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Cellular Membranes: Structure, Assembly, and Asymmetry Study Guide

This guide covers the essential mechanisms of protein translocation into the endoplasmic reticulum (ER). It details the function of the ER signal sequence, the signal-recognition particle (SRP) pathway, and the differences in translocation for soluble versus transmembrane proteins. Key terms and concepts are reviewed for a comprehensive understanding of this fundamental cellular process.

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Structure and Fluidity of Lipid Bilayers

Membrane Lipid and Protein Structure

Membrane Assembly and Phospholipid Asymmetry

Newly synthesized phospholipids are redistributed and selectively transferred to establish asymmetric distribution within cellular membranes.

  • Lipid bilayer fluidity
  • Phospholipid synthesis
  • Endoplasmic reticulum membrane assembly
  • Scramblase
  • Golgi apparatus
  • Flippases
  • Membrane asymmetry
  • Membrane orientation
  • Vesicle budding and fusing
  • Glycolipids

Structure and Function of Plasma Membranes

The plasma membrane consists of a lipid bilayer and membrane proteins that serve functions such as transporting molecules, acting as anchors, detecting signals, or catalyzing reactions.

  • Phospholipids
  • Glycolipids
  • Cholesterol
  • Membrane proteins
  • Transmembrane proteins
  • Transporters
  • Ion channels
  • Anchors
  • Receptors
  • Enzymes
  • Membrane carbohydrates
  • Hydrophobic and hydrophilic regions

Classification and Structure of Membrane Proteins

Membrane proteins are classified as integral or peripheral and associate with the lipid bilayer as transmembrane, monolayer-associated, or lipid-linked structures.

  • Integral membrane proteins
  • Peripheral membrane proteins
  • Transmembrane proteins
  • Monolayer-associated proteins
  • Lipid-linked proteins
  • Beta barrel
  • Hydrophobic side chains
  • Polypeptide backbone
  • Hydrogen bonds
  • Porin proteins
  • Detergents

Solubilization and Purification of Membrane Proteins

Detergents disrupt the lipid bilayer to solubilize membrane proteins into protein–detergent complexes for further analysis.

  • Detergents
  • Sodium dodecyl sulfate (SDS)
  • Hydrophilic end
  • Hydrophobic portion
  • Micelles
  • Membrane proteins
  • Protein–detergent complexes
  • Lipid–detergent complexes
  • X-ray crystallography
  • Cryo-electron microscopy
  • Bacteriorhodopsin

Principles of Transmembrane Transport

Mechanisms of Gradient-Driven Membrane Transport

Gradient-driven pumps move solutes across the membrane as symports, antiports, or uniports using electrochemical gradients.

  • Symport
  • Antiport
  • Uniport
  • Gradient-driven pumps
  • Electrochemical Na+ gradient
  • Glucose–Na+ symport
  • Passive diffusion
  • Concentration gradient
  • Epithelial cells
  • Plasma membrane
  • Tight junctions
  • Na+–H+ exchanger
  • Ca2+ pump

Protein Sorting and Organelle Import Mechanisms

Protein Translocation in the Endoplasmic Reticulum

Ribosomes synthesize water-soluble and transmembrane proteins that are directed to the endoplasmic reticulum by an ER signal sequence and an SRP.

  • Endoplasmic reticulum
  • Rough endoplasmic reticulum
  • Ribosomes
  • ER signal sequence
  • Signal-recognition particle (SRP)
  • SRP receptor
  • Protein translocator
  • Translocation
  • Water-soluble proteins
  • Transmembrane proteins
  • Signal peptidase
  • Stop-transfer sequence
  • Cytosolic proteins
  • Cytosol

Membrane Protein Function, Structure, and Mobility

Bacteriorhodopsin Function and Cell Cortex Structure

Bacteriorhodopsin functions as a proton pump, while the cell cortex provides structural support to the plasma membrane.

  • Bacteriorhodopsin
  • Proton pump
  • Retinal
  • Proton gradient
  • Plasma membrane
  • Spectrin
  • Red blood cells
  • Biconcave shape

Plasma Membrane Protein Mobility and Structure

This text examines how plasma membrane proteins move via lateral diffusion and how their mobility is restricted by the cell cortex, extracellular matrix, and diffusion barriers.

  • Lateral diffusion
  • Spectrin meshwork
  • Membrane domains
  • Tight junctions
  • Glycocalyx
  • Glycoproteins
  • Proteoglycans
  • Lectins
  • Fluorescence recovery after photobleaching (FRAP)
  • Single-particle tracking (SPT) microscopy
  • Reconstitution in artificial phospholipid vesicles

Transmembrane Pumps, Ion Channels, and Membrane Potential

Transmembrane Pumps and Ion Channels

Transmembrane pumps and ion channels facilitate the transport of solutes and ions across cell membranes through electrochemical gradients and gated mechanisms.

  • Electrochemical H+ gradients
  • Transmembrane pumps
  • ATP hydrolysis
  • Ion channels
  • Ion selectivity
  • Selectivity filter
  • Gated ion channels
  • Mechanically gated channels
  • Ligand-gated channels
  • Voltage-gated channels
  • Membrane potential
  • Resting membrane potential
  • Nernst equation
  • Patch-clamp recording

Neuronal Structure and Action Potentials

Neurons communicate through electrical signals called action potentials mediated by voltage-gated Na+ and K+ channels.

  • Neuron structure
  • Cell body
  • Dendrites
  • Nerve terminal
  • Action potential
  • Membrane potential
  • Depolarization
  • Voltage-gated Na+ channels
  • Voltage-gated K+ channels
  • Resting membrane potential
  • Threshold potential
  • Inactivation mechanism
  • Refractory period
  • Na+ pumps

Synaptic Signaling and Neurotransmitter Function

Synaptic Transmission and Neurotransmitter Signaling

Electrical signals are converted into chemical signals via neurotransmitters released from synaptic vesicles into the synaptic cleft to communicate between presynaptic and postsynaptic cells.

  • Synapse
  • Presynaptic cell
  • Postsynaptic cell
  • Synaptic cleft
  • Neurotransmitter
  • Action potential
  • Voltage-gated Ca2+ channels
  • Exocytosis
  • Transmitter-gated ion channels
  • Ligand-gated ion channels

Synaptic Signaling and Transmitter-Gated Ion Channels

Neurotransmitters convert chemical signals into electrical signals by binding to transmitter-gated ion channels to alter the membrane potential of postsynaptic cells.

  • Postsynaptic membrane depolarization
  • Action potential
  • Transmitter-gated ion channels
  • Neuromuscular junction
  • Acetylcholine receptor
  • Excitatory neurotransmitters
  • Inhibitory neurotransmitters
  • Ligand-gated cation channels
  • Ligand-gated Cl– channels
  • Synaptic cleft
  • Conformational change
  • Electrochemical gradient
  • Psychoactive drugs

Neuron Structure and Light-Gated Ion Channels

The structure of a neuron includes a cell body, dendrites, and an axon, while light-gated ion channels can be used to manipulate the activity of neurons.

  • Neuron structure
  • Cell body
  • Dendrites
  • Presynaptic nerve terminals
  • Synapses
  • Action potentials
  • Ion channels
  • Plasma membrane
  • Channelrhodopsin
  • Depolarization
  • Neural circuits

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