Molecular Cell Biology Review Flashcards

Comprehensive vocabulary flashcards covering core topics in molecular cell biology, genetics, bioinformatics, cell signaling, cytoskeleton, cell cycle, cancer hallmarks, and stem cells.

Compartmentalization

The division of a eukaryotic cell's interior into distinct membrane-bound regions with specific chemical environments to optimize cellular functions and separate metabolic or gene expression processes.

Nuclear Localization Signal (NLS)

A sorting sequence consisting of positively charged amino acids that directs target proteins to be imported into the cell nucleus via Nuclear Import Receptors (importins).

Ran-GTP / Ran-GDP Gradient

A nucleocytoplasmic gradient maintained by nuclear Ran-GEF (which exchanges GDP for GTP) and cytoplasmic Ran-GAP (which hydrolyzes Ran-GTP to Ran-GDP), driving the directionality of nuclear transport.

Sec61 Complex

The translocase channel in the endoplasmic reticulum membrane through which polypeptide chains pass during protein translocation into the ER lumen.

C-Terminal Domain (CTD)

The tail region of RNA Polymerase II that, when hyperphosphorylated by TFIIH, triggers transcription initiation and recruits RNA-processing enzymes for 5' capping, polyadenylation, and splicing.

Operon

A prokaryotic transcription unit in which multiple functionally related genes sharing a single promoter and terminator are co-regulated and transcribed into a single polycistronic mRNA.

Histone Code

The specific combination of post-translational modifications (such as acetylation, methylation, and phosphorylation) on histone tails that dictates chromatin packaging and regulates gene expression.

cDNA (Complementary DNA)

Double-stranded DNA synthesized from mature, spliced mRNA using reverse transcriptase and DNA polymerase, containing only exonic sequences without introns.

Real-Time Quantitative PCR (qPCR)

A PCR method that quantifies DNA or cDNA amplification in real time during each cycle using fluorescent probes or reporters.

RNA Interference (RNAi)

A post-transcriptional gene silencing mechanism where small guide RNAs (such as siRNA) direct the RISC complex to degrade target mRNAs or inhibit their translation.

CRISPR/Cas9

A targeted genome-editing system where a guide RNA (gRNA) directs the Cas9 nuclease to introduce double-strand breaks at specific DNA sequences, repaired via NHEJ or HDR.

Next-Generation Sequencing (NGS)

High-throughput sequencing technologies—such as Illumina, PacBio, and Nanopore—that enable parallel sequencing of millions of DNA or cDNA fragments.

CpG Islands

Genomic regions rich in unmethylated cytosine-guanine dinucleotides, commonly located in active gene promoters, that serve as markers for active transcription.

Single Nucleotide Polymorphism (SNP)

A variation at a single nucleotide position in the DNA sequence that occurs naturally between individuals, typically found approximately once every $1000$ base pairs.

Mediator Complex

A multiprotein co-activator complex that acts as a bridge between specific transcription factor activators bound to distant enhancers and the basal transcription machinery at the promoter.

Transcriptional Pausing

A regulatory mechanism where RNA Polymerase II initiates transcription but pauses $20$ to $50$ nucleotides downstream from the promoter until activated by specific transcription signals.

Riboswitch

An mRNA secondary structure that directly binds a specific metabolite or ligand, altering its conformation to regulate transcriptional attenuation or translation termination.

Heteroplasmy

The presence of a mixture of both normal and mutated mitochondrial DNA (mtDNA) genomes within a single cell or tissue.

DNMT1 (DNA Methyltransferase 1)

The maintenance enzyme that recognizes hemimethylated DNA following replication and copies the parental strand's cytosine methylation pattern onto the new daughter strand.

Genomic Imprinting

An epigenetic process where only one parental allele of a gene is expressed (maternal or paternal) while the other allele is epigenetically silenced via DNA methylation.

MicroRNA (miRNA)

Endogenous small non-coding RNAs (~$22$ nucleotides) generated by Drosha and Dicer that bind to the $3'\text{-UTR}$ of target mRNAs in RISC to inhibit translation or promote mRNA degradation.

piRNA (Piwi-Interacting RNA)

Small non-coding RNAs (~$21$ to $30$ nucleotides) that associate with Piwi proteins in germ cells to suppress transposon movement via RNA cleavage and heterochromatin induction.

Epithelial-to-Mesenchymal Transition (EMT)

A cellular process in which epithelial cells downregulate E-cadherin, lose polarity and cell-cell adhesion, and acquire a migratory, invasive mesenchymal phenotype.

Warburg Effect

A metabolic adaptation in cancer cells characterized by increased glucose uptake and aerobic glycolysis to produce laktate in the cytosol even in the presence of oxygen.

Dynamic Instability

The rapid alternating cycles of assembly (growth) and disassembly (catastrophe) at the plus-end of microtubules, governed by GTP-tubulin capping.

Chemotaxis

Directional cell migration along a chemical gradient, coordinated by mutually antagonistic front-edge Rac activation (actin polymerization) and rear-edge Rho activation (actomyosin contraction).

G-Protein Coupled Receptor (GPCR)

A seven-transmembrane cell-surface receptor that, upon ligand binding, acts as a GEF to exchange GDP for GTP on the $\text{G}\alpha$ subunit of an intracellular heterotrimeric G-protein.

β-Catenin

A dual-function protein that acts as an adhesion component and a transcriptional co-activator in the canonical Wnt pathway when stabilized against proteasomal degradation.

Receptor Tyrosine Kinase (RTK)

A class of cell surface receptors that undergo ligand-induced dimerization and trans-autophosphorylation on intracellular tyrosine residues to activate downstream signal transduction.

Cyclin-Dependent Kinases (CDKs)

Master regulatory serine/threonine protein kinases that drive cell cycle progression, requiring binding of regulatory cyclin subunits and specific phosphorylation events for activity.

Nucleotide Excision Repair (NER)

A DNA repair pathway that removes bulky DNA lesions that distort the double helix (such as UV-induced pyrimidine dimers) by excising a single-stranded patch of ~$30$ nucleotides.

Homologous Recombination (HR)

An accurate double-strand break repair mechanism active during S and G2 phases that uses an intact homologous sister chromatid template to restore DNA sequences without indels.

Transposons

Mobile genetic elements ("jumping genes") capable of moving or replicating within a genome via direct cut-and-paste mechanisms (DNA transposons) or RNA intermediates (retrotransposons).

Site-Specific Recombination (SSR)

A DNA rearrangement mechanism where specific recombinase enzymes recognize, cut, and join designated target DNA sequences (e.g., Cre-LoxP or V(D)J recombination).

Apoptosome

A multiprotein complex formed by Cytochrome c and Apaf-1 in the intrinsic apoptosis pathway that recruits and activates initiator procaspase-9 to trigger the caspase cascade.

Senescence-Associated Secretory Phenotype (SASP)

A secretome produced by senescent cells consisting of pro-inflammatory cytokines, chemokines, growth factors, and proteases that influences the tissue microenvironment.

Induced Pluripotent Stem Cells (iPSCs)

Pluripotent stem cells reprogrammed directly from mature somatic cells (such as fibroblasts) by expressing specific transcription factors (Oct4, Sox2, Klf4, Myc).

Stem Cell Niche

The specialized microenvironment consisting of neighboring support cells, extracellular matrix components, and signaling factors that preserves stem cell identity and regulates self-renewal vs. differentiation.