Test 2 Unit 2 Flashcards
How do the protein/lipid contents vary in different membranes of the cell?
It varies depending on the type of membrane. Plasma membrane and mithochondrial membrane don’t have the same content.
Because they are larger than lipid molecules, proteins move more slowly in the fluid environment of the membrane. Proteins are larger and therefore easily make up a bigger part of the membrane content.
What are the 4 types of membrane proteins?
- Transport (aquaporins): provides a channel/change its shape for the movement of a specific molecule
- Enzymatic activity (respiratory and photosynthetic enzymes)
- Signal transduction (insulin receptor): receptor proteins bind to specific chemicals and the receptor triggers changes on inside of membrane.
- Attachment/recognition (tight junctions): attachment points for cytoskeleton elements.
What is the difference between passive transport and active transport?
The need for ATP!
Passive: no need to expend chemical energy by diffusion down a concentration gradient.
Active: energy-dependent transport that moves molecules against a concentration gradient.
What are the types of passive transport?
- Simple diffusion
- Facilitated diffusion
- Osmosis (SD across membrane or FD through aquaporins)
Describe simple diffusion.
Simple diffusion is the movement of molecules directly across a membrane WITHOUT the involvement of a transporter. Goes from high to low concentration. The rate depends on molecular SIZE and lipid SOLUBILITY.
Describe facilitated diffusion.
It is the movement of molecules WITH the involvement of a transporter (transport protein)
What are the types of channel proteins from facilitated diffusion?
- AQUAPORINS: diffusion of water only (does not allow the diffusion of ions)
- Gated channels: can open/close (Na+, K+, Ca2+, and Cl-)
- Leak channels: lets SOME ions move (tight)
- Voltage-gated ion channels : nerve conduction + muscle contraction
What is the difference between dialysis and osmosis?
Dialysis is the movement of molecules in solute (e.g. glucose) and osmosis is the movement of the solvent (water) itself across a semi-permeable membrane.
By what does osmosis occur?
- Passive diffusion
- and also by simple AND facilitated diffusion
- dictated by solute concentration (goes from LOW to HIGH solute conc.
Explain hypotonic and hypertonic environmental conditions.
- Hypotoninc: env. has LOWER solute conc. than inside the cell = cell swells/turgid
- Hypertonic: env. has HIGHER solute conc. than inside the cell = cell shrinks/plasmolyzed
Explain the relation between osmosis and cell walls (turgor pressure) in a hypotonic env.
In plants, the cell wall prevents the cells from bursting in a hypotonic solution because of its rigidity. Instead the cell pushes against the cell wall, resulting in what is called turgor pressure.
How can water be drawn into aquaporins?
Aquaporins are made of non polar alpha helices to keep the protein embedded in the cell membrane and contains 2 + CHARGED POLAR A.A. that draw water into the channel. In fact, the partial negative charge on the oxygen is attracted to the + a.a.
What do you say of plant cells in different osmotic pressure conditions?
- Hypertonic: plasmolyzed, microtubules still attached to cell wall, membrane turned inwards,small vacuole.
- Isotonic: flaccid, vacuole 90% of volume, no pressure on cell wall
- Hypotonic: turgid, over filled vacuole pushing against cell wall
What do you say of animal cells in different osmotic pressure conditions?
- Hypertonic: crenated, surface is scalloped due to shrinkage
- Isotonic: biconcave disk
- Hypotonic: swollen, fully spheric
What are the types of active transport?
- Primary: the same protein that transports the molecules also hydrolyzes ATP to directly power the transport.
- Secondary: the transport is indirectly driven by ATP.
Describe the different primary active transports.
-Na+/K+ pump: pushes 3Na+ ions out of the cell and two K+ ions into the cell
-Ca2+ pump: pushes from the cytoplasm to the cell exterior, and from the cytoplasm into the ER lumen
-H+ pump: push from the cytoplasm to the cell exterior.
They create an electrochemical gradient because of the concentration and electrical charge difference
Describe the different secondary active transports.
The
- symport: cotransport, same direction as the driving ion
- antiport: exchange diffusion, opposite direction
Describe an electrochemical gradient.
Because of difference in charge as well as from the unequal distribution of ions. It stores energy that is used for other transport mechanisms. A gradient across the membrane that is involved with the movement of ions associated with nerve impulse transmission
Why is endo/exocytosis useful?
To import/export larger molecules.
Do endocytosis and exocytosis require energy?
Yes. both.
Descrive and explain endocytosis.
IMPORTS.
- Bulk-phase: cell drinking. No binding by surface receptors
- Receptor-mediated: the molecules to be taken in are bound to the outer cell surface by receptor proteins (integral proteins)
Descrive and explain exocytosis.
EXPORTS.
Secretory vesicles move through the cytoplasm and contact the plasma membrane. The vesicle membrane fuses with the plasma membrane, releasing the vesicle’s contents to the cell exterior.
True or False? Exocytosis is used by neurons during the synapse process.
True.
What is phosphorylation?
A signalling mechanisms where the signal is relayed inside the cell by protein kinases, enzymes that transfer a phosphate group from ATP to one or more sites on particular proteins one after the other like a cascade.
