CH 5 — membrane dynamics Flashcards
What are the 4 types of membrane proteins based on function?
- membrane transport
- structural proteins
- membrane enzymes
- membrane receptors
What are the 2 types of membrane transport?
- carrier proteins: active (primary/secondary), or passive
- channel proteins (open/leaky, or gated —> mechanically, voltage, chemically/ligand)
What types of membrane transport uses ATP?
active carrier proteins (primary uses ATP directly, secondary not directly)
What types of membrane transport does not use ATP?
- passive carrier proteins
- facilitated diffusion
- open/leaky channel proteins
- gated channel proteins
What are structural proteins used for?
used to anchor cell junctions and cytoskeleton
What are membrane enzymes used for?
metabolism and signal transfer
What are membrane receptors used for?
- receptor mediated endocytosis
- signal transfer
- open and close chemically gated channels
What fills channel proteins?
they have a water-filed pore in the center
What determines what ions pass through a channel protein?
the structure (they are made of multiple protein subunits that assemble in the membrane
What part of the channel allows ions to pass through?
the hydrophilic amino acids that line the channel
What are the types of carrier proteins that regulate the number of molecules transported?
- unimportant carriers: move 1 molecule
- cotransporters: move more than one type of molecule (at different times) (can NOT move more than 3)
What are symport carriers?
- carrier proteins
- all the things it moves go in the same direction
What are antiport carriers?
- carrier proteins
- things go in opposite direction (one molecule to ECF, other to ICF)
What are GLUT transporters?
- helps with passive transport (does NOT use ATP)
- always goes down concentration gradient
- facilitates the transport of glucose across the cell membrane
How are carrier proteins (protein-mediated transport) DIFFERENT than channel proteins?
- never open to ICF and ECF at the same time
- does not actually “carry” because they stay in the membrane —> just changes shape
What is primary (direct) active transport?
- a type of protein mediated transport from carrier proteins
- uses ATP directly
- ATP hydrolysis changes shape of the protein
What is secondary (indirect) active transport?
- a type of protein mediated transport from carrier proteins
- uses potential energy stored in concentration gradients of one molecule to push another molecule against its gradient
What is an example of using a carrier protein? Is it active or passive?
- Na K ATPase (sodium potassium pump)
- moves Na into the cell, and K out of the cell
- uses energy from ATP (hydrolyzes it)
Slide 38 has sodium potassium pump
What is an example of secondary active transport?
- SGLT (sodium-glucose cotransport)
- sodium and glucose transported into the ICF together
- the Na binds to create a high affinity for glucose
- No ATP used, just concentration gradient driving it
What type of membrane protein exhibits specificity, competition, and saturation? What do they mean?
- carrier-mediated transport
1. Specificity: moving only one molecule or group of related molecules
2. Competition: transporter ay move related substrates, but those substrates compete with one another for binding sites (competitive inhibitor)
3. Saturation: the rate of substrate transport depends on the substrate concentration and the number of carrier molecules
What is phagocytosis?
the process by which a cell engulfs a particle into a vesicle by using the cytoskeleton to push the membrane around the particle
- actin mediated process
- the membrane surface pushes out
- is triggered by the presence of a substance to be ingested
What is endocytosis?
- the membrane surface indents
- forms small vesicles
- constitutive: an essential function always taking place
- active: requires energy from ATP
- can be non selective (allowing extracellular fluid to enter the cell) or can be selective
- can be receptor-mediated endocytosis
What is exocytosis?
- intracellular vesicles move to the cell membrane and fuse with it
- they then release their contents to the extracellular fluid
- cells use exocytosis to export large lipophobic molecules, get rid of wastes left in the lysosomes from intracellular digestion
What is a phagosome?
the vesicle formed around ingested material during phagocytosis
- site of digestion
What is receptor-mediated endocytosis?
- takes place in regions of the cell known as “coated pits” (indentations where cytoplasmic side of the membrane has high concentrations of protein)
- Most common protein found is Clathrin
What is transcellular transport?
- transport through the epithelial cells themselves
- crosses 2 membranes
- uses combo of active and passive transport
What is paracellular transport?
- transport thorugh the junctions between adjacent cells
- very little in in “tight” epithelia (cell-cell junctions are like barriers)
What is transcytosis?
- a combination of endocytosis, vesicular transport across the cell, and exocytosis
- used to move macromolecules across an epithelium
- makes it possible for large proteins to move across an epithelium and remain intact
What is absorption?
transfer of substance from the lumen of the kidney or GI tract to the extracellular space
What is secretion?
- when materials move from the ECF to the lumen
- EX: salivary glands secret saliva
- can also just mean the release of a substance from a cell
What is the net charge of the ICF?
negative (compartments are in disequilibrium)
What is the net charge between the ECF?
positive (compartments are in disequilibrium)
What is the law of conservation of electrical charge?
the net amount of electrical charge produced in any process is zero
- for every positive charge ion there is an electron on another ion
- overall body is electrically neutral
Which ion is the main regulator of membrane potential?
potassium (K+ leak channels) (most cells about 40x more permeable to K+ than Na+
What does the nernst equation tell us?
- used for a cell that is freely permeable to only one ion at a time
- equation used to calculate equilibrium potential for any concentration gradient
- is not used to calculate the actual membrane potential of the cells
What is depolarization, repolarization, and hyperpolarization?
- depolarization: increase in RMP charge (more positive
- repolarization: decrease in RMP charge (more negative)
- hyperpolarization: happens after repolarization when the membrane becomes more negative
What is the NA K ATPase used for in membrane potential?
helps maintain the resting membrane potential by removing Na+ that leaks into the cell and returning K+ that has leaked out
Study the integrated membrane processes: insulin secretion (last couple of slides)
