Biological Membrane, Transport Systems, and Peptides

Flashcards covering biological membrane structure, fluid mosaic model, transport mechanisms (passive diffusion, facilitated diffusion, active transport, uniport, symport, antiport), ion pumps, osmosis, macromolecule transport (endocytosis, exocytosis), and peptide structures based on lecture notes.

Plasma Membrane

An envelope surrounding the cell that separates and protects it from the external environment while providing a connecting system between the cell and its environment.

Amphipathic Lipids

Lipids containing both hydrophobic and hydrophilic groups, such as phospholipids, glycolipids, and cholesterol found in animal membranes.

Glycocalyx

A thick coating of complex polysaccharides found on many animal cell membranes.

Fluid Mosaic Model

A membrane structure model proposed by S.J. Singer and G. Nicolson in 1972 describing membrane proteins inserted into a fluid lipid bilayer.

Biological Membrane Thickness

The standard thickness of a biological membrane, which usually ranges from $5 - 8\,\text{nm}$.

Hydrophobic Region of Lipid Bilayer

The nonpolar fatty acid tails region of lipids facing each other at the core of the membrane bilayer.

Hydrophilic Region of Lipid Bilayer

The polar phosphate group head region facing outward toward the extracellular fluid or cytoplasm.

Extrinsic Membrane Proteins

Proteins loosely held to the surface of the membrane that can be easily separated, such as cytochrome c of mitochondria.

Intrinsic Membrane Proteins

Proteins tightly bound to the lipid bilayer that can be separated only using detergents or organic solvents, such as hormone receptors.

Cytochrome c

An example of an extrinsic (peripheral) membrane protein located in the mitochondria.

Passive Diffusion

The movement of substances across a biological membrane along a concentration gradient without cellular energy or transport proteins.

Facilitated Diffusion

A passive transport process where solutes move along a concentration gradient through the mediation of specific carrier or transport proteins.

Active Transport

The movement of a substance across a biological membrane against its concentration or electrochemical gradient with energy input ($\text{ATP}$) and specific transport proteins.

Passive Transport

The diffusion of substances across a biological membrane that occurs without the use of cellular energy.

Carrier Protein

A specific transport protein that mediates facilitated diffusion for specific molecules such as glucose, galactose, leucine, and phenylalanine.

Ping Pong Model

A mechanism proposed to explain facilitated diffusion where a transport protein exists in two conformational states (pong and ping).

Pong Conformation

The state of a transport protein in the ping pong model where it is exposed to the side with high solute concentration to allow solute binding.

Ping Conformation

The state of a transport protein in the ping pong model after undergoing a conformational change to expose to the side with low solute concentration where the solute is released.

Insulin

A hormone secreted via exocytosis that increases glucose transport in muscle and adipose tissue.

Intracellular Ion Environment

The biological cellular environment requiring high intracellular $\text{K}^+$ concentration and low intracellular $\text{Na}^+$ concentration for cell survival.

Pyruvate Kinase

An enzyme essential for optimal glycolysis whose activity is dependent upon $\text{K}^+$.

Nerve Impulse Transmission

A physiological process that requires $\text{Na}^+$ and $\text{K}^+$ gradients maintained across the plasma membrane.

$\text{Na}^+\text{-K}^+$ ATPase

An integral plasma membrane protein enzyme responsible for maintaining high intracellular $\text{K}^+$ and low $\text{Na}^+$ concentrations.

$\text{Na}^+\text{-K}^+$ ATPase Subunit Structure

An integral membrane enzyme consisting of two $\alpha$ and two $\beta$ subunits, represented as $[\alpha\beta]_2$.

$\text{Na}^+\text{-K}^+$ ATPase Transport Stoichiometry

Pumps $3\text{Na}^+$ ions from inside the cell to outside and brings $2\text{K}^+$ ions from outside to inside per intracellular ATP hydrolyzed.

$\text{Na}^+\text{-K}^+$ ATPase Chemical Equation

The stoichiometry equation: $3\text{Na}^+_{\text{(in)}} + 2\text{K}^+_{\text{(out)}} + \text{ATP} \rightarrow 3\text{Na}^+_{\text{(out)}} + 2\text{K}^+_{\text{(in)}} + \text{ADP} + \text{P}_i$.

Ouabain

A steroid derivative extracted from the seed of an African shrub that inhibits the $\text{Na}^+\text{-K}^+$ ATPase pump.

