final exam genetics

Phosphatidylinositol (PIP) Signaling Pathways

  • PIP3 Formation:

    • PIP3 is formed from PIP2 through the action of PI 3-kinase.

    • PIP2 is dephosphorylated into diacylglycerol (DAG) and inositol triphosphate (IP3).

  • Impact of Inhibition:

    • If PI 3-kinase is inhibited, apoptosis will be more likely.

    • The signaling cascade that prevents apoptosis requires active PI 3-kinase, which promotes cell survival.

    • In the absence of this signaling, cells become more susceptible to apoptotic pathways.

AKT Activation

  • Mechanism of AKT Activation:

    • AKT must be brought to the membrane to be phosphorylated.

    • Phosphorylation by PDK1 releases AKT from the membrane, allowing it to exert its effects.

Croton Oil and PKC Activation

  • Effect of Croton Oil:

    • Croton oil mimics DAG, increasing activated Protein Kinase C (PKC) levels.

    • It removes the need for ligand binding and activation of phospholipase C (PLC) to signal calcium release from the endoplasmic reticulum (ER).

    • It necessitates a source of calcium for PKC activation.

Lysosomal Targeting Sequences

  • Identification of Targeting Sequences:

    • Experimental approaches include gain-of-function and loss-of-function mutations to determine the role of specific sequences in protein localization.

  • Protein Transport to Lysosome:

    • Proteins are synthesized on ribosomes located on the rough ER (not smooth ER).

    • Mutations in sequences required for ER targeting will result in proteins being retained in the cytoplasm.

  • Glycosylation Process:

    • Proteins entering the ER undergo glycosylation, adding sugars that act as tags for correct sorting.

    • Glycosylated proteins are then packaged into vesicles for transport to the lysosome.

Mechanisms of Vesicle Targeting

  • Role of SNARE Proteins:

    • Vesicles and target membranes utilize SNARE proteins (v-SNARE and t-SNARE) for specific docking and fusion.

    • Mannose-6-phosphate is a crucial tag for lysosomal proteins. It signals that a vesicle should transport its cargo to the lysosome.

  • Consequences of Targeting Errors:

    • Mutated lysosomal targeting sequences may result in proteins being misrouted to other organelles or secreted from the cell.

GTP Hydrolysis and Cellular Effects

  • Impact on Microtubules and Cell Cycle:

    • Increased GTP hydrolysis rates can affect microtubule stability, making them less stable and preventing their proper function.

    • This instability leads to longer metaphase durations as microtubules struggle to attach to chromosomes.

  • Cell Cycle Effects:

    • Changes in GTP hydrolysis can impact mitosis, potentially slowing down the cell cycle due to the difficulties in microtubule stabilization.

Energy Transfer in Cells

  • Types of Energy:

    • Energy is stored in chemical bonds and is transferred during various cellular processes, such as ATP production.

  • Examples of Energy Transfers:

    • Proton motive force established by the mitochondrial electron transport chain helps synthesize ATP via ATP synthase.

    • The flow of protons back into the mitochondrial matrix generates kinetic energy that is converted into the chemical energy of ATP.

DNP and Its Effects on Respiration

  • Mechanism of DNP Action:

    • DNP uncouples oxidative phosphorylation by allowing protons to bypass ATP synthase, resulting in heat production instead of ATP synthesis.

    • This process leads to hyperthermia as energy is released as heat instead of being captured in ATP.

  • Physiological Consequences:

    • Individuals taking DNP may suffer from a lack of ATP and increased metabolic stress as the body tries to compensate for the energy deficit.

Cell Cycle Signaling

  • Signaling Proteins in the Cell Cycle:

    • Different checkpoints in the cell cycle, such as the role of p21, can affect progression through various phases.

    • Inhibition of proteins like p21 can speed up the cell cycle, impacting overall cellular division.

Membrane Fluidity and Composition

  • Temperature Effects on Membrane Composition:

    • Bacteria alter their membrane by incorporating more saturated fatty acids at higher temperatures to maintain membrane stability, while they will introduce unsaturated fatty acids to maintain fluidity at lower temperatures.

    • These changes are important for adapting to environmental conditions while ensuring cellular integrity.

  • Stabilization of Bacterial Membranes:

    • Other components, such as polysaccharides, are utilized by some bacteria for membrane stabilization, although this varies widely depending on bacterial type.