Biology 120: Cell Biology, Macromolecules, and Microscopy Vocabulary

Vocabulary flashcards covering macromolecules, cell theory, light and electron microscopy, prokaryotic vs. eukaryotic cell structure, the endomembrane system, semi-autonomous organelles, and cytoskeletal components.

Dehydration synthesis

A chemical reaction in which monomer subunits are joined together into a larger polymer by removing the components of a water molecule ($H_2O$).

Hydrolysis

A chemical reaction that breaks down polymers into smaller monomer subunits by adding the components of a water molecule ($H_2O$).

Primary protein structure

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

Secondary protein structure

Local spatial conformations of the polypeptide backbone, such as $\alpha$-helices and $\beta$-sheets, stabilized by hydrogen bonds between nearby amino and carboxyl groups.

Tertiary protein structure

The overall three-dimensional folded shape of a single polypeptide chain, determined by sidechain interactions including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

Quaternary protein structure

The higher-order structural assembly formed when two or more individual polypeptide chains assemble into a functional protein complex.

Cell Theory

The fundamental biological principle stating that all organisms consist of one or more cells, the cell is the basic structural and functional unit of life, and all cells arise exclusively from pre-existing cells.

Resolution

The minimum distance by which two separate points can be separated and still be distinguished as distinct objects under a microscope.

Differential Interference Contrast (DIC) microscopy

A light microscopy technique, also known as Nomarski optics, that exploits phase shifts in light passing through a specimen to generate high-contrast images with a pseudo-3D appearance.

Fluorescence

The physical process wherein an electron absorbs a photon of light at a shorter wavelength (higher energy) and emits a photon at a longer wavelength (lower energy).

Confocal fluorescence microscopy

An optical imaging method that passes emitted fluorescent light through a small pinhole to eliminate out-of-focus light, capturing sharp, thin optical slices of a specimen.

Transmission Electron Microscopy (TEM)

An electron microscopy method in which an electron beam passes through thin microtome sections stained with heavy metals to visualize internal cellular ultrastructure.

Scanning Electron Microscopy (SEM)

An electron microscopy method that scans an electron beam across the gold-coated surface of an intact specimen to produce three-dimensional images of surface contours.

Prokaryotic cell structure

A cellular architecture lacking membrane-bound organelles and a true nucleus, containing a nucleoid region with a single circular chromosome, cytoplasm, plasma membrane, cell wall, and $70S$ ribosomes.

Nucleoid

The non-membrane-bound cytoplasmic region in a prokaryotic cell where the circular chromosome is concentrated.

Central dogma of molecular biology

The framework describing the flow of genetic information in living systems: DNA is transcribed into RNA, which is translated into protein.

Cytosol

The aqueous fluid component of the cytoplasm surrounding organelles, containing dissolved ions, small metabolites, and macromolecules.

Ribosome

A macromolecular complex composed of ribosomal RNA (rRNA) and proteins that coordinates the translation of mRNA into polypeptide chains ($70S$ in prokaryotes, $80S$ in eukaryotes).

Differential centrifugation

A cell fractionation technique that separates subcellular components based on size and density by subjecting lysate to successive spins at increasing centrifugal speeds (g-forces).

Supernatant and pellet

The two distinct fractions produced by centrifugation: the pellet consists of dense packed material at the bottom of the tube, while the supernatant is the liquid liquid layer remaining above.

Nuclear envelope

The double membrane structure enclosing the eukaryotic nucleus, perforated by nuclear pore complexes and continuous with the rough endoplasmic reticulum.

Nucleolus

A dense nuclear sub-region dedicated to the transcription of rRNA and the assembly of ribosomal subunits.

Endomembrane system

A network of interconnected eukaryotic membranes—including the nuclear envelope, ER, Golgi complex, vesicles, lysosomes, vacuoles, and plasma membrane—that work together to synthesize, modify, package, and transport proteins and lipids.

Rough Endoplasmic Reticulum (Rough ER)

A region of the endoplasmic reticulum characterized by flattened cisternae studded with ribosomes on its cytosolic surface, dedicated to protein synthesis, folding, and modification.

Smooth Endoplasmic Reticulum (Smooth ER)

A region of the endoplasmic reticulum consisting of tubular cisternae lacking ribosomes, involved in lipid and steroid synthesis, carbohydrate metabolism, and drug detoxification.

Golgi complex

An organelle composed of stacks of flattened membranous cisternae ($cis$-face to $trans$-face) that receives vesicles from the ER, performs post-translational modifications, and routes proteins and lipids to cellular destinations.

Lysosome

A membrane-bound organelle containing acid hydrolases that digest foreign materials engulfed by phagocytosis or recycle old cellular components via autophagy.

Exocytosis

The active transport mechanism wherein an intracellular vesicle fuses with the plasma membrane to discharge its lumenal contents into the extracellular environment and incorporate its membrane components into the cell surface.

Mitochondrion

A semi-autonomous organelle enclosed by a double membrane with inner folds (cristae) and a fluid matrix, responsible for ATP generation through cellular respiration.

Chloroplast

A semi-autonomous photosynthetic organelle surrounded by a double boundary membrane, containing an internal thylakoid membrane system stacked into grana within a fluid stroma.

Endosymbiotic theory

The evolutionary concept that mitochondria and chloroplasts originated from free-living prokaryotic endosymbionts that were engulfed by ancestral eukaryotic cells, retaining circular DNA, double membranes, and $70S$-like ribosomes.

Amyloplast

A non-pigmented plant plastid (leucoplast) specialized for the synthesis and storage of starch grains.

Microtubule

A hollow cytoskeletal cylinder measuring $25\,nm$ in diameter made of $13$ parallel protofilaments of $\alpha/\beta$-tubulin dimers, possessing structural polarity and exhibiting dynamic instability.

Microfilament

A solid cytoskeletal filament measuring $7\,nm$ in diameter, consisting of two helical strands of polymerized actin monomers that exhibit polarity and mediate cell motility, cytokinesis, and cytoplasmic streaming.

Intermediate filament

A fibrous cytoskeletal element measuring $8\text{--}12\,nm$ in diameter composed of varied protein subunits (such as keratin or collagen) that provides mechanical support and structural integrity without exhibiting polarity or dynamic instability.

Motor protein

An ATP-driven enzyme (such as myosin, kinesin, or dynein) that binds to cytoskeletal filaments and walks unidirectionally to transport vesicles, organelles, or macromolecules.