Cellular And Molecular Bases 2 Flashcards
Differentiate passive and active transport across the membrane.
Passive transport/ Diffusion
- Molecules move down concentration gradient
- does not require energy
—> uses kinetic energy
Active transport
- molecules move against energy gradient
- uses cellular energy to move
What is simple diffusion?
- goes through lipid bilayer
- no specific protein is needed
-rate of diffusion is directly proportional to lipid solubility of substance
—> I.e. oxygen, nitrogen, CO2 and alcohols diffuse directly
List the different types of active transport and describe how they work.
Primary Active Transport
- energy derived directly from breakdown of ATP
- transport is AGAINST a concentration/ electrochemical gradient (Ie. sodium potassium pump )
Secondary Active Transport
- energy is provided by the concentration gradient of the driving ion
- transport protein couples movement of an ion ( Na+ and H+ ) DOWN its electrochemical gradient to uphill movement of another molecule or ion AGAINST a concentration/ electrochemical gradient
—> Co - transport
—> counter - transport
Describe endocytosis and exocytosis.
- impermeable molecules transport across membrane via endo or exocytosis
- endocytosis = going into the cell
—> phagocytosis = ingestion of large particles
—> pinocytosis = ingestion of small particles
—> receptor mediated endocytosis = cholesterol - exocytosis = going out of cell
—> constitutive secretion =
——> all cells
——> no signal sequence
——> proteins incorporated into membrane, extracellular matrix or signaling proteins
—> regulated secretion =
——> specialized cells
——> need signal to stimulate fusion and release to cell exterior
What is osmosis?
- Net movement of water caused by concentration difference of water across a membrane
- water diffusion
—> water can diffuse through lipid bilayer via aquaporins
——> highly specialized and are at least 13 types in various mammals
—> pressure can also influence water diffusion
——> OSMOTIC PRESSURE is amount of pressure required to stop osmosis
What are the differences in hypertonic, hypotonic, and isotonic osmotic solution?
- Hypertonic = movement of water out of the cell leaving cell shriveled and crenated
- Hypotonic = movement of water into the cell leaving cell swollen and possible rupture
- Isotonic = no osmotic flow, cell appears normal
What is facilitated diffusion?
- no cellular energy required
- carrier/channels only act upon specific substrates
- rate of transport will reach max based on # of carriers available in membrane
- rate of diffusion cannot exceed Vmax of carrier protein
—> different from simple diffusion where rate of diffusion is proportional to concentration of diffusing substance.
What is a carrier protein?
- responsible for facilitated diffusion of sugars, amino acids and nucleosides
—> bind to specific molecules
—> undergo conformational changes
—> allow molecules to pass
What are the different channels use in passive transport?
- Aquaporins
- Ion channels
- voltage gated
- ligand gated
—> many are highly selective
—> selectively comes from diameter, shape, and nature of electrical charges and bonds along its inside surface
Describe an ion channel.
- mediate passage of ions across plasma membrane
- gate of channel controls permeability
—> some are always open ( leak channels )
—> some have gates - can be opened by several stimuli
—> changes in voltage across membrane
—> ligand ( intracellular or extracellular )
—> mechanical stimuli
What is a voltage gated channel?
- present in plasma membrane of excitable cells ( nerve, muscle, endocrine and egg cells
—> responsible for neuron ability to transmit info along length and release neurotransmitter - range of membrane potentials that cause channels to open
—> CHANNEL THRESHOLD = minimum membrane potential that causes opening of the channels
Describe a ligand gated channel?
- found in membrane of :
—> skeletal muscle cells
—> some neurons of ANS and brain - channel open in response to ligand binding ( ie. ACh liberated from neuron binds nicotinic ACh receptor in the skeletal muscle cells
What is co transport/ symport?
- simultaneous transport of two substances across membrane in same direction
Ie. Na+ - D - glucose co transporter ( SGLT1 )
What is counter transport/ Antiport?
- simultaneous transport of two substances across membrane in opposite directions.
Ie. Na+ H+ antiporter in kidneys
What is trans cellular/ epithelial transport?
- transport of substances across cell, from one ECF compartment to another
- active transport through cell membrane on one side
- simple diffusion/ facilitated diffusion through membrane on other side
