Cell Membranes and Bio-Energetics

• Credit value: 15 credits at Level 4
• Convenor: Dr Richard Rayne
• Assessment: computer-based (MCQ) tests and online short-answer tests (100%)

This is the second module in a three-module sequence at Level 4 designed to develop your knowledge and understanding of foundational principles underpinning the functioning of cells in higher organisms. A sound background in this subject matter is required by biomedical scientists and molecular biologists and is preparatory for modules in later years of the programme.

We will focus on cell membranes and emphasise their roles in controlling material flow into and out of cells, and in cellular energetics.

Indicative syllabus

• Cell membranes: molecular composition, structure, and physicochemical properties
• Transport of materials across membrane barriers: diffusion; osmosis; protein-mediated transport systems (channels, transporters, pumps)
• Transmembrane gradients: concentration gradients vs. electrochemical gradients
• The genesis and maintenance of a cell’s resting transmembrane electrical potential
• How and why cell transmembrane potentials vary in excitable cells that are engaged in electrical signalling (e.g. via action potentials)
• How the structure and functioning of membranes and membrane-associated proteins are critical in the mechanism of mitochondrial respiration: chemiosmotic coupling between electron transport and ATP synthesis

Alongside treatment of the above topics, there will be an emphasis on the concept of free energy (G) and how consideration of free energy change (∆G) allows us to understand and predict the direction and extent of solute transport across membranes.

By the end of this module, you will be able to:

• analyse the features/components of a cell membrane to explain its behaviour as a selectively permeable boundary between extracellular and intracellular (and other) compartments
• distinguish between molarity, osmolarity and tonicity; describe solutions in terms of comparative osmolarities (iso-, hypo-, and hyper-) and predict the tonicity (iso-, hypo-, hyper-) of a specified solution relative to a cell
• explain whether a molecule is likely/able to cross a cell membrane by simple diffusion, protein-mediated transport, or vesicular transport, based on an analysis of its physicochemical properties (size, polarity/charge, lipophilicity, etc)
• differentiate between the major categories of protein-mediated transport, diagram the mechanisms of each, and comment on their energetics
• apply the principles embodied within the Nernst and GHK equations to explain: (a) how permeant ions contribute to the resting membrane potential, and (b) how changes in membrane permeability to each of these ions would affect the resting membrane potential
• define the terms exergonic and endergonic and indicate how these relate to the sign (+/-) of free energy change (∆G) for a reaction or process
• describe generally how a gradient (dis-equilibrium) can be harnessed to perform work and apply this description to an explanation of the chemiosmotic mechanism used by mitochondria to synthesise ATP.