Exam I
Which of the noncovalent interactions below will contribute most to the strong and specific binding of two molecules, such as a pair of proteins?
A. hydrogen bonds
B. electrostatic interactions
C. hydrophobic interactions
D. van der Waals attractions
B. electrostatic interactions
List all elements of the endomembrane system.
Nuclear envelope, lysosomes, vesicles, ER, Golgi apparatus, the plasma membrane
Trimeric G proteins:
A. Are only active when all the subunits separate so they can act independently
B. Are active when they exist as a trimer
C. Do not interact with 7-transmembrane-domain receptor proteins (GPCRs)
D. Bind a guanine nucleotide in their alpha subunit
D. Bind a guanine nucleotide in their alpha subunit
(remember the "G" in GTP/GDP stands for guanine)
What protein, when mutated, would inhibit backward, but not outward, transport along axon microtubules?
Kinesin
Levels of CDK activity change during the cell cycle, in part because:
A. the CDKs phosphorylate each other
B. the CDKs activate the cyclins
C. cyclin levels change during the cycle
D. CDK degradation precedes entry into the next phase of the cell cycle
C. the levels of cyclin change during the cell cycle
The potential energy stored in high-energy bonds is commonly harnessed when the bonds and split by the addition of _____ in a process called _____.
water;hydrolysis
What is the purpose of the nuclear localization sequence on a nuclear protein?
A. It prevents the protein from diffusing out of the nucleus
B. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore
C. It aids in protein unfolding to thread the protein through the nuclear pore
D. It is a hydrophobic sequence that enables the protein to enter the nucleus
B. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore
The role of nitrous oxide within signal propagation is best described as a:
A. kinase-activating molecule
B. kinase-inhibiting molecule
C. ligand
D. secondary messenger
D. secondary messenger
Draw the placement of the following cytoskeletal elements in a gut epithelial cell:
- Microtubules
- Intermediate filaments
- Actin
:)
Which of the following statements about intermediate filaments are false?
A. Each filament is made of 8 strands, and each strand is made from staggered tetramers linked end-to-end
B. Intermediate filaments protect cells from mechanical stress because they have high tensile strength and resist stretching
C. Intermediate filaments are constructed of identical subunits found in all eukaryotic cells
D. Intermediate filaments can connect cells at cell-cell junctions called desmosomes
C; all cells have intermediate filaments, but they are not all the same
Bal 31 is an enzyme that assists in degrading both DNA and RNA. Into which classification of enzymes does it fall?
Nuclease
(the other types are protease, isomerase, and hydrolase)
All of the following targeting sequences are cleaved off during the import process except:
A. The nuclear localization sequence
B. The chloroplast targeting sequence
C. The ER signal sequence
D. The mitochondrial targeting sequence
A. The nuclear localization sequence
When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a:
A. Dissolved gas
B. Hormone
C. Neurotransmitter
D. Nerve impulse
B. hormone
What is the purpose of tubulin being able to hydrolyze GTP to GDP?
It allows for dynamic instability!
How do spindle microtubules attach to chromosomes?
The microtubules bind to kinetochore complexes through a connecting protein.
The relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called?
FRAP; fluorescence recovery after photobleaching
ATP is important for chaperone protein function. Why would protein into mitochondria be disrupted if ATP were depleted from inside the mitochondria?
The protein could slip back out of the mitochondria during transport.
What is GAP and what is its function in a signaling pathway?
GTPase-activating protein; to activate an inactive G protein :)
What could potentially be a problem resulting from mutations in keratin filaments that disrupt cross-linking and stabilization between each other/relevant proteins?
- Corneal damage caused by cell rupture from mechanical trauma
- Muscle weakness (desminopathy, skeletal myopathy, cardiomyopathy)
- Severe skin blistering/fragile of epidermis and/or mucosal epithelia (epidermolysis bullosa simplex)
What phases of the cell cycle do the following occur in?
- DNA synthesis
- Cell growth
- Normal cell activity only
- Cell division
- S phase
- G1 phase
- G0 phase
- M phase (cytokinesis)
Porin proteins form large, barrel-like channels in the membrane. Which of the following statements is false?
A. The are made primarily of alpha helices
B. They have alternating hydrophobic and hydrophilic amino acids
C. They cannot form narrow channels
D. They are made primarily of beta sheets
A. They are made primarily of alpha helices
Porins are made of beta sheets that run anti-parallel, forming a beta barrel structure.
Choose all true statements regarding proteins in the ER lumen:
A. Proteins in the lumen of the ER are synthesized by ribosomes on the ER membrane
B. Proteins in the lumen of the ER cannot end up in the extracellular space
C. Proteins in the lumen of the ER can end up in the plasma membrane
D. Proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system
A and D are true
Bonus: What would you change about the statements in B and C to make them true, and why?
What type of signaling is involved in inflammatory responses after you get a paper cut?
Paracrine signaling
What roles does cyclin play in the process of mitosis?
Cyclin (M and S types) bind to cyclin-dependent kinases, which are responsible for the initiation of S and M phases.
What is the difference between apoptosis and necrosis?
In apoptosis, cells die in a clean, non-disruptive manner to the surrounding tissues. Cells that necrose explode and damage/inflame the surrounding tissues.
For bonus points, what is one way apoptosis is triggered?