Cell Signaling
A signaling molecule is hydrophobic and enters a target cell. Why might its receptor be located inside the cell rather than on the plasma membrane?
Hydrophobic signaling molecules can cross the plasma membrane, allowing them to bind to intracellular receptors.
Why is receptor dimerization important for activating RTKs?
Dimerization brings the receptors together so they can phosphorylate each other and create docking sites for signaling proteins.
What is the equation for cellular respiration?
C6H12O6 (sugar) + O2 --> CO2 + H2O + energy (ATP)
What is the equation for photosynthesis?
CO2+H20+light energy --> C6H12O5 (sugar) + O2
Mithochondria and chloroplasts are thought to have originated from what kind of organisms?
A mutation prevents a G protein's alpha subunit from exchanging GDP for GTP. What effect would this have on the signaling pathway?
The G protein would remain inactive, so it would not properly activate its downstream targets, such as adenylyl cyclase or phospholipase C.
Ras-GEF is unable to function. What happens to Ras activation, even if an RTK has successfully dimerized and phosphorylated itself?
Ras cannot efficiently exchange GDP for GTP, so Ras activation and downstream MAP kinase signaling are reduced.
If the mitochondrial membrane becomes permeable to protons, what happens to the proton gradient and ATP synthesis?
The proton gradient dissipates, reducing the force that drives ATP synthase. ATP production decreases.
A plant is exposed to light, but the light reactions cannot produce NADPH. Which stage of photosynthesis is directly affected by the lack of NADPH?
The Calvin cycle because NADPH is an input.
A protein destined for the mitochondrial matrix has a mutation that disrupts its N-terminal targeting sequence. What is the likely consequence?
The protein may not be properly recognized or imported into the mitochondrial matrix.
A drug inhibits adenylyl cyclase. Predict what happens to cAMP levels and protein kinase A (PKA) activity after a GPCR is activated.
cAMP production decreases, so PKA activation decreases
A mutation prevents the final MAP kinase in the cascade from functioning. What happens to the upstream kinases, and what happens to the final response?
The upstream kinases may still activate one another, but the final MAP kinase cannot carry out its downstream effects, disrupting the full response.
A cell has plenty of glucose available, but its NADH production is severely reduced. Why might ATP production decrease?
NADH normally carries high-energy electrons to the cytochromes in the electron transport chain. With less NADH, the proton pump will not be as strong; so ATP synthase is not working as hard.
Does NADH or NAD+ have more potential energy?
NADH, because it is the reduced form of the molecule (it has gained high-energy electrons)
A folded mitochondrial protein reaches the TOM transport, but cannot get through. Why?
It must unfold before passing through the TOM transport channels.
A mutation causes a G protein's alpha subunit to be unable to hydrolyze GTP. How would this affect the duration of the signal?
The alpha subunit would remain active longer because it could not convert GTP to GDP. This would cause prolonged activation of downstream targets.
Both GPCRs and RTKs can activate phospholipase C. What second messengers does this enzyme produce, and what are their targets?
IP3 targets IP3 receptors, promoting calcium release, while DAG activates PKC.
Predict how inhibiting glycolysis could affect the production of pyruvate, acetyl-CoA, and the outputs of the citric acid cycle.
Less pyruvate is produced, so less acetyl-CoA is made. This can reduce the citric acid cycle's production of NADH and FADH2.
If a plant cell's mitochondria cannot produce enough ATP, can the ATP made by the chloroplast's light reactions supply the rest of the cells energy needs?
No, ATP formed in the chloroplast is directly used in the Calvin cycle and cannot be used by other organelles in the cell.
Why does the heart mitochondria have more folds in the cristae than the skin mitochondria?
More ATP is needed in the heart, more surface area for ATP synthase and cytochromes!
PLC is inhibited. Predict the effects on IP3, DAG, calcium release, and PKC activation.
IP3 and DAG production decrease. IP3-mediated calcium release decreases, and PKC activation decreases because DAG is reduced.
PI3K is inhibited, but RTK activation and Ras signaling still occur. Which signaling pathway is directly disrupted, and what important cellular functions could be affected?
The Akt pathway is disrupted. Akt's promotion of cell growth and survival could be reduced, even if Ras remains functional.
Describe the Carbons at each stage of cellular respiration. How are carbons released?
Glucose (6 carbons) --> 2 pyruvates (3 carbons each --> acetyl-coa (2c) --> both lost in the citric acid cycle.
Carbons released as CO2!
Why does the Calvin cycle slow down if the light reactions stop, even though the Calvin cycle does not directly require light?
The calvin cycle uses inputs of ATP and NADPH produced by the light reactions. When these are low, the Calvin cycle cannot continue normally.
What is the endosymbiotic theory? List three pieces of evidence that support the endosymbiotic theory.
The theory that mitochondria and chloroplasts originated from free-living bacteria. Evidence: circular DNA, bacterial like ribosomes, binary fission, double membranes, porins, etc.