Biology Chapters 4 & 5: Cell Signaling, Cell Structure, and Membrane Dynamics

Comprehensive vocabulary flashcards generated from Biology lecture materials covering cell signaling mechanism, prokaryotic and eukaryotic cell structures, organelles, membrane permeability, transport mechanisms, and cell junctions.

Endocrine Signaling

A mechanism of cell signaling where cells release hormones into the blood to be transported to distant target cells.

Autocrine Signaling

A cell signaling mechanism in which a secreted signal molecule binds to and acts on the very same cell that produced it.

Paracrine Signaling

A localized cell signaling process where signaling molecules diffuse through interstitial fluid and act on nearby target cells.

Juxtacrine Signaling

Cell-to-cell communication that requires signaling cells to make direct physical contact with adjacent target cells.

Ligand

A specific signaling molecule that binds to a complementary receptor to initiate a signal transduction pathway.

Protein Kinase

An enzyme that transfers a phosphate group from ATP to a specific protein (phosphorylation), typically activating or deactivating that protein.

Phosphatase

An enzyme that catalyzes the removal of a phosphate group from a protein via hydrolysis, deactivating or resetting the protein.

Second Messengers

Small intracellular signaling molecules (such as cAMP) produced in large quantities upon receptor activation to relay and amplify signals throughout the cytosol.

G Protein-Coupled Receptors

Transmembrane receptors containing an extracellular ligand-binding domain and an intracellular domain that interacts with a guanine nucleotide-binding G protein.

Tyrosine Kinase

An enzyme region within enzyme-linked receptors that transfers phosphate groups from ATP to specific tyrosine amino acid residues on a target protein.

Transcription Factors

Proteins or activated receptor complexes that bind to specific DNA sequences in the nucleus to regulate gene expression by turning transcription on or off.

Cell Theory

The unifying biological concept stating that all organisms are composed of cells, cells are the basic units of life, and all cells arise from pre-existing cells.

Surface Area-to-Volume Ratio

A critical mathematical relationship (calculated as surface area divided by volume) that limits cell size by regulating the movement of materials across the plasma membrane.

Magnification

The ratio of the size of an image produced by a microscope to the actual size of the observed object.

Resolution

The minimum distance between two separate points at which they can still be distinguished as distinct entities under a microscope.

Cell Fractionation

A biochemical method using centrifugation to break open cells (homogenization) and separate cellular organelles based on size and mass.

Prokaryotic Cells

Unicellular organisms (Bacteria and Archaea) characterized by the absence of a membrane-bound nucleus and membrane-enclosed organelles.

Eukaryotic Cells

Complex cells (found in animals, plants, fungi, and protists) containing a membrane-bound nucleus and highly organized, membrane-enclosed organelles.

Endosymbiotic Theory

The theory stating that energy-converting organelles (mitochondria and chloroplasts) originated when a larger host eukaryotic cell engulfed ancestral prokaryotic cells.

Nucleolus

A dense body within the eukaryotic cell nucleus where ribosomal RNA (rRNA) is synthesized and ribosome subunits are assembled.

Ribosomes

Non-membrane-bound organelles consisting of a large and small subunit made of RNA and protein that synthesize polypeptides during protein translation.

Smooth Endoplasmic Reticulum

A region of the endomembrane system lacking ribosomes that synthesizes lipids (phospholipids and cholesterol) and breaks down toxic substances.

Rough Endoplasmic Reticulum

A network of internal membranes studded with ribosomes that synthesizes proteins destined for secretion or membrane insertion.

Golgi Complex

An organelle consisting of flattened membranous sacs (cis face entry, trans face exit) that processes, sorts, modifies, and packages proteins into vesicles.

Lysosomes

Membranous digestive sacs in animal cells produced by the Golgi complex that maintain an acidic pH (about 5) to break down wastes, debris, and ingested particles.

Peroxisomes

Membrane-bound organelles containing oxidative enzymes that break down fatty acids, produce hydrogen peroxide ($H_2O_2$), and use catalase to degrade $H_2O_2$ into $H_2O$ and $H^+$.

Apoptosis

Programmed cell death that occurs as a normal part of development and tissue maintenance, triggered by deliberate changes in cellular energy metabolism.

Thylakoids

Interconnected, flattened sac-like membranes inside chloroplast stroma that are stacked into grana and contain chlorophyll for capturing light energy.

Kinesin

A motor protein that utilizes ATP to transport vesicles and organelles along microtubules toward the positive ($+\text{end}$) direction (anterograde movement).

Dynein

A motor protein that transports cellular cargo along microtubules toward the negative ($-\text{end}$) direction (retrograde movement).

Centrioles

A pair of hollow cylindrical structures located in animal cell centrosomes, arranged in a $9 \times 3$ microtubule triplet pattern, that function in cell division.

Amphipathic Molecules

Molecules possessing both hydrophilic (polar, water-attracting) and hydrophobic (nonpolar, water-repelling) regions, such as phospholipids.

Fluid Mosaic Model

The accepted structural model of biological membranes, describing them as two-dimensional fluid phospholipid bilayers in which proteins float freely like mosaic icebergs.

Integral Membrane Proteins

Amphipathic membrane proteins that are firmly bound within the lipid bilayer, often spanning across it completely (transmembrane proteins).

Peripheral Membrane Proteins

Proteins located exclusively on the inner or outer surface of the plasma membrane, non-covalently bound to exposed regions of integral proteins.

Glycoproteins

Proteins with covalently attached carbohydrate chains located on the extracellular side of the plasma membrane, acting in cellular recognition and identification.

Aquaporins

Gated transmembrane channel proteins that facilitate the rapid passive movement of water molecules across biological membranes.

Osmosis

The passive net movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

Hypertonic Solution

A surrounding solution with a higher solute concentration relative to the cytosol, causing net movement of water out of the cell and cellular shrinkage.

Hypotonic Solution

A surrounding solution with a lower solute concentration relative to the cytosol, causing net water movement into the cell and resulting in swelling or turgor pressure.

Plasmolysis

The process in plant cells where the plasma membrane detaches and shrinks away from the rigid cell wall when exposed to a hypertonic environment.

GLUT 1

A specific transmembrane carrier protein that undergoes reversible conformational shape changes to transport glucose down its concentration gradient into cells.

Sodium-Potassium Pump

An active transport carrier mechanism in animal cells that uses ATP energy to export three $Na^+$ ions out of the cell for every two $K^+$ ions imported.

Phagocytosis

A type of endocytosis where a cell extends plasma membrane pseudopodia to engulf large solid particles or microorganisms into a food vacuole.

Pinocytosis

A type of endocytosis where plasma membrane invaginations trap micro-droplets of extracellular fluid and dissolved substances into small cytosolic vesicles.

Desmosomes

Specialized cell junction structures that anchor adjacent cells together at specific spots via cadherins attached to intermediate filaments, maintaining structural integrity.

Tight Junctions

Impermeable cell connections that completely seal intercellular space between adjacent animal epithelial cells, preventing fluid leakage across cell layers.

Gap Junctions

Intercellular junction channels that bridge adjacent animal cells, permitting the direct transfer of small molecules, ions, and electrical signals.

Plasmodesmata

Membrane-lined cytoplasmic channels penetrating plant cell walls that function analogously to animal gap junctions to allow water, ions, and small solutes to pass between adjacent cells.