Chapter 3 - Cell Biology and Membrane Transport

Flashcards covering cell theory, structural components, membrane transport mechanisms, organelles, cell cycle, protein synthesis, and cellular pathologies as detailed in the lecture transcript.

Cell Theory

A concept stating that cells are the structural and functional unit of living things, organism activity depends on cell activity, biochemical functions are dictated by cell shape/subcellular structures, and cells arise only from preexisting cells.

Plasma membrane

A flexible outer boundary of the cell that acts as a selectively permeable barrier, separating the intracellular fluid from the extracellular fluid.

Cytoplasm

The intracellular fluid containing organelles, located between the plasma membrane and the nucleus.

Nucleus

The $DNA$-containing control center and largest organelle of the generalized cell.

Hydrophilic

A molecule or region of a molecule that is attracted to water.

Hydrophobic

A molecule or region of a molecule that repels and is repelled by water.

Amphipathic

A molecule that contains both a hydrophilic and a hydrophobic region.

Glycocalyx

A 'sugar coating' on the cell surface consisting of glycolipids and glycoproteins that functions as biological markers for cell-to-cell recognition.

Intracellular fluid (ICF)

The fluid contained within the interior of the cell.

Extracellular fluid (ECF)

The fluid environment outside the enclosure of the cell membrane.

Interstitial fluid (IF)

The specific term for extracellular fluid that is not contained within blood vessels.

Extracellular matrix

A substance found outside cells that acts as glue to hold cells together.

Integral proteins

Proteins firmly inserted into the membrane, often transmembrane, possessing both hydrophobic and hydrophilic regions.

Peripheral proteins

Proteins loosely attached to integral proteins that function as enzymes, motor proteins, and cell-to-cell connections.

Tight junctions

Impermeable junctions where integral proteins on adjacent cells fuse, preventing fluids and most molecules from moving between cells.

Desmosomes

Anchoring junctions consisting of plaques and linker proteins ($cadherins$) that interlock like a zipper to help keep cells from tearing apart.

Gap junctions

Communicating junctions where transmembrane proteins ($connexons$) form tunnels allowing ions and small molecules to pass between cells.

Simple Diffusion

The movement of nonpolar lipid-soluble substances directly through the phospholipid bilayer from an area of higher to lower concentration.

Facilitated diffusion

A passive transport process for substances that cannot cross the lipid bilayer due to size, charge, or polarity, utilizing carrier or channel proteins.

Aquaporins (AQPs)

Specific water channels through which water diffuses during osmosis.

Osmolarity

The measure of the concentration of the total number of solute particles in a solvent.

Hydrostatic pressure

Outward pressure exerted on the cell side of the membrane caused by increases in cell volume due to osmosis; also called 'back pressure'.

Osmotic pressure

Inward pressure due to the tendency of water to be 'pulled' into a cell with higher osmolarities.

Isotonic solution

A solution with the same osmolarity as the inside of the cell, resulting in no change in cell volume.

Hypertonic solution

A solution with higher osmolarity than the cell, causing water to flow out and the cell to shrink ($crenation$).

Hypotonic solution

A solution with lower osmolarity than the cell, causing water to flow in and the cell to swell or burst ($lysing$).

Primary active transport

A process where solutes are moved against electrochemical gradients using energy supplied directly from $ATP$ hydrolysis.

Secondary active transport

Transport driven indirectly by energy stored in ionic gradients created by primary active transport, often using $symporters$.

$Na^+-K^+$ pump

A primary active transport system that continuously ejects $3Na^+$ out of the cell and brings $2K^+$ back inside to maintain electrochemical gradients.

Resting membrane potential (RMP)

Electrical potential energy produced by the separation of oppositely charged particles across the plasma membrane, typically ranging from $-50$ to $-100\,mV$.

Phagocytosis

A type of endocytosis ('cell eating') where a cell engulfs a large particle by forming a projecting $pseudopod$.

