jan 19

Discussion on the accessibility of campus for students, emphasizing walkways, transport options, and accessibility features for students with disabilities.
Recap of the previous class focused on E3 ligases, explaining their role in the ubiquitin-proteasome system and how they target specific substrates for degradation.

Question posed to the students: What determines whether a protein would be monoubiquitinated?
A hypothetical scenario: Designing a protein that cannot be proteasomally degraded, exploring implications in cellular regulation and disease.
Discussion of the 'N-end rule' and possible alternatives, which play a role in determining protein half-lives based on the identity of the N-terminal residue.
Consideration of lysine positions and their importance in ubiquitination:
- Lysine 63 on ubiquitin discussed as a targeting mechanism for protein interactions and signaling pathways.
- If a protein lacks a lysine, it cannot be ubiquitinated, affecting its degradation and functional lifespan in the cell.
- Discussion of hydrophobic regions impacting targeting, particularly how they can influence protein stability and localization.
Affirmation of student participation and ideas by prompting examples of proteins affected by ubiquitination.

Mention of components:
- Ubiquitin receptors that recognize ubiquitinated substrates.
- Ubiquitination and proteasomal cap function to ensure substrates are properly processed before degradation.
Confirmation of students’ understanding of the basics through interactive questions.

Distinction between soluble proteins and membrane proteins, emphasizing structural differences and functional roles.
Introduction to biological membranes and their significance in maintaining cellular integrity and communication.

Description of the cell with various compartments:
- Endoplasmic Reticulum (ER) – site of protein synthesis and folding.
- Golgi Apparatus – processing and sorting center for proteins and lipids.
- Peroxisomes – organelles involved in lipid metabolism and detoxification.
- Mitochondria – energy production through oxidative phosphorylation.
- Lysosomes – degradation of macromolecules and cellular waste.
Concept of membrane-bound organelles maintaining independence and specific functions, and coordination among organelles.

Need for a transportation network in the cell to ensure proper distribution of proteins and lipids.
The Secretory Pathway:
- From ER to Golgi, then to the plasma membrane for secretion.
- Internalization through endosomes, with degradation in lysosomes emphasized.
Explanation of vesicular transport:
- Proteins and lipids made in the ER are trafficked to various locations to fulfill cellular functions.
- The structure of vesicles:
- Ensure contents do not mix with cytosol, maintaining compartmentalization.
- Luminal environments similar to extracellular space but distinct from cytosol, providing specialized conditions for biochemical reactions.

The importance of different environments in cellular compartments, including:
- Differences in ion concentrations (e.g., potassium, sodium, calcium) between cytosol and organelles that affect cellular signaling.
- Reducing environment in cytosol vs. oxidizing environment in ER lumen, impacting protein folding and modifications.

Not limited to the plasma membrane; also includes organelle membranes, each with unique functional aspects.
Roles of membranes include:
- Enclosure of organelles, acting as barriers that ensure separate functional domains.
- Regulated transport between compartments, crucial for maintaining cellular homeostasis.
- Biochemical reaction sites, facilitating necessary metabolic processes.
- Controlling environmental contact, facilitating cell motion, and signal transmission for cellular responses.
Membrane properties include hydrophobic barriers, flexibility for shape changes, and selective permeability, allowing for controlled interactions.

Membrane made of lipid molecules and proteins:
- Lipid bilayer with polar outsides and a hydrophobic middle, crucial for membrane integrity.
- Phospholipids as primary constituents, serving as the building blocks for membranes.
- Importance of lipid organization for membrane integrity, stability, and functionality in biological processes.

Explanation of fluidity in membranes:
- Proteins can rotate and diffuse laterally, contributing to membrane dynamics and function.
- Membrane dynamics compared to an ocean with waves, allowing for interaction and signaling.

Description of common phospholipids and their structure, providing bilayer formation.
Phosphatidylethanolamine, phosphatidylcholine, and variation in fatty acyl chains influencing membrane properties.
Amphipathic nature leading to membrane formation, with hydrophilic heads and hydrophobic tails.

Difference between sphingolipids and phospholipids:
- Amide linkage vs. ester linkages, impacting their function and structure.
Role in cellular functions, especially in neural tissues for signaling and structural integrity.

Importance as a signaling molecule:
- Its derivatives act as second messengers in pathways like protein kinase C activation.
Variation in positions of phosphate groups leading to diverse functions, particularly in signal transduction pathways.

Discussion of chain lengths (14-24 carbons) and saturation effects, impacting membrane fluidity.
The impact of unsaturation and double bonds on membrane fluidity and thickness, which affects functionality.

Definition and significance in cell recognition and signaling.
Structure: Sphingolipid or glycerolipid base with sugar additions, impacting membrane properties.

Unique rigid structure with steroid ring system, impacting fluidity and stability.
Role in membrane stability and fluidity, particularly in plasma membranes under varying temperature conditions.

Concept of leaflets in membranes: outer vs. inner, influencing lipid distribution and functional outcomes.
Implications for lipid distribution, particularly in apoptosis signaling and cellular communication.

Definition of microdomains as specialized lipid rafts that enrich specific lipids.
Enrichment of specific lipids leading to functional differences, impacting cellular signaling and interactions.

Synthesis location: Cytosolic side of ER, where lipid advent is vital for membrane expansion.
Energy dynamics involving Coenzyme A and head group attachment crucial for lipid formation and membrane extension.

Mechanisms for lipid flipping and movement through the membrane:
- Enzymes involved: flipases, flopases, and scramblases that maintain membrane asymmetry.
Transport strategies for maintaining membrane asymmetry and correct lipid orientation, essential for cellular function and signaling.

Recap of the importance of lipid composition in determining membrane properties and functions, underlining their effects on cellular operation.
Overview of membrane trafficking pathways for proteins and lipids, emphasizing the significance of compartmentalization in cellular efficiency.

Understanding differences in lipid types and their functions, preparing students for practical applications in cellular biology.
Preparation for upcoming lectures focusing on advanced topics in membrane dynamics and signaling.