Exam 3 Flashcards
Charles Overton (1890s)
Membranes are basically a lipid substance
Longmuir (1900s)
Lipids are phospholipids
Gorther & Grendel (1925)
Forms a lipid bilayer
Davson Danielli (1985)
Membranes contain proteins “protein sandwich model” proteins on outside
Robertson (1950s)
“Unit membrane” membranes function as an inseparable unit lie, membranes cannot be partial & still be functional
Hydrophobic tails
nonpolar
Hydrophilic
“polar heads” outside
Fluid Mosaic Model (1972) Singer & Nicholson
- characteristics of membranes are “two-dimensional fluids” (lipids and proteins flow laterally) composed of:
- Lipid bilayer: “fluid proteins embedded in the lipid bilayer like pieces of mosaic - membranes are asymmetric the two monolayers are composed of different lipids and proteins:
- Two “faces”
- Exoplasmic face (E face): faces “outside”
- Protoplasmic (P faces): also cytoplasmic face (C face): faces “inside”
Exoplasmic face (E face)
faces “outside”
Protoplasmic (P faces)
Also cytoplasmic face (C face): faces “inside”
Glycolipid
carbohydrate chains “antennae” - receptors sensors - environment
Hydrophobic force
holds the bilayer together
Chlorestrol
animal cell membranes only never plant cell fluidity
Transmembrane protein
all the way through. Many transmembrane proteins are transport proteins that facilitate proteins of chemicals through membrane
Channel proteins
small, inorganic molecules (porins, aquaporin) or ions (ion channels) by facilitated diffusion
integral proteins (transmembrane proteins)
partially or all the way through
uniport
one molecule one direction passing by facilitated diffusion
symport
2 molecules, same direction, one passing by facilitated diffusion the other by “piggyback”
antiport
2 molecules in opposite directions one passing by facilitated diffusion but generates energy to drive the other by active transport in the other direction
Carrier proteins (transporters permeases)
large organic molecules by various mechanisms passing facilitated diffusion or by active transport, except never by ATP hydrolysis
Diffusion
sometimes called simple diffusion to distinguish it from facilitated diffusion (later)
- the net, (no energy inherent tendency) movement that results from the random kinetic movement of individual molecules from a region of high to low concentrations
Measuring Diffusion
the rate of diffusion is a complex function of:
1. The concentration gradient
2. the “resistance” to flow a complex interaction of such characteristics
2.a) The physical and chemical properties of the medium through which the substance is diffusing (density, visiosity, polarity)
2.b) Molecular weight of the diffusing substance according to Graham’s law rate of diffusion
2.c) Temperature: increases the thermal agitation of all molecules
Facilitated Diffusion
The membrane protein “facilitated” diffusion through the membrane by opening a “tunnel”
Osmosis
The diffusion of a solvent through a semi-permeable membrane
- permeable to the solvent (water solvent can pass through) not permeable to the solute (solute cannot pass through) high to low concentration of water
solute
the molecule that is dissolved
solvent
the substance that the solute is dissolved in
osmotic solute has these characteristics
- soluble in the solvent
- cannot pass through the membrane
hypotonic osmotic system
water flows into cell
isotonic osmotic system
no net movement of H2O in and out
Hypertonic osmotic system
water flows out of the cell
components of the cytoskeleton summarized
- microtubules: largest thickest 25nm in diameter
- microfilaments
- intermediate filaments
(components “associated with the cytoskeleton”) known as “motor proteins” or “ mechanoenzymes”
they interact with components of the cytoskeleton (above) to produce cellular motion (ATP hydrolysis –> mechanical energy –> movement)
(components “associated with the cytoskeleton”) Associated with microtubules
- dyneins: movement in cilia and flagella
- kinesins: movement in mitotic spindle fibers
Dyneins
movement in cilia and flagella
Kinesins
movement in mitotic spindle fibers
(components “associated with the cytoskeleton”) Associated with microfilaments
- myosins: associated with actin in muscle cell contraction
Microtubules
largest (thickest) elements of the cytoskeleton, 25nm in diameter
- long hollow tubules
- globular protein, tubulin: two versions, alpha and beta, bond together to form alphabeta dimer
Microtubules are assembled in the microtubule organizing center (MTOC)
- in animals cells, MTOC is the centrosome
- in plants cells, MTOC is unknown
- evidence in MTOC is nuclear envelope
MTOC is responsible for organizing
- centrioles: spindle-shaped bundles of microtubules located in the centrosome
centrioles
Assemble basal bodies located at the base of every cilium (singular) and flagellum (singular)
basal bodies
assemble cillia (plural) and flagella (plural)
Cilia and flagella
essentially the same type of structure, differing:
1. length: cilia are short, flagella are long
2. number: cilia are numerous, flagella only one or two per cell
microfilaments
- smallest, thinner 7 nm thick
- structural support of cell, many cell movements:
- pseudopods in amoeba –> skeletal muscle contraction
alpha-actin
in skeletal muscle cells
F actin
filament formed from 2 chains of g-actin coil around each other
G actin
globular protein- forms a chain
Troponin complex
protein with 3 subunits:
- one subunit attaches troponin to the actin filaments
- one subunit attaches troponin to tropomyosin
- one subunit binds to Ca2+
Tropomyosin
filamentous proteins runs along the outer edge of the F-actin filaments
Intermediate filaments
- “Intermediate” in thickness 10nm in diameter
- consists of various rope like fibrous protein with high tensile strength (resist being pulled apart. ex: tug-a-war
- main function: enables cell to with stand mechanical stresses when stretched
Keratin
In epithelial cells of vertebrates especially in skin
keratin (fibers)
hair, feathers, scales, claws, nails
vimentin & desmin
in connective tissue cells, muscle cells, & the glial cells of nerve cells
Neurofilaments
neurons in cytoplasm
Nuclear lamins
nuclear envelope