Ouabain Historical Application

A poison used by tribal hunters in Africa to tip hunting arrows.

Uniport System

A transport system involving the movement of a single molecule through the biological membrane.

Uniport Example

The transport of glucose into erythrocytes.

Symport System

A transport system involving the simultaneous transport of two different molecules in the same direction.

Symport Example

The simultaneous transport of $\text{Na}^+$ and glucose into intestinal mucosal cells from the gut.

Antiport System

A transport system involving the simultaneous transport of two different molecules in opposite directions.

Erythrocyte Antiport Example

The exchange of $\text{Cl}^-$ and $\text{HCO}_3^-$ in erythrocytes.

Gastric Proton Pump

An antiport transport system in gastric parietal cells brought about by the enzyme $\text{H}^+\text{-K}^+$ ATPase to maintain highly acidic conditions in the stomach lumen.

Gastric Parietal Cells

Cells in the stomach that utilize the proton pump antiport system to maintain acidity.

$\text{H}^+\text{-K}^+$ ATPase Stoichiometry

Antiports two cytoplasmic protons ($2\text{H}^+$) and two extracellular potassium ions ($2\text{K}^+$) for each molecule of ATP hydrolyzed.

Gastric HCl Formation

The reaction occurring in the stomach lumen when chloride ions secreted by $\text{Cl}^-$ channels combine with protons to form gastric $\text{HCl}$.

Osmosis

The passive transport phenomenon of movement of water from low osmotic pressure (dilute solution) to high osmotic pressure (concentrated solution) across a biological membrane.

Dilute Solution (Osmosis Context)

A solution of low osmotic pressure from which water moves during osmosis.

Concentrated Solution (Osmosis Context)

A solution of high osmotic pressure toward which water moves during osmosis.

Medical Complications of Osmosis Disturbance

Health complications including edema, cholera, diarrhea, and tissue inflammation caused by osmotic disturbances.

Coated-Pits

Characteristic regions occupying approximately $2\%$ of the exterior surface of the plasma membrane that internalize to form coated vesicles.

Clathrin

An unusual protein contained within coated vesicles formed from internalized coated-pits.

Endocytosis

The process of intake of macromolecules, solids, or liquids by cells when the plasma membrane is pulled inwards to form a vesicle.

LDL Uptake

A primary example of receptor-mediated endocytosis in cells.

Exocytosis

The release of macromolecules from cells to the outside when internal vesicles fuse with the plasma membrane.

Golgi Apparatus Role in Exocytosis

The organelle through which the release of macromolecules mostly occurs by transporting them in vesicles to the plasma membrane.

Constitutive Secretion

Unregulated exocytosis pathway supplying newly synthesized plasma membrane lipids and proteins directly to the cell surface.

Regulated Secretion

Exocytosis pathway where secretory vesicles store proteins until triggered by an extracellular signal or signal transduction.

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved substances.

Phagocytosis

A form of endocytosis depicted as bringing in solid particles using pseudopodia.

Peptide Bond

An amide link formed between two amino acids, specifically between the $-\text{COO}^-$ of one amino acid and the $-\text{NH}_3^+$ of the next.

Dipeptide

A molecule consisting of two amino acids joined by a peptide bond.

Tripeptide

A molecule consisting of three amino acids joined by peptide bonds.

Polypeptide

A macromolecule containing many amino acids linked by peptide bonds.

Protein (Definition by Amino Acid Count)

A biological macromolecule containing at least $40$ amino acids.

N-Terminal Amino Acid

The end of an amino acid chain with the free $-\text{NH}_3^+$ group (written at the right per lecture notes text).

C-Terminal Amino Acid

The end of an amino acid chain with the free $-\text{COO}^-$ group (written at the left per lecture notes text).

Alanine (Ala)

An amino acid that reacts with serine to form the dipeptide alanylserine (Ala-Ser).

Serine (Ser)

An amino acid containing a hydroxyl group that combines with alanine to form alanylserine (Ala-Ser) or acts as the N-terminal residue in Ser-Phe-Asp.

Alanylserine (Ala-Ser)

A dipeptide formed by linking alanine and serine via a peptide bond.

Ser-Phe-Asp

A tripeptide sequence composed of serine, phenylalanine, and aspartate.

Biological Membrane Composition Ratio

The chemical proportion of lipids, proteins, and carbohydrates, which differs from tissue to tissue.

