diffusion and membrane Flashcards
three types of fibers in cytoskeleton
microtubules, microfilaments, intermediate filaments
microtubules
thicket, hollow rods constructed from globular proton dimers called tubulin
- grow out of centrioles
- control beating of cilia and flagella
microtubules functions
shape and support cell,
guide movements of organelles, separate chromosomes during cell division
flagella (1/few per cell) and cilia (many per cell)
differ in beating patterns
- structure: group of microtubules enclosed by plasma membrane, basal body that anchors
- dynein (motor protein) drives bending movement
dynenin
dyne arms contact, move and release out microtubules
- microtubules held together by flexible cross-linking proteins
microfilaments (actin filaments)
- thinnest, solid rods built from molecules of globular actin subunits
- bear tension
- make up core of microvilli of intestinal cells
centrosome
has pair of centrioles, each with 9 triplets of microtubules arranged in a ring
microfilaments functions
- maintain cell shape
- muscle contraction
- cytoplasmic streaming
- cell motility
- cell division
intermediate filaments
- larger than microfilaments
- smaller than microtubules
- only in animals, vertebrates
- support cell shape and fix organelles in place
- more permanent than other two
cell junctions
neighboring cells in animal or plant often adhere, interact and communicate through direct physical contact
- plasmodesmata
- tight junctions
- desmosomes
- gap junctions
tight junctions
forms a water-tight seal between cells
desmosomes
act like velcro and fasten cells together
gap junctions
act like secret passageways and allow materials to pass between cells
plasma membrane
fluid mosaic of lipids and proteins
- selective permeability
- passive transport = no energy investment
- active transport = requires energy
- phospholipids (most abundant lipid in membrane) are amphipathic
fluid mosaic model
the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids with hydrophobic portion protruding
- proteins (more slow) and lipids (rapid) shift laterally
membrane fluidity and temperature
as temp cools it becomes solid
- remains fluid at cooler temp if rich in phospholipids with unsaturated hydrocarbon tails
cholesterol effect on temperature
at warm it restrains movement, at cool it prevents tight packing
what determines most of the membrane’s specific functions?
proteins
integral proteins
penetrate hydrophobic interior of bilayer
- hydrophobic part of integral ha non polar HAs coiled into alpha helix
transmembrane proteins
integral proteins that span the membrane
peripheral proteins
loosely bound to the surface of the membrane
six major functions of membrane proteins
transport
enzymatic activity
signal transduction
cell-cell recognition
intercellular junction
attachment to cytoskeleton and extracellular matrix (ECM)
cell-cell recognition
bind to surface of molecule containing carbs on the extracellular surface of membrane
- carbs bonded to lipids (glycolipids) or proteins (makes glycoproteins)
Permeability of Lipid Bilayer
- hydrophobic/non polar molecules, like hydrocarbons, cross easily
- hydrophilic/polar molecules, like sugars, do not cross easily
Transport proteins
allow passage of hydrophilic substances
- channel proteins
carrier proteins
channel proteins
aquaporins: facilitate passage of water
Ion channels (gated open and close in response to stimuli)
carrier proteins
bind to molecule, change shape to shuttle them across
diffusion
molecules spread out evenly into the available space
- passive transport
- diffuses down the concentration gradient (more concentrated to less)
osmosis
diffusion of free water across membrane
- low solute concentration too high solute concentration
tonicity
ability of a surrounding solution to cause a cell to gain or lose water
isotonic
same solute in and out; no movement of water
hypertonic
more solute concentration than inside cell; cell loses water
hypotonic
solute concentration lower than inside cell; cell gains water
facilitated diffusion
transport proteins speed passive movement of molecules
Active transport uses energy to…
move solutes agains the grain
- ATP
- sodium potassium pump (2 K+ in, 3 Na+ out)
plant example
hypotonic: swells until wall opposes; turgid
isotonic: no water movement; flacccid
hypertonic: membrane pulls away from wall; plasmolysis
membrane potential and voltage
voltage across a membrane
- voltage = distribution of + and - ions across membrane
electrochemical gradient
drive diffusion of ions across a membrane
- chemical force: ion’s concentration gradient
- electrical force: effect of voltage on ion’s movement
electrogenic pump
transport protein that generates voltage across a membrane
- sodium potassium pump
- protein pump
- her store energy for cellular work
cotransport
occurs when active transport of a solute indirectly drives transport of other solutes
- sucrose proton cotransporter
bulk transport require…
energy and use vesicles for exocytosis and endocytosis
exocytosis
transport vesicles migrate to the membrane, fuse with and release their contents
endocytosis
cell brings in molecules/particulate matter by forming new vesicles from the membrane
- phagocytosis (cellular eating)
- pinocytosis (cellular drinking)
receptor-mediated endocytosis
metabolism
getting energy from food to create all our chemical reactions
- all the chemical reactions that occur in living organisms
- anabolism and catabolism
- metabolic pathway: molecule -> product (each step catalyzed by a specific enzyme)
anabolism
set of metabolic pathways that construct polymers from monomers
-consume energy
catabolism
set of metabolic pathways that deconstruct polymers into monomers
- releases energy
Energy
capacity to cause change
- kinetic, thermal, heat, potential, chemical , light
kinetic energy
associated with motion
thermal
kinetic associated with random movement of atoms
heat
thermal energy transferred from one about to another
potential
energy because of location or structure
chemical
potential available for release in a chemical reaction
