cell bio exam 3

man fuck

diffusion

movement of a substance across the membrane

permeability

the rate of diffusion

the rate of permeability varies in accordance with..

the size and polarity of the molecule thats diffusing

the limited permeability of ions enables..

a cell to have an ion profile that differs from its immediate environment

chemical gradients

based on concentration differences across the membrane

electrical gradeints

based on the differences in net charge across the membrane

• resting membrane potential ~-70mV (negative on inside of the cell)

wetherb y difference in concentration or voltage, molecules tend to move ____ electrochemical gradients to a point of equilibrium

DOWN

membrane proteins called ________ and ______ facilitate the diffusion of molecules across membrane bilayers

transporters and channels

transporters

discriminate on the basis of molecules they specifically bind.

• if there is binding then there can be transport

channel

discriminate on the basis of size and charge.

• when open, only molecules small enough + appropriately charged can pass through

simple diffusion

result of random molecular movement across a semi-permeable membrane in response to existing electrochemical gradients

1.) down an electrochemical gradient

2.) rate of diffusion depends on size + polarity of molecule

passive transport

for large, polar, or charged molecules, simple diffusion is difficult!

• also known as facilitated diffusion (thru channels + transporters)

occurs down electrochemical gradient

rate of transport depends on the number of transporters or channels, and the specificity they exhibit for molecules and ions they move across membranes

active transport

cells generate large elctrochemical gradients + unusually high solute concentrations that belie the existence of simple diffusion + passive transport alone

continual energy must be eexpended in order to transport molecules across the membrane against their gradients + to maintain those gradients in the cell

1.) active transport occurs up the gradients and requires energy

2.) the rate of transport depends on the number and properties of the transporter and the specificity they exhibit for the molecules they move across membranes

controllers of membrane permeability

the amphipathicity of the lipid bilayer

the diffusing molecule’s characteristics

existing electrical/chemical gradients of the diffusing molecules

integral proteins (transporters + channels)

primary active transport pumps

couple atp-binding/hydrolysis to a conformational change in the transporter in order to enable movement of molecules up their electrochemical gradienta

secondary active transport pumps

use the free energy available in established electrochemical gradients to move one molecule down its respective gradient in order to move another molecule up its respective gradient

glucose transporter

passive transport protein, glucose (uncharged, polar) uses this transporter to move down its gradient

• directionality of glucose transport depends on the glucose concentration inside/outside the cell

1/3 of a cell’s energy drives the transport activity of the _________ or ______, a primary active transporter that moves both Na+ and K+ against their gradients

Na+ - K+ ATPase, Na+-K+ pump

Na+-K+ Atpase

acts as an electrogenic pump, helps maintain the resting membrane potential of -70mV by pummping 3 Na+ ions out of the cell and 2 K+ ions in the cell

• contributes to cellular osmotic balance

  • if gradients become excessively high/atp levels in the cell decline, the Na+-K+ ATPase can work in reverse + generate atp

secondary active transport

uses stored potential energy, does not directly use atp

• Na+-glucose symporter uses energy of existing electrochemical Na+ gradients to drive the active transport of glucose

channel protein

downhill trafficking only

number in the hundreds

most commonly act as ‘ion channels’ for Na+, K+, H+, Ca2+, and Cl-

gated by stimuli (mechanical, voltage, ligands)

electrical signaling

most cells exhibit electrical signaling based on voltage, involves a change in membrane potential

fixed anions anions inside the cell contribute to this resting potential

resting membrane potential is counter balanced by Cl-, an extracellular anion, and by K+ an intracellular ion

K+ leak channel

main channel open in a resting cell

movement of K+ thru these channels is dictated by its current gradient, when channels are open K+ can move out down its chemical gradient or in down its electrical gradient

elequilibrium potential

when K+ is balanced and there is no net flow of K+ across the membrane, the electrochemical gradient is considered to be 0

neurons

receive, conduct, and transmit electrical signals to other neurons and muscle cells

• electrical signals are propagated along the membranes of neurons as part of an action potential/nerve impulse

action potentials are mediated by voltage-gated cation channels

1.) nerve impulses begin with a depolarization event that shifts the resting membrane potential (less negative)

2.) increase in potential opens voltage gated na+ channels, na+ enters the cell down its steep gradient

3.) leads to amplification, raising the potential to +60mV

4.) counter acted by the opening of delayed voltage-gate K+ channels, and inactivation of voltage-gated na+ channels

