Cell Bio exam 2 ch 3,4,12,17,15
biomolecular
2 mcs
when an inhibitory neurotransmitter such as GABA opens Cl- channels in the plasma membrane of a postsynaptic neuron, why does this make it harder for an excitatory neurotransmitter to excite the neuron?
very little Cl- enters which opposes influx. if Cl and Na channels are open at same time, the Cl neutralizes Na thus suppressing action potential making harder to depolarize.
keq means
they are not bonded
keq is used in
unimolecular reactions a = A
biomolecular association
A + B = AB
Consider a cell whose glucose transporter is knocked out. If it is placed in a solution that contains 1 mM glucose, then how many glucose molecules will enter the cell in 10 seconds via diffusion? Assume that (i) the cell contains no glucose, (ii) the surface area of the cell's plasma membrane is 5 μm2, and (iii) the permeability of a lipid bilayer for glucose is 10-8 cm/sec. A. 3000 B 60 C 600 D 300
A 3000
Assume that the kinetics of a phosphorylation reaction carried out by a kinase can be appropriately described by the Michaelis-Menten relationship. Competitive inhibition of this kinase by a drug molecule will a) Alter the slope of the line in the Lineweaver-Burk plot, but not the maximum rate of the reaction. b) Alter the slope of the line in the Lineweaver-Burk plot and reduce the maximum rate of the reaction. c) Change the maximum rate of the reaction, but not the slope of the line in the Lineweaver-Burk plot. d) Alters neither the rate of the reaction nor the maximum rate of the reaction.
A Alter the slope of the line in the lineweaver Burk plot but not the maximum rate of the reaction
which of the following statements are correct? Explain your answers. A the plasma membrane is highly impermeable to all charged mc. B channels have specific binding pockets for the solute mcs they allow to pass. C transporters allow solutes to cross a membrane at much faster rates than do channels. D certain H+ pumps are fueled by light energy. E plasma membrane of many animal cells contain open K+ channels, yet the K+ concentrations in the cytosol is much higher than outside the cell. F symport would function as an antiport if its orientation in the membrane were reversed (if the portion of the mc normally exposed to the cytosol faced the outside of the cell instead) G membrane potential of an axon temporarily become more negative when an action potential excites it.
A F selective permeability to many but not all B F channel do not have binding pockets. selectivity to acheived by size of pore C F transporters are slower. D T E T contain K+ leak channels but membrane potential is neg so keeps K+ from leaking. F F turning it around would cause it to be anitport G F shift it from neg to pos.
T or F? A kinesin moves ER membranes along microtubules so that the network of ER tubules becomes stretched throughout the cell B without actin, cells can form functional mitotic spindle and pull their chromosomes apart but cannot divide C lamellipodia and filopodia are feelers that cell extends to find anchor points on the substratum that it will then crawl over D GTP is hydrolized by tubulin to cause the bending of flagella
A T absence of microtub. causes collapse toward center of cell B T C T both extensions are associated with transmembrane proteins that protrude from plasma membrane and enable the cell to form new anchor points D F to cause bending, ATP is hydrolyzed on outer microtub. of flagella
Name at least one similarity and at least one difference between the following: A symport and anitport B active and passive transport C membrane potential and electrochemical gradient D pump and transporter E axon and telephone wire F solute and ion
A both couple movement of two solutes. symports in same direction and antiport in opposition directions. B both mediate membrane transport proteins. passive no energy, downhill and active is uphill, needs energy C both are gradients across membranes. membrane potential is voltage gated and electrochemical is voltage gradient and concentration gradient. D pump transport uphill E both transmit electrical signals. wire are made of copper. axon signal passing down does not diminish bc its self amplifying and wire decreases over distance F both affect osmotic pressure in cell. ion is solute that bears a charge.
