Cell Biology: Test #2 Study Guide Flashcards

Comprehensive vocabulary flashcards covering membrane transport, cellular respiration, junctions, cytoskeleton, chromatin architecture, DNA replication, and transcription.

Free Energy of Charged Solute Inward Transport ($$\Delta G_{\text{inward}}$)

The electrochemical potential driving solute movement into the cell, calculated as $\Delta G_{\text{inward}} = RT\ln\left(\frac{[S]_{\text{inside}}}{[S]_{\text{outside}}}\right) + zFV_m$, where $z$ is the ion charge, $F$ is the Faraday constant ($23{,}062\,\text{cal/mol-V}$), and $V_m$ is membrane potential in volts.

Uniport

A carrier transport protein that moves a single solute across the membrane in one direction down or against its gradient.

Symport

A coupled transport process in which two different solutes are transported across a membrane simultaneously in the same direction.

Antiport

A coupled transport mechanism where two solutes move across a biological membrane in opposite directions.

Direct Active Transport

Transport across a membrane directly powered by metabolic energy via the hydrolysis of $\text{ATP}$.

Indirect Active Transport

Active transport powered not directly by $\text{ATP}$, but by the electrochemical gradient established by another solute.

Glycolysis

A cytoplasmic metabolic pathway that splits one glucose molecule into two pyruvate molecules to produce metabolic energy ($\text{ATP}$ and $\text{NADH}$).

Three Fates of Pyruvate

Pyruvate produced by glycolysis can undergo: (1) Anaerobic lactic acid fermentation into lactate, (2) Aerobic oxidation into Acetyl-CoA ($+\text{CO}_2$) feeding the citric acid cycle, or (3) Anaerobic alcoholic fermentation into acetaldehyde and ethanol ($+\text{CO}_2$).

Fermentation

An anaerobic metabolic pathway occurring in the cytoplasm that regenerates $\text{NAD}^+$ from $\text{NADH}$ while reducing pyruvate to products such as lactate or ethanol.

Mitochondria

The organelle site where pyruvate is metabolized, the Krebs (TCA) cycle takes place, and the electron transport chain operates to produce the majority of the cell's $\text{ATP}$ and $\text{CO}_2$.

Simple vs. Stratified Epithelia

Simple epithelia consist of a single layer of cells functional in secretion and absorption, whereas stratified epithelia consist of multiple cell layers specialized for protective functions.

Tight Junctions

Cell junctions formed around the core transmembrane protein claudin that provide a cell-to-cell seal, establish a barrier, and maintain apical-basolateral membrane polarity.

Adherens Junctions

Cell-cell anchoring junctions formed around cadherins that provide adhesion and physically connect adjacent cells by linking to actin filaments.

Desmosomes

Button-like anchoring cell junctions built around desmosomal cadherins that attach to intermediate filaments to confer mechanical strength to tissue.

Gap Junctions

Intercellular channels formed by connexins that allow direct metabolic and electrical communication between adjacent cell cytoplasms.

Hemidesmosomes

Cell-matrix junctions composed of integrins that anchor the cell's intermediate filaments and actin cytoskeleton to the basal lamina extracellular matrix.

Junctional Complex

The structured arrangement of cell-cell junctions found near the apical region of epithelial cells, consisting of a tight junction, an adherens junction, and a desmosome.

Actin Filaments

Cytoskeletal polymers composed of actin monomers that maintain cell shape, drive cell motility, and anchor adherens junctions.

Microtubules

Hollow cylindrical cytoskeletal structures composed of tubulin heterodimers that function as intracellular transport highways for motor proteins.

Intermediate Filaments

Rope-like cytoskeletal filaments assembled from protein monomers such as keratin that impart mechanical and tensile strength to withstand physical stress.

