Chapter 7 Flashcards
what is the plasma membrane?
it is the boundary that separates the living cell from its surroundings (8mm)
- it is selectively permeable
what is selective permeability?
allowing some substances to cross it more easily than others
what lipid is the most abundant in the plasma membrane?
the phospholipids are the most abundant lipid in the plasma membrane
- phospholipids are also amphipathic molecules
- phospholipids can move within the bilayer
what are amphipathic molecules?
molecules that contain a hydrophobic and a hydrophilic region(s)
what is the fluid mosaic model?
it states that the membrane is a fluid structure with a “mosaic” of various proteins embedded in it or attached.
hydrophobic interactions are what?
they are weaker than covalent bonds
and membranes are held together by these types of bonds
what rarely happens across a membrane?
rarely does a molecule flip-flop transversely across the membrane
How are the membrane of a cell and temperature related?
- As temperatures cool, membranes switch from a fluid state to a solid state
- the temperature at which a membrane solidifies depends on the type of lipids
- membranes must be fluid to work properly
membranes rich in…?
membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
At warm temperatures of about 37 degrees celsius?
cholesterol restricts the movement of phospholipids
- at cool temperatures it maintains fluidity by preventing tight packing
proteins do what?
- proteins determine most of the membranes specific functions
- proteins can be peripheral( attached outside the membrane) or integral (within the membrane)
what are peripheral proteins?
they are like appendages bound loosely to the surface of the membrane
what are integral proteins?
they penetrate the hydrophobic core
- integral proteins that span the membrane are called TRANSMEMBRANE PROTEINS
Integral proteins contain how many regions?
2 regions
hydrophobic region: consists of one or more stretches of nonpolar amino acids, often coiled into alpha helices
hydrophilic region: is in contact with the aqueous solution
what are the 6 major functions of membrane proteins?
- transport
- enzymatic activity
- signal transduction
- cell - cell recognition
- intercellular joining
- attachement to the cytoskeleton and extracellular matrix (ECM)
what is the role of carbohydrates in cell- cell recognition?
- cells recognize each other by binding to surface molecules, often carbohydrates (there are 15 sugars), on the plasma membrane
- Carbohydrates act as makers to distinguish one cell from another
- Membrane carbohydrates maybe covalently bonded to lipids (glycolipids) or more commonly proteins (glycoproteins)
The asymmetrical distribution of lipids, proteins and carbohydrates in the membrane is determined when?
This is determined when the membrane is built by the golgi apparatus and the ER
what is the Asymmetry of membrane lipids?
- Inner and outer membrane leaflets have different lipid compositions
- Provides different physicochemical properties appropriate for different interactions
- membrane lipids move easily within a leaflet but only rarely flip-flop
Hydrophobic (non-polar) molecules can?
can dissolve in the phospholipid bilayer and pass through the membrane rapidly
(hydrocarbons, oxygen, and carbon dioxide)
Hydrophilic (polar) molecules?
do not cross the membrane as easily (sugars, ions and water)
what are transport proteins?
allow passage of of hydrophilic substances across the membrane without coming in touch with the hydrophobic part
what are channel proteins?
A type of transport protein that has a hydrophilic that certain ions or molecules can use as a tunnel
what is an aquaproin?
a channel protein that facilitate the passage of water
what are carrier proteins?
bind to molecules and change the shape to shuttle them across the membrane
transport proteins are an example of what?
active transport, which means they require energy to go through with reactions
what is passive transport?
is diffusion of a substance across a membrane with no energy investment
what is diffusion?
is the tendency for molecules to spread out evenly into the available space
- goes from high to low concentration
what is a concentration gradient?
the difference in concentration of a substance from one area to another
- no work must be done to move substances down their concentration gradient
a concentration gradient represents what?
potential energy
what is osmosis?
is the diffusion of water across a selectively permeable membrane
- goes from lower solute concentration to higher solute concentration
what is tonicity?
is the ability of a solution to cause a cell to gain or lose water
what is an isotonic solution?
solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
what is a hypertonic solution?
solute concentration is greater than that inside the cell, cell loses water
what is a hypotonic solution?
solute concentration is less than that inside the cell, cell gains water
what is facilitated diffusion?
transport proteins speed the passive movement of molecules across the plasma membrane
- channel proteins provide corridors that allow a specific molecule or ion to cross the membrane
channel proteins include?
- aqauporins for facilitated diffusion of water
- ion channels that open and close in response to a stimulus (Gated Channels)
what is active transport?
active transport moves ions against their concentration gradients and they require energy to do this
- allows cells to maintain concentration gradients that differ fro their surroundings
what is the sodium-potassium pump?
is one type of active transport system
- found in animal cells
- the pump is an integral membrane glycoprotein ( an antiporter)
- for every 3 Na+ that goes in 2 K+ go out
what is primary active transport?
requires direct hydrolysis of ATP
what s secondary active transport?
energy comes from an ion concentration gradient that is established by primary active transport
what is membrane potential?
is the voltage difference across a membrane
- all membrane have a potential of -50mV to -200mV because the inside of the cell is more negative than the outside of the cell
what is voltage?
voltage is created by differences in the distribution of positive and negative ions
what is an electrochemical gradient?
DRIVE THE DIFFUSION OF IONS ACROSS A MEMBRANE
- A chemical force (the ion’s concentration gradient)
- An electrical force ( the effect of the membrane potential on the ion’s movement)
- Ions will diffuse down the concentration gradient and down the electrochemical gradient
what is an electrogenic pump?
is a transport protein that generates voltage across a membrane
- the sodium-potassium pump is the major electrogenic pump of animals
what is a proton pump?
The main electrogenic pump of plants, fungi, and bacteria
what is co-transport ?
Occurs when active transport of a solute indirectly drives transport of another solute
what is the Glucose Transporter?
an example of facilitated diffusion
- the gradient for glucose entry into the cell is maintained by phosphorylation of glucose in the cytoplasm
- insulin stimulates glucose uptake by causing the insertion into cell membrane vesicles containing preformed glucose transporters
what is exocytosis?
transport vesicles migrate to the membrane, fuse with it, and release their contents
bulk transport across the plasma membrane occurs by?
exocytosis and endocytosis
what is endocytosis?
the cell takes in macromolecules by forming vesicles from the plasma membrane
- there are three types of endocytosis
what are the 3 types of endocytosis?
- phagocytosis ( cellular eating)
- pinocytosis ( cellular drinking)
- Receptor-mediated endocytosis
what is phagocytosis?
A cell engulfs a particle in a vacuole, the vacuole fuses with the lysosome to digest the particle
what is pinocytosis?
molecules are taken up when extracellular fluid is “gulped” into tiny vesicles
what is receptor-mediated endocytosis?
binding of ligands to receptors triggers vesicle formation
what are ligands?
any molecule that binds specifically to a receptor site of another molecule
