GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Protein Regulation
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Help With Vesicle Transport
Botulinum toxin is a neurotoxin that causes paralysis of the muscles. This is accomplished by cleavage of SNARE proteins contained within the presynaptic compartment of the neuron. Given this information, which of the following best describes how botulinum toxin causes paralysis?
Disruption of SNAREs reverses transport of vesicles to a retrograde direction, taking them away from the muscle and towards the cell soma
Cleavage of SNAREs inhibits vesicles containing neurotransmitters from fusing to the membrane and stimulating the post-synaptic muscle
The toxin is globally toxic and the organism is paralyzed as the tissue becomes necrotic
The toxin prevents the SNAREs from stimulating proper synthesis of neurotransmitters in the neuron
Cleavage of SNAREs disrupts the propagation of the action potential from the axon hillock to the presynaptic membrane
Cleavage of SNAREs inhibits vesicles containing neurotransmitters from fusing to the membrane and stimulating the post-synaptic muscle
This requires knowing that SNARE proteins are required for proper vesicle fusion to the membrane, thereby permitting exocytosis of neurotransmitters into the synaptic cleft and activating the next target; muscle in this case. Paralysis comes because the muscle is not receiving any input once the toxin has cleaved/destroyed the SNARE proteins.
Example Question #1 : Help With Vesicle Transport
Which of the following motor proteins carries vesicular cargo along microtubules exclusively towards the microtubule organizing center (MTOC)?
Microfilament
Kinesin
Actin
Dynein
Myelin
Dynein
Actin (microfilaments) is a cytoskeletal component, and myelin is an axon wrapping component; not molecular motors. Kinesin is a motor that moves in the plus-end direction, away from the MTOC. Dynein is the correct answer; it moves in the minus-end direction towards the MTOC.
Example Question #3 : Help With Vesicle Transport
SNARE (soluble NSF attachment protein receptor) proteins are crucial molecular mediators of vesicular exocytosis. SNAREs require calcium to mediate exocytosis; namely, one protein component of the SNARE complex interacts with synaptotagmin in a calcium dependent fashion. Which of the following answers lists the SNARE proteins that interacts with synaptotagmin?
Exo70
Sec1
Synaptobrevin
Syntaxin
SNAP-25
Syntaxin
Synaptotagmin is a calcium sensor that is associated with the vesicle to be exocytosed. In a high calcium environment, synaptotagmin becomes activated and interacts with syntaxin, a SNARE protein docked in the membrane from which the vesicle will be exocytosed. This interaction permits selective exocytosis during processes such as neurotransmission when there is a large calcium influx, indicating a message must be relayed to the next cell.
Example Question #1 : Help With Other Protein Regulation
How do Bax and Bak promote cell death?
They bind and block Bcl2 from inhibiting Bax and Bak activators
They allow the release of cytochrome c from the mitochondria into the cytosol, which activates procaspase
They cleave procaspase into caspase, which initiates the caspase cascade
They are a major component of the apoptosome
They allow the release of cytochrome c from the mitochondria into the cytosol, which activates procaspase
Bax and Bak dimerize to form a pore in the mitochondria outer membrane, which allows cytochrome c to escape into the cytosol. When cytochrome c is found in the cytosol, procaspase becomes activated and is cleaved into caspase. Once the caspase cascade begins the cell is destined for death.
Bax and Bak have nothing to do with the apoptosome and, while Bcl2 does block Bax and Bak from dimerizing, Bax and Bak do not prevent the action of Bcl2.
Example Question #111 : Cell Biology
What is the key functional difference between GEFs (guanine nucleotide exchange factors) and GAPs (GTPase activating proteins)?
GEFs add guanine nucleotides to small GTPases and GAPs cleave them to promote activation.
GEFs are cytosolic and act on proteins there, while GAPs are nuclear and act on proteins within the nucleus.
GEFs 'deactivate' small GTPases and GAPs 'activate' small GTPases.
GEFs 'activate' small GTPases and GAPs 'deactivate' small GTPases.
GEFs and GAPs have no functional difference, only slight differences in structure.
GEFs 'activate' small GTPases and GAPs 'deactivate' small GTPases.
A GEF activates a small GTPase by exchanging a bound GDP (which confers an inactive state) for a GTP (which is higher energy, and activates the protein). A GAP performs the opposite; GAPs enhance the intrinsic GTPase activity of the small GTPase, which causes hydrolysis of the GTP on the active protein, thus converting it back to GDP and an inactive state.
Example Question #43 : Cellular Processes
One commonly studied outcome of G protein-coupled receptor (GPCR) activation is the activation of phospholipase C (PLC). What two important second messengers are formed when PLC cleaves phosphoinositide-4,5-bisphosphate 
Protein kinase C (PKC) and
Protein kinase C (PKC) and
Interactions between 
Example Question #112 : Cell Biology
What provides the necessary information to specify the three dimensional shape of proteins?
The proteins interactions with chaperone proteins
Specific hydrogen bonds
The proteins peptide bonds
The amino acid sequence
The protein's interactions with other polypeptides
The amino acid sequence
Proteins have different level of protein structure, termed primary, secondary, and tertiary (quarternary is also a type in certain proteins). The 3D shape of proteins is largely due to the tertiary structure of a protein. This level is dictated by the specific amino acid sequence of the protein.
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