functions of NaK pump
- facilitation of glucose transcellular transport - nerve conduction - maintenance of resting membrane potential - regulation of cell volume
patch clamping
- measures kinetics nobel prize 1. clamp patch with suction 2. put in container + solution salt water 3. attach electrode and get current each peak is a ion channel
Gating and 4 types
- open/close in response to stimuli 1. voltage gating 2. extracellular ligand gated 3. intercellular ligand gated 4. mechanically gated
energetic and kinetic analysis provide
- quantitatively evaluate specific roles - physical and mechanical insights - info. necessary to develop predictive models
resting potential
-20 to -120 mV
free energy changes to memorizes (2)
1 ATP to ADP + Pi -7.3kcal/mol 2 glucose + 6CO2 to 6CO2 + 6H2O -686 kcal/mol
1 dm^3
1 L
delayed rectifier K+ channels
1. closed- resting 2. open- depolarized 3. inactive- too much out
voltage gated Na+ channels
1. closed- resting 2. open- slightly depolarized 3. inactive- completely reverses, inside is pos. has transmembrane helix attached to outside
3 types of active transporters
1. coupled 2. ATP driven 3. Light diven
hydrophobic interior
1. permits passage of hydrophobic solutes 2. barrier for translocation of polar solutes and ions bc need transporter needs help- small or larger uncharged polar mc and IONS
2 types of mem transport proteins
1. transporter- transport solute with structural change of protein 2. channel- not accompanied, open for solute to enter
the curve shown in figure is described by the MM equation: rate(v)=Vmax [S] / (Km+[S]) Can you convince yourself that the features qualitatively described are accurately represented by this equation? In particular, how can the equation be simplified when the substrate concentration [S] is in one of the following ranges: A [S] is much smaller than Km B [S] equals the Km C [S] is much larger than the Km
A (Km +[S]) approaches Km. so rate is proportional to [S] B [S]/(Km +[S]) equals 1/2. so reaction rate is half of maximal rate Vmax C [S]/(Km +[S]) equals 1. reaction occurs at maximal rate Vmax
During actin filament reorganization, Cofilin a) helps in removing hydrolyzed actin monomers from actin filaments. b) sequesters actin monomers and prevents them from assembling into filaments. c) helps in bundling together actin filaments. d) caps actin filaments.
A helps in removing hydrolyzed actin monomers from actin filaments
Activation of RhoA GTPases in cells _______. a) Increases formation of stress fibers. b) Decreases formation of stress fibers. c) Decreases myosin activity. d) Induces formation of lamellipodium.
A increases formation of stress fibers
Myelination of axons A Increases the rate of nerve conduction. B Slows down nerve conduction. C Does not affect the rate of nerve conduction. DLeads to a disease called Multiple Sclerosis.
A increases the rate of nerve conduction
when delta G is more negative in unimolecular reactions, then ...
A is more abundant than a
Which of the following is true about nucleotides bound to actin monomers? a) Nucleotide hydrolysis decreases affinity between monomer and filament. b) Nucleotide hydrolysis increases affinity between monomer and filament. c) Monomer dissociation from filament triggers nucleotide hydrolysis. d) Monomer binding to filament triggers conversion of ADP to ATP.
A nucleotide hydrolysis decreases affinity between monomer and filament
a typical time course of polymerization of purified tubulin to form microtubules is shown in figure. A explain the different parts of the curve (A,B,C) draw a diagram that shows the behavior of tubulin subunits in each of the 3 phases. B how would the curve in the figure change if centrosomes were added at the outset?
A phase A=lag phase which tubulin dimers assemble to form nucleation centers. phase B= rising phase, to plateau value as dimers add to microtub. phase C= equilibrium is reached so microtub. growing and other shrinking B only phase A would be eliminated, B and C would remain unchanged
dynamic instability cause microtubules either to grow or shrink rapidly. A what must happen at the end of the microtubule in order for it to stop shrinking and to start growing? B how would a change in the tubulin concentration affect this switch? C what would happen if only GDP, but no GTP were present in solution? D what would happen if the solution contained an analog of GTP that cannot by hydrolyzed?
