Biol 314 Exam 2 Iowa State

If the solute concentration inside a cell is 400 mM and the solute concentration outside of the cell is 800 mM, which direction will water move by osmosis

Out of the cell (because it moves to the higher solute concentration)

Transporters review: which of the following statements is incorrect?

-Transporters can transport molecules against their concentration gradients by coupling transport to an energy source

-Transporters cannot transport ions against their electrochemical gradient, as this is energetically unfavorable

-The Na+-K+ pump uses ATP to drive transport of the Na+ and K+ ions

Transporters cannot transport ions against their electrochemial gradient, as this is energetically unfavorable

Which of the following statements is true?

-Channel proteins can perform both active and passive transport

-Channels can switch between open and closed forms

-Channels are non-selective --> they transport all types of small molecules

-Membrane potentials are generated by the Na+/K+ pump in a process that does not involve channels

Channels can switch between open and closed forms

If a stimulus causes the membrane of the neuron below (that has a threshold potential of -40 mV and above) to depolarize to -50 mV, would an action potential be generated?

No, it needs to be at least -40 mV or higher

What is the main function of lysosomes?

Protein degradation

Imagine you are studying the transport of proteins into mitochondria. You engineer a mitochondrial protein to remove its predicted sorting signal and see that it is now found in the cytosol. This tells you that the sorting signal is:

Necessary for targeting to mitochondria

Which of the following statements is incorrect?

-Nuclear pores can transport both RNA and protein molecules

-Small molecules can freely diffuse through nuclear pores

-Transport of proteins into the nucleus does not require energy

-Receptor proteins recognize proteins with a nuclear localization signal and transport them into the nucleus

Transport of proteins into the nucleus does not require energy

What is one difference between protein transport into the nucleus and protein transport into mitochondria?

Proteins have to be unfolded for transport into mitochondria, whereas folded proteins can be transported into the nucleus

Imagine you are studying a protein with multiple trans-membrane regions that is inserted into the ER membrane. The protein has a typical cleavable N-terminal ER signal sequence. Which side of the membrane would you expect the N-terminus to be?

-Cytosol

-ER lumen

-No way to predict

ER Lumen

You are studying a mutant that is defective in the formation of clathrin-coated vesicles. When you look at your mutant using electron microscopy, you see structures accumulating as seen below. Which component is likely to be defective in the mutant?

-Clathrin

-Adaptin

-Cargo receptor

-Dynamin

-Cargo

Dynamin

You have identified a yeast mutant that accumulates a vacuolar protein in the Golgi. Which trafficking step would you conclude is blocked?

-ER to Golgi

-Golgi to ER

-Golgi to vacuole

-Golgi to plasma membrane

Golgi to vacuole

Which of the following is an example of constitutive secretion?

-Secretion of cell wall materials in plants

-Secretion of neurotransmitters into a synaptic cleft

-Secretion of insulin by pancreatic cells

-Secretion of digestive enzymes after a meal

Secretion of cell wall materials in plants

What prevents lysosomal hydrolyses from degrading important proteins in the cytosol?

-Compartmentalization; the lysosomal membrane acts as a barrier

-The hydrolases are not active at the neutral pH of the cytosol

-Cystolic proteins are resistant to hydrolysis

-Both 1 & 2

- Both 2 & 3

Both 1 and 2:

-Compartmentalization- the lysosomal membrane acts as a barrier

-The hydrolases are not active at the neutral pH of the cytosol

Atoms form covalent bonds with each other by

sharing electrons

Atoms form ionic bonds with each other by

transferring electrons from one atom to the other

The relative molecular mass of glucose is 180. How many grams of glucose would you dissolve in water to make 0.1 L of a 0.1 M solution?

