Biochem Exam II practice questions Flashcards
Receptor Tyrosine Kinases
1. transport ligands across the cell membrane
2. dephosphorylate proteins when the RTK is inactive
3. are activated by dimerization and phosphorylate downstream signaling proteins
4. hydrolyze lipids
5. have seven transmembrane helices
6. phosphorylate PIP2
7. none of the above
- are activated by dimerization and phosphorylate downstream signaling proteins
Amplification can occur in a signaling pathway only if
1. the pathway involves several protein kinases
2. the pathway involves a second messenger
3. the pathway involves an ion, such as sodium or calcium
4. one molecule of a protein in the pathway can signal to many molecules of its downstream effector
5. there are many substrates for a protein kinase in the pathway
6. the pathway leads to increased gene expression
- one molecule of a protein in the pathway can signal to many molecules of its downstream effector
In 2015, the number of drugs approved by the FDA that target human proteins was approximately 1200. Which statement does NOT describe the distribution of protein families targeted by approval drugs?
1. Several signaling proteins such as kinases are included
2. Both ligand-gated and electrochemical channel receptors are included
3. Many drugs target membrane receptors in signaling, while drugs targeting nuclear receptors have not yet been approved
4. GPCR’s are the highest fraction of targets
5. 1&2
6. 3&4
7. 2&4
- 2&4
-both ligand-gated and electrochemical channel receptors are included
-GPCR’s are the highest fraction of targets
The cycle for signaling through hetero-trimeric G proteins
1. involves amplification of the signal by the GPCR GEF activity
2. includes a monomeric G protein, such as Ras, at one step of the cycle
3. includes the G protein trimer interacting with downstream signaling proteins
4. can include the production of cAMP, a second messenger
5. depends on hydrolase activity of the GPCR
6. 1&3
7. 1&4
8. 1,3 & 4
- 1,3 &4
-involves amplification of the signal by the GPCR GEF activity
-includes the G protein trimer interacting with downstream signaling proteins
-can include the production of cAMP, a second messenger
Ras, a monomeric G protein, is mutated and permanently active in 90% of pancreatic cancers. What is a reasonable explanation for why the Ras mutation would cause Ras to be highly activated?
1. The mutation affects the conformational change in the switch regions and prevents Ras binding to GTP
2. The mutation impairs Ras hydrolysis of GTP so that Ras is highly active
3. the mutation impairs the GEF exchange activity so that the GDP-bound form is increased and highly active
4. The mutation converts Ras monomeric G protein into a trimeric G protein that is overly active
- The mutation impairs Ras hydrolysis of GTP so that Ras is highly active
Adenylate cyclase is a signaling enzyme that does NOT
1. Convert ATP into a second messenger
2. cyclize ATP to form cyclic-AMP
3. Get inhibited by Gai
4. interact with Gas
5. Produce ATP in cells from cyclic-AMP by the reverse reaction of cyclization
- produce ATP in cells from cyclic-AMP by the reverse reaction of cyclization
Calmodulin is
1. a nonspecific kinase
2. a key effector in calcium signaling
3. a second messenger that triggers Ca2+ release from the ER through gated channels
4. a cytokine receptor
5. a protein that binds DAG
6. a protein that binds Ca2+ with a KD value greater than the basal Ca2+ concentration in the cytoplasm (=10^-7 M)
7. A transcription factor
8. 6&7
9. 2&6
10. 2, 6 & 7
- 2&6
-a key effector in calcium signaling
-a protein that binds Ca2+ with a KD value greater than the basal Ca2+ concentration in the cytoplasm (=10^-7 M)
In phospholipid signaling
1. phosphatidylinositol is a substrate for both kinases and phospholipases
2. the same O-P bond of phosphatidylinositol is hydrolyzed by all phospholipases
3. PIP3, IP3 and diacylgylcerol are 1st messengers
4. Ras and protein kinase A move into the nucleus to activate CREB
5. DAG is generated by phospholipases and moves to the ER to trigger the release of calcium through channels in the ER
6. GEFs are activated to promote GDP/GTP exchange
- phosphatidylinositol is a substrate for both kinases and phospholipases
The role of PCNA in replication is:
1. to convert DNA polymerase to a processive enzyme
2. to act as a clamp loader
3. to maintain DNA as single stranded
4. to act as sliding clamp
5. 3&4
6. 1&4
7. 1&2
- 1&4
-To convert DNA polymerase to a processive enzyme
-to act as a sliding clamp
Which of the following proteins phosphorylate licensing factors to initiate replication?
1. cyclin A
2. cyclin H
3. Cdc6
4. CDK2
5. CDC45
6. none of the above
- CDK2
Replication and transcription utilize similar but distinct mechanisms for initiation. Which phrase is true for both replication and transcription?
1. Use both DNA strands as a template
2. Require a primer for synthesis
3. Occur mainly during S phase
4. Require phosphorylation for initiation
5. use dGMP as one of the building blocks
6. Requires a ligase
- Require phosphorylation for initiation
TFIIH is a critical factor for initiating transcription. Which of the following is not a function of TFIIH?
1. ATPase
2. Phosphatase
3. Helicase
4. Kinase
5. DNA binding
6. 2&5
7. 1&3
- Phosphatase
Most of the transcription start sites for RNA polymerase II transcribed genes in humans lack a recognizable TATA box. How is it possible to initiate transcription at those transcription start sites that lack a recognizable TATA box?
1. Initiation of transcription at those sites uses an alternative mechanism that does not involve TBP or TATA boxes
2. Additional transcription factors stabilize the TBP interaction with DNA at “weak binding” TATA box sequences that occur at these sites lacking recognizable TATA boxes
3. There are several paralogs of TBP that can bind to DNA at sequences that are different from the recognizable (classical) TATA box sequence
4. DNA methylation of some DNA sequences allows for TBP to bind to the methylated DNA near the transcription start sites
5. Phosphorylation of TBP allows it to bind to sequences at these sites even though they lack a recognizable (classical) TATA box sequence
- Additional transcription factors stabilize the TBP interaction with DNA at “weak binding” TATA box sequences that occur at these sites lacking recognizable TATA boxes
Which of the following is true about the action of HDAC inhibitors?
1. They (indirectly) reduce protein synthesis
2. They inhibit transcription
3. They prevent DNA methylation
4. They (indirectly) increase histone acetylation
5. They decrease nucleosome mobility
- They (indirectly) increase histone acetylation
What three enzyme activities does the 20S proteasome possess?
1. Trypsin, chymotrypsin and caspase
2. Trypsin, kinase and caspase
3. Phosphatase, ligase and caspase
4. Helicase, chymotrypsin and phosphatase
5. Phosphatase, kinase and chymotrypsin
6. Caspase, trypsin and ligase
- Phosphatase, ligase and caspase