A shrinks bc GTP cap is off, grows when GTP loaded tubulin add to end B more tubulin more growth or vise versa C microtub. would continue shrinking and eventually disappear D microtub. would continue to grow until all free tubulin have been used
Which of the following statements is true about biological reactions? a) Some biological reactions can occur without enzymes. b) All biological reactions need to be coupled to exergonic reactions. c) The standard free energies of reactions are always negative. d) The free energy released during ATP hydrolysis does not depend on temperature.
A some biological reactions can occur without enzymes
Which channel needs to be in the open state during the rising phase of an action potential? a) Voltage-gated Na+ channels b) Voltage-gated K+ channels c) NaK pumps d) Delayed rectifier K+ channels
A voltage gate Na+ channels
A. how many ATP mcs could maximally be generated from one mc of glucose, if the complete oxidation of 1 mol of glucose to CO2 and H2O yields 2687 kJ of free energy and the useful chemical energy available in the high energy phosphate bond of 1 mol of ATP is 50kJ? B. Respiration produces 30 mol of ATP from 1 mol of glucose. compare this number with your answer in part A. what is the overall efficiency of ATP production from glucose?
A. 2867/50= 57 ATP mc. B. 30/57= 53% efficiency of ATP production
Protein A binds to protein B to form a complex AB. At equilibrium in a cell the concentrations of A, B, and AB are all at 1 um. A referring tot he figure, calculate the equilibrium constant for reaction A + B = AB. B. what would the equilibrium constant be if A, B, and AB were each present in equilibrium at the much lower concentrations of 1nM each?
A. K=[AB]/ ([A]*[B]) 10^-6=1um 10^-6/(10^-6*10^-6) so = 10^-6 L/mol B. 10^-9/(10^-9*10^-9) so = 10^-9 L/mol
in a simple reaction A to A* a mc is interconvertible between two forms that differ in standard free energy Gô by 18kJ/mol with A* having the higher Gô. A use table to find how many more mcs will be in state A* compared with state A at equilibrium. B if an enzyme lowered the activation energy of the reaction by 11.7 kJ/mol, how would the ratio of A to A* change?
A. from table we know that it is 10^-3. [A*]/[A]= 1000 fold lower than A B. ratio would be unchanged, however the reaction would accelerate bc activation energy barrier would lower
Proteins A, B and C bind to each other to form a complex, ABC. Under equilibrium the concentrations of A, B, C and ABC are 10-2 M. The standard free energy of this reaction at T=300 K is a) -8.3 kcal/mol. b) -5.5 kcal/mol. c) -4.1 kcal/mol. d) -2.8 kcal/mol. e) -1.4 kcal/mol.
B -5.5 kcal/mol -2.3 * .002 * 300 * log 10 10^-2/10^-2*10^-2*10^-2
Ion channels cannot transport ions across membranes at rates faster than those predicted by Fick's law. a) True. b) False.
B False
complete the following sentence accurately, explaining your reason for accepting or rejecting each of the 4 phases. the role of calcium in muscle contraction is: A to detach myosin heads from actin B to spread the action potential from the plasma membrane to the contractile machinery C to bind to troponin cause it to move tropomyosin and thereby expose actin filaments to myosin head D to maintain the structure of the myosin filament
B and C is correct.
The microvilli of specialized epithelia are structurally composed of a) Plasma membrane covering a microtubule cytoskeleton. b) Plasma membrane covering an actin bundle. c) Plasma membrane covering various organelles like mitochondria or endoplasmic reticulum. d) Plasma membrane only.
B plasma membrane covering an actin bundle
The action potential does not reverse direction on its own because a) The voltage-gated K+ channels are in their open state. b) The voltage-gated Na+ channels cannot transition directly from inactive to open states. c) The voltage-gated Na+ channels are in their inactivated states. d) The delayed rectifier K+ channels cannot transition directly from inactive to open states.
