Module 4-7: Cell Structures, Physiology and Immunology

Vocabulary flashcards covering cellular membrane structure, transport mechanisms, blood components, immunology (innate and adaptive), and neuro-muscular physiology based on the Module 4-7 transcripts.

Fluid mosaic model

A model describing the membrane as a "sea of lipids in which proteins float like icebergs." The membrane is $~8\,nm$ thick, $50\%$ lipid and $50\%$ protein, held together by hydrogen bonds.

Amphipathic

Having BOTH a polar (hydrophilic) region AND a nonpolar (hydrophobic) region in the same molecule.

Cholesterol

Lipids scattered among phospholipids that DECREASES membrane fluidity by filling gaps between phospholipids.

Glycolipids

Phospholipids with carbohydrate chains attached, found ONLY on the outer leaflet, and involved in cell recognition.

Integral proteins

Proteins that extend INTO or ACROSS the membrane (transmembrane) and are amphipathic.

Peripheral proteins

Proteins attached to the SURFACE of the membrane only and are easily removed.

Ion channels

Proteins that form water-filled pores allowing rapid ion transport ($>1\,million\,ions/second$) where ions do NOT bind to the channel.

Transporter proteins

Proteins that bind specific molecules and carry them across the membrane by changing shape (conformational change).

Diffusion

Random movement of particles from HIGH to LOW concentration until equilibrium is reached, driven by the kinetic energy of molecules.

Concentration gradient

A difference in concentration of a substance between two regions, which drives diffusion from high to low.

Electrical gradient

The difference in electrical charge across the membrane (membrane potential) which attracts ions of opposite charge.

Electrochemical gradient

The COMBINED effect of concentration gradient AND electrical gradient on ion movement.

Osmosis

Net movement of water through a selectively permeable membrane from LOW solute (HIGH water) to HIGH solute (LOW water) concentration.

Osmotic pressure

The pressure needed to PREVENT water from flowing into a solution by osmosis; higher solute concentration results in higher osmotic pressure.

Hypotonic solution

A solution with LOWER solute concentration than the cell, causing water to flow INTO the cell, making it swell or lyse.

Hypertonic solution

A solution with HIGHER solute concentration than the cell, causing water to flow OUT of the cell, making it shrink.

Isotonic solution

A solution with equal solute concentration to the cell where there is no net water movement and no change in cell volume.

Aquaporins

Water channels that allow FAST, temperature-INDEPENDENT, and mercury-SENSITIVE water movement (Pf).

Passive transport

Movement of substances DOWN their concentration or electrochemical gradient using only kinetic energy, requiring NO ATP.

Channel gating

The opening and closing of ion channels in response to stimuli such as voltage, ligand binding, cell volume, $pH$, or phosphorylation.

Patch clamp technique

A method using a glass pipette to seal onto a membrane patch to measure currents ($~10^{-12}\,amp$) from single ion channels.

Carrier-mediated (facilitated) diffusion

Passive movement where a substrate binds to a transporter protein, triggering a shape change to move the substance down its concentration gradient.

Transport maximum ($T_{max}$)

The maximum rate of carrier-mediated transport reached when ALL binding sites on the transporter are occupied (saturated).

Active transport

Movement of molecules AGAINST their concentration or electrochemical gradient, which requires energy.

Primary active transport

Transport that DIRECTLY uses ATP hydrolysis to move substances against their gradient, such as the $Na^{+}/K^{+}$ ATPase pump.

Secondary active transport

Transport that uses energy stored in ion gradients (created by primary active transport) to move substances against their own gradient.

Electrogenic

A term for the $Na^{+}/K^{+}$ ATPase because it moves 3 positive charges out for every 2 that return, making the inside of the cell more NEGATIVE.

Symporter

A carrier protein that moves $Na^{+}$ and another substance in the SAME direction, such as SGLT.

Antiporter

A carrier protein that moves $Na^{+}$ in one direction while another ion moves in the OPPOSITE direction, such as the $Na^{+}/Ca^{2+}$ exchanger.

Tight junctions

Structures that serve as BARRIERS to restrict paracellular movement and FENCES to prevent membrane proteins from diffusing between apical and basolateral surfaces.

Apical membrane

The membrane facing the LUMEN (e.g., intestinal contents or tubule fluid).

Basolateral membrane

The membrane facing the BLOOD supply and basement membrane.

Transcellular transport

Movement THROUGH the cell via transport proteins on both apical and basolateral membranes.

Paracellular transport

Movement BETWEEN cells through tight junctions, governed by diffusion and junction tightness.

CFTR ($Cystic\,Fibrosis\,Transmembrane\,conductance\,Regulator$)

The apical $Cl^{-}$ channel requiring phosphorylation by PKA and ATP binding to open; it is the rate-limiting step in $Cl^{-}$ secretion.

Cystic fibrosis

An autosomal recessive disorder caused by a mutation in the CFTR gene, commonly the deletion of phenylalanine ($\Delta F508$).

Plasma

The liquid fraction of blood AFTER centrifugation that still contains fibrinogen and clotting factors.

