Recording-2025-03-12T15:59:33.247Z

Cell Signaling and Growth Factors

• Cell Division Stimulation

  • Specific proteins, such as epidermal growth factor (EGF), stimulate cell division and growth.

  • EGF receptors pair with protein tyrosine kinases for signal transduction.

• G Proteins

  • G proteins are crucial in signal transduction; they mediate the exchange of GDP for GTP to activate the signaling cascade for cell growth.

  • When activated, G proteins lead to the growth of epidermal tissue for functions such as healing wounds or replacing damaged cells.

  • Mutations or improper activation of G proteins and tyrosine kinases can lead to uncontrolled cell proliferation, often correlated with cancer development.

  • The inactive state has GDP attached, while the active state has GTP, indicating a switch in activity.

  • If GTP cannot be hydrolyzed back to GDP, active signaling continues leading to excessive cell growth.

Cancer and Apoptosis

• Uncontrolled Cell Growth

  • Cancer cells often result from g protein signaling being constantly active due to lack of regulation (inability to revert back to inactive state).

  • Consequences include the formation of tumors and masses of cells.

• Apoptosis

  • The programmed cell death mechanism prevents damaged or infected cells from spreading harm to other cells.

  • Key triggers of apoptosis include detachment from the extracellular matrix and damage signaling.

  • Important during stages like embryonic development and as a defense mechanism against cancerous cells.

Cell Communication

• Extracellular Matrix (ECM)

  • Cells attached to ECM receive constant signals indicating they are healthy and continue to grow.

  • Detaching cells may induce apototic pathways due to unfavorable conditions.

• Paracrine Signaling and Yeast Growth

  • Yeast cells release a signaling molecule called mating factor to induce a different growth cycle in neighboring yeast.

  • This form of signaling is localized and affects only surrounding cells.

Bacterial Communication: Quorum Sensing

• Autoinducers

  • Bacterial cells release autoinducers to communicate density to surrounding bacteria.

  • In low density, the signal does not provoke a strong response; in high density, it triggers a positive feedback loop promoting collective behaviors (e.g., toxin production).

• Amplified Behavior

  • When bacteria sense a high density of their kind, they ramp up production of autoinducers which encourages cooperation and actions like toxin secretion to enhance survival and resource exploitation.

Metabolic Pathways

• Glycolysis

  • Divided into two phases: the energy-requiring phase (first half) and the energy-releasing phase (second half).

  • Important for understanding metabolic efficiency and energy extraction from glucose.

• Pyruvate to Acetyl CoA

  • During conversion, carbon is removed, indicating the decarboxylation step that links glycolysis to the citric acid cycle.

Electron Transport Chain and Chemiosmosis

• Proton Gradient

  • Energy released from electronic transfer generates a proton gradient across the mitochondrial membrane, driving ATP synthesis via chemiosmosis.

Photosynthesis Concepts

• Single plants exposed to various light colors show differential absorption; chlorophyll reflects green light and absorbs blue and red effectively.

• Calvin Cycle Activation

  • Requires carbon dioxide and regenerates key intermediates (e.g., RuBP) to sustain photosynthesis.

Immune Response and Key Proteins

• Upon bacterium ingestion, white blood cells release chemical messengers that initiate inflammation response proteins synthesis by the liver.

• G Protein Activation

  • Active when GTP is bound; inability to hydrolyze GTP means a protracted active state leading to amplified immune responses.