Overview
This lecture covers the structure and function of biological membranes, the basics of gene expression (transcription and translation), and mechanisms of molecular transport across membranes.
Biological Membranes
- Biological membranes are composed mainly of a phospholipid bilayer with embedded proteins.
- Membranes form selective barriers that regulate the passage of substances in and out of cells.
- Fluid mosaic model describes membranes as flexible with proteins and lipids moving laterally.
- Membrane proteins serve roles in transport, signaling, and structural support.
Gene Expression
- Gene expression includes transcription (DNA to RNA) and translation (RNA to protein).
- Transcription occurs in the nucleus and is catalyzed by RNA polymerase.
- mRNA leaves the nucleus and is translated by ribosomes in the cytoplasm.
- Regulation of gene expression occurs at transcriptional, post-transcriptional, and translational levels.
Molecular Transport
- Passive transport moves molecules down their concentration gradient without energy input.
- Simple diffusion allows small, nonpolar molecules to pass through the membrane.
- Facilitated diffusion uses membrane proteins to help polar or charged molecules cross.
- Active transport moves substances against their concentration gradient using energy (usually ATP).
- Primary active transport involves direct use of ATP, e.g., sodium-potassium pump.
- Secondary active transport uses an existing gradient to drive transport of another substance.
Key Terms & Definitions
- Phospholipid Bilayer — double layer of phospholipids forming the core of cell membranes.
- Fluid Mosaic Model — describes the dynamic arrangement of proteins and lipids in membranes.
- Transcription — process of copying DNA into RNA.
- Translation — synthesis of proteins from mRNA template.
- Passive Transport — movement of substances across membranes without energy input.
- Active Transport — movement of substances against their gradient, requiring energy.
- Facilitated Diffusion — passive transport aided by membrane proteins.
Action Items / Next Steps
- Review textbook chapters on membranes, gene expression, and transport mechanisms.
- Complete assigned practice problems on molecular transport.
- Prepare questions for next class on membrane protein functions.