Cell Biology and Membrane Structure

Flashcards covering cell organization, organelle structure and functions, cytoskeleton, cell junctions, and membrane transport concepts from the lecture notes.

Cytology

The study of cell structure.

Light Microscopy

Microscopy based on passing a beam of light through a specimen, suitable for viewing plant and animal cells, nucleus, and bacteria.

Electron Microscopy

Microscopy based on passing a beam of electrons over or through a specimen (such as viruses, ribosomes, and proteins), offering higher resolution and magnification.

Resolution

The minimum distance $2$ points can be separated and still distinguished.

Magnification

The ratio of an object's image size to its real size.

Contrast

The difference in brightness between light and dark areas of an image.

Eukaryotic Cells

Animal and plant cells containing DNA located within a membrane-enclosed nucleus.

Plasma Membrane

A selectively permeable liquid bilayer that surrounds the cell.

Cytoplasm

The interior of a cell containing organelles suspended in a jelly-like substance called cytosol.

Endomembrane System

A cellular system connected via direct physical continuity or through the transfer of vesicles (small, fluid-filled sacs) that stores and transports materials.

Chromatin

Material made up of DNA and proteins that constitutes chromosomes inside the nucleus.

Nuclear Lamina

A network of protein filaments lining the nuclear envelope that provides structural scaffolding for the nucleus.

Nucleolus

A structure within the nucleus that serves as the location for RNA transcription and ribosome assembly.

Ribosomes

Non-membrane-bound complexes of protein and rRNA responsible for protein synthesis, existing either as free ribosomes in the cytosol or bound ribosomes on the ER/nuclear envelope.

Endoplasmic Reticulum (ER)

A membranous system of interconnected tubules and flattened sacs (cisternae) enclosing an internal compartment called the ER lumen.

Smooth ER

A region of the endoplasmic reticulum lacking associated ribosomes that aids in metabolic processes such as lipid synthesis and calcium storage.

Rough ER

A region of the endoplasmic reticulum covered in bound ribosomes that synthesizes proteins for membranes or export outside the cell.

Transitional ER

A region of the rough ER where transport vesicles bud off to move to other cellular destinations.

Golgi Apparatus

A series of $4$ to $8$ flattened membranous sacs (cisternae) with cis and trans faces that alters macromolecule structures, synthesizes secreted polysaccharides, and sorts vesicles for transport.

Lysosomes

Membranous sacs with an acidic interior (low pH) containing hydrolytic enzymes that cause hydrolysis of macromolecules during phagocytosis and autophagy.

Phagocytosis

The internalization (endocytosis) of large particles to aid in digestion and killing invaders, forming food vacuoles.

Autophagy

The cellular process of recycling a cell's own organic material.

Contractile Vacuoles

Vacuoles present in aquatic, unicellular eukaryotes that pump excess water out of the cell.

Central Vacuole

A large vacuole in plant cells that stores inorganic ions and contributes to cell growth and structural stability.

Mitochondria

Organelles enclosed by a double lipid bilayer membrane that contain their own DNA and ribosomes, serving as the powerhouse of the cell by producing ATP from fuels and oxygen.

Cristae

Convoluted folds of the inner mitochondrial membrane that increase surface area for membrane-bound cellular respiration enzymes.

Chloroplasts

Specialized double-membrane plastids containing their own DNA and ribosomes that serve as the site of photosynthesis, producing sugars from $CO_2$, water, and light.

Stroma

The fluid compartment located outside the thylakoids inside a chloroplast.

Thylakoid

A membrane system of flattened interconnected sacs inside chloroplasts; stacks of thylakoids are known as grana.

Endosymbiont Theory

An evolutionary theory stating that mitochondria and chloroplasts originated from oxygen-using and photosynthetic prokaryotes that were engulfed by ancestral host eukaryotic cells.

Peroxisome

An organelle bound by a single lipid bilayer containing enzymes that remove H atoms from molecules and transfer them to $O_2$, forming hydrogen peroxide ($H_2O_2$) before converting it into water.

Cytoskeleton

A dynamic network of fibers extending throughout the cytoplasm that is constantly removed and rebuilt to provide mechanical support, structure, anchorage, and cell motility.

Microtubules

Hollow rods made from dimers of alpha-tubulin and beta-tubulin with the largest diameter in the cytoskeleton, serving as tracks for motor proteins and forming centrioles, cilia, and flagella.

Centrosome

A region near the nucleus where microtubules grow, containing a pair of centrioles composed of $9$ sets of triplet microtubules.

Microfilaments (Actin Filaments)

Double-twisted chains of actin subunits with the smallest cytoskeletal diameter that contribute to cell shape, tension bearing, and motility.

Intermediate Filaments

Cytoskeletal fibers intermediate in diameter and more permanent, composed of diverse proteins (such as keratins) that maintain cell shape in select eukaryotic cells.

Middle Lamella

An extracellular layer made of pectin that glues adjacent plant cell walls together.

Extracellular Matrix (ECM)

An extracellular layer around animal cells containing glycoproteins, polysaccharides, proteoglycans, and fibronectins attached to integrins.

Plasmodesmata

Channels connecting adjacent plant cells that allow the transfer of compounds between cells.

Gap Junctions

Intercellular channels connecting animal cells, serving as the animal cell equivalent of plasmodesmata.

Tight Junctions

Continuous seals between adjacent animal cells that prevent the leakage of extracellular fluid.

Desmosomes

Intercellular junctions that fasten animal cells together, anchored into the cytoplasm by intermediate filaments.

Prokaryotic Cells

Cells that lack a nucleus (DNA resides in a non-membrane-bound nucleoid) and lack an endomembrane system, though they contain flagella and cell walls.

Fluid Mosaic Model

A model describing cellular membranes as fluid lipid bilayers containing a mosaic of phospholipids, proteins, and carbohydrates.

Integral Proteins

Membrane proteins that penetrate the hydrophobic interior of the lipid bilayer, including transmembrane proteins.

Peripheral Proteins

Membrane proteins loosely bound to the surface of the membrane and often associated with integral proteins.

Diffusion

The movement of particles down their concentration gradient to spread out into available space until dynamic equilibrium is reached.

Electrochemical Gradient

The diffusion gradient of an ion influenced jointly by ion concentration and membrane potential (charge across the membrane).

Osmosis

The diffusion of free water across a selectively permeable membrane.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water, categorized into isotonic, hypertonic, and hypotonic states.

Passive Transport

The diffusion of a molecule across a biological membrane down its electrochemical gradient without requiring energy input.

Active Transport

The movement of a solute across a cell membrane against its electrochemical gradient via a carrier protein, directly or indirectly powered by ATP hydrolysis.

Cotransport

A transport mechanism coupling the downhill diffusion of one molecule along its electrochemical gradient with the uphill movement of another molecule against its gradient.

Bulk Transport

The process of exporting (exocytosis) or importing (endocytosis, pinocytosis, receptor-mediated endocytosis) large molecules across membranes via vesicles.