BIO 140: Cell Biology, Transport, Enzymes, and Cytoskeleton

Comprehensive vocabulary review flashcards covering cell structure and organelles, cell transport mechanisms, enzyme energetics and kinetics, and cytoskeletal filaments from BIO 140.

Nucleoid

The region in a prokaryotic cell where circular DNA is concentrated, not enclosed by a membrane.

Peptidoglycan

The polymer consisting of sugars and amino acids that forms the bacterial cell wall, providing protection, shape maintenance, and hydration.

Nucleolus

A dense region inside the eukaryotic nucleus where ribosomes are assembled and formed.

Nuclear Envelope

A double membrane enclosing the nucleus equipped with protein-lined nuclear pores that regulate the transport of materials in and out.

Ribosome

A cellular structure composed of ribosomal RNA and proteins, consisting of large and small subunits, that functions as the site of protein synthesis.

Mitochondria

Organelles enclosed by a double membrane with inner foldings called cristae that carry out cellular respiration to produce energy in the form of $\text{ATP}$.

Peroxisome

An organelle that houses enzymes for oxidative metabolism, including the detoxification of harmful compounds and the breakdown (oxidation) of fatty acids and amino acids.

Central Vacuole

A large plant cell organelle filled with cell sap that stores water, nutrients, and waste, exerting turgor pressure against the cell wall to maintain rigidity and cell shape.

Centrosome

The microtubule-organizing center of animal cells that contains a pair of centrioles and plays a key role in organizing the mitotic spindle during cell division.

Lysosome

An animal cell organelle packed with hydrolytic enzymes that digests macromolecules, food particles, cellular debris, and foreign invaders.

Chloroplast

A plant and algal organelle containing chlorophyll, its own DNA, and ribosomes, which serves as the site of photosynthesis by converting solar light energy into chemical energy.

Microvilli

Finger-like plasma membrane projections found on epithelial cells of the small intestine that increase surface area for nutrient absorption.

Cytosol

The gel-like aqueous fluid portion of the cytoplasm that surrounds organelles and contains dissolved ions, nutrients, and molecules.

Passive Transport

The net movement of solutes down a concentration gradient from higher to lower concentration without the expenditure of cellular energy ($\text{ATP}$).

Simple Diffusion

A form of passive transport where small, nonpolar molecules traverse the phospholipid bilayer directly without transport proteins.

Facilitated Diffusion

Passive transport of polar or larger molecules across the plasma membrane with the assistance of channel or carrier proteins.

Osmosis

The net diffusion of free water molecules across a selectively permeable membrane toward a region of higher solute concentration.

Osmolarity

The total solute concentration of a solution, determining the osmotic pull on water molecules across a selectively permeable barrier.

Tonicity

The capability of an extracellular solution to alter cell volume and shape by influencing the net osmotic movement of water.

Active Transport

The movement of ions or molecules across a membrane against their concentration or electrochemical gradient (low to high), requiring energy usually provided by $\text{ATP}$.

Electrochemical Gradient

The combined influence of a chemical concentration gradient and an electrical charge differential across a biological membrane.

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

An active antiporter membrane pump that utilizes $\text{ATP}$ to transport $2\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell to preserve resting membrane potential.

Uniporter

An integral membrane transport protein that moves a single type of solute across the membrane in one direction.

Symporter

A secondary or primary membrane cotransporter that moves two different solutes across the membrane in the same direction simultaneously.

Antiporter

A carrier protein that moves two different ions or solutes across the membrane in opposite directions.

Bulk Transport

The vesicular transport of macromolecules, large particles, or whole cells across the plasma membrane, requiring cellular energy.

Phagocytosis

A form of endocytosis known as 'cell eating,' in which a cell wraps its plasma membrane around a large particle or microorganism to internalize it in a vacuole.

Pinocytosis

A mode of bulk endocytosis termed 'cell drinking,' where a cell invaginates its membrane to take up drops of extracellular fluid and dissolved solutes into tiny vesicles.

Receptor-Mediated Endocytosis

A selective bulk transport mechanism in which target extracellular molecules bind to specific membrane receptors, triggering coated vesicle internalization.

Exocytosis

The process by which intracellular transport vesicles fuse with the plasma membrane to secrete substances such as hormones, enzymes, neurotransmitters, or cellular waste out of the cell.

Activation Energy ($E_{\text{a}}$)

The minimum quantity of free energy required to destabilize existing bonds and reach the transition state in a chemical reaction.

Transition State

An unstable, high-energy intermediate configuration of reactants formed during a chemical reaction as original bonds are breaking and new ones are forming.

Induced Fit

The conformational adjustment of an enzyme's active site upon substrate binding that aligns catalytic residues and binds the substrate more snugly.

Saturation Kinetics

The characteristic behavior of enzyme-catalyzed reactions where the reaction rate plateaus at high substrate concentrations because virtually all enzyme active sites are occupied.

Cofactor

An inorganic ion (such as $\text{Mg}^{2+}$, $\text{Zn}^{2+}$, or $\text{Fe}^{2+}$) that associates with an enzyme to assist its catalytic function, such as $\text{Mg}^{2+}$ stabilizing phosphate charges for DNA polymerase.

Coenzyme

A non-protein organic cofactor (such as $\text{NADH}$ or $\text{FADH}_2$) that functions as a transient carrier of chemical groups or electrons during enzyme-mediated reactions.

Prosthetic Group

A non-amino acid moiety permanently bonded to a protein that is indispensable for its biological activity, such as the iron-containing heme ring in hemoglobin and myoglobin.

Competitive Inhibition

A regulatory mechanism where an inhibitory molecule of similar size and geometry directly competes with the substrate for binding to the enzyme's active site.

Allosteric Regulation

The modulation of enzymatic function caused by the non-covalent binding of an effector molecule to an allosteric site separate from the active site, inducing a conformational change.

Phosphofructokinase-1 (PFK-1)

A regulatory allosteric enzyme that acts as a pacemaker in glycolysis; activated by $\text{ADP}$ and $\text{AMP}$, and inhibited by $\text{ATP}$ and citrate.

Statins

A class of pharmaceutical agents that lower blood cholesterol by acting as competitive inhibitors of $\text{HMG-CoA reductase}$, the rate-limiting enzyme in cholesterol biosynthesis.

Cytoskeleton

A dynamic cytoplasmic network of protein filaments that provides structural framework, maintains cell morphology, anchors organelles, and directs intracellular trafficking.

Microfilaments

The narrowest cytoskeletal fibers (approximately $7\,\text{nm}$ diameter), composed of double-helical actin strands, that support cell shape at the cortex, drive muscle contraction with myosin, and participate in cell division.

Intermediate Filaments

Rope-like cytoskeletal polymers measuring $8\text{--}10\,\text{nm}$ across composed of fibrous proteins like keratin and neurofilaments, primarily providing mechanical strength and anchoring the nucleus.

Microtubules

Hollow, cylindrical cytoskeletal fibers ($25\,\text{nm}$ diameter) formed from $\alpha$- and $\beta$-tubulin heterodimers that provide tracks for vesicle transport and form the spindle apparatus during mitosis.

Axoneme

The core microtubular architecture of eukaryotic cilia and flagella characterized by a $9+2$ arrangement of peripheral doublets surrounding two central singlet microtubules.