Lecture 1.1 - Cell membrane and function

Question 1

What is noteworthy about the membrane function of the loop of Henle?

Answer 1

The tubule consists of epithelial cells which form a barrier to water

Question 2

How is the permeability barrier maintained?

Answer 2

• The apical membrane outer leaflet has lipids that help prevent water transport
• Tight junctions prevent mixing between apical and basolateral outer leaflets and also seal gaps between epithelial cells in the sheet

Question 3

Membrane features: structure, thickness, boundaries, covalency of assemblies, symmetry, fluid, polarity, do they process information, and how are they made?

Answer 3

• Sheet-like
• 6-10nm
• Tendency to form closed boundaries
• Non-covalent assemblies formed
• Asymmetrical
• Fluid; two dimensional fluid
• Mostly electrically polarised - negative inside
• Yes, Cell membranes process information
• They are self-renewing

Question 4

Glycerol-backed phospholipids: what are they and what do they do?

Answer 4

• Glycerophospholipids/phosphoglycerides - central glycerol molecule binding hydrophobic fatty acid tails, hydrophilic phosphate head, and a choline group (?). The main component of membranes

Question 5

Sphingosine-backed lipids: what are they and what do they do?

Answer 5

• Sphingophospholipids - Involved in myelin formation, nerve impulse conduction, signal transduction and as receptor component for certain hormones / bacterial toxins
• Glycolipids - glycoconjugates of lipids that are generally found on the extracellular face of eukaryotic cellular membranes, and function to maintain the stability of the membrane and to facilitate cell-cell interactions and can also act as receptors for viruses and other pathogens to enter cells

Question 6

Sterols: what are they and what do they do?

Answer 6

Sterols - regulate biological processes and sustain the domain structure of cell membranes where they are considered as membrane reinforcers (cholesterol)

Question 7

How do different lipids impact the membrane?

Answer 7

Membrane dynamic - thickness, fluid, shape

Surface biochemistry - Surface protein binding

Lipid subdomains - intracellular trafficking/signalling (allows release of lipid-based metabolites and signal molecule binding)

Question 8

Membrane composition

Answer 8

Composed of carbohydrates, lipids and proteins

Lipids and proteins are in a 4:1 to 1:4 ratio

Question 9

The four functions of cell membranes

Answer 9

Separation - form a semi-permeable diffusion barrier

Exchange - allow transport of metabolites and macromolecules in and out of cell compartments as well as aiding trafficking of membrane components

Integration - mediate cell-to-cell communication, cell adhesion and signalling

Metabolism - Membranes are an integral part of metabolic pathways and contain machinery for membrane synthesis, remodelling and degradation

Question 10

Membranes: how are they made?

Answer 10

Inherited during cell division (cytokinesis)

Question 11

How do membranes do their job?

Answer 11

By forming a double sheet with an internal hydrophobic environment, substances struggle to pass through this barrier without aid