Sterols Flashcards
What is most common sterol found in animals?
Cholesterol
What is most common sterol found in yeast and fungi?
Ergosterol
What is most common sterol found in plants?
Sitosterol and stigmasterol
What is generic structure of sterols?
- Four rigidly fused carbon rings forming the steroid nucleus
- Hydroxyl group attached to first group
- Hydrocarbon chain attached to fourth ring
What is effect of stiff fused ring structure?
Adds righty to bilayers and strengthens them
What is cholesterol the metabolic precursor of?
Steroid hormones (progestins, glucocorticoids, mineralocorticoids, oestrogen, androgens)
Describe interaction between sphingomyelin and cholesterol
OH group of cholesterol is masked by polar head of sphingomyelin
How do cholesterol and sphingomyelin form lipid rafts?
H formed between OH of cholesterol and NH group of sphingomyelin
These interactions can result in lipid rafts in membrane that are rich is cholesterol and sphingolipids
What are lipid rafts?
A patch where the average composition of lipid is different from bulk composition within a membrane (will be thicker)
Characterised by lipid molecules being in the lipid ordered phase
Float freely in bilayer
How do lipid rafts affect structure of membrane?
Offer more structure and rigidity compared to the rest of the membrane
What are these rafts rich in?
Cholesterol and sphingomyelin
What can excessive sphingomyelin in lipid rafts lead to?
Insulin resistance
How are lipid rafts involved in viruses entering cells?
Endocytosis
- Membranes can form caveolae from lipid rafts and invaginate
- This helps viruses become internalised into cells
- Caveolae are made as viruses accumulate
- Induce polymerisation of proteins in lipid rafts
- Virus attaches itself to raft and mimics cellular uptake mechanism and uses mechanisms to escape lