-coding RNA of approximately $22$ nucleotides that pairs semi-complementarily to endogenous target transcripts to suppress translation or trigger mRNA degradation.

small interfering RNA (siRNA)

A non-coding RNA of roughly $22$ nucleotides that binds target RNA (such as foreign RNA or transposons) with high complementarity to guide target cleavage.

RISC

RNA-induced silencing complex; a predominantly cytoplasmic protein complex that utilizes small non-coding RNAs to mediate post-transcriptional gene silencing.

RITS

RNA-induced transcriptional silencing complex; a nuclear complex that uses small RNAs to orchestrate chromatin modifications and transcriptional gene silencing.

Flippases and Floppases

ATP-dependent lipid transport enzymes responsible for establishing and preserving plasma-membrane lipid asymmetry between bilayer leaflets.

FRAP

Fluorescence recovery after photobleaching; an experimental technique where a laser irreversibly bleaches a defined membrane area to quantify lateral mobility as unbleached fluorophores diffuse in.

Frye–Edidin experiment

A landmark cell-fusion study creating mouse–human hybrid cells that verified the lateral mobility of integral membrane proteins by monitoring surface protein mixing over time.

Single-particle tracking

A high-resolution optical microscopy method that tracks individual membrane proteins tagged with antibody-conjugated gold beads to evaluate lateral diffusion trajectories.

Equilibrium potential ($V_x$)

The membrane voltage at which electrical and chemical driving forces balance for a given ion, defined by $V_x = \left(\frac{59\,\text{mV}}{z}\right) \times \log_{10}\left(\frac{[X]_{\text{out}}}{[X]_{\text{in}}}\right)$.

Refractory period

The temporary state immediately behind an advancing action potential wave front caused by voltage-gated $\text{Na}^+$ channel inactivation, preventing backward propagation.

Histone acetylation

The covalent addition of acetyl groups to lysine residues of histone proteins, neutralizing positive charges, weakening histone-DNA interactions, and decondensing chromatin.