Chapter 7: Membrane Structure and Formula Flashcards
What are the stable ingredients of membranes?
lipids
What is an amphipathic molecule?
a molecule with a hydrophobic/hydrophilic region
What is the fluid mosaic model?
the membrane is a “mosaic” of protein molecules bobbing in a fluid bilayer of phospholipids
Membranes (are/are not) static sheets of molecules locked in place.
are not
What will cause membrane fluid to solidify?
low temperature
What is cholesterol?
a steroid which is found wedged between phospholipids
What is the effect of cholesterol at high temperatures?
restrains phospholipid movements and helps make the membrane less fluid
What is the effect of cholesterol on membrane packing?
Restricts phospholipids from tightly packing together
What are integral proteins?
penetrate the hydrophobic region of membrane
What are transmembrane proteins?
span the entire depth of the membrane
What are peripheral proteins?
are not embedded in the lipid membrane at all
Peripheral proteins are loosely bond to _________
the surface of the membrane
What holds membrane proteins on the cytoplasmic side?
cytoskeleton
What is cell to cell recognition?
A cell’s ability to distinguish one type of neighboring cell from another
What is an example of cell to cell recognition?
The sorting of cells into tissues and organs in an animal embryo
how do cells recognize other cells?
by binding to molecules on the extracellular surface of the cell membrane
What are membrane carbohydrates?
short, branched chains of fewer than 15 sugar units
What are glycolipids?
a lipid w/ one or more covalently bonded carbohydrates
What are glycoproteins?
a protein with one or more covalently bonded carbohydrates
What are membrane sidedness?
the asymmetrical arrangement of proteins, lipids, and their associated carbohydrates
What is a supra molecule structure?
many molecules ordered into a higher level of organization
What is the best applicable example of a supra molecule structure?
A biological membrane
What are non polar molecules, and some examples?
hydrophobic molecules that can dissolve in the lipid bilayer and cross easily without membrane proteins
ex: hydrocarbons, CO2, O2…
What are polar molecules, and some examples?
pass through the membrane very slowly (ex. glucose and other sugars)
What are transport proteins?
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Why are transport proteins needed?
To help ions cross the membrane
What are channel proteins?
function by having hydrophilic channels that certain ions or molecules use as a tunnel through the membrane
What is an example of a channel proteins?
Aquaporins
What are aquaporins?
specific channel proteins that facilitate the passage of water molecules through the membrane in certain cells
What are carrier proteins
a type of transport protein that hold onto their passengers and change shape in a way that shuttles them across the membrane
What property allows O2 and CO2 to cross a lipid bilayer w/o the aid of membrane proteins?
O2 and CO2 are both non polar molecules that can therefore easily move through the hydrophobic interior
Why is a transport protein needed to move many water molecules across a membrane?
H2O is a polar molecule meaning that unassisted it cannot pass rapidly through hydrophobic regions
Aquaporins exclude passage of hydronium ions (H3O+) but some aquaporins allow passage of glycerol, a 3 carbon alchohol as well as H2O. Since H3O+ is closer in size to water than glycerol, yet cannot pass through. What may be the basis of this selectivity?
The hydronium ion is charged the glycerol is not
What is diffusion?
the movement of particles of any substance so that they spread out into available spaces
what is the concentration gradient?
a region along which the density of a chemical substance increases or decreases
What is passive transport?
requires no input of energy
What is osmosis?
diffusion of water
what is tonicity?
the ability of a solution surrounding a cell to cause that cell to gain or lose water
what is isotonic?
referring to a solution that when surrounding a cell causes no net movement of water into or out of the cell
what is a hypertonic solution?
referring to a solution that when surrounding a cell will raise a cell to loose water
what is a hypotonic solution?
referring to a solution that when surrounding a cell will raise a cell to absorb water
what is facilitated diffusion?
the passage of water molecules or ions down their electrochemical diffusion gradient across a biological membrane w/ the assistance of specific transmembrane proteins (requiring no energy expenditure)
what are gated channels?
open/close in response to stimulus
what is active transport?
movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins (requiring an expenditure of energy)
what is a sodium potassium pump?
a specific case of active transport
What are the 6 steps of a sodium potassium pump?
