Lecture 7 Flashcards
What is the function of the cell membrane?
compartmentalize the cell and form a barrier between extracellular environment and cytoplasm
What are membranes made of?
Lipids
What are three properties of membranes?
- stable lipid bilayer which form spontaneously in water
- Stabilized by hydrophobic interactions
- low permeability
4 characteristics of liposomes
- are most stable 50-500nm range
- Larger liposomes break up because of thermo-motion
- high salt concentrations stabilize liposomes
- carriers of hydrophilic molecules
What two things form the membrane?
Lipids + cholesterol
What does more structure mean within lipid movements
less structure = less movement
What 3 things affects lipid fluidity
- temperature
-unsaturated fatty acids - cholesterol
What does it mean for the membranes to be asymmetric?
It means the two bilayer are different
What can easily pass though the membrane?
Small, non-charged molecules
O2, CO2, N2
Can small uncharged polar molecules pass through the membrane?
The permeability of membranes is in part determined by lipid composition, water can move through but no very fast
h2O, ethanol, glycerol
Can larger uncharged polar molecules pass through the cellular membrane?
They can, but very slow
Amino acids, glucose, and nucleotides
Can ions pass through the membrane?
No
H+, Na+, K+, Ca2+
What is osmolarity?
total concentration of all solute particles
What has higher osmolarity, cytoplasm or extracellular space?
cytoplasm
What causes turgor pressure?
Water pushing into the cell from the cytoplasm, having a higher osmolarity
What allows for fast exchange of water?
aquaporins
What keeps the plants “in shape”
Turgor pressure
What stabilizes the plasma membrane of mammalian cells
cytoskeleton
What is cytosol low in and high in
Low in Na+ and Ca2+
High in K+
What is the concentration gradient?
Higher concentration of molecules on one side of the membrane compared to other side
What is membrane potential?
Unequal charge distribution across the membrane
Concentration gradient + membrane potential = ????
Electrochemical gradient
What is electrochemical gradient?
determines which direction charge solutes will move
What are two ways to transport molecules across membranes
- transporter
- Channels
What are characteristics of transporters?
Contains a central binding site for the molecule/solute. The binding site chances accessibility from one side of the membrane to the other
What are characteristics of channels?
Channels are selective pores
Channels allow ions to pass membranes
Electrochemical gradient determines the direction of flow
What is passive transporter?
Follows the concentration gradient
What is an active transporter?
Works against concentration gradient
Describe the alternate access model of transporter function
- central binding pocket is accessible either from the outside or the cytosol
- glucose transporters can function in both directions and thus follows concentration gradient
What is hexokinase?
(Converting glucose to glucose-6-phosphate) drives the import forward. The transport across the membrane is passive, by the system uses energy to trap glucose which makes the glucose import an active transport system
What drives the ion gradient?
ATP
Amino acids can be imported or synthesized from what …
glucose
What are the jobs of ion channels?
The selectivity filter allows only specific ions to pass through (no water)
Job of the gates in ion channels
signal open and close
Where is the tetrametric protein complex found?
plasma membrane
What is the function of the tetrametric protein?
pain receptor
When is the tetrametric protein activated and what happens?
Activated by high temperature or chemicals which causes cations to flux
What is a good example of ion channel?
neurons
What is the job of the neuron?
Neurons receive information from other neurons on the dendrites, process the information, and send a signal down the axon to other neurons
What are signals neurons use?
Changes in membrane potential
Action potential = ???
a rapid and local change in membrane potential propagating along the membrane of neurons
What is synapses?
Specialized areas of the neurons that make contact with other cells and deliver a signal to the postsynaptic cell
What makes synapses unique?
Large number of vesicles present
What occurs during step 1 of synaptic activity?
- the action potential from the axon ends up in synapses which include calcium channels
- the calcium triggers the fusion of synaptic vesicles with the plasma membrane, which release a neurotransmitter
What occurs during step 2 of synaptic activity?
- the neurotransmitter diffuses across the synaptic cleft and opens a cation channel in the postsynaptic neuron
- the influx of cations produces an action potential in the postsynaptic neuron
