Cell Biology: Fundamental Principles, Macromolecules, and Information Flow

Comprehensive vocabulary flashcards reviewing cell biology, covering cell theory, chemical bonds, macromolecules, DNA packaging, gene transcription, translation, membrane structure, organelle function, and membrane transport mechanisms.

Cell Theory

The foundational principle of biology stating that all living organisms are composed of one or more cells, the cell is the structural and functional unit of life, and all cells arise only from pre-existing cells.

Viroids

Infectious agents consisting solely of small circular $RNA$ lacking a protein coat that depend entirely on host cellular machinery to replicate.

Prions

Proteinaceous infectious particles composed entirely of protein that lack nucleic acids and cause normal proteins to misfold into pathological forms.

Endomembrane System

An interconnected internal membrane network in eukaryotic cells that builds, modifies, and transports cellular materials, comprising the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and plasma membrane.

Valence Electrons

Electrons occupying an atom's outermost orbitals that determine the number and configuration of covalent or ionic bonds the atom can establish.

Hydrogen Bond

A weak electrostatic bond formed between an electronegative atom (such as oxygen or nitrogen) and a hydrogen atom already covalently linked to another electronegative atom.

Condensation Reaction

A dehydration synthesis reaction where monomers are covalently joined to produce a polymer, requiring energy and releasing a molecule of $\text{H}_2\text{O}$ as a byproduct.

Hydrolysis Reaction

A cleavage reaction where a chemical bond within a polymer is broken by the insertion of a water molecule ($\text{H}_2\text{O}$), releasing energy and yielding monomer subunits.

Pyrimidines

Single-ring nitrogenous bases found in nucleotides, consisting of cytosine ($\text{C}$), thymine ($\text{T}$) in $\text{DNA}$, and uracil ($\text{U}$) in $\text{RNA}$.

Purines

Double-ring nitrogenous bases found in nucleotides, consisting of adenine ($\text{A}$) and guanine ($\text{G}$).

Glycosidic Bond

A covalent linkage formed through a condensation reaction connecting carbon-1 ($\text{C1}$) of one monosaccharide to a hydroxyl ($\text{-OH}$) group on another monosaccharide.

Amphipathic

A molecular property characterized by having distinct hydrophilic (polar) and hydrophobic (nonpolar) domains within the same structure, as seen in phospholipids.

DNA Packaging Hierarchy

The multi-tier structural compaction of eukaryotic genetic material progressing from a $2\,\text{nm}$ diameter $\text{DNA}$ duplex to a $10\text{--}11\,\text{nm}$ nucleosome fiber, a $100\,\text{nm}$ coiled chromatin fiber, a $300\,\text{nm}$ coiled coil, and ultimately a $600\,\text{nm}$ condensed chromatid.

Griffith's Bacterial Inoculation Experiment

The $1928$ study using Streptococcus pneumoniae in mice showing that virulent strains cause fatal pneumonia whereas nonvirulent strains allow host survival, leading to the discovery of the transforming principle.

Central Dogma

The fundamental framework of molecular biology stating that genetic information flows sequentially from $\text{DNA}$ through transcription into $\text{RNA}$, and from $\text{RNA}$ through translation into protein.

Promoter

A specific sequence of $\text{DNA}$ upstream of a gene that is recognized and bound by transcription factors and $\text{RNA}$ polymerase to direct the initiation of transcription.

Sigma Factor

A bacterial protein that binds $\text{RNA}$ polymerase to facilitate promoter sequence recognition and transcription initiation.

Polycistronic mRNA

A single messenger $\text{RNA}$ molecule, characteristic of prokaryotic organisms, that carries coding sequences for multiple independent polypeptide chains.

Alternative Splicing

A eukaryotic post-transcriptional mechanism in which exons can be selectively included or excluded and introns removed from a primary transcript, enabling a single gene to encode multiple distinct proteins.

Zwitterion

A dipolar molecule carrying both positive and negative charges at physiological $\text{pH}$ ($7.4$) while maintaining an overall neutral net charge.

Secondary Structure

The local conformation of a polypeptide backbone resulting from hydrogen bonding between backbone carbonyl ($\text{C=O}$) and amide ($\text{N-H}$) groups, commonly forming an $\alpha$ helix or $\beta$ sheet.

Alpha ($\alpha$) Helix

A right-handed helical protein secondary structure stabilized by backbone hydrogen bonds between each carbonyl oxygen and the amide hydrogen located four amino acids downstream in the sequence.

Peptidyl Transferase Center

An $\text{rRNA}$-based catalytic domain positioned between the A site and P site of the large ribosomal subunit that catalyzes peptide bond formation during translation elongation.

Aminoacyl tRNA Synthetase

An enzyme that couples a specific uncharged $\text{tRNA}$ molecule to its corresponding amino acid at the $3'$ $\text{CCA}$ attachment site to form a charged $\text{tRNA}$.

Shine-Dalgarno Sequence

A conserved prokaryotic consensus sequence ($5'\text{-AGGAGGU-}3'$) located upstream of the start codon on $\text{mRNA}$ that positions the ribosome for translational initiation.

Signal Recognition Particle (SRP)

A ribonucleoprotein complex that binds to the amino-terminal signal sequence of a nascent polypeptide, halts translation, and targets the ribosome to the rough endoplasmic reticulum membrane.

Phospholipid Structures in Aqueous Solutions

The self-assembled arrangements formed spontaneously by phospholipids in water, yielding spherical micelles (single tail, bulky head), extended planar bilayers, or closed vesicular liposomes (two tails, smaller head).

Fluid Mosaic Model

The model representing cellular membranes as dynamic, two-dimensional fluids consisting of a continuous lipid bilayer embedded with a mosaic of mobile integral proteins, peripheral proteins, and carbohydrates.

Lysosome

A specialized membrane-enclosed digestive vesicle derived from the Golgi apparatus that contains acid hydrolases and uses an active proton pump to maintain an internal acidic environment near $\text{pH} \approx 5$.

Endosymbiotic Theory

The evolutionary model proposing that eukaryotic mitochondria and chloroplasts originated as free-living proteobacteria and cyanobacteria, respectively, engulfed by ancestral host cells.

Tonicity Effects on Animal and Plant Cells

The cellular volume responses triggered by surrounding osmolarity: hypertonic environments cause shriveling (crenation) in red blood cells and plasmolysis in plant cells; hypotonic environments cause swelling and bursting (hemolysis) in red blood cells and turgor pressure (turgid state) in plant cells.

Facilitated Diffusion

A form of passive membrane transport wherein specific polar or charged solutes diffuse down their concentration gradient through integral channel proteins or carrier proteins without direct energy expenditure.

$$\text{Na}^+/\text{K}^+\text{-ATPase}$$

An integral membrane antiporter that uses the energy of $\text{ATP}$ hydrolysis to pump $3\,\text{Na}^+$ ions out of animal cells and $2\,\text{K}^+$ ions into the cell against their respective concentration gradients.

Secondary Active Transport

A transport mechanism in which the movement of a solute against its concentration gradient is powered by the potential energy stored in an electrochemical gradient generated by primary active transport.

Phagocytosis

A specialized form of endocytosis in which cells engulf large particulate matter or pathogens via plasma membrane invaginations, producing an intracellular phagosome that fuses with a primary lysosome for digestion.