1.8 grams

(Ch. 12) T/F The plasma membrane is highly impermeable to all charged molecules

False. The plasma membrane contains transport proteins that confer selective permeability to many but not all charged molecules. In contrast, a pure lipid bilayer lacking proteins is highly impermeable to all charged molecules

(Ch. 12) T/F Channels have specific binding pockets for the solute molecules they allow to pass

False. Channels do not have binding pockets for the solute that passes through them. Selectivity of a channel is achieved by the size of the internal pore and by charged regions at the entrance of the pore that attract or repel ions of the appropriate charge

(Ch. 12) T/F Transporters allow solutes to cross a membrane at much faster rates than channels do

False

(Ch. 12) T/F Certain H+ pumps are fueled by light energy

True. The bacteriorhodospin of some photosynthetic bacteria pumps H+ out of the cell, using energy captured from visible light

(Ch. 12) T/F The plasma membrane of many animal cells contains open K+ channels, yet the K+ concentration in the cytosol is much higher than outside the cell

True. Most animal cells contain K+ leaky channels in their plasma membrane that are predominantly open. The K+ concentraion inside the cell still remains higher than outside, because the membrane potential is negative and therefore inhibits the (+) charged K+ from leaking out K+ is also continually pumped into the cell by the Na+ pump

(Ch. 12) T/F A symport would function as an antiport if its orientation in the membrane were reversed (i.e., if the portion of the molecule normally exposed to the cytosol faced the outside of the cell instead).

False

(Ch. 12) T/F The membrane potential of an axon temporarily becomes more negative when an action potential excites it

False

Symport v. Antiport

Both couple the movement of two different solutes across a cell membrane. Symports transport both in the same direction, whereas antiports transport the solutes in opposite directions

Active v. Passive transport

Both are mediated by membrane transport proteins. Passive transport of a solute occurs downhill, in the direction of its concentration or electrochemical gradient, whereas active transport occurs uphill and therefore needs an energy source. Active transport can be mediated by transporters but not by channels, whereas passive transport can be mediated by either

Membrane potential v. Electrochemical gradient

Both terms describe gradients across a membrane. The membrane potential refers to the voltage gradient; the electrochemical gradient is a composite of the voltage gradient and the concentration gradient of a specific charged solute (ion). The membrane potential is defined independently of the solute of interest, whereas an electrochemical gradient refers to the particular solute.

Pump v. Transporter

A pump is a specialized transporter that uses energy to transport a solute uphill-against an electrochemical gradient for a charged solute or a concentration for an uncharged solute

Axon v. Telephone wire

Both transmit electrical signals by means of electrons in wires and ion movements across the plasma membrane in axons. The signal passing down an axon does not diminish in strength, because it is self-amplifying, whereas the signal in a wire decreases over distance

Solute v. Ion

Both affect the osmotic pressure in a cell. An ion is a solute that bears a charge.

(Ch. 12) In a phospholipid bilayer you have Na+ and K+ pumps. What would happen if:

(A)Your vesicles were suspended in a solution containing both Na+ and K+ ions and had a solution with the same ionic composition inside them

Nothing. You require ATP to drive the Na+ pump

(Ch. 12) In a phospholipid bilayer you have Na+ and K+ pumps. What would happen if:

(B)You add ATP to the suspension described in (A)

The ATP becomes hydrolized, and Na+ is pumped into the vesicles, generating a concentration gradient of Na+ across the membrane. At the same time, K+ is pumped out of the vesicles, generating a concentration gradient of K+ of opposite polarity. When all the K+ is pumped out of the vesicle or the ATP runs out, the pump would stop.

(Ch. 12) In a phospholipid bilayer you have Na+ and K+ pumps. What would happen if:

(C)You add ATP, but the solution-outside as well as inside the vesicles- contains only Na+ ions and no K+ ions

The pump would initiate a transport cycle and then cease.

(Ch. 12) In a phospholipid bilayer you have Na+ and K+ pumps. What would happen if:

(D)The concentrations of Na+ and K+ were as in (A) but half of the pump molecules embedded in the membrane of each vesicle were oriented the other way around so that the normally cytosolic portions of these molecules faced the inside of the vesicles. You then add ATP to the suspension.