B the voltage gate Na+ channel cannot transition directly from inactive to open states
Consider the reaction under physiological conditions of temperature and pressure: glucose +6CO2 to 6Co2 + 6H2O Which of the following is true? A) Entropy decreases. B) ∆H<0. C) ∆G0>0. D) None of the above are true.
B) delta H <0 entropy increases, delta H would have to be negative
which of the following types of cells would you expect to contain a high density of intermediate filaments in their cytoplasm? A amoeva proteus B skin epithelial cell C smooth muscle cell in the digestive tract D escherichia coli E nerve cell in the spinal cord F sperm cell G plant cell
B, C, E are rich in intermediate filaments
Which of the following accelerates filament nucleation? a) Filamin b) Kinesin 19 c) ARP complex d) Taxol
C ARP complex
Which of the following statement is true about intermediate filaments? a) Intermediate filaments display treadmilling b) Once formed, intermediate filaments cannot be disassembled. c) Intermediate filaments play a key role in the formation of cell-cell junctions. d) Intermediate filaments are a major component of the mitotic spindle
C intermediate filaments play key role in the formation of cell cell junction
Which is the following is true about the NaK pump? a) For each molecule of ATP hydrolyzed inside the cell, it transports 3 Na+ inside the cell and 2 K+ outside the cell. b) For every 2 molecules of ATP hydrolyzed inside the cell, it transports 3 Na+ inside the cell and 2 K+ outside the cell. c) It helps regulate cell volume. d) It is an ion channel.
C it helps regulate cell volume
Neurotransmitters that open Cl- channels in the post-synaptic cell membrane a) Depolarize the post-synaptic cell membrane b) Do not affect the electrical potential of the post-synaptic cell membrane c) Produce a similar effect as neurotransmitters that open K+ channels in the post- synaptic cell membrane d) Are called excitatory neurotransmitters.
C produce a similar effect as neurotransmitters that open K+ channels in the post synaptic cell membrane
During muscle contraction, Ca2+ ions in the muscle cell are needed for a) Muscle relaxation. b) Hydrolyzing ATP in myosin-II heads. c) Releasing tropomyosin from the myosin-binding sites on actin. d) Packing the SR with Ca2+.
C releasing tropomyosin from the myosin binding sites on actin
The diameter of a microtubule is a) 7 Å b) 25 Å c) 7 nm d) 25 nm
D 25nm
Which of the following could be affected by a mutation in the actin protein? I. Muscle contractionII. Cell locomotionIII. Mitosis IV. Cell shape a) I and II only. b) I and III only. c) I, II and III only. d) I, II, III and IV.
D I,II,III,IV
Primary Ciliary Dyskinesia (PSD) is a rare genetic lung disorder, aka immotile cilia syndrome. For people with PCD, the tiny hair-like structures (cilia) in the respiratory tract become non-motile. What is the most likely clinical manifestation of the disease? A. Lung tissue becomes more elastic B. lung cells can no longer divide C. lungs loose their capacity to expand D. Mucus accumulates in the lungs
D Mucus accumulates in the lungs
Release of ADP from the Myosin-II head a) Produces the power stroke for Myosin-II to move on the actin filament. b) Causes the Myosin-II head to detach from the actin filament. c) Weakens interaction between Myosin-II head and actin filament. d) Strengthens the binding of the Myosin-II head to the actin filament.
D strengthens the binding of the mysoin II head to the actin filament
A mutation is discovered that results in the myelin sheath overgrowing and covering all the space along the axon where there would normally be Nodes of Ranvier. Which of the following would be expected of such a neuron? A) Close to normal functioning. B) Repeated spontaneous signal transmission down the axon. C) Inability to be stimulated by action potential. D) Inability to propagate an action potential down the axon.
D) Inability to propagate an action potential down the axon.
