Cell Structure and Cell Transport

Vocabulary flashcards covering cellular structures, organelles, cell membrane dynamics, and transport mechanisms based on veterinary physiology lecture notes.

Cytosol

The liquid component of the cytoplasm that surrounds intracellular organelles.

Cytoplasm

All contents of a cell except the nucleus, including both the cytosol and all intracellular organelles.

Chromatin

Loosely packed DNA spread throughout the nucleus that represents the active, working DNA.

Chromosomes

Densely packed DNA structures formed specifically for cell division.

Nucleolus

A region inside the nucleus where ribosomal RNA and proteins accumulate to synthesize ribosome subunits.

Ribosome

An organelle composed of rRNA and proteins (large and small subunits) that translates mRNA into polypeptide chains during protein synthesis.

Polysome

A complex formed during protein synthesis when multiple ribosomes are attached to a single mRNA strand.

Rough Endoplasmic Reticulum (RER)

An organelle organized into branching tubules and flattened sacs with attached ribosomes that synthesizes membrane proteins, secretory proteins, and lysosomal proteins.

Smooth Endoplasmic Reticulum (SER)

A network of tubules and vesicles lacking ribosomes that synthesizes lipids and serves as an intracellular calcium store.

Golgi Apparatus

A collection of flattened membrane-enclosed compartments (cisternae) that modifies, sorts, and packages proteins and lipids received from the ER.

Lysosome

A vesicular organelle packed with digestive hydrolase enzymes that breaks down damaged cellular structures, ingested food particles, and foreign matter.

Peroxisome

A vesicular organelle containing oxidases and catalase that breaks down fatty acids via $\beta$-oxidation and detoxifies hydrogen peroxide ($H_2O_2$).

Mitochondrion

A self-replicating organelle that burns food molecules to produce ATP by oxidative phosphorylation.

Vacuole

A small, membrane-bound sac within the cytoplasm used for temporary storage of nutrients or waste products.

Cytoskeleton

A network of fibrillar proteins (microfilaments, microtubules, and intermediate filaments) that provides cell shape, mechanical strength, division, and movement tracks.

Tight Junctions

Intercellular junctions that form a seal to prevent the passage of molecules between adjacent cells.

Gap Junctions

Intercellular junctions made of connexin transmembrane proteins that create channels for direct communication and exchange of ions/molecules between cells.

Adherens Junctions

Anchoring intercellular junctions that connect actin filaments of neighboring cells to provide mechanical stability.

Desmosomes

Strong anchoring intercellular junctions that connect intermediate filaments between neighboring cells to provide cell-cell adhesion.

Integral Proteins

Permanently attached membrane proteins embedded in the lipid bilayer that act as channels, transporters, and receptors.

Peripheral Proteins

Membrane proteins attached to only one surface of the lipid bilayer or to integral proteins, acting as enzymes or channel controllers.

Simple Diffusion

Passive movement of molecules directly through the lipid bilayer down their concentration gradient without requiring transport proteins or energy.

Facilitated Diffusion

Passive transport of molecules across a membrane down their concentration gradient using specific carrier or channel proteins, reaching a maximum transport rate ($V_{\max}$).

Osmolarity

The amount of solute particles per liter of solution.

Osmolality

The amount of solute particles per kilogram of solvent, unaffected by temperature and pressure (normal plasma osmolality is approximately $275\text{--}295\,\text{mOsm/kg}$).

Effective Osmoles

Solutes (such as ions, albumin, and mannitol) that are unable to penetrate the membrane between compartments and create lasting osmotic gradients.

Ineffective Osmoles

Solutes (such as ethanol and urea) that freely cross cell membranes and do not create lasting osmotic gradients.

Tonicity

The effective osmotic pressure generated by non-permeant solutes, which determines the direction of passive water movement across a semipermeable membrane.

Hypertonic Solution

A solution with a higher effective osmole concentration than the cell, causing water to leave the cell and the cell to shrink (crenate).

Hypotonic Solution

A solution with a lower effective osmole concentration than the cell, causing water to enter the cell and the cell to swell or lyse.

Isotonic Solution

A solution with the same effective osmole concentration as the cell, resulting in no net water movement across the cell membrane.

Primary Active Transport

Transport of molecules across a membrane against their concentration gradient using direct cellular energy derived from ATP breakdown.

Secondary Active Transport

Transport of a substance against its concentration gradient driven by the downhill concentration gradient of a coupled driving ion (such as $\text{Na}^+$ or $\text{H}^+$).

Symport

A secondary active transport mechanism (cotransport) where two substances are transported simultaneously across a membrane in the same direction.

Antiport

A secondary active transport mechanism (counter-transport) where two substances are transported simultaneously across a membrane in opposite directions.

Transcellular Transport

Transport of substances across an entire cell from one ECF compartment to another, combining active transport on one membrane side and diffusion on the opposite side.

Transcytosis

A cellular process where macromolecules enter one side of a cell via endocytosis, move across the cell in vesicles, and exit the opposite side via exocytosis.

Voltage-gated Ion Channel States

The three functional states of a voltage-gated channel: deactivated (closed but ready to open), activated (open), and inactivated (closed and unable to open).