LSU BIOL 4190 T4 Exam Questions and
Answers (Graded A)
Section 1: Molecular and Cellular Biology
1. Question: Describe the process of protein trafficking in eukaryotic cells
and discuss the role of the signal recognition particle (SRP).
o Answer: Protein trafficking involves the transport of proteins to
their appropriate cellular or extracellular locations. The SRP recognizes a signal
peptide on a nascent protein emerging from the ribosome and pauses translation.
The SRP-ribosome complex docks to the SRP receptor on the endoplasmic
reticulum (ER) membrane. Translation resumes, and the protein is co-
translationally translocated into the ER lumen or membrane. Post-translational
modifications and sorting ensure delivery to final destinations, including the
Golgi apparatus, lysosomes, or plasma membrane.
2. Question: Explain how phosphoinositides contribute to cell signaling
pathways.
o Answer: Phosphoinositides are phosphorylated derivatives of
phosphatidylinositol that serve as key signaling molecules. For instance,
PI(4,5)P2 is cleaved by phospholipase C into IP3 and DAG, triggering calcium
release from the ER and protein kinase C activation. Phosphoinositides also
, recruit and activate signaling proteins at specific membrane locations,
coordinating processes like cytoskeletal rearrangements and vesicular trafficking.
3. Question: Compare and contrast the mechanisms of receptor tyrosine
kinases (RTKs) and G-protein-coupled receptors (GPCRs) in signal transduction.
o Answer: RTKs are activated by ligand binding, leading to
dimerization and autophosphorylation of tyrosine residues, which recruit
signaling proteins. GPCRs undergo conformational changes upon ligand binding,
activating intracellular G proteins by promoting GDP-GTP exchange. While
RTKs rely on phosphorylation cascades, GPCRs often activate second messengers
like cAMP or calcium.
Section 2: Genetics and Genomics
4. Question: Describe the CRISPR-Cas9 system and its application in
functional genomics.
o Answer: CRISPR-Cas9 is a genome-editing tool derived from
bacterial adaptive immunity. It uses a guide RNA (gRNA) to target specific DNA
sequences, where the Cas9 nuclease introduces double-strand breaks. These
breaks are repaired by non-homologous end joining (NHEJ) or homology-directed
repair (HDR), enabling gene knockout or precise sequence modification.
Applications include studying gene function, creating disease models, and
developing gene therapies.
5. Question: Explain how RNA interference (RNAi) is used to study gene
function.
Answers (Graded A)
Section 1: Molecular and Cellular Biology
1. Question: Describe the process of protein trafficking in eukaryotic cells
and discuss the role of the signal recognition particle (SRP).
o Answer: Protein trafficking involves the transport of proteins to
their appropriate cellular or extracellular locations. The SRP recognizes a signal
peptide on a nascent protein emerging from the ribosome and pauses translation.
The SRP-ribosome complex docks to the SRP receptor on the endoplasmic
reticulum (ER) membrane. Translation resumes, and the protein is co-
translationally translocated into the ER lumen or membrane. Post-translational
modifications and sorting ensure delivery to final destinations, including the
Golgi apparatus, lysosomes, or plasma membrane.
2. Question: Explain how phosphoinositides contribute to cell signaling
pathways.
o Answer: Phosphoinositides are phosphorylated derivatives of
phosphatidylinositol that serve as key signaling molecules. For instance,
PI(4,5)P2 is cleaved by phospholipase C into IP3 and DAG, triggering calcium
release from the ER and protein kinase C activation. Phosphoinositides also
, recruit and activate signaling proteins at specific membrane locations,
coordinating processes like cytoskeletal rearrangements and vesicular trafficking.
3. Question: Compare and contrast the mechanisms of receptor tyrosine
kinases (RTKs) and G-protein-coupled receptors (GPCRs) in signal transduction.
o Answer: RTKs are activated by ligand binding, leading to
dimerization and autophosphorylation of tyrosine residues, which recruit
signaling proteins. GPCRs undergo conformational changes upon ligand binding,
activating intracellular G proteins by promoting GDP-GTP exchange. While
RTKs rely on phosphorylation cascades, GPCRs often activate second messengers
like cAMP or calcium.
Section 2: Genetics and Genomics
4. Question: Describe the CRISPR-Cas9 system and its application in
functional genomics.
o Answer: CRISPR-Cas9 is a genome-editing tool derived from
bacterial adaptive immunity. It uses a guide RNA (gRNA) to target specific DNA
sequences, where the Cas9 nuclease introduces double-strand breaks. These
breaks are repaired by non-homologous end joining (NHEJ) or homology-directed
repair (HDR), enabling gene knockout or precise sequence modification.
Applications include studying gene function, creating disease models, and
developing gene therapies.
5. Question: Explain how RNA interference (RNAi) is used to study gene
function.