Which of the following will leave a chemical reaction rate unaffected? A) Placing an exergonic reaction in an ice bath. B) Increasing the concentration of a reactant in a closed container. C) Putting the reactants into an aqueous solution. D) Removing products of an irreversible (unidirectional) reaction.
D) Removing products of an irreversible (unidirectional) reaction.
which of the following changes take place when a skeletal muscle contracts? A Z discs move farther apart B actin filament contract C myosin filament contract D sarcomeres become shorter
D. upon contraction Z disc move closer. actin and myosin don't contract
When cells enter mitosis, their existing array of cytoplasmic microtubules has to be rapidly broken down and replaced with the mitotic spindle that forms to pull the chromosomes into the daughter cells. The enzyme katanin, named after Japanese samurai swords, is activated during the onset of mitosis, and chops microtubules into short pieces. What do you suppose is the fate of the microtubule fragments created by katanin? Explain your answer.
Katanin breaks microtub. along their length, and at positions remote from their GTP caps. fragments that form therefore contian GDP tubulin at their exposed ends and rapidly depolymerize. Katanin provides a quick means of destroying existing microtub.
dissociation constant
Kd- [A] [B] / [AB]
free energy with concentration
G= G° +2.3 RT log 10 [A] R .002 kcal/mol/K
Lineweaker Burk plot
MM relationship multiple experiments, increase initial rate of substrate each time curved- Rm [So] / Km + [So] linear- [Km/Rmax (slope)] 1/[So] + 1 / Rmax
list the following compounds in order of decreasing lipid bilayer permeability: RNA, Ca2+, glucose, ethanol, N2, water
N2> ethanol > water > glucose > Ca2+ > RNA
flux 1 to 2
RATE of movement of particles unit- number / time / area mol/sec/cm2
Discuss the following statement, "whether the delta G for a reaction is larger, smaller, or the same as delta Gô depends on the concentration of the compounds that participate in the reaction"
True. Criteria is delta G and take the concentration of the reacting components.
a rise in the intercellular Ca2+ concentration causes muscles cells to contract. in addition to an ATP-driven Ca2+ pump, muscle cells that contract quickly and regularly, such as those of the heart, have an addition type of Ca2+ pump- an anitport that exchanges Ca2+ for extracellular Na+ across the plasma membrane. the majority of the Ca2+ ions that have enter the cell during contraction are rapidly pumped back out of the cell by this antiport, thus allowing the cell to relax. Ouabain and digitalis are used for treating patients with heart disease bc they make heart muscle cell contract more strongly. both drugs function by partially inhibiting the Na+ pump in the plasma membrane of these cells. Can you propose an explanation for these effects of the drugs in the patients? What will happen if too much of either drug is taken?
Using these drugs, electrochemical gradient of Na+ is less steep. Ca2+ and Na+ antiport is less efficient and Ca is removed slower. leads to a higher Ca2+ concentration and leads to a stronger longer muscle contraction. these drugs are deadly if too much is taken.
why do you suppose it is much easier to add tubulin to existing microtubules than to start a new microtubule from scratch? explain.
a tubulin dimer has a high affinity with existing end of microtubule.
non-competitive inhibitor
allostatic, binds away and changes rate that enzyme competes reaction changes 1/Vmax
reaction rate depends on
barrier height bigger barrier = slower reaction
competitive inhibitor
binds exactly where substrate binds so no change to 1/Vmax
KD is for ______ reactions
biomolecular
enzyme speed up reactions by lower activation energy, how?
by stretching bond, attracting pos on neg and neg enzyme to pos side
examples of ATP driven pumps
calcium pump proton pump NaK pump
The drug Taxol, extracted from the bark of yew trees, has an opposite effect to the drug colchicine, an alkaloid from autumn crocus. Taxol binds tightly to microtubules and stabilizes them; when added to cells, it causes much of the free tubulin to assemble into microtubules. In contrast, colchicine prevents microtubule formation. Taxol is just as pernicious to dividing cells as colchicine, and both are used as anticancer drugs. Based on your knowledge of microtubule dynamics, suggest why both drugs are toxic to dividing cells despite their opposite actions.
