Biochemistry, Proteins, Nucleic Acids, and Cell Physiology

Comprehensive vocabulary flashcards covering organic molecules, protein levels, enzymatic function, nucleic acids, cell membrane transport mechanisms, resting potential, and organelle functions based on lecture notes.

Primary Structure

The linear sequence of amino acids forming a polypeptide chain.

Secondary Structure

The local folding of a primary amino acid chain into coiled alpha (\alpha) helices or accordion-like beta (\beta) pleated sheets, maintained by hydrogen bonds.

Tertiary Structure

The three-dimensional folding pattern of a protein resulting from interactions and bonding among secondary structures.

Quaternary Structure

The structural level of a protein formed by the interaction and combination of two or more distinct polypeptide chains.

Fibrous Proteins

Strandlike, water-insoluble, and stable structural proteins that provide tensile strength and mechanical support, such as collagen, elastin, and keratin.

Globular Proteins

Compact, spherical, water-soluble functional proteins containing specific active sites that are sensitive to environmental changes, such as antibodies, hormones, and enzymes.

Protein Denaturation

The process where globular proteins unfold and lose their functional three-dimensional shape and active site deactivation due to extreme changes in pH or increased temperature.

Enzymes

Globular proteins that act as biological catalysts to increase the speed of chemical reactions without being consumed, by lowering the required activation energy.

Holoenzyme

A complete, functional enzyme consisting of an apoenzyme (protein portion) joined with a cofactor (metal ion) or coenzyme (organic molecule).

Apoenzyme

The tissue or protein portion of an enzyme that requires a binding cofactor or coenzyme to become fully functional.

Coenzyme

An organic cofactor, often derived from a vitamin, that assists an enzyme in catalyzing a reaction.

Activation Energy

The initial threshold amount of energy required to initiate a chemical reaction.

Deoxyribonucleic Acid (DNA)

A double-stranded helical nucleic acid molecule stored in the cell nucleus that carries genetic blueprints for protein synthesis, composed of purines (adenine, guanine) and pyrimidines (cytosine, thymine).

Ribonucleic Acid (RNA)

A single-stranded linear nucleic acid containing ribose sugar and uracil instead of thymine, active mostly outside the nucleus to execute DNA commands for protein synthesis.

Nucleotide

The monomer unit of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and a phosphate group.

Purines

Two-ring nitrogenous base molecules found in nucleic acids, specifically adenine (A) and guanine (G).

Pyrimidines

Single-ring nitrogenous base molecules found in nucleic acids, specifically cytosine (C), thymine (T), and uracil (U).

Adenosine Triphosphate (ATP)

The primary chemical energy carrier in body cells, structured as an adenine-containing RNA nucleotide with two additional high-energy phosphate groups.

Fluid Mosaic Model

A description of the plasma membrane structure as a flexible lipid bilayer composed of phospholipids, cholesterol, and moving proteins.

Phospholipid Bilayer

The core double layer of the plasma membrane, composed of polar, hydrophilic phosphate heads facing outward and nonpolar, hydrophobic fatty acid tails facing inward.

Glycocalyx

A carbohydrate-rich coating on the outer cell surface composed of glycolipids and glycoproteins, functioning as biological identification markers for cell recognition.

Integral Proteins

Transmembrane proteins firmly inserted into the plasma membrane that contain both hydrophobic and hydrophilic regions.

Peripheral Proteins

Proteins attached loosely to the intracellular or extracellular membrane surfaces that support the plasma membrane, act as enzymes, or assist in cellular connections.

Tight Junctions

Impermeable cell connections where integral proteins of adjacent cells fuse together to block fluids and small molecules from moving through the intercellular space.

Desmosomes

Anchoring cell junctions consisting of interlocking cadherin linker proteins connected to internal plaque regions and keratin filaments, allowing give under mechanical stress.

Gap Junctions

Communicating cell junctions composed of transmembrane connexon proteins that form hollow channels to allow ions, sugars, and electrical signals to pass between cells.

Simple Diffusion

Passive transport of nonpolar, lipid-soluble, or very small substances directly through the lipid bilayer down their concentration gradient without cellular energy.

Facilitated Diffusion

Passive transport of polar or large molecules across a membrane down their concentration gradient via specific carrier or channel proteins.

Osmosis

The diffusion of a solvent, usually water, across a selectively permeable membrane toward an area of higher solute concentration.

Aquaporins

Transmembrane channel proteins that facilitate the rapid passage of water molecules across plasma membranes.

Osmolarity

The measure of total concentration of solute particles present in a solvent.

Hydrostatic Pressure

The back-pressure exerted outward on the plasma membrane by the increased volume of fluid entering a cell via osmosis.

Osmotic Pressure

The inward pressure reflecting the tendency of water to move into a cell along its solute concentration gradient.

Tonicity

The capacity of an extracellular solution to alter a cell's shape or volume by inducing net water movement via osmosis.

