Cell Biology Lecture Series

Flashcards covering the major concepts and vocabulary from Cell Biology Lectures 1-14, including cell structures, membrane transport, signaling, organelles, and cell division.

Antibodies (Immunoglobulins)

Glycoproteins produced by specific cells of the immune system in response to a foreign protein/antigen (e.g., bacteria, viruses, chemicals).

Fluorochromes (Fluorescent dyes)

Chemicals that absorb light of different wavelengths and then emit visible light of a specific wavelength (e.g., green, yellow, red).

Polyclonal antibodies

Antibodies produced in immunized animals by many clones of B lymphocytes that recognize different regions of a single antigen.

Monoclonal antibodies

Antibodies produced by immortalized antibody-producing cell lines by a single group (clone) of identical B lymphocytes.

Hybridization

The association of two nucleic acid strands together by hydrogen bonding (base pairing).

In situ hybridization (ISH)

Binding of a nucleotide probe to the DNA or RNA sequence of interest within cells or tissues to localize specific sequences in place.

Autoradiography

Technique using a photographic emulsion placed over a tissue section to localize radioactive material within probes, cells, or tissues.

Mesosomes

In-folds of the prokaryotic plasma membrane that bear respiratory enzymes and play a role in replication and division of nuclear material.

Slimy capsule (Glycocalix)

A gelatinous coat composed largely of polysaccharides and polypeptides outside the cell wall that protects prokaryotic cells from desiccation, viruses, and phagocytosis.

Nucleoid

The region in a prokaryotic cell where the genetic material (a coiled single chromosome) lies directly in the cytoplasm without a nuclear envelope.

Plasmids

Small circular double-stranded DNA molecules in bacteria often used by scientists as vectors to artificially introduce foreign DNA.

Capsid

The protein coat that encloses the core of genetic material in a virus particle.

Fluid-mosaic model

A model of the plasma membrane where the phospholipid bilayer is viscous (fluid) and embedded with a mosaic of proteins.

Lipid rafts

Areas of the plasma membrane characterized by high concentrations of glycosphingolipids, cholesterol, and specific proteins involved in cell signaling.

Flip-flop movements (transverse diffusion)

The movement of phospholipids from one monolayer to another, catalyzed by enzymes such as scramblases and flippases.

Integral membrane proteins

Proteins that are embedded within the lipid bilayer, including transmembrane proteins and integral monotopic proteins.

Peripheral membrane proteins

Proteins that are not embedded within the lipid bilayer but are attached to the outer or inner surface of the membrane.

Aquaporins (AQP)

A family of integral membrane proteins that form water-filled tubes allowing water to cross membranes very quickly and selectively.

Transporters (Carrier proteins)

Proteins that bind to a molecule, undergo conformational changes, and release the molecule on the other side of the membrane.

Channel proteins

Proteins that form hydrophilic pores through the plasma membrane that fluctuate between open and closed states.

Passive transport (Facilitated diffusion)

'Downhill' movement of molecules across a membrane without energy use, determined by concentration or electrochemical gradients.

Active transport

'Uphill' movement of solutes against their electrochemical gradient, requiring the cell to use energy (e.g., ATP-driven pumps).

Symport

A type of coupled pump that moves both solutes across the membrane in the same direction.

Antiport

A type of coupled pump that moves two solutes across the membrane in opposite directions.

Pinocytosis

A type of endocytosis where the cell engulfs liquid material, often referred to as 'cell drinking.'

Phagocytosis

The ingestion of large, non-dissolved particles such as cell debris or bacteria into large vesicles called phagosomes.

Receptor-mediated endocytosis

A selective mechanism where receptors on the cell membrane bind specific ligands before entering the cell, often involving clathrin.

Caveolae

Flask-shaped invaginations of the plasma membrane (50–100 nm) that are specialized lipid rafts containing the protein caveolin.

Exocytosis

An active process where substances are released out of the cell by the fusion of a vesicle with the plasma membrane.

Paracrine signaling

Communication where signal molecules diffuse over small distances through extracellular fluid to reach target cells in the neighborhood.

Autocrine signaling

A form of signaling where cells respond to local mediators that they themselves produce.

Juxtacrine signaling (Contact-dependent)

Signaling where a cell-surface-bound molecule binds to a receptor on an adjacent target cell without releasing a secreted molecule.

Gap junctions (Nexus)

Tiny water-filled channels (connexons) directly connecting neighboring cells to allow small signaling molecules to diffuse between them.

Nuclear receptors

Intracellular receptors (cytosolic or nuclear) that act as ligand-activated transcription factors when bound to small hydrophobic molecules like steroids.

G-protein-coupled receptors (GPCRs)

A large class of cell-surface receptors that activate trimeric GTP-binding proteins to relay signals inside the cell.

Second messengers

Small, non-protein molecules or ions ($cAMP$, $Ca^{2+}$, $IP_3$, $DAG$) that diffuse quickly through the cytosol to relay surface signals.

Cell Adhesion Molecules (CAMs)

Transmembrane integral membrane proteins composed of intracellular, transmembrane, and extracellular domains that mediate cell attachment.

Cadherins

$Ca^{2+}$-dependent CAMs that participate in homophilic adhesions like adherens junctions and desmosomes.

