Cell Membranes & Transport Flashcards

Flashcards covering molecular composition, fluidity, selectively permeable membrane properties, passive/active transport mechanisms, osmosis, and endocytosis from Unit 1.3 Cell Membranes & Transport lecture notes.

What is the key structural difference between a biological membrane and a pure phospholipid bilayer?

A pure phospholipid bilayer consists solely of phospholipids, whereas a biological membrane contains a mixture of various lipids (such as glycolipids and cholesterol) as well as embedded and associated proteins.

Which cellular organelles or structures are enclosed by two membranes separated by an intermembrane space?

The nucleus, mitochondrion, and chloroplast.

What naturally occurring 3-carbon alcohol serves as a basic building block for glycerides, and what is its chemical formula?

Glycerol (also called glycerin), which has the chemical formula $C_3H_8O_3$.

What type of chemical bond is formed when a hydroxyl ($-OH$) group of glycerol reacts with the carboxyl ($-COOH$) group of a fatty acid?

An ester bond.

How do saturated fatty acids differ structurally from unsaturated fatty acids in terms of double bonds and chain shape?

Saturated fatty acids contain no carbon-carbon double bonds and have straight chains, whereas unsaturated fatty acids contain at least one double bond that introduces a bend or "kink" in the hydrocarbon chain.

What are the molecular components that make up a phospholipid?

A glycerol backbone bound to two fatty acid tails and a negatively charged phosphate group attached to the third carbon of the glycerol.

What does it mean for a phospholipid to be described as "amphipathic"?

It possesses both a hydrophilic (polar/charged head) region that interacts with water and a hydrophobic (nonpolar hydrocarbon tail) region that repels water.

What structure is depicted in this detailed molecular diagram of a phospholipid?

A single amphipathic phospholipid showing its hydrophilic polar head group (containing choline, phosphate, and glycerol backbone) attached to two hydrophobic nonpolar fatty acid tails.

What spherical structures enclose an aqueous compartment when phospholipid bilayers close spontaneously in water?

Liposomes.

How do integral membrane proteins differ from peripheral membrane proteins?

Integral membrane proteins are embedded within the lipid bilayer (many span the bilayer as amphipathic proteins), whereas peripheral membrane proteins are loosely associated with the membrane surface or integral proteins and do not span the bilayer.

What four general functional roles of membrane proteins are illustrated in this diagram?

Transporter (moving molecules across), Receptor (binding signal molecules), Enzyme (catalyzing reactions), and Anchor (attaching to structural elements).

What are the four main functions performed by membrane proteins according to the lecture notes?

Transporting substances across the membrane, catalyzing enzymatic reactions at the membrane surface, cell recognition and adhesion, and acting as receptors to bind chemical signals.

How do unsaturated fatty acid tails affect cell membrane fluidity compared to saturated fatty acid tails?

Unsaturated fatty acid tails increase membrane fluidity because their kinked tails prevent tight packing, while saturated tails pack closely together to decrease fluidity.

How does cholesterol buffer cell membrane fluidity at high versus low temperatures?

At low temperatures, cholesterol prevents tight phospholipid packing to maintain fluidity; at high temperatures, it restrains phospholipid movement to limit excess fluidity.

What effect does temperature have on molecular movement, membrane fluidity, and diffusion rates?

Higher temperatures make molecules move faster, generally increasing membrane fluidity and diffusion rates; lower temperatures slow molecular movement, decreasing fluidity and diffusion rates.

According to this membrane permeability summary chart, which class of molecules passes most freely through a pure lipid bilayer?

Gases such as $CO_2$, $N_2$, and $O_2$, along with small uncharged polar molecules like ethanol.

Which types of molecules are completely impermeable to a pure phospholipid bilayer without helper proteins?

Ions (e.g., $K^+$, $Mg^{2+}$, $Ca^{2+}$, $Cl^-$, $HCO_3^-$, $HPO_4^{2-}$) and large or charged polar molecules (e.g., glucose, fructose, amino acids, ATP, proteins, nucleic acids).

What is simple diffusion, and does it require energy?

Simple diffusion is the passive movement of substances along their concentration gradient from an area of high concentration to low concentration; it requires no cellular energy.

What condition is reached when solute concentrations become equal on both sides of a membrane?

Equilibrium (where molecules continue moving randomly in both directions with no net movement).

What is osmosis?

Osmosis is the net diffusion of water across a selectively permeable membrane from a region of lower solute concentration (higher water concentration) to a region of higher solute concentration (lower water concentration).

What happens to a cell when it is placed in a hypertonic environment?

Water moves out of the cell toward the higher extracellular solute concentration, causing the cell to shrink.

What happens to a red blood cell when it is placed in a hypotonic environment?

Water moves into the cell toward the higher intracellular solute concentration, causing the cell to swell and potentially lyse (burst).

What physiological states of red blood cells are shown in this diagram under hypertonic, isotonic, and hypotonic conditions?

Shrunk (hypertonic), Normal (isotonic), and Lysed (hypotonic).

What structural components prevent plant cells from bursting when exposed to hypotonic environments?

The cell wall (which provides mechanical resistance against swelling) and the cytoskeleton (which offers internal structural support).

What is facilitated diffusion?

A passive transport process in which substances move down their concentration gradient across a cell membrane with the assistance of specific transport proteins.

How do carrier proteins transport large polar molecules like glucose across the cell membrane?

The target substance binds specifically to the carrier protein, causing a conformational change in the protein that imports the molecule across the bilayer (e.g., GLUT-1).

What are channel proteins, and what specific type of channel protein facilitates water movement?

Channel proteins are specific transmembrane proteins that form openable/closeable pores for ions or water; aquaporins are the specific channel proteins used for water movement.

How does active transport differ from passive transport with respect to concentration gradients and energy requirements?

Active transport moves substances against their concentration gradient (from low to high concentration) using protein pumps and requires energy input (such as ATP), whereas passive transport moves substances along their concentration gradient without energy.

What three distinct forms of endocytosis are depicted in this diagram?

(a) Phagocytosis (taking in large particles), (b) Pinocytosis (taking in fluid and small dissolved particles), and (c) Receptor-mediated endocytosis (selective uptake triggered by specific ligand-receptor binding).