Cell Membranes III Flashcards
What determines what crosses the selectively permeable cell membrane?
Depends on the properties of the cell membrane (lipid and protein composition) and the size and lipid solubility of the substance
What are the active transport?
Vesicular transport (exocytosis, endocytosis, phagocytosis), direct or primary active transport, indirect or secondary active transport
What are the passive transports?
Facilitated diffusion/ion channel, aquaporin channel (osmosis), simple diffusion
What are protein-mediated transports?
Primary and secondary active transport, facilitated diffusion/ion channel, aquaporin channel
What is diffusion?
Movement of molecules from area of higher concentration to an area of lower concentration
Properties of diffusion?
- Uses kinetic energy of molecular movement and no outside energy source
- Diffused from higher concentration to lower
- Continues until concentration come to equilibrium, molecular movement continues after equilibrium
- Diffusion is faster along higher concentration gradient, shorter distances, higher temperatures, smaller molecules
- Can take place over open system or across a partition that separates two systems
What is Fick’s law of diffusion?
Rate of diffusion = surface area x concentration gradient x membrane permeability
Simple diffusion for what lipophilic molecules?
O2, CO2, NH3, lipids, steroids
Rate of simple diffusion is faster if:
- membrane surface area larger
- membrane is thinner
- concentration gradient is larger
- membrane is more permeable to the molecule
Membrane permeability to molecule depends on:
- molecules lipid solubility
- molecules size
- lipid composition of the membrane
What are channel proteins?
- made of membrane spanning protein subunits that create a cluster of cylinders with a pore through the center
- channels from water filled pore that links ICF to ECF and allows substances to move between
- 2 classifications: open “leak” channels and gated channels
-facilitated diffusion (>10 million ions per second)
What are gated channels?
-chemically gated (ligand)
-voltage gated
-mechanically gated
-all need stimulus to open
How is selectivity of channel proteins determined?
- size of pore
- charge of the amino acids lining the pore (opposites attract)
What are carrier proteins?
- large, complex
- change conformation to move molecules
- never form open channel between the ICF and ECF
- slow (1000 to 1,000,000 per/sec)
- moves small organic molecules
How are carrier proteins classified?
- uniport carriers: transport only one kind of substance
- symport carriers (cotransporters): move two or more substrates in same direction
- antiport carriers (exchangers): move substrates in opposite directions
What is facilitated diffusion?
- uses channels or carrier proteins
- move down concentration gradient or electrochemical gradient
- no energy
- stops when equilibrium reached
What is active transport?
- moves molecules against their concentration gradients: from low to high
- requires energy
- support state of disequilibrium
- uses carrier proteins
- two types: primary and secondary
What is primary active transport?
- energy to move molecule comes directly from hydrolyzing ATP (ATPase)
- most important: Na+/K+ ATPase (3 Na+ out, 2 K+ in)
What is secondary active transport?
- uses potential energy stored in concentration gradient of one molecule to push another molecule against concentration gradient
- need Na+ concentration gradient to move second molecule against
- molecule 1 moves down which causes molecule 2 to move against
- can move symport or antiport
What is specificity?
Refers to the ability of a transporter to move one molecule or a closely related group of molecule
What is competition?
A carrier may move several members of a related group of substances but these substances compete with one another
-carrier may have a preference for one family member
What is saturation?
Rate of transport depends on concentration and number of transporters
Transport normally increases with increasing concentration until transport maximum is reached (all of the transporters are in use)
What is vesicular transport?
Macromolecules that cannot fit through a carrier or channel
-phagocytosis, endocytosis, exocytosis
What is phagocytosis?
Creates vesicles using cytoskeleton
- requires ATP to move cytoskeleton and for intracellular transport of the vesicle (active transport)
What is endocytosis?
- membrane indents, vesicles smaller, requires ATP
- non-selective: pinocytosis
- selective: receptor mediated transport
- caveolae or clathrin coated pits used
- protein hormones, growth factors, antibodies, plasma proteins
What is exocytosis?
-vesicles filled with large lipophobic molecules such as proteins synthesized in cell or wastes left by lysosomes at pushed out
-can occur continuously or initiated by signal
-requires ATP, can be regulated by calcium
