The Membrane Flashcards
(30 cards)
What are the key roles of the plasma membrane?
Forms a boundary around the cell.
Maintains cytosol composition, enabling biochemical reactions.
Prevents unwanted compounds from entering the cytosol.
How do intracellular membranes benefit eukaryotic cells?
Compartmentalization of organelles (ER, Golgi, mitochondria).
Allow ion gradients, essential for:
ATP generation (ATP synthase)
Molecular transport
Nerve & muscle signalling
What are key physical properties of biological membranes?
Thin (~5 nm), flexible, semi-permeable.
Self-repairing and spontaneously form in water.
What are membranes made of?
Lipids & proteins (held together by non-covalent interactions).
What is the fluid mosaic model?
Singer & Nicholson’s theory → Membranes are fluid & dynamic.
Non-polar molecules are sequestered from water, while polar molecules interact with water.
What is the primary lipid in eukaryotic membranes?
Phosphoglycerides.
What makes phospholipids amphipathic?
Hydrophilic headgroup interacts with water.
Hydrophobic tail drives membrane formation & stability.
What are sphingolipids?
Structurally similar to phosphoglycerides but chemically distinct.
Over 60 human sphingolipids—many have signalling roles.
Which sphingolipid defines blood groups?
Glycosphingolipids.
How is sphingomyelin functionally important?
Major component of myelin sheath in neurons.
What diseases result from sphingomyelin dysregulation?
Niemann-Pick disease → Sphingomyelin buildup causes mental retardation & early death (<3 years old).
Multiple Sclerosis (MS) → Excess sphingomyelinase leads to myelin sheath breakdown, causing numbness, vision issues & poor coordination.
What is the role of cholesterol in membranes?
Intercalates between lipids, stiffening the headgroup.
Reduces membrane permeability.
How do lipids move within the bilayer?
Lateral diffusion, rotation, and flip-flop (rare).
What experimental technique measures fluidity?
Fluorescence Recovery After Photobleaching (FRAP).
How does FRAP demonstrate integrin mobility?
Fast recovery → Free diffusion.
Slow recovery → Integrins anchored to ECM proteins in focal adhesions.
What are lipid rafts?
Localized membrane domains enriched in cholesterol & sphingolipids.
Thicker than surrounding bilayer, influencing protein segregation.
What proteins are enriched in lipid rafts?
GPI-anchored proteins (e.g., NCAM for cell-cell communication).
Palmitoylated/myristoylated proteins (e.g., Caveolin).
What proteins are excluded from lipid rafts?
Prenylated proteins.
How are lipids distributed asymmetrically?
Inner leaflet → PE & PS.
Outer leaflet → PC & sphingomyelin.
What proteins maintain lipid asymmetry?
Flippases & Floppases → Maintain asymmetry.
Scramblases → Alter leaflet distribution.
What are functional consequences of PS externalization?
Marks apoptotic cells for phagocytosis.
Creates a procoagulant surface for platelets (wound healing).
What do membrane proteins do?
Transport, signaling, structural support.
Integral membrane proteins vary based on function.
How does membrane protein composition vary across membranes?
Mitochondrial membrane → High protein content.
Plasma membrane → Intermediate protein content.
Myelin sheath → Low protein content.
What are major membrane protein classifications?
1️ Single-pass transmembrane α-helix.
2️ Multipass transmembrane α-helices.
3️ Multipass transmembrane β-sheets.
4️ Monotopic α-helix.
5️ Lipid-anchored proteins in cytosolic leaflet.
6️ Oligosaccharide-linked proteins on extracellular leaflet (e.g., GPI-anchor).
7️ Peripheral membrane proteins attached non-covalently.
