Question 1

The movement and placement of organelles within animal cells is controlled by 2 ATP-binding motor
Proteins called kinesin and dynein. Mutations in either of these 2 proteins that interfere with these processes would most likely be associated with defective binding to which of the following structures?
A) actin filaments
B) ciliary doublets
C) intermediate filaments
D) microtubules
E) myosin fibrils

Accepted Answer

Kinesin and dynein are motor proteins that move along microtubules, which are part of the cytoskeleton, to transport organelles and other cellular components.  Dynein and kinesin transport various cellular components by "walking" along cytoskeletal microtubules. Dyneins move toward the minus end of the microtubule, which is usually oriented toward the cell center. Thus, they are called minus end- directed motors. In contrast, kinesins are motor proteins that move toward the microtubules' plus end, are called plus end-directed motors. Microtubules are filamentous intracellular structures that are responsible for various kinds of movements in all eukaryotic cells. Microtubules are involved in nuclear and cell division, organization of intracellular structures, and intracellular transport, as well as ciliary motility

Question 2

An insoluble form of a prion protein accumulates
In the brains of patients who have CreutzfeldtJakob disease, CJD. Conversion of the normal
Soluble form of the prion protein to the pathologic
Insoluble form is thought to involve conversion
Of α-helices to β-pleated sheets. In order for this
Structural transition to occur, which of the following is most likely disrupted and reformed?
A) disulfide bonds
B) hydrogen bonds
C) peptide bonds
D) salt bridges
E) zinc fingers

Accepted Answer

The conversion from α-helices to β-pleated sheets involves the disruption and reformation of hydrogen bonds, which are crucial in maintaining these secondary structures.  The α-helix and β-sheet structures in proteins result from the formation of hydrogen bonds between the amide hydrogen of one peptide bond and an adjacent carbonyl oxygen in another peptide bond. For an α-helix to convert into a β-sheet it is required that the hydrogen bonds holding the structure together be broken and then a different series of hydrogen bonds need to form to generate the β-sheet structure.

Question 3

Eukaryotic ribosomes consist of 2 subunits designated as 40S and 60S. The S value is most dependent on which of the following properties of the subunit?
A) composition of the RNA bases
B) interactions between the RNA and protein components
C) protein content
D) RNA content
E) shape and size of the subunit

Accepted Answer

The S value, or Svedberg unit, is a measure of the rate of sedimentation during centrifugation, which is influenced by the shape and size of the subunit rather than its composition or interactions.  The "S" in 40S and 60S refers to the Svedberg coefficient, which is a unit of measure for sedimentation rate. The sedimentation rate is the rate at which particles of a given size and shape travel to the bottom of the tube under centrifugal force. The Svedberg coefficient is technically a measure of time and offers a measure of particle size based on its rate of travel in a tube subjected to high gravitational force.

Quiz 5: Protein Structure and Function

Eukaryotic ribosomes consist of 2 subunits designated as 40S and 60S. The S value is most dependent on which of the following properties of the subunit?