cell division depends of ability to polymerize and depolymerize of microtub. this rearrangement is not possible with taxol bc division is blocked bc spindle cannot be assembled.
myelination
certain portions of axon is covered in myelin sheath myelination is process of wrapping around axon to keep axon health and increase rate of conduction
saltatory condution
conduction of myelinated neurons
in myelination, increase conduction rate =
decrease consumption
free energy
delta G = delta H - T delta S delta S is NEGATIVE
free energy with concentration KD
delta G° -2.3 RT log 10 KD kd- [a][b] / [ab]
ion concentrations _____ slightly across plasma membranes
differ
coupling endergonic rxn w exergonic
exergonic coupled with endergonic to compensate for positive delta G, otherwise would be energetically unfavorable
facilitated passive transport
facilitated in someway faster than predicted by fick's law
Fick's law
flux 1 2 = -P (C2-C1) concentration mc/volume permeability length/time
standard free energy
free energy that accompanies the formation of 1 M of a compound under standard conditions
action potential jumps
from one NOR to next
positive flux
going along direction 1 2
negative flux
going opposite direction 2 1
acetylcholine gated cation channels do not discriminate between Na, K and Ca ions, allowing all to pass through them freely. so why is it that when acetylcholine binds to this protein in plasma membrane of muscle cells, the channel opens and there is a large net influx of primarily Na ions?
high extracellular Na+ concentration so mostly Na enter cell. Other will enter with a much lower concentration.
in the disease myasthenia gravis, the body makes by mistake antibodies to its own acetylcholine receptor mcs. these mc bind and inactivate acetylcholine receptors on the plasma membrane of muscle cells. leads to progressive weakening of muscles. early on, difficulty open eyelids or animals bunnies can't hold up ears. difficulty swallowing or speaking. eventually impaired breathing that lead to death. which step of muscle function is affected?
if the # of acetylcholine receptors is reduced by the antibodies, the neurotransmitter that is released from the nerve terminals cannot stimulate the muscle to contract.
multiple sclerosis
immune system destroys myelin sheath
name the three ways in which an ion channel can be gated
ion channels can be ligand gates, voltage gates, and mechanically (stress) gated
nerve impulse
large neurons use active signaling where signal is regenerated along axon primarily Na, K and NaK pumps
amino acids are taken up by animal cells using a symport in plasma membrane. what is most likely ion whose electrochemical gradient drives the import? is ATP consumed in the process? if so how?
likely Na+. ATp is needed to fuel Na+ pump to maintain gradient.
the more negative delta G, the ...
stronger a and b bond and more stable
symporter vs antiporter
symporter- both to other side antiporter- one from one side and another from other swap
neurons
nerve cells dendrites receive signal axon transports signal
Michaelis-Menton relationship
performance of enzyme depends on how fast it processes substrate. R0= Rmax [So] / Km + [So] so- initial concentration Ro- initial rate of reaction Rmax- max rate of reaction possible Km- MM rate constant k-1 + k2 / k1
nodes of raniver
placed on axon NOT covered w myelin sheath
endergonic reaction
products to reactants delta H is - NEG delta G is + POS
exergonic reactions
reactants to products delta H is - NEG delta G is - NEG
membrane transport proteins
regulate transport of solutes across lipid bilayers
parts of action potential graph
rising phase- depolarization of Na+ -55- threshold, Na channels open, Na goes in 0- potential reverses, Na inactivated, K channels outs outside + inside - peak falling phase- voltage of K inactivated, but some much is out its undershot resting potential- return with NaKpump and is ready to fire again (na and k are closed)
electrochemical gradient same and opposite
same- + to - opposite + to +, repel
myelin are formed by
schwann cells from glial cells