Membrane Flashcards
phospholipid structure
amphipathic molecules that make up the bilayer of the plasma membrane and keep the membrane fluid
consist of a glycerol molecule, two nonpolar hydrophobic fatty acids, and a polar hydrophilic phosphate group
cholesterol
embedded in phospholipid bilayer - resists changes in membrane fluidity
glycolipid
lipid attached to carbohydrate on surface of membrane that aids in cell-to-cell recognition
glycoprotein
protein attached to carbohydrate on the surface of membrane that serves as identification tag, aiding in cell-to-cell recognition
integral protein
a transmembrane protein with the hydrophobic region extending into and often completely spanning the hydrophobic interior of the lipid bilayer. The hydrophilic regions are exposed to the aqueous solutions on either side of the membrane.
carry out transmembrane movement (ex, facilitated diffusion, active transport), intercellular joining, signal transduction
peripheral protein
not embedded in the lipid bilayer and loosely bound to the membrane or to the exposed parts of integral proteins (ex. enzymes that carry out sequential steps of a metabolic pathway, cell communication, conduct signals from the exterior to the interior or vice versa)
hydrophilic end of phospholipid
orientated outwards and exposed to water; polar phosphate head
hydrophobic end of phospholipid
nonpolar fatty acid tails in nonaqueous environment
cytoskeleton
maintain cell shape, rigidity, and structure
lipid bilayer
through selective permeability, the passage of substances across the membrane is regulated (nutrients and solutes and transported in while waste products are eliminated); allows cell to maintain different solution than surrounding environment
selective permeability: ions
no permeability because ions are charged
selective permeability: large, polar biomolecules
some permeability with difficulty because of polarity and large size
selective permeability: small, polar molecules
some permeability because of small size and polarity
selective permeability: small, nonpolar molecules
high permeability because of non-polarity and small size
Passive transport
Does not require energy: diffusion, osmosis, and facilitated diffusion
diffusion
the tendency for molecules of any substance to spread out evenly into the available space; down the concentration gradient from an area of high to low concentration; spontaneous process
facilitated diffusion
when a transport protein embedded in the membrane assists in the passive transport of polar molecules and ions impeded by the lipid bilayer
active transport
the expenditure of energy (usually from ATP) to pump a molecule across a membrane against its concentration gradient
protein pumps
The transfer of the terminal phosphate group of ATP to the transport protein powers active transport, inducing the protein to change its conformation, translocating a solute
ex. sodium potassium pump
endocytosis
the transport of macromolecules and particulate matter into the cell through vesicles
exocytosis
the transport of macromolecules out of the cell through the fusion of vesicles with the plasma membrane
Factors that Affect Fluidity
temperature, saturated v unsaturated tails, cholesterol
How does temperature affect fluidity?
As temperature decreases so does membrane fluidity and permeability until solidification occurs
As temperature increases, membrane fluidity and permeability increases until disassociation occurs
How does saturated v unsaturated tails affect fluidity?
Phospholipids with unsaturated hydrocarbon tails will remain fluid at lower temperatures because of kink caused by double bond- decreases chance of solidification
In phospholipids with saturated hydrocarbon tails, fluidity decreases because of the absence of double bonds/kinks and the chance of solidification increases.
How does cholesterol affect fluidity?
Cholesterol between phospholipids acts as a temperature buffer
• Prevents solidification at low temperatures
• Restrains fluidity at body temperature
Membrane Protein Functions
Transport • Enzymatic Activity • Signal Transduction • Cell-cell recognition – Glycoproteins and glycolipids • Intercellular joining • Attachment to cytoskeleton & extracellular matrix
Transport
provides hydrophilic channel that allows molecules to pass through cell membrane that otherwise could not
- passive (facilitated) and active (protein pump) transport
Enzymatic Activity
proteins are embedded in the sequence of the metabolic pathway, increasing efficiency and productivity
Signal Transduction
protein receptor binds to chemical messenger; the signal may cause the conformational change in the protein (receptor) that relays the message to the inside of the cell
Cell to Cell recognition
glycoproteins and glycolipids act as markers that indicate information to surrounding cells
ex. blood type
Intercellular Joining
proteins of adjacent cells hook/join together
Attachment to cytoskeleton and ECM
microfilaments of cytoskeleton bond to proteins, maintaining cell shape
protein attaches to extracellular matrix to stabilize location of certain membrane proteins
Surface Area to Volume
volume increases at a greater rate than surface area
a greater surface area to volume ratio is ideal for efficient transport of solutes, nutrients,and elimination of waste
Why are animal cells basically spherical whereas plants and fungi are filmentous?
Animals are comprised of specialized organ systems dedicated to the transport of substances throughout the body, so a greater SA/V ratio is not necessary. In plants, the xylem (water & solutes) and phloem (sugars), transport substances. In fungi, there is greater need for larger SA/V ratio because all environmental interaction is with soil, which fungi are entirely dependent on for nutrients and waste storage.
Water Potential
A property that predicts the direction of water flow based on solute concentration & physical pressure (measured in bar or Mpa)
Water moves from _____ to _____, so water will move towards the more ________
water potential
high; low
negative
pure water has Ψ of
0
at standard atmospheric pressure Ψ of hypertonic is __ Ψ of hypotonic solution so net movement is __________ → __________
Ψ of hypertonic
is < Ψ of hypotonic solution
hypotonic → hypertonic
equation for water potential
Ψ= Ψs + Ψp
Ψs
water movement is influenced by the solute concentration on either side (always -)
• Proportional to the amount of dissolved solute
• As solutes are added the Ψs decreases because solute molecules are binding with water as solutes dissolves and water forms hydration shells, preventing it from doing work (free water)
Ψp
water movement is directly proportional to pressure (maybe be +,-,0)
• Pressure potential is the physical pressure on a solution
if pressure is applied, Ψp increases, if no pressure, Ψp=0, if pressure is decreased (more volume), Ψp decreases
how to calculate solute potential
Ψs = -iCRT i: ionization constant (1 for sucrose, 2 for NaCl) • C: concentration in moles/L (molarity) • R: pressure constant (0.0831) • T: temperature in Kelvin
Electrochemical Gradient
The different gradient of an ion across a membrane
– Cytoplasm is negative compared to the extracellular fluid so cations (+) move in and anions (-) out
Each positive charge removed from cytoplasm is stored energy as voltage
-chemical force (ion’s concentration gradient) and electrical force (effect of membrane potential on the ion’s movement)
electrogenic pumps
proteins that generate voltage across a membrane (Na+/K+ pumps in animals; 3Na+ out, 2K+ in)
Proton pumps
actively transport H+
ions out of the cell (in plants, fungi, & bacteria)
Cotransport
A pump transports a molecule that drives the active transport of others
• The cotransporter protein couples diffusion of a pumped substance to the transport of a second substance up the concentration gradient
• Example: Sucrose-H+
transporter
Types of Endocytosis
phagocytosis, pinocytosis, receptor-mediated endocytosis
all are bulk transport
phagocytosis
cell eating
cell engulfs a particle collecting food which is digested by lysosome
pinocytosis
cell drinking
cell gulps droplets of extracellular fluid
• Non specific type of transport
receptor-mediated endocytosis
cell acquires bulk quantities of a specific substance
• Ligands attaches to receptors inducing vesicle creation
