Chap 7 - Membranes Flashcards
Vesicle merges with cell membrane to chuck out stuff.
Exocytosis
Cell membrane pinches in to make a vesicle
Endocytosis
Factors impacting membrane fluidity
Temperature (solidifies when cold)
Saturation of phospholipids (if there are kinks in the fatty acid tails, they will be more spread apart)
Cholesterol (reduces movement of phospholipids)
Adapting membrane fluidity
Varying amounts of unsaturated phospholipids in their membrane depending on the climate they live in. Some have different types of lipids that solidify at different temperatures.
Some plants/cells can change the amount of unsaturated phospholipids at different seasons or external temperatures.
Integral proteins
Rooted into the hydrophobic centre of phospholipid bilayer.
May pierce through the membrane entirely (transmembrane protein), or only partly.
Hydrophobic regions of integral proteins
Made of sections of non-polar amino acids (usually 20-30 amino acids long)
Peripheral proteins
Proteins that are not embedded into the hydrophobic centre of lipid bilayer.
Only loosely bound or attached to integral proteins.
Membrane sided-ness
The 2 lipid layers can consist of different phospholipids.Interior of lumen membrane is the same as the exterior of plasma membrane.
Steps of synthesis of a membrane glycoprotein
Protein synthesised in the Rough ER, where it is embedded into RER membrane. In the lumen, carbohydrates added to the protein.Transported to Golgi apparatus, where carbohydrate is modified.Vesicle from Golgi fuses with plasma membrane.
6 functions of membrane proteins
Cell-cell recognitionCell-cell attachmentAttachment to ECMTransport EnzymesSignalling molecules
Cross-membrane movement of non-polar molecules
Non-polar molecules are hydrophobic and dissolve easily through the lipid bilayer.CO2, O2, hydrocarbons
Cross-membrane movement of polar molecules
Polar molecules are hydrophilic. Even small molecules such as water move through the membrane much slower than non-polar molecules.H2O, sugars, ions.
Aquaporin
Membrane protein.
Provides channel for water to pass through much faster than through the lipid bilayer.
Methods of facilitated diffusion
Protein channels (eg. aquaporin) just provide a hydrophillic hole for molecules to move through.Carrier proteins (eg. glucose transporter) change shape upon binding to a molecule which moves them to the other side.
Passive transport types
Diffusion (small molecules usually)Facilitated diffusion (some larger molecules)Osmosis
Sodium-potassium pump
Carrier protein; Transports 3 Na+ outside the cell when a phosphate group (from ATP) is added to change its shape.2 K+ ions from outside the cell can bind to the protein after this.K+ are released into the cell when the phosphate group is released.
Membrane potential
Cytoplasmic side is about -50 to -200 mV more negative than outside the cell.
Electrochemical gradient
Combines concentration gradient with the electric forces of a membrane potential.
Ions and other charged particles are impacted.
Electrogenic pump
An active transport protein that also creates a membrane potential.
Eg. sodium-potassium pump that removes 3 Na+ but only introduces 2 K+ so contributes to a negative membrane potential.
Major electrogenic pump in animals
Sodium-potassium pump.
Major electrogenic pump of plants/fungi/bacteria
Proton pump
Cotransport
The diffusion of one substance down the concentration gradient is used to power the active transport of another thing against its concentration gradient.
Eg. Plant cells transport glucose and amino acids in the cell when protons enter (because of the negative membrane potential). Protons trigger active transport protein in the membrane!
Amphipatic
Possessing both hydrophobic and hydrophilic parts