ATP would become hydrolyzed, and NA+ and K+ would be pumped across the membrane as described in (B). However the pump molecules would sit in the membrane in reverse orientation would be completely inactive

(Ch. 12) In a phospholipid bilayer you have Na+ and K+ pumps. What would happen if:

(E)You add ATP to the suspension described in (A), but in addition to Na+ pumps, the membrane of your vesicles also contains K+ leak channels

ATP becomes hydrolized, and Na+ and K+ are pumped across the membrane, as described in (B). K+, however immediately flows back into the vesicles through the K+ leak channels.

(Ch. 12) Amino acids are taken up by animal cells using a symport in the plasma membrane. What is the most likely ion whose electrochemical gradient drives the import? Is ATP consumed in the process? If so, how?

Animal cells drive most transport processes across the plasma membrane with the electrochemical gradient of Na+. ATP is needed to fuel the Na+ pump to maintain the Na+ gradient

QUESTION 15-4 (IMPORTANT!)

(A) Predict the membrane orientation of a protein that is synthesized with an uncleaved, internal signal sequence (shown as the red start-transfer sequence in F. 15-17) but does not contain a stop-transfer sequence

The internal signal sequence functions as a membrane anchor, as shown in Figure 15-17. Because there is no stop-transfer squence, however, the C-terminal end of the protein continues to be translocated into the ER lumen. The resulting protein therefore has its N-terminal domain in the cytosol, followed by a single transmembrane segment, and a C-terminal domain in the ER lumen.

QUESTION 15-4 (IMPORTANT!)

(B) Similarly, predict the membrane orientation of a protein that is synthesized with an N-terminal cleaved signal sequence followed by a stop-transfer sequence.

The N-terminal signal sequence initiates translocation of the N-terminal domain of the protein until translocation is stopped by the stop-transfer sequence. A cytosolic domain is synthesized until the start-transfer sequence initiates translocation again. The situation now resembles that described in (A), and the C-terminal domain of the protein is translocated into the lumen of the ER. The resulting protein therefore spans the membrane twice. Both its N-terminal and C-terminal domains are in the ER lumen, and a loop domain between the two transmembrane regions is exposed in the cytosol

QUESTION 15-4 (IMPORTANT!)

(C) What arrangement of signal sequences would enable the insertion of a multipass protein with an odd number of transmembrane segments?

It would need a cleaved signal sequence, followed by an internal stop-transfer sequence, followed by pairs of start and stop transfer sequences

(Ch. 15) T/F Ribosomes are cytoplasmic stuctures that, during protein synthesis, become linked by an mRNA molecule to form polyribosomes

True

(Ch. 15) T/F The amino acid sequence Leu-His-Arg-Leu-Asp-Ala-Gln-Ser-Lys-Leu-Ser-Ser is a signal sequence that directs proteins to the ER

False. The signal sequences that direct proteins to the ER contain a core of eight or more hydrophobic amino acids. The sequence shown here contains many hydrophilic amino acid side chains, including charged amino acids His, Arg, Asp, and Lys, and the uncharged hydrophilic amino acids Gln and Ser

(Ch. 15) T/F All transport vesicles in the cell must have a v-SNARE protein in their membrane

True. Otherwise they could not dock at the correct target membrane or recruit a fusion complex to a docking site

(Ch. 15) T/F Transport vesicles deliver proteins and lipids to the cell surface

True

(Ch. 15) T/F If the delivery of prospective lysosomal proteins from the trans Golgi network to the late endosomes were blocked, lysosomal proteins would be secreted by the constitutive secretion pathways in F. 15-30

True. Lysosomal proteins are selected in the trans Golgi network and packaged into transport vesicles that delvier them to the late endosome. If not selected, they would enter by default into transport vesicles that move constitutively to the cell surface

(Ch. 15) T/F Lysosomes digest only substances that have been taken up by cells by endocytosis

False. Lysosomes also digest internal organelles by autophagy

(Ch. 15) T/F N-linked sugar chains are found on glycoproteins that face the cell surface, as well as on glycoproteins that face the lumen of the ER, trans Golgi network, and mitochondria

False. Mitochondria do not participate in vesicular transport, and therefore N-linked glycoproteins, which are exclusively assembled in the ER, cannot be transported to mitochondria