Chapter 5: Cell Membranes and Signaling Flashcards
fluid mosaic model
The general design of the phospholipid bilayer serves as a lipid lake in which proteins float in
domains
the hydrophobic regions of phospholipids
Hydrophilic region of a phospholipid
Phosphorous containing head
electrically charged
gets along really well with polar water molecules
Hydrophobic regions of a phospholipid
associate with other hydrophobic substances
Long, non polar fatty acid tails
Phospholipid bilayer
the tails interact on the inside while the heads are on the outside
lipid composition
the kinds of lipids that make up the membrane/their proportion
Lipid Composition
One of the two factors that affects membrane fluidity
Cholestorl and saturated fats pack together and are less fluid
Unsaturated fats or ones with short chains increase membrane fluidity
Temperature
One of the two factors that affects membrane fluidity
Fluidity declines under cold temperatures
some animals change lipid composition to get through this problem by replacing saturated with unsaturated
Peripheral membrane proteins
lack exposed hydrophobic groups and are not embedded in the bilayer
Instead, had polar or charged regions that interacted with exposed parts of the integral membrane proteins or with the polar heads of the phospholipids
Integral membrane proteins
at least partly embedded in the phospholipid bilayer
have hyrophobic and hydrophilic regions
anchored membrane proteins
have fatty acids or lipid groups covanlently attached to them
hydrophobic lipid components that anchor them in the phospholipid bilayer
transmembrane protein
an integral membrane protein that extends all the way through the phospholipid bilayer and protrudes on both sides
always oriented the same way
Transmembrane domains
extend through the bilayer
transmembrane proteins have them
glycolipid
carbohydrate covalently bonded to a lipid
carb goes out of cell surface and may serve as a recognition signal
glycoprotein
carbohydrate covalently bonded to a protein
The carbohydrate is an oligosaccharide of 15 or fewer monosaccharide units
often function as signaling units
selective permeability
biological membranes allow some sometimes, but not others to pass through
like the bachelor (not everyone gets a rose)
Passive transport
direct input of metabolic energy is NOT required to drive these processes
kind of just happens
gradients though
Active transport
requires the input of metabolic energy from an outside source
diffusion
process of random movement toward a state of equilibrium
net movement from greater concentration to lower
very slow process in living tissues
equilibrium
the state in which a solution in which solute molecules are evenly distributed is in
Factors that determine how fast a substance diffuses
diameter of molecules or ions: smaller diffuses faster
temperature of the solution: higher temperature, more movement, faster diffusion
concentration gradient: change in solute concentration with distance in a given direction
greater concentration gradient, the more rapidly it diffuses
simple diffusion
just passes through
in membranes, must be teeny weeny, hydrophobic, and lipid solubles
Osmosis
the movement of water across membranes
signal transduction pathway
a sequence of molecular events and chemical reactions that lead to a cell’s response to that signal
Autocrine signals
affect the same cells that release them
ex. many tumor cells make their own division singles
Paracrine signals
diffuse to and affect nearby cells
ex. neurotransmitter made by one cell stimulates an adjacent one
hormones
signals to distant cells that travel through the circulatory system
Can any cells respond to any stimulus?
NOPE!
Only the cells with the necessary receptors can respond
allosteric regulation
involves an alteration in the three dimensional shape of a protein as a result of the binding of another molecule at a site other than the active site
ex. gated channel
law of mass action
binding is reversible (noncovalent bonding)
generally favored though
Inhibitor or antagonist
binds to receptor protein and prevents the binding of the normal ligand
Girlfriend by Avril Lavigne
like competitive inhibition
Cytoplasmic receptors
small or nonpolar ligands can diffuse across the phospholipid bilayer of the plasma membrane and enter the cell
ex. estrogen
many regulate gene expression
Membrane receptors
Large or polar ligands cannot cross the lipid bilayer
ex. Insulin
binds to transmembrane receptor with an extracellular binding domain
Protein kinases
catalyze this reaction:
ATP + protein —-> ADP + phosphorylated protein
simple diffusion
to use this to pass through the bilayer, a molecule must be small, hydrophobic, and lipid soluble
osmosis
diffusion of water across a membrane
If the total solute concentration is high, then the the concentration of water molecules is….?
lower
hypertonic solution
higher solute concentration than the other solution
Isotonic solution
equal solute concentrations
Hypotonic
Lower solute concentration than the other one
turgor pressure
The pressure within a cell with a cell wall that comes from the limited amount of water the cell can take in, building up internal pressure and preventing water from entering
channel proteins
integral membrane proteins that form channels actoss the membrane through which certain substances can pass
carrier proteins
Membrane proteins that speed up diffusion rate through the bilayer
Facilitated diffusion
Diffuse according to gradients, but made easier by channel or carrier proteins
Ion Channels
famous
specific
Gated channel
opens when a stimulus causes a change in the three-dimensional shape of the channel
Ligand
binding of a chemical signal
can be the stimulus of a gated channel
Ligand-gated channels
channels controlled by ligands
Voltage-gated channels
Opens or closes based on changes in the voltage across the membrane
Aquaporins
Water is special and gets its own super cool channel to use to diffuse
allow large amounts of water to follow concentration gradients
saturated
increases in concentration gradient are no longer accopmanied by increased diffusion rates
Primary active transport
uses ATP directly
Secondary Active transport
does not use ATP directly
energy comes from electron or ion concentration gradient
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