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Flashcards in Practice Exam Questions Deck (17):

Which of the following amino acids is likely to form ionic bonds with the cytoplasmic head group
of Phosphatidyl-Serine (PS) (4 pts)?

A. Aspartic Acid (D)
B. Arginine (R)
C. Glycine (G)
D. Leucine (L)

PS is negative thus you want a polar charged molecule that is positive.

Aspartic Acid is Polar charged negative
Glycine is non charged
Leucine is nonpolar.

Thus, Arginine is the correct choice because it is polar charged positive.


Which of the following can most readily diffuse between the phospholipids of the plasma
membrane in an animal cell? (4pts)
A. O2.
B. Sucrose.
C. Na+.

O2 because it is a small gas.

Sucrose is a large polar molecule, Na+ is a charged molecule, and ATP is an energy molecule (doesn't diffuse).


What happens when a Serine within a protein is de-phosphorylated (loses its phosphate group)?

It goes from being negatively charged to polar.


Which amino acid often marks the hinge on a bending alpha-helix?



How does glucose cross the epithelial membranes?

Glucose enters the cells against its concentration gradient when coupled to the transport of Na+ down its concentration gradient. (Active transport)
- The Na+ gradient is established by the Na+/K+ pump and requires ATP.

- In the case of intestinal epithelial cells, the transport of glucose through the basolateral membrane is through facilitated passive transport.


Which non covalent bond contributes most to the secondary structure of proteins?

Hydrogen bonds.


What determines the direction of movement of Na+ through the voltage-gated Na+ channel?

The concentration of Na+ on each side of the membrane.


What could lead to amyloid plaques in an Alzheimer’s patient?

The AB42 peptide aggregates.


Which event is NOT found in the heat shock response?
A. Protein oligomerization.
B. Translocation of a protein to the nucleus.
C. Transcription of chaperone genes.
D. Externalization of phosphatidylserine (PS).

D. Externalization of phosphatidylserine (PS).


FRAP experiments are intended to allow you to measure what property of a membrane protein?

D. Its rate of lateral mobility.

FRAP = Fluorescence recovery after photobleaching.

1. Label proteins with fluorescent dye
2. Photobleach spot
3. Recovery.


How does the conformation of the wild type PrP protein differ from the conformation of prion
disease-forming PrP protein?

Prion forming PrP adopts the B-sheet conformation. Wild type non-prion forming is alpha-helical.


Briefly describe/draw how protein folding is assisted by Hsp70 chaperones and GroEL/GroES

1. Nascent polypeptides associate with Hsp70 chaperones when they are still bound to ribosomes.
2. Hsp70 recognizes hydrophobic stretches of polypeptides.
3. Prevents protein aggregation and promotes folding.
4. If a protein cannot fold properly with just Hsp70, it is transferred to the GroEL/GroES chaperonins.
5. Protein binds to GroEl chamber and then GroES binds after to initiate folding. Protein is ejected upon completion.


Some lipid-anchored proteins receive glycophosphatidylinositol (GPI)-modifications in the ER lumen. Where will these modifications be on the GPI-anchored proteins that end up on the plasma

On the extracellular leaflet of the plasma membrane.
- PI = negative phospholipid.
- Cytoplasmic leaflet is negative so the protein will repel and be on the furthest side away.


Explain why detergents can be used to extract and solubilize integral membrane proteins. What
will likely happen if detergents and residual lipids are removed by dialysis from the solubilized
membrane proteins?

1. Detergents are amphipathic molecules that disrupt membrane bilayers and extract integral membrane proteins.
2. Their hydrophobic groups interact with and stabilize the hydrophobic transmembrane domains of membrane proteins.
3. If detergents are removed, the exposed hydrophobic transmembrane domains will likely cause the aggregations of the membrane proteins.


What is the order of an action potential?

1. Membrane is depolarized from -70mV to -55mV.
2. Influx of Na+ ions into the cytoplasm through the voltage gated sodium channel.
3. Efflux of K+ out of the cell through the voltage gated potassium channel.
4. The inactivation of the Na+ and K+ channels
5. The voltage gated Ca2+ channel opens following membrane depolarization.


What is the role of phosphorylation of the Na+/K+ ATPase pump?

Phosphorylation alters the affinity of the chamber for the two ions.


Describe a property of the voltage-sensing domain of the K+ channel that allows it to sense
membrane depolarization?

Domain has positive charged residues that detect increase in positive charge on cytoplasmic side.
- This causes channel conformation change to open and K+ flows out.