Serum

Plasma minus clotting factors; the clear yellow liquid remaining after blood has clotted and the fibrin clot is removed.

Oxyhaemoglobin

Haemoglobin bound to $O_2$, formed in the lungs and characterized by a bright red color.

Carbaminohaemoglobin

Haemoglobin bound to $CO_2$, formed in the tissues and characterized by a dark red color.

Coagulation

A proteolytic activation cascade that converts fibrinogen to fibrin to form an insoluble clot.

Thrombolysis

The dissolution of blood clots through the conversion of plasminogen to PLASMIN, which digests fibrin.

Platelet plug

Primary haemostasis where platelets adhere, activate, and aggregate at the site of vessel damage.

Complement system

A proteolytic activation cascade of blood proteins providing rapid innate defense against pathogens.

Opsonization

The process where $C3b$ binds covalently to bacteria to label them for phagocytosis.

Anaphylatoxins

Small complement fragments ($C3a, C4a, C5a$) that act as powerful chemoattractants to recruit phagocytes.

MAC ($Membrane\,Attack\,Complex$)

A lytic pore formed by complement proteins $C5b, C6, C7, C8, C9$ on bacterial membranes.

sialyl Lewis X (sLex)

A carbohydrate antigen on the surface of neutrophils that binds endothelial selectins to mediate rolling.

PAMPs ($Pathogen\,Associated\,Molecular\,Patterns$)

Structurally complex, stable molecules unique to microbes, such as Lipopolysaccharide ($LPS$).

PRRs ($Pattern\,Recognition\,Receptors$)

Host cell receptors, such as Toll-Like Receptors ($TLRs$), that detect PAMPs and trigger immune responses.

Septic shock

A potentially fatal condition caused by massive systemic $LPS$ release leading to extreme vasodilation and blood pressure collapse.

CDRs ($Complementarity\,Determining\,Regions$)

The 6 hypervariable loops at the antibody antigen-binding site, with $CDR3$ showing the most hypervariability.

Fab region

Fragment antigen binding; the variable arms of the Y-shaped antibody unique for each antibody.

Fc region

Fragment crystallisable; the constant effector region of the antibody that binds complement and phagocyte receptors.

Affinity

The strength of a SINGLE antigen-antibody bond.

Avidity

The COMBINED strength of ALL contacts between one antibody and one antigen.

Clonal selection

The process by which an antigen selects and activates the specific B cell clone with a matching BCR.

Affinity maturation

The process where random somatic hypermutations in Ig genes lead to B cell clones with higher affinity antibodies.

Hybridoma

An immortal cell line formed by fusing a B cell with a myeloma cell, used to produce monoclonal antibodies ($mAbs$).

MHC Class I

Molecules expressed on ALL nucleated cells that present intracellular/viral antigens to $CD8^{+}$ cytotoxic T cells.

MHC Class II

Molecules expressed ONLY on professional APCs that present extracellular/bacterial antigens to $CD4^{+}$ helper T cells.

MHC restriction

The requirement for T cells to recognize both the self-MHC molecule and the foreign peptide simultaneously.

Hypersensitivity

An inappropriate immune response; Type I involves $IgE$, Type II/III involve antibodies/complement, and Type IV is T-cell mediated.

Resting membrane potential (RMP)

The voltage across a neuron membrane at rest, approximately $-70\,mV$, inside negative.

Equilibrium (Nernst) potential

The voltage at which one specific ion is at electrochemical equilibrium with no net movement.

Depolarisation

A change in membrane potential where the inside becomes less negative, moving toward zero or positive.

Repolarisation

The return of the membrane potential back toward its resting negative state after depolarisation.

Hyperpolarisation

A change in membrane potential where the inside becomes more negative than the resting potential.

Absolute refractory period

The period where NO action potential is possible because $Na^{+}$ channels are inactivated.

Relative refractory period

The period where an action potential is possible but requires a STRONGER than normal stimulus.

Graded potential

A potential whose amplitude varies with stimulus strength and can decrement with distance, such as EPSPs or IPSPs.

Spatial summation

The adding together of effects from multiple synapses active at DIFFERENT LOCATIONS at the same time.

Temporal summation

The adding together of effects from one synapse firing REPEATEDLY in quick succession.

Saltatory conduction

The method where an action potential "jumps" from node to node in myelinated axons.

Intercalated discs

Specialised junctions in cardiac muscle containing gap junctions for electrical coupling and desmosomes for mechanical coupling.

Excitation-contraction coupling

The process linking a muscle action potential to calcium release and subsequent cross-bridge cycling.

SERCA

SR $Ca^{2+}$-ATPase, which pumps calcium back into the sarcoplasmic reticulum using ATP to cause relaxation.

Isometric contraction

Contraction where muscle tension increases but the muscle length stays the same.

Isotonic contraction

Contraction where muscle tension remains constant but the muscle changes length.

Tetanus (physiological)

A sustained maximal muscle contraction caused by high-frequency stimulation.

MLCK ($Myosin\,Light\,Chain\,Kinase$)

The key regulatory enzyme in smooth muscle contraction activated by the $Ca^{2+}$-calmodulin complex.