Cell bio test 2 (1): chapter 11

Vocabulary practice flashcards covering key terms and concepts from Chapter 11 on Membrane Structure.

Phospholipids

The most abundant lipid component in cell membranes, comprising a polar hydrophilic head (containing a polar group, phosphate, and glycerol) and two nonpolar hydrophobic fatty acid tails.

Amphipathic

Describing a molecule that possesses both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Lateral diffusion

The side-to-side translational movement of lipids or proteins within the same monolayer of a membrane bilayer.

Flip-flop

The transfer of a phospholipid molecule from one monolayer of a membrane bilayer to the opposite monolayer, a movement that rarely occurs spontaneously.

Cholesterol

An amphipathic sterol molecule containing a rigid planar steroid ring structure that fills spaces between phospholipids in the bilayer, making the membrane stiffer and less fluid.

Scramblase

An enzyme in the endoplasmic reticulum (ER) membrane that catalyzes the transfer of random phospholipids from one monolayer to another, enabling symmetric growth of both halves of the lipid bilayer.

Flippase

An enzyme in the Golgi apparatus and other cell membranes that catalyzes the transfer of specific phospholipids to the cytosolic monolayer, establishing asymmetric membrane distribution.

Integral membrane proteins

Proteins directly attached to or extending through the lipid bilayer, which can only be extracted or solubilized from the membrane using detergents.

Peripheral membrane proteins

Proteins loosely associated with the membrane surface via noncovalent interactions with other membrane proteins, which can be released by gentle extraction methods without disrupting the bilayer.

$\beta$-barrel

A membrane-spanning protein structure formed by a large, curved $\beta$ sheet where alternating amino acid side chains are hydrophobic facing the lipid bilayer core and hydrophilic facing a central water-filled pore.

Detergents

Small, amphipathic molecules with a single hydrophobic tail that form monolayer micelles in water and are used to solubilize integral membrane proteins by disrupting hydrophobic associations.

Cell cortex

A framework of fibrous proteins, notably including spectrin, attached to the cytosolic surface of the plasma membrane that provides mechanical strength and restricts the mobility of membrane proteins.

Tight junctions

Specialized cell junctional barriers that restrict membrane proteins to specific domains (such as apical or basal/lateral surfaces) of epithelial cells to preserve asymmetric protein distribution.

Glycoprotein

A cell surface protein with short, covalently attached oligosaccharide sugar chains.

Proteoglycan

A membrane protein containing one or more long attached oligosaccharide sugar chains.

Lectins

Transmembrane proteins on endothelial cells that specifically recognize and bind oligosaccharide chains on target cells, such as neutrophils, facilitating white blood cell recruitment to infection sites.

Plasma membrane

Enclosed cells that separate the interior of the cell from the external environment, regulating the movement of substances in and out.

Internal membrane

enclosing an intracellular compartment

What is the membrane’s first role?

To receive information

What’s the membrane’s second role?

import and export of small molecules

What’s the membrane’s third roll?

Capacity for movement and expansion

Role of membrane fluidity in protein interactions

Allows membrane proteins to diffuse laterally within the bilayer to meet and interact with one another.

Role of membrane fluidity in protein and lipid trafficking

Enables lipids and membrane proteins to diffuse from their initial site of insertion after synthesis to their designated site of function.

Role of membrane fluidity in temperature regulation

Allows cell membranes to adapt and maintain optimal physiological function during changes in environmental temperature.

Role of membrane fluidity in cell division

Ensures the proper and equal distribution of membrane lipids and proteins to daughter cells during division.

Three main structural factors that affect membrane fluidity

Fatty acid chain length, fatty acid saturation (presence of double bonds), and sterol content such as cholesterol.

Effect of fatty acid chain length on membrane fluidity

Shorter fatty acid chains reduce tail interactions, which increases membrane fluidity.

Effect of fatty acid saturation on membrane fluidity

Unsaturated fatty acid chains with double bonds create kinks that prevent tight packing, thereby increasing membrane fluidity.

Effect of cholesterol on membrane fluidity

Inserts rigid steroid rings between phospholipids to stiffen the bilayer and decrease fluidity, though it can increase fluidity if fatty acids are primarily saturated.

is butter a SFA or USFA?

SFA

is olive oil a SFA or USFA?

USFA

Four primary functional classes of membrane proteins

Transporters, anchors, receptors, and enzymes.

Transporters (membrane protein function)

Proteins that selectively move specific solutes or ions across the lipid bilayer.

Anchors (membrane protein function)

Proteins that physically attach the cell membrane to macromolecules such as the cell cortex or extracellular matrix.

Receptors (membrane protein function)

Proteins that bind extracellular chemical signals and transmit those signals into the cell.

Enzymes (membrane protein function)

Membrane-associated proteins that catalyze specific chemical reactions at the membrane surface.

Membrane asymmetry

The distinct, unequal distribution of specific phospholipids and glycolipids between the cytosolic and extracellular monolayers of a cell membrane.

Primary site of membrane synthesis

The endoplasmic reticulum (ER), where newly synthesized phospholipids are added directly to the cytosolic monolayer of the membrane.

Scramblase function in the ER

An enzyme in the ER membrane that catalyzes the non-specific, random transfer of phospholipids between monolayers, promoting symmetric growth of the lipid bilayer.

Organelle where membrane asymmetry is established

The Golgi apparatus, where specific flippases selectively move targeted phospholipids to the cytosolic monolayer.

Flippase function in the Golgi

An enzyme that selectively catalyzes the transfer of specific phospholipids from the non-cytosolic monolayer to the cytosolic monolayer to create asymmetric membrane composition.

Structure of a single-pass transmembrane $\alpha$-helix

A continuous $\alpha$-helix composed predominantly of nonpolar amino acid side chains facing outward toward the hydrophobic lipid tails, while the hydrophilic polypeptide backbone hydrogen-bonds internally.

Hydrophilic pore formation by $\alpha$-helices

An assembly of multiple amphipathic $\alpha$-helices positioned so that their hydrophobic side chains face the lipid bilayer core while their hydrophilic side chains face inward to create a water-filled channel.

Four mechanisms that restrict membrane protein mobility

Tethering to the cell cortex inside the cell, tethering to the extracellular matrix outside, binding to surface proteins of an adjacent cell, or blockage by diffusion barriers such as tight junctions.

Effect of fatty acid chain length on membrane fluidity

Shorter fatty acid chains reduce tail interactions, which increases membrane fluidity.

Physical state differences between saturated and unsaturated fats

Saturated fatty acids lack double bonds and pack tightly to form solids like butter, whereas unsaturated fatty acids contain double bonds that cause kinks and form liquids like olive oil.

Cholesterol structural behavior in membranes

An amphipathic molecule with a rigid planar steroid ring structure that fills spaces between adjacent phospholipid tails to stiffen the membrane.