Chapter 7 Flashcards
Plasma Membrane
- selectively permeable
- bilayer of phospholipids
- colder temperatures (depending on lipids) = fluid membrane becomes more solid
- more unsaturated fatty acids = more fluid membrane
- must be fluid to properly function
- have distinct inside and outside faces determined when formed by ER and Golgi
- hydrophobic (nonpolar) molecules can pass easy, like oxygen
- hydrophillic (polar) molecules need transport proteins to pass through, like sugar
Phospholipids
- amphipathic, means they have hydrophillic heads and hydrophobic tails; needed for membrane to be selectively permeable
- most abundant lipid in membrane
- are able to move within the bilayer, creating fluidity
- usually shift laterally, rarely flipper to other side of membrane
- unsaturated makes tails bent (which creates distance between phospholipids which creates fluidity), saturated makes tails extremely straight
Integral proteins
- imbedded in cell membrane
- has hydrophillic region - part that sticks out of the membrane, and hydrophobic region - part that is within the bilayer
- if they span the membrane, they are called transmembrane proteins
Fluid mosaic model
- theory for cell membrane structure proposed by Singer and Nicolson
- where proteins are imbedded within the bilayer
- free fracture procedure (splitting membrane bilayer apart) proved this correct
Cholesterol
- amongst the phospholipids in a membrane
- when temperatures get hot, cholesterol restricts fluidity, holding membrane together
- when temperatures get cold, cholesterol maintains fluidity, preventing tight packing of phospholipids
Membrane proteins
- drift in bilayer, more slowly than lipids because bigger
include: peripheral proteins - not embedded and on either surface of membrane and integral proteins
Six major membrane protein functions
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachment to the cytoskeleton and extracellular matrix (ECM)
Membrane carbohydrates
- is the main molecule on the plasma membrane that helps with cell to cell recognition
includes: glycolipids - carbohydrates covalently bonded to lipids, or glycoproteins - carbohydrates covalently bonded to proteins - vary among species / individuals
Transport proteins
- helps hydrophillic substances get through membrane
includes: channel proteins - hydrophilic channel that molecules or ions can use as a tunnel, carrier proteins - bind to molecules and change shape to transport across membrane - aquaporins: channel proteins that transport water
- specific for the substances they move
Passive transport
- diffusion of substance across membrane without using energy
- includes when substances move down their concentration gradient (not against it)
Diffusion
- tendency for molecules to spread out evenly into available space
- molecules can move randomly as individuals, but as a population they can have a general, all-together direction
- dynamic equilibrium: the same # of molecules that cross one way also cross in the other direction
- substances diffuse down their concentration gradient, like sliding down a hill
Osmosis
- diffusion of water across a selectively permeable membrane
- direction of process is determined by difference in total solute concentration
- water diffuses from lower to higher solute concentration
What are the three types of solute concentration solutions?
1) hypertonic: outside solute concentration is greater than concentration inside the cell; cell loses water (because it goes from low to high solute concentration)
2) isotonic: outside solute concentration is the same as concentration inside the cell; no water movement
3) hypotonic: solute concentration is less than concentration inside the cell; cell gains water
Why do some cells have osmolarity problems?
- cells without cell walls cannot regulate water intake as well as cells with them
- causes osmolarity problems for these cells in hypotonic and hypertonic solutions
- cells must have adaptations to compensate, like contractile vacuoles
Cell walls (osmolarity and water wise)
- help maintain water balance
- in a hypotonic solution, cell wall it swells until it opposes uptake; the cell is now turgid
- in isotonic solutions, the cell becomes flaccid (limp) and the plant may wilt
- in hypertonic solution, cell loses water; membrane eventually pulls away from the wall, usually killing it the cell - called plasmolysis
Facilitated diffusion
- passive transport (moves down gradient) with the help of transport, channel, or carrier proteins
- transport proteins: speed molecular movement across membrane
- channel proteins: provide corridors that allow a specific molecule or ion to cross the membrane
- carrier proteins: undergo a subtle change in shape that moves the solute-binding site across the membrane
Active transport
- uses energy (ATP) to move solutes AGAINST concentration gradient
- done through some transport proteins or specific proteins embedded in membrane
- sodium-potassium pump is an example; when NA is expelled it changes the proteins shape, then allowing for K to enter (which returns the shape back to NA usable)
Membrane potential
- voltage difference across a membrane
Electrochemical gradient
- two forces that drives ion diffusion across membrane
- chemical force: ion’s concentration gradient
- electrical force: membrane potential effect on ion’s movement
Electrogenic pump
- a transport protein that hydrolyzes ATP and uses the energy released from ATP hydrolysis to transport ions across membranes, which also moves net charge across membrane
- main pump of plants, fungi, and bacteria is a proton pump
- plant cells use hydrogen ion gradient to use active transport to get nutrients inside
Cotransport
- occurs when active transport of one solute indirectly drives transport of another solute
Exocytosis
- handles bulk transport across membrane
- where transport vesicles migrate to the membrane, fuse with it, and release their contents
- secretory cells use this to export their products
How do small and large molecules enter and leave the cell?
- small: through bilayer or by transport proteins
- big (polysaccharides or proteins): by vesicles
Endocytosis
- handles bulk transport across membrane
- where the cell takes in macromolecules by forming vesicles from the plasma membrane
- reversal of exocytosis with different proteins
- 3 types: Phagocytosis (“cellular eating”) - cell engulfs particle in a vacuole, Pinocytosis (“cellular drinking”)- cell creates vesicle around fluid, and Receptor-mediated endocytosis - binding of ligands to receptors triggers vesicle formation
Ligand
- an ion or molecule attached to a metal atom by coordinate bonding.
- bind on outside of the cell?
amphipathic
A molecule that has a hydrophilic region and a hydrophobic region is
receptor mediated endocytosis
A type of endocytosis in which the cell takes in specific substance after the substances bind to ligands in a coated pit on the cell membrane.
phagocytosis
A type of endocytosis in which the cell takes in a particle by wrapping pseudopodia around it and packaging it into what will become a food vacuole.
In what way do the membranes of eukaryotic cells vary?
certain proteins are unique to each membrane
According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
they can move laterally among the membrane
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
it exhibit a specificity for a particular molecule
glycoprotein
a protein with a short, usually branched chain of carbohydrates attached to it.
glycolipid
a short, usually branched carbohydrate attached to a phospholipid in the membrane
sodium potassium pump
An important transport system in animal cells which exchanges sodium and potassium ions across a membrane.
proton pump
A pump in the membrane of cells that pumps hydrogen ions (H+) out of a cell or into an intermembrane space.
electrogenic pump
A transport protein that generates voltage across a membrane, such as the sodium potassium pump.
In a hypotonic solution an animal cell will?
lyse
The sodium-potassium pump is called an electrogenic pump because it?
contributes to the membrane potential
carrier molecules are passive or active transport?
active
