Cell Bio

Which factor allows K+ and not Na⁺ to pass through a K⁺ channel?

specific placement of carbonyl oxygen atoms in the selectivity filter

Which part of a neuron releases a neurotransmitter into a synaptic cleft?

nerve terminal

With the Na⁺/K⁺ pump, which step is energetically favorable and drives the exchange of ions across the intestinal epithelial cell membrane?

ATP hydrolysis

At neuromuscular junctions, if a neurotransmitter triggers the opening of a Na⁺ channel in the postsynaptic cell, this is considered a(n) _______ synapse.

excitatory

Which of the following is an example of how a negative membrane potential can arise from a plasma membrane that originally has no net charge on each side?

the opening of a K⁺ leak channel and the flow of K⁺ out of the cell

What limits the resolving power of a transmission electron microscope?

the numerical aperture of the objective lens and the wavelength of an electron

You discovered a new fluorescent protein that has a peak absorption at 545 nm and a peak emission at 580nm. Which of these filter sets are appropriate for your new fluorescent protein? Filter 1 is placed between the light sourceand the sample. Filter 2 is placed between the sample and the eyepiece.

Filter 1: passes all wavelengths between 425 and 550 nm

Filter 2: passes wavelengths between 555 and 590 nm

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

switching between lipid layers

How can proteins with polar peptide bonds integrate into the membrane?

they can integrate as an alpha-helix, in which the polar peptide bonds are driven to form hydrogen bonds with one another

Which of the following changes in lipid composition would make the membrane more fluid?

a decrease in the length of the fatty acid tail

The plasma membrane's barrier to passive diffusion is primarily a function of the membrane's _________.

phospholipids

In a typical mammalian cell, the concentration of ______ is higher on the inside, and the concentration of ______ is higher on the outside.

K⁺ ; Na⁺ and Cl^-

Active transport is transport in an energetically _______.

unfavorable direction, always coupled to another reaction or source of energy

Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?

by opening Cl^- channels

What is the smallest distance two points can be separated and still resolved using light microscopy?

200 nm

Which statements comparing co-translational and post-translational transport into the ER are TRUE?

both require that the translocated protein have a signal sequence.

both require that the protein is not folded before it enters the ER.

both use the Sec61 translocator.

Fully folded proteins can be transported into which organelles?

nucleus and golgi

Ricin is one of the most powerful toxins. The protein consists of two subunits: the A chain is an enzyme that inhibits translation and the B chain is a lectin that binds to carbohydrates on the cell surface. What is the most likely mechanism by which ricin enters the cell?

the protein is internalized by endocytosis

During nuclear import, what coincides with the binding of Ran-GTP to the receptor?

the cargo is released in the nucleus

In glycolysis, the key control enzyme that is inhibited by excess ATP is:

phosphofructokinase

During nuclear export, what allows the release of the cargo into the cytosol?

RanGTP hydrolysis

In which organelles are proteins glycosylated?

ER and golgi

What component of the mitochondrial outer membrane allows ATP to pass easily through the outer membrane?

a specialized lipid bilayer that contains porins made of beta-barrels

Once a vesicle has reached the right target membrane, which of the following are required directly for the fusion of a vesicle with the target membrane?

SNARE proteins

Approximately how many molecules of ATP can be produced in mitochondria from the complete oxidation of a single glucose molecule?

30

During nuclear export, what coincides with the binding of Ran-GTP to the receptor?

the receptor loads the cargo

Which translocator inserts proteins encoded by the mitochondria into the inner membrane?

OXA

The link between bond-forming reactions and membrane transport processes in the mitochondria is called ______.

chemiosmotic coupling

Which monomeric GTPase is required for COPII assembly?

Sar1

What is the role of autophagy in the cell?

to break down worn out organelles

Why is an in vitro microtubule polymerization assay faster if a filament seed is added?

the nucleation phase is decreased

Which of the following is NOT true of receptor tyrosine kinase (RTK) signaling?

RTKs use the hydrolysis of GTP to transfer a phosphate onto their substrates.

What do IP₃ and ryanodine receptors release when open?

Ca²⁺

What is a consequence of adding Phalloidin to the cell?

actin filaments are stabilized

Which of the following actin regulators sequesters actin monomers?

thymosin

Once NO is made, it diffuses across the membrane into the smooth muscle. What does NO bind in the smooth muscle cell to produce cGMP?

guanylyl cyclase

Which of the following chemical inhibitors leads to microtubule depolymerization?

nocodazole

Which of the following statements about molecular switches are TRUE?

protein kinases transfer the terminal phosphate from ATP onto a protein

serine/threonine kinases phosphorylate serine and threonine residues

a GEF stimulates GTP-binding protein to exchange its bound GDP for GTP to become activated

Which of the following statements about the gamma-Tubulin Ring Complex (gamma-TURC) are TRUE?

it nucleates microtubules and facilitates the organization of a polarized microtubule array

it is concentrated at the centrosome

it caps the minus ends of microtubules

Which of the following is an example of negative feedback?

Activation of a kinase by phosphorylation and then inhibition of the kinase by a phosphatase that was activated by the kinase.

An actin-binding protein called cofilin binds preferentially to ADP-containing actin filaments rather than ATP-containing actin filaments. Based on this preference, which is true?

cofilin binds to older actin filaments.

When cells respond to an extracellular signal, they most often convert the information carried by this molecule from one form to another. What is this process called?

signal transduction

If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens?

the microtubule depolymerizes

For skeletal muscle contraction, what allows the release of Ca2+ from the sarcoplasmic reticulum?

a Ca²⁺ release channel on the membrane of the sarcoplasmic reticulum

CAK

adds activating phosphate to inactive M-Cdk (activating it)

Wee1

adds inhibitory phosphate to M-Cdk (inactivating it)

Cdc25

once active, it activates M-Cdk

PP2A-B55

activates Wee1 by removing inhibitory phosphate

inactivates Cdc25 by removing activating phosphate

(works to inactivate M-Cdk)

M-Cdk positive feedback

activates Cdc25 by adding activating phosphate

inactivates Wee1 by adding inhibitory phosphate

inhibits PP2A-B55

(works to activate itself)

intrinsic apoptotic pathway

Bax or Bak form pore in mitochondrial membrane → release of cyt. c from mitochondria → activation of adaptor protein through binding to cyt. c → many active adaptor proteins form apoptosome → recruitment of procaspase-9 to apoptosome → caspase cascade leading to apoptosis

extrinsic apoptotic pathway

killer lymphocyte with Fas ligand (activated by bacterial/viral infection) binds to Fas death receptor on target cell → DISC forms on inside of cell connected to Fas d.r. composed of FADD adaptor—DEDs—caspase-8 (caspase-8 activation by dimerization → caspase-8 cross-cleavage and subunit rearrangement → executioner caspases released and activate apoptosis