- Sodium binds to the sodium-potassium pump
- Sodium binding stimulates a phosphate from ATP to bind to the pump
- protein changes shape and releases sodium on the other side of the membrane
- The new shape has high affinity for potassium which binds to the ECM side and triggers phosphate to release
- Loss of phosphate group retires original shape which has a lower affinity for potassium
- potassium is released and gains affinity for sodium (starting cycle over again)
What is voltage in cells?
electrical potential- a separation of opposite charges
What is the voltage of the cytoplasmic side?
negative relative to the ECM
What is membrane potential?
the voltage across the membrane ranges from about -50 to -200 millivolts
What are the forces that drive diffusion of ions?
chemical force: ions concentration gradient
electrical force: the effect of membrane potential on the ion’s movement
What is the electrogenic pump?
a transport protein that generates voltage across a membrane
What is a proton pump?
major electronic pump of plants that actively transport H+ ions out of the cell
What is cotransport?
a transport protein that can couple the “downhill” diffusion of the solute to the “uphill” transport of a second substance against its own concentration gradient
What kind of cotransport to plants use?
H+/sucrose
Do sodium potassium pumps make or use ATP?
They use ATP tp pump ions against their gradients
What kind of transport does the active transport use? Why?
active transport
to pump ions against concentration gradient
What kind of active transport does a cotransporter use? Why?
active transport
pumps down concentration gradient and pumps second substance against concentration gradient
Why is the sodium potassium pump not considered a cotransporter?
The sodium potassium pump is not considered a cotransporter bc it does not pump ions down its concentration gradient
Given the internal environment of a lysosome, what transport protein might you expect to see in its membrane?
The internal environment of a lysosome is acidic, therefore there will be a higher concentration of H+ ions inside meaning you will most likely see a proton pump
How do small solutes cross membranes?
transport proteins
How do large molecules cross membranes?
vesicle (that require energy)
What is exocytosis
cells secrete certain molecules by the fusion of vesicles w/ the plasma membrane
What are the steps of exocytosis?
- a transport protein buds from the Golgi apparatus
- moves along a microtubule and travels to the plasma membrane
- vesicle fuses to cell membrane
- the cells release particles outside the cell
How does a vesicle fuse to the cell membrane?
special proteins rearrange lipids in phospholipid bilayers
What happens to the vesicle after it binds to the plasma membrane?
the membrane becomes part of the cell membrane
What is endocytosis?
cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane
What is the relationship between endocytosis and exocytosis?
endocytosis is the reverse of exocytosis but proteins are different
What are the three types of endocytosis?
- phagocytosis
- pinocytosis
- receptor mediated
What is phagocytosis?
the ingestion of bacteria or other material by phagocytes and amoeboid protozoans
What are the steps of phagocytosis?
- Macrophage
- Engulfment by endocytosis
- Phagosome formation
- Phage-Lysosome mergers
- killing and digestion
- ingestion of debris and antigen presentation
What is pinocytosis?
a type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes
in many case the parts of the plasma membrane that form vesicles are lines w/ ______ layers
fuzzy
What is receptor mediated endocytosis?
the movement of specific molecules into a cell by infolding of vesicles containing proteins w/ receptor sires specific to the molecules being taken in
What does receptor-mediated endocytosis enable?
A cell to acquire bulk quantities of specific substances
As a cell grows its plasma membrane expands. Does this involve endocytosis or exocytosis?
Exocytosis. When a vesicle membrane bonds w/ the plasma membrane it becomes part of the cell membrane
Animal cells make an ECM. Describe the cellular pathway of synthesis and deposition of an ECM glycoprotein?
- The glycoprotein begins synthesis in the ER lumen
- Golgi apparatus
- Breaks off in a vesicle
- Travels to the plasma membrane
- dissolves into the plasma membrane