5.) restoration of resting potential inactivates the delayed voltage channels and resets the channels to their original closed conformation

propagated along the length of the long axonal extensions of neurons

neurotransmitters

excitatory or inhibitory

excitatory: Na+ channel, help to depolarize the postsynaptic neuron so that a membrane potential can be propagated in that cell. the signal must be strong because their numbers within the initial segment of post synaptic neuron are few

inhibitory: Cl- channel, help to restore the resting membrane potential of the cell

NADH (NADPH)

activated carriers for redox reactions

• vitally important for breakdown (catabolism) of macromolecules found in food so that ATP can be generated

conversion of food energy to ATP

1.) polymers (food) →monomers (food)

2.) glucose → pyruvate (glycolysis) → acetyl CoA makes activated carriers: NADH/ATP

3.) acetyl CoA + 02 → Co2 + H2O (citric acid cycle/oxidative phosphorylation)

50% efficient, even lost energy dissipated as heat increases catabolic efficiency

glycolysis

anaerobic process by which the 60carbon sugar glucose is initially oxidized into two 3-carbon pyruvate moolecules, nets 2 ATP and 2 NADH molecules per molecule of glucose

1.) energy investment to be recouped later(1 glucose molecule)

2.) cleavage of six-carbon sugar to two three-carbon sugars (fructose 1,6, biphosphate → two molecules of glyceraldehyde 3-phosphate)

3.) energy generation (two molecules of pyruvate)

in the continued absence of O2, NADH helps reduce pyruvate into lactate or ethanol and Co2 during fermentation rxns

porin

allows entry into mitochondria, large channel protein that allows molecules less than 5kDa to cross the outer mitochondrial membrane

MPC1/2

allows entry into the matrix, a pyruvate transporter of the inner mitochondrial membrane

mitochondrial acetyl CoA

marks a conversion point for cellular catabolic pathways

can be completely oxidized to NADH, CO2, and H2O in the presence of O2

• accomplished in the mitochondrial matrix as part of the citric acid cycle

each turn in the cycle generates..

3 molecules of NADH

1 molecule of FADH2

1 molecule of GTP

2 molecules of CO2 (waste product)

oxidative phosphorylation

passes the electrons from NADH to an electron transport chain located in the inner mitochondrial membrane in order to generate ATP

anerobic process

In oxidative phosphorylation, ATP production is coupled to the events in the electron-transport chain. What is accomplished in the final electron-transfer event in the electron-transport chain?

O2 is reduced to H2O

Which signaling molecule is NOT correctly paired with the enzyme that turns off its signaling?

Phosphoprotein: Kinase

Depicted in this cartoon of a cell are the concentration gradients for Na+, K+, and glucose (top), the membrane potential, and several transporters: the Na+-K+ ATPase (lower left) and two other transporters for Y and Z (lower right). Based on the presented information, could the molecules Y or Z be accurately substituted with glucose (i.e. could you replace molecule Y in this image with glucose, and could you replace molecule Z with glucose)?

Only Y could be substituted with glucose.

Proteins that stimulate cell proliferation or survival are often classified as 'oncoproteins' while proteins that inhibit cell proliferation or survival are often classified as 'tumor suppressors'. In a classic enzyme-coupled receptor signaling pathway that involves protein kinase B, which protein could best be classified as a 'tumor suppressor'?

PTEN

A protein kinase can act as an INTEGRATING device in signaling if it __________.
[INTEGRATE:  To condense multiple signaling pathways into a single signaling pathway.]

is activated by two or more proteins in different signaling pathways

Which of the following statements about redox potential is true?

For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative. 

Which of the following signaling scenarios would likely take the longest to elicit a behavioral response in the cell?

The ability of a bacterial cell to react to and then hydrolyze lactose.

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell?

They keep the electrochemical gradient for K+ at zero.

Which generates the most NADH from cellular respiration?

the citric acid cycle

Which of the following does NOT contribute to the negative resting potential of a cell?

Chloride Anions

proton motive force

pumping of protons by the electron transport chain creates a steep electrochemical proton gradient across the inner mitochondrial membrane

drives the synthesis of ATP via the enzyme ATP synthase

drives the import of pyruvate and the ATP building block inorganic phosphate thru symporters

the large proton motive force also drives an antiporter (ANT) for ADP (3 negative charges) into the matrix and ATP (4 negative charges) out of the matrix

glycolysis

oxidezes glucose in a series of anaerobic reactions producing pyruvate, ATP, and NADH

the citric acid cycle

shuttles acetyl CoA (from pyruvate or from fatty acid oxidation) into a series of anaerobic rxns that give rise to more NADH, FADH2, GTP, and waste CO2