Phospholipids

Amphipathic lipid molecules arranged as a bilayer with polar phosphate heads and nonpolar fatty acid tails.

Glycolipids

Amphipathic membrane lipids containing carbohydrate groups bound to lipids.

Cholesterol

An amphipathic lipid present in animal cell membranes.

Transmembrane Proteins

Intrinsic proteins that completely span the biological lipid bilayer.

Peripheral Proteins

Extrinsic proteins associated loosely with the external or internal surface of the membrane.

S.J. Singer

Co-proposed the Fluid Mosaic Model for biological membrane structure in 1972 along with G. Nicolson.

G. Nicolson

Co-proposed the Fluid Mosaic Model for biological membrane structure in 1972 along with S.J. Singer.

Membrane Permeability

Biological membranes are relatively impermeable, forming a natural barrier to the free passage of compounds.

Energy Requirement of Passive Transport

Passive transport processes occur spontaneously without utilizing cellular ATP energy.

Energy Requirement of Active Transport

Active transport systems require metabolic energy input in the form of ATP.

Specific Carrier Protein Substrates

Isolated carrier proteins that specifically mediate the transport of glucose, galactose, leucine, or phenylalanine.

Primary Active Transport Systems

Active transport systems that directly utilize ATP, with ion pumps being the most important examples.

Role of Intracellular Potassium

Required intracellularly for optimal pyruvate kinase enzyme activity in glycolysis and for protein biosynthesis.

Role of Sodium and Potassium Gradients

Transmembrane electrochemical gradients necessary for generating and transmitting nerve impulses.

Intracellular ATP Hydrolysis in $\text{Na}^+\text{-K}^+$ Pump

Powers the outward transport of $3\text{Na}^+$ ions and inward transport of $2\text{K}^+$ ions.

Arrow Poison (Ouabain)

An African tribal poison acting specifically as an inhibitor of the $\text{Na}^+\text{-K}^+$ ATPase pump.

Intestinal Mucosal Cell Transport

Utilizes a symport system to transport $\text{Na}^+$ and glucose simultaneously from the gut.

Chloride-Bicarbonate Exchange

An antiport exchange mechanism of $\text{Cl}^-$ and $\text{HCO}_3^-$ occurring in erythrocytes.

Gastric Acid pH Maintenance

Maintained by the antiport action of $\text{H}^+\text{-K}^+$ ATPase in the gastric parietal cells.

Gastric Parietal Cell Antiport Ratio

Moves two cytoplasmic protons ($2\text{H}^+$) out and two extracellular potassium ions ($2\text{K}^+$) in per ATP hydrolyzed.

Water Transport Mechanism

Occurs passively across membranes via osmosis without cellular energy expenditure.

Edema

A health complication directly caused by a disturbance in osmosis.

Cholera

A medical condition associated with severe fluid loss due to osmotic disturbances.

Diarrhea

A health condition linked to imbalances in intestinal osmosis.

Tissue Inflammation

A complication involving tissue swelling caused by osmotic disturbance.

Macromolecules

Large biological molecules such as proteins, polysaccharides, and polynucleotides transported via endocytosis or exocytosis.

Coated Vesicles

Cytoplasmic vesicles formed from internalized plasma membrane coated-pits lined with clathrin.

Membrane Pocket Formation

The mechanism during endocytosis where the plasma membrane pulls inward, encloses a substance, and pinches off.

Secretory Vesicle

A vesicle storing synthesized proteins that fuses with the plasma membrane during regulated secretion.

Signal Transduction in Secretion

An extracellular signal mechanism required to trigger regulated exocytosis of stored proteins.

Ingestion of Dissolved Substances

The hallmark feature of pinocytosis, where cells swallow fluid containing dissolved solutes.

Amide Linkage

The specific chemical linkage forming a peptide bond between the carboxyl and amino groups of adjacent amino acids.

Tripeptide Structure

A chain consisting of three amino acids linked sequentially by two peptide bonds.

Minimal Protein Length

A threshold requirement of at least $40$ amino acids for a polypeptide chain to be termed a protein.

Carbohydrates in Plasma Membrane

Membrane components found linked to lipids (glycolipids) or proteins (glycoproteins) forming the extracellular glycocalyx.

Cytoskeleton Filaments

Protein filaments located in the cytoplasm that connect to the plasma membrane framework.