Midterm 1

Question 1

Epithelial cells lining the intestine take glucose out of the gut and into the cell using ___, which is made possible by establishing potential energy through the ___.

Answer 1

• Na+ symporter

- an Na+/K+ ATPase

Question 2

Western blot on SDS-PAGE: Where does protein A reside if it is present in the crude lysate and 600xg pellet?

Answer 2

Nucleus

Question 3

Western blot on SDS-PAGE: Which protein is most likely to be in the cytoplasm?

Answer 3

Only present in the crude lysate and supernatants

Question 4

Western blot on SDS-PAGE: Which protein is most likely to be a membrane protein?

Answer 4

• Crude lysate
• 15,000xg supernatant
• 100,000xg pellet

Question 5

T/F: An antiporter would function as a symporter if its orientation in the membrane were reversed (that is, if a portion of the protein normally exposed to the cytosol faced the outside of the cell instead).

Answer 5

False

Question 6

T/F: Although lipid molecules are free to diffuse in the plane of the bilayer, they cannot flip-flop across the bilayer unless enzyme flippase is present in the membrane

Answer 6

True

Question 7

What event requires active transport to maintain acidic pH in the stomach lumen?

Answer 7

Import of H+ into the stomach lumen and export of K+ from the stomach lumen by K+/K+ ATPase

Question 8

Which protein would you not expect to find in a typical eukaryotic cell?

Answer 8

Lipid-anchored membrane proteins

Question 9

NUC1 is a large protein that contains 3500 AAs. NUC1 fused to GTP localizes to the nucleus. When the first 10 AAs of NUC1 are expressed as fusion w/ GFP in cells, it localizes to the nucleus. We therefore conclude that the first 10 AAs of NUC1 are ___ for nuclear localization.

Answer 9

Sufficient

Question 10

T/F: Membranes that contain many single pass and multi-pass transmembrane proteins are not fluid.

Answer 10

FALSE

Question 11

Western blot on SDS-PAGE (control, + trypsin): If the protein doesn’t change after trypsin treatment, what type of membrane protein is it?

Answer 11

Peripheral cytoplasmic protein

Question 12

Western blot on SDS-PAGE (control, + trypsin): If the protein travels faster after trypsin treatment, what type of membrane protein is it?

Answer 12

Transmembrane protein w/ large domain exposed outside

Question 13

Western blot on SDS-PAGE (control, + trypsin): If the protein disappears after trypsin treatment, what type of membrane protein is it?

Answer 13

Peripheral extracellular protein

Question 14

You are working w/ two proteins CaM and SOUL in your PhD thesis project. You perform a FRAP experiment to determine the turnover rate of SOUL protein compared to CaM. You see that CaM recovers its fluorescence while SOUL does not. What is your best conclusion?

Answer 14

CaM is more dynamic than SOUL

Question 15

What does the Na+-K+ pump do? How does it work?

Answer 15

Dephosphorylation of the pump transports K+ into the cytosol

Question 16

What is this: A membrane protein has binding sites for solute B and for solute A. This membrane protein can switch between that two conformational states only if both binding sites are occupied or if both sites are empty.

Answer 16

Symporter

Question 17

You add a PKKKRKV to the end of a protein that normally localizes in the cytoplasm. Where would you now predict the new protein to localize?

Answer 17

The nucleus

Question 18

What characteristic distinguishes plant cells from animal cells?

Answer 18

Plant cells have cell wall; animal cells do not

Question 19

If you fuse lysine rich sequence to the N-terminus of the green fluorescent protein, where would you expect to see this protein in the microscope?

Answer 19

Nucleus

Question 20

According to Singer and Nicolson’s proposed model, membrane contains what?

Answer 20

Proteins are embedded in the lipid bilayer and both lipids and proteins can freely diffuse

Question 21

The conventional fluorescence microscope images are not as good as confocal laser scanning fluorescence microscope (CLSM) because?

Answer 21

None of the above

Question 22

The gene Rb normally inhibits cell division. When the growth factors are present, Rb is inactivated to allow the cell to divide. A mutant form of Rb is found in many cancer tumors. The mutant form of Rb is inactive in the absence of growth factors. Rb is a ___?

Answer 22

Tumor suppressor gene

Question 23

The complexity of genomes in multi-cellular organisms increases due to an expanded number of genes involved in ___?

Answer 23

Receptors

Question 24

Which of the following is not true of GFP?

• GFP can be viewed using a fluorescence microscope
• GFP can be viewed in live cells
• GFP does not disrupt the protein it is fused to
• GFP can be used to study dynamics of proteins in a membrane
• GFP was originally identified from a jellyfish

Answer 24

GFP does no disrupt the protein it is fused to

Question 25

Antibodies (IgG) are powerful reagents b/c they bind to a specific antigen via the ___ and bind to ___ via the Fc region.

Answer 25

• Variable domain

- Protein A

Question 26

Why is dry lens resolution not as good as oil-immersion lens

Answer 26

Numerical aperture of dry lens is less than oil-immersion lens

Question 27

Using sequential differential centrifugation steps, you fractionate cellular organelles from a wild-type and mutant cell line. You then run the fractions on SDS-PAGE and use antibodies against he C-term of your protein is in. Normally you find your favorite protein in the total cell lysate, the 600xg supernatant and the 15,000xg pellet. In the mutant cell line your favorite protein is still in the total cell lysate and the 600xg supernatant, but is now instead in the 15,000xg supernatant and the 100,000xg supernatant. Where are the wild-type and mutant versions located?

Answer 27

The wild-type is in the lysosome and the mutant version is in the cytoplasm

Question 28

You isolate a loss of function mutation in a bacterial gene that codes for a fatty acid saturase. You are now proposing to analyze membranes from this mutant strain of bacteria. What do you expect to find?

Answer 28

An increase in the number of carbon double bonds and an increase in membrane fluidity

Question 29

Cholesterol in animal cells functions to ___?

Answer 29

Stiffen the membrane and decrease the melting point

Question 30

The Langmuir trough was used to support what model?

Answer 30

The membrane contains bilayer of lipids