Cell Biology: Molecular Structure, Genome Packaging, Proteins, and Cell Culture

Vocabulary flashcards covering cellular biology basics, nucleic acids, DNA packaging, protein conformation, and cell culture equipment.

Cell Biology

The study of cell structure and function, built on the core concept that the cell is the fundamental unit of life.

Nucleotide

The basic monomeric building block of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

Purine

A class of double-ringed nitrogenous bases that includes adenine and guanine.

Pyrimidine

A class of single-ringed nitrogenous bases that includes cytosine, thymine (found in DNA), and uracil (found only in RNA).

Nucleoside

A structure formed by a nitrogenous base linked to the $1'$ carbon of a pentose sugar via a glycosidic bond.

Phosphodiester Linkage

A covalent linkage connecting the $5'$ carbon of one pentose sugar ring to the $3'$ carbon of the next through a phosphate group, directing DNA synthesis in a $5'$ to $3'$ direction.

Nucleoid

The region and structural matrix in prokaryotes that contains protein-bound DNA without a surrounding nuclear membrane.

Chromatin

The eukaryotic nuclear complex composed of giant DNA molecules bound to histone and nonhistone proteins.

Euchromatin

Loosely packed, highly dispersed eukaryotic chromatin containing active single-copy genes undergoing active transcription.

Heterochromatin

Densely packed regions of eukaryotic chromatin with low transcriptional activity, predominantly concentrated near centromeres.

Constitutive Heterochromatin

Chromatin regions that remain permanently condensed and inactive as heterochromatin across all cellular states.

Facultative Heterochromatin

Condensed chromatin domains that retain the capacity to convert into transcriptionally active euchromatin.

Nucleosome

The basic repeating packaging unit of eukaryotic chromatin, consisting of roughly $200$\,bp of DNA wrapped around a core histone octamer.

Core Histones

Highly conserved, basic DNA-binding proteins—H2A, H2B, H3, and H4—that pair up to construct the central octamer bead of a nucleosome.

Linker Histone

The H1 histone protein that binds outside the central nucleosome bead to stabilize higher-order $30$\,nm chromatin fibers.

Histone Fold

A conserved protein structural motif present in core histones, composed of three alpha-helices connected by two internal loops.

Histone Code Hypothesis

The concept that specific post-translational chemical modifications on histone tails regulate chromatin structure and localized gene expression.

Ubiquitination

An ATP-dependent, enzyme-catalyzed pathway that attaches ubiquitin to target proteins to direct their rapid destruction during protein homeostasis.

Locus Control Region (LCR)

A cluster of cis-regulatory DNA elements functioning as a super-enhancer to coordinate expression across a cluster of related genes.

Insulator

A specialized DNA sequence that prevents improper enhancer-promoter interactions, protecting gene domains from unwanted activation or silencing.

Translational Nucleosome Positioning

The location of a histone octamer relative to the linear DNA sequence, dictating which bases lie in linker regions versus around the octamer.

Rotational Nucleosome Positioning

The orientation of the DNA double helix relative to the octamer surface, determining which major or minor grooves face outward toward surrounding solvent.

Primary Structure

The specific linear sequence of amino acids in a polypeptide chain connected by covalent peptide bonds.

Protein Conformation

The unique, folded three-dimensional shape of a protein that achieves its thermodynamically stable state with minimal free energy ($G$).

Denaturation

The unfolding of a protein's functional 3D conformation caused by chemical solvents or heat that disrupt non-covalent interactions.

Molecular Chaperones

Dedicated helper proteins that guide correct folding of nascent polypeptides during synthesis and promote refolding of denatured proteins.

Coiled-Coil

A structural motif in which multiple alpha-helices twist together to shield nonpolar hydrophobic amino acids from aqueous exposure.

Amyloid Structure

An insoluble protein aggregate consisting of stacked rows of beta-sheets, involved in tissue damage in diseases such as Alzheimer's and Huntington's.

Prion

An infectious protein particle formed by misfolded prion proteins (encoded by the PRNP gene) that causes healthy host proteins to misfold.

Disulfide Bridge

A strong covalent bond formed between the sulfur atoms of two cysteine residues that stabilizes tertiary protein structure, common in mitochondria and chloroplasts.

Ligand

A specific molecule or ion that selectively binds to a designated binding site on a target protein or macromolecule.

Scaffold Protein

An accessory protein that physically anchors multiple signaling proteins to facilitate specific binding site-ligand interactions.

Western Blot

An analytical technique used to separate and identify specific proteins based on molecular weight using gel electrophoresis followed by membrane transfer.

Carbohydrate

An organic compound following the empirical formula $\text{(CH}_2\text{O)}_n$, where $n$ equals 3, 4, 5, or 6.

Endosymbiontic Theory

The theory proposing that mitochondria and chloroplasts originated from distinct prokaryotic cells that established symbiotic relationships inside early host cells.

Amphipathic Molecule

A molecule possessing both hydrophobic (water-repelling) and hydrophilic (water-attracting) structural regions, such as a fatty acid.

Condensation Reaction

A chemical reaction where two monomeric subunits bond covalently while expelling a molecule of water ($\text{H}_2\text{O}$).

Hydrolysis Reaction

A chemical reaction that breaks a covalent bond between monomers by consuming a molecule of water ($\text{H}_2\text{O}$).

Cell Culture

The process of growing and maintaining cells in an artificial in vitro environment outside of a living organism.

Primary Cells

Cells taken directly from living organism tissue that exhibit a limited capacity for population doublings before entering senescence.

Cell Line

A cell population that has been immortalized naturally or artificially, capable of indefinite population doublings under proper growth conditions.

HeLa Cells

The first established continuous human cell line, isolated in 1951 from Henrietta Lacks' cervical cancer and immortalized by integration of HPV-18.

Class II Biological Safety Cabinet

An enclosed laboratory workstation engineered to protect the user, environment, and cell culture product using filtered, laminar airflow.

CO2 Incubator

A specialized cell culture enclosure that simulates physiological growth conditions at $37$\,\text{°C}, $5\%$\,\text{CO}_2$for pH buffering, and approximately$95\%$$ humidity.