Pinocytosis

A type of endocytosis ('cell drinking') where the cell gulps a drop of extracellular fluid into tiny vesicles without using receptors.

Exocytosis

The process of packaging material into a vesicle inside the cell and fusing it with the membrane to release contents into the extracellular space.

Cytosol

A gel-like solution within the cytoplasm made up of water and soluble molecules like proteins, salts, and sugars.

Mitochondria

The 'power plant' of cells that produces most energy ($ATP$) via aerobic cellular respiration; it contains its own $DNA$, $RNA$, and ribosomes.

Ribosomes

Nonmembranous organelles made of protein and $rRNA$ that serve as the site of protein synthesis.

Rough Endoplasmic Reticulum (RER)

A network of cisterns studded with ribosomes; the site for synthesis of proteins to be secreted or incorporated into membranes.

Smooth Endoplasmic Reticulum (SER)

A network of tubules involved in lipid metabolism, cholesterol/steroid synthesis, detoxification, and storage of calcium.

Golgi apparatus

Stacked membranous sacs that modify, concentrate, and package proteins and lipids received from the rough $ER$.

Peroxisomes

Membranous sacs containing $oxidase$ and $catalase$ that neutralize toxic free radicals and break down fatty acids.

Lysosomes

Spherical bags containing digestive enzymes ($acid\,hydrolases$) that digest bacteria, viruses, toxins, and nonfunctional organelles.

Microfilaments

The thinnest cytoskeletal elements, composed of the protein $actin$, which strengthen the cell surface and assist in cell motility.

Intermediate filaments

Tough, insoluble ropelike protein fibers (e.g., $keratin$) that help cells resist pulling forces and attach to desmosomes.

Microtubules

The largest cytoskeletal elements made of $tubulin$; they determine cell shape and act as tracks for motor proteins.

Cilia

Whiplike, motile extensions on cell surfaces that move substances like mucus in one direction across the surface.

Microvilli

Fingerlike projections of the plasma membrane that increase surface area for absorption, containing a core of actin microfilaments.

Nucleosome

The fundamental unit of chromatin, consisting of $DNA$ wrapped around eight histone proteins.

Interphase

The period of the cell cycle (subphases $G_1$, $S$, and $G_2$) during which the cell grows, carries out routine activities, and replicates $DNA$.

Semiconservative replication

The mechanism of $DNA$ replication where each new double-stranded molecule consists of one old (parental) strand and one newly synthesized strand.

Mitosis

The division of the nucleus, consisting of prophase, metaphase, anaphase, and telophase.

Prophase

The phase of mitosis where chromatin condenses into chromosomes, the mitotic spindle forms, and the nuclear envelope breaks up.

Anaphase

The shortest phase of mitosis where centromeres split and sister chromatids are pulled toward opposite poles.

Cytokinesis

The division of the cytoplasm into two distinct cells via a contractile ring of actin microfilaments that forms a cleavage furrow.

Transcription

The process of transferring information from a $DNA$ gene base sequence to a complementary $mRNA$ molecule.

Translation

The process where genetic information carried by $mRNA$ is decoded in the ribosome to form a polypeptide chain.

Codon

A three-base sequence on $mRNA$ that specifies a particular amino acid.

Anticodon

The consecutive base sequence on $tRNA$ that recognizes and binds to a complementary $mRNA$ codon.

Exons

Segments of a gene that actually code for amino acids.

Introns

Noncoding segments of a gene interspersed among exons.

Totipotent

Stem cells with the potential to differentiate into any of the cells needed for an organism to grow and develop.

Autophagy

The 'self-eating' process of disposing of nonfunctional organelles and cytoplasmic bits via autophagosomes and lysosomes.

Apoptosis

Programmed cell death where a cell self-destructs through the activation of $caspases$ and is then phagocytized by macrophages.

Hyperplasia

Accelerated growth that increases cell numbers when needed.

Atrophy

A decrease in cell or organ size resulting from loss of stimulation or use.