Isotonic Solution

A solution possessing the same solute concentration as the cell interior, leading to zero net water movement and constant cell volume.

Hypertonic Solution

A solution with a higher solute concentration than the cell cytoplasm, drawing water out of the cell and causing shrinkage (crenation).

Hypotonic Solution

A solution with a lower solute concentration than the cell cytoplasm, forcing water into the cell and causing swelling or rupture (lysis).

Primary Active Transport

Movement of solutes across a plasma membrane against their concentration gradient powered directly by ATP hydrolysis.

Sodium-Potassium Pump

A primary active transport enzyme ($Na^+-K^+$ ATPase) that pumps $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per molecule of ATP hydrolyzed.

Secondary Active Transport

Cotransport mechanism where a solute is driven against its concentration gradient using energy stored in an ionic gradient previously established by primary active transport.

Antiporters

Active transport carrier proteins that move two different substances across the plasma membrane in opposite directions.

Symporters

Active transport carrier proteins that transport two distinct substances across the plasma membrane in the same direction.

Phagocytosis

A form of endocytosis ("cell eating") in which pseudopod extensions wrap around solid particles to form an internalized vesicle termed a phagosome.

Pinocytosis

A form of endocytosis ("cell drinking" or fluid-phase endocytosis) where the cell membrane infolds to engulf surrounding extracellular fluid and dissolved solutes into an internal vesicle.

Receptor-Mediated Endocytosis

A selective form of endocytosis in which target molecules bind to specialized surface receptors in clathrin-coated pits or caveolae before being drawn into the cell.

Exocytosis

A vesicular process in which secretory vesicles dock via v-SNARE binding to membrane t-SNARE proteins to fuse with the plasma membrane and release contents outside the cell.

Resting Membrane Potential (RMP)

The separation of oppositely charged ions across the plasma membrane of a resting cell, resulting in a voltage difference ranging between $-50\,mV$ and $-100\,mV$.

Cell Adhesion Molecules (CAMs)

Sticky surface glycoproteins that anchor cells to each other or the extracellular matrix, assist white blood cell migration, and transmit intracellular signals.

Cytosol

The semitransparent, gel-like fluid portion of the cytoplasm composed of water, proteins, salts, and dissolved sugars.

Mitochondria

Double-membrane organelles containing inner cristae folds that produce ATP through aerobic cellular respiration and possess independent DNA, RNA, and ribosomes.

Ribosomes

Nonmembranous cytoplasmic structures constructed from rRNA and proteins that serve as the site of cellular protein synthesis.

Rough Endoplasmic Reticulum

A network of interconnected flattened cisterns studded with ribosomes, responsible for synthesizing membrane proteins, phospholipids, and proteins destined for secretion.

Smooth Endoplasmic Reticulum

A network of membranous tubules devoid of ribosomes that catalyzes lipid synthesis, chemical detoxification, glycogen conversion to glucose, and calcium storage.

Golgi Apparatus

Stacked, flattened membranous sacs that receive proteins at the cis face from the rough ER to modify, package, and export them from the trans face via vesicles.

Peroxisomes

Membranous sacs carrying oxidase enzymes to convert metabolic free radicals into hydrogen peroxide ($H_2O_2$), and catalase enzymes to break down hydrogen peroxide into water.

Lysosomes

Spherical membranous organelle sacs filled with acidic hydrolases designed to digest engulfed debris, pathogens, and nonfunctional cell parts, or cause autolysis.

Microfilaments

The thinnest cytoskeletal strands (approximately $7\,nm$ wide) made of actin subunits that provide cell surface strength, resist compression, and drive cell motility.

Intermediate Filaments

Tough, insoluble ropelike cytoskeletal fibers (approximately $10\,nm$ wide) formed by coiled tetramer fibrils that resist pulling forces on the cell.

Microtubules

Hollow cytoskeletal cylinders (approximately $25\,nm$ wide) made of tubulin protein dimers that maintain cell structure and serve as tracks for motor protein transport.

Centrosome

A microtubule organizing center near the nucleus composed of a granular matrix and a perpendicular pair of barrel-shaped centrioles.

Cilia

Whiplike motile cell extensions composed of microtubules that move synchronously to sweep materials across cell surfaces.

Flagella

Long microtubule-based cellular extensions that function specifically to propel an entire cell through its environment, such as a sperm tail.

Microvilli

Small, fingerlike projections of the plasma membrane containing an actin microfilament core that expand cell surface area for increased absorption.

Nuclear Envelope

A double-membrane barrier enclosing the nucleoplasm, lined by the nuclear lamina and pierced by nuclear pore complexes that control macromolecular transport.

Nucleolus

A dense body inside the nucleus containing nucleolar organizer regions responsible for synthesizing rRNA and assembling ribosome subunits.

Chromatin

Threadlike cellular structure composed of nucleosomes—DNA wrapped around histone proteins—that coils tightly into chromosomes during cell division.