Dynamic Instability (GTP Cap Model)

The alternating cycle of microtubule growth and catastrophic depolymerization governed by $\text{GTP}$ cap presence: high $\text{GTP}$-tubulin maintains the cap for growth, while $\text{GTP}$ hydrolysis depletes the cap and triggers catastrophe.

Nucleosome

The fundamental repeating structural unit of chromatin ($10\,\text{nm}$ 'beads on a string'), consisting of $2\,\text{nm}$ double-helical $\text{DNA}$ wound around an octamer of histone proteins, connected by linker $\text{DNA}$.

Higher-Order Chromatin Condensation

The structural progression of eukaryotic $\text{DNA}$ packaging from $300\,\text{nm}$ looped domains to $700\,\text{nm}$ heterochromatin, condensing into a $1400\,\text{nm}$ duplicated metaphase chromosome with sister chromatids and a centromere.

Euchromatin vs. Heterochromatin Regulation

Epigenetic regulation of chromatin states where histone acetylation and phosphorylation promote open, transcriptionally active euchromatin, while $\text{DNA}$ methylation (such as on cytosines) and histone methylation promote dense, transcriptionally silent heterochromatin.

Replication Bubble

A bidirectional structure formed during $\text{DNA}$ replication starting at an origin of replication ($\text{oriC}$), displaying two replication forks with continuous leading strands and discontinuous lagging strands made of Okazaki fragments initiated by $\text{RNA}$ primers.

DNA Helicase

An enzyme that unzips the parental $\text{DNA}$ double helix at the replication fork by breaking hydrogen bonds between base pairs.

Topoisomerase

An enzyme that relieves the torsional strain and supercoiling created ahead of the advancing replication fork during $\text{DNA}$ unwinding.

DNA Polymerase

The primary enzyme responsible for synthesizing new $\text{DNA}$ daughter strands exclusively in the $5'$ to $3'$ direction from a template strand.

Primase

An $\text{RNA}$ polymerase enzyme that synthesizes short $\text{RNA}$ primers to supply free $3'\text{-OH}$ groups required for $\text{DNA}$ polymerase initiation.

Single-Stranded Binding Proteins (SSBP)

Proteins that bind and stabilize exposed single-stranded $\text{DNA}$ templates to prevent reannealing or degradation during replication.

Telomerase

A specialized reverse transcriptase ribonucleoprotein enzyme that extends and maintains telomeres at the ends of linear chromosomes.

Transcription Bubble

A localized region of unwound $\text{DNA}$ where $\text{RNA}$ polymerase reads the template strand to synthesize an $\text{RNA}$ transcript from $\text{NTPs}$ from the promoter to the terminator.

Degeneracy of the Genetic Code

The property that multiple distinct three-nucleotide codons can translate into the exact same single amino acid.

Alternative Splicing

A post-transcriptional process generating multiple distinct mature $\text{mRNAs}$ from a single pre-$\text{mRNA}$ via alternative $5'$ splice sites, alternative $3'$ splice sites, retained introns, or mutually exclusive exons.

Post-Transcriptional RNA Processing

Three critical modifications applied to eukaryotic pre-$\text{mRNA}$: $5'$ capping, addition of a $3'$ poly-A tail, and removal of non-coding introns via $\text{RNA}$ splicing.

Ran-Dependent Transport

The active mechanism of nuclear transport through nuclear pore complexes utilizing Ran GTPase gradients to regulate nuclear export signals ($\text{NES}$) and nuclear import/export receptors.

Motor Proteins (Kinesins and Dyneins)

$\text{ATP}$-driven mechanochemical enzymes that move directionally along cytoskeletal microtubules to transport vesicles and intracellular cargo.

Rho Family GTPases

Small signaling $\text{GTP}$-binding switch proteins including Rho, Rac, and Cdc42 that regulate actin cytoskeleton remodeling, dynamics, and cell polarity.

Clathrin

A protein that forms a polyhedral lattice coat on vesicles during receptor-mediated endocytosis and vesicle budding from the trans-Golgi network.