Selectins

Cell surface lectins (P, E, and L types) that mediate the rolling and trapping of leukocytes and platelets during inflammation.

Integrins

Transmembrane heterodimers that link the extracellular matrix to the cytoskeleton and participate in bidirectional signaling.

Extracellular Matrix (ECM)

A complex network of macromolecules (proteins and polysaccharides) secreted by cells that fills spaces between cells or forms basement membranes.

Glycosaminoglycans (GAGs)

Large, charged polysaccharides composed of repeating disaccharide units that provide hydration and resistance to compression in the ECM.

Proteoglycans

Complexes composed of a core protein with GAGs attached, providing hydration and serving as structural components of tissues.

Fibronectin

A multi-adhesive glycoprotein of the interstitial matrix that has binding sites for integrins, collagen, and heparin.

Laminins

Large, crosslike multi-adhesive proteins that are major components of the basal lamina and help anchor epithelial cells.

Matrix Metalloproteinases (MMPs)

A group of extracellular enzymes responsible for the degradation and remodeling of the extracellular matrix.

Tight junction (Zonula occludens)

An occluding junction that forms a tight seal between adjacent cells to prevent the passage of macromolecules.

Desmosome (Macula adherens)

Spot-like cell-cell adhesions that link to intermediate filaments and provide mechanical strength to tissues under stress.

Connexon

A hexameric assembly of six membrane-spanning connexin subunits that forms one half of a gap junction channel.

Hemidesmosomes

Asymmetrical structures that anchor the basal domain of an epithelial cell to the underlying basal lamina via integrins and intermediate filaments.

Motor proteins

Proteins (kinesins, dyneins, myosins) that utilize ATP hydrolysis to travel along microtubules or actin filaments to move cargo.

Kinesins

Motor proteins that generally move toward the plus ($+$) end of a microtubule, outward from the cell body.

Dyneins

Motor proteins that move toward the minus ($-$) end of a microtubule, typically toward the microtubule-organizing center.

Centrosome

The primary microtubule-organizing center (MTOC) in animal cells, containing a pair of centrioles.

Treadmilling

A dynamic state in actin filaments where monomers are added at the plus end and removed at the minus end at the same rate.

Sarcomeres

The structural and functional units of myofibrils in skeletal and cardiac muscle, delimited by two Z discs.

Nuclear lamina

A meshwork of intermediate filaments (lamins) located just under the nuclear envelope that provides structural support to the nucleus.

Endoplasmic Reticulum (ER)

A complex network of single membrane-enclosed channels involved in the synthesis, modification, and transport of proteins and lipids.

Golgi apparatus

An organelle composed of flattened cisternae that functions as the main glycosylation, sorting, and packaging center of the cell.

Vesicular transport

The process of moving material as cargo between membrane-bound compartments using coated vesicles (Clathrin, COPI, COPII).

Lysosomes

Single-membrane-bound organelles containing acid hydrolases for the intracellular digestion of macromolecules and worn-out organelles.

Peroxisomes

Small membranous sacs containing enzymes involved in lipid metabolism and detoxification, which replicate by division.

Mitochondria

Double-membrane-enclosed organelles specialized for ATP synthesis through oxidative phosphorylation, possessing their own DNA.

Nuclear Pore Complex (NPC)

Large protein assemblies that span the nuclear envelope and control the bidirectional traffic of molecules between the nucleus and cytoplasm.

Nucleolus

The site within the nucleus where ribosomal RNA ($rRNA$) is synthesized and ribosomal subunits are assembled.

Euchromatin

Diffuse, transcriptionally active chromatin that represents approximately 90% of the total chromatin in the nucleus.

Heterochromatin

Highly condensed, transcriptionally inactive chromatin, which includes constitutive and facultative types.

Nucleosomes

The basic unit of eukaryotic chromosome structure, consisting of a histone octamer core wrapped by approximately two turns of DNA.

Promoter

The region of a gene where RNA polymerase and general transcription factors bind to initiate transcription.

Codon

A group of three consecutive nucleotides in mRNA that specifies a particular amino acid in a polypeptide chain.

Proteasomes

Large protein-degrading machines that hydrolyze proteins marked by the covalent attachment of ubiquitin.

Interphase

The period of the cell cycle between divisions, comprising the $G_1$, $S$, and $G_2$ phases.

Telomeres

Repetitive DNA sequences at the tips of eukaryotic chromosomes that protect internal gene regions from being lost during replication.

Cyclin-dependent kinases (Cdks)

Protein kinases that, when bound to cyclins, control the progression of the cell cycle through phosphorylation.

Mitosis

Division of the cell nucleus resulting in two genetically identical sets of chromosomes, divided into five stages ($Prophase$ to $Telophase$).

Meiosis

A specialized cell division that reduces the chromosome number from diploid ($2n$) to haploid ($1n$) to produce gametes.

Stem cells

Undifferentiated cells capable of self-renewal and differentiation into various specialized cell types.

Apoptosis

Programmed cell death; a tidy, deliberate suicide mechanism involving a proteolytic cascade mediated by caspases.

Caspases

Cysteine-dependent aspartate-directed proteases that are activated during apoptosis to cleave specific intracellular proteins.