Summary
Highlights
The lecture begins by discussing engineered viruses, noting that they are heritable but not stable without artificial selection. Successful engineered fungal cells limited bacterial division, mirroring how eukaryotic cells regulate mitochondria. This regulation is crucial to prevent the endosymbionts from overwhelming the host cell and consuming all resources.
The discussion shifts to the ethical implications of creating organisms with new traits, such as those that degrade plastics, by integrating entire organisms rather than just genes. The professor emphasizes the importance of bioethics in scientific exploration, mentioning how engineered organisms could have unintended consequences if they escape control.
The lecture transitions to the properties of cell membranes. It reviews the structure of phospholipids, which are amphipathic with hydrophilic heads and hydrophobic tails. The importance of saturated and unsaturated fatty acids in maintaining membrane fluidity across seasons is explained, along with the role of sterols like cholesterol in membrane stability.
The fluid mosaic model is discussed, explaining that phospholipids can easily move laterally but rarely 'flip-flop' across the membrane due to the energy required for polar heads to pass through the hydrophobic interior. This leads to a discussion of an experiment demonstrating the lateral movement of integral membrane proteins.
Various components of the cell membrane are detailed, including integral and peripheral proteins, glycoproteins, and glycolipids. These components are crucial for cellular functions such as enzymatic activity, structural support, cell signaling, and especially cell-cell recognition, which differentiates self from foreign entities.
The lecture briefly explains how the SARS-CoV-2 (COVID-19) spike protein uses glycans to evade the immune system and attaches to the ACE2 receptor on human cells. An enzyme, TMPRSS2, then cleaves the spike protein, exposing hydrophobic regions that facilitate the fusion of the viral membrane with the host cell membrane, leading to infection.
The concept of selective permeability of the plasma membrane is introduced, differentiating between hydrophobic molecules (like hydrocarbons and oxygen) and hydrophilic molecules (like water, sugars, and ions) in their ability to cross the membrane. The lecture also reviews tonicity (hypertonic, hypotonic, isotonic solutions) and its effect on water movement across membranes in plant cells.
The final concept discussed is facilitated diffusion, which requires proteins for transport but does not consume cellular energy because it is a passive process. The instructor clarifies that there is no such thing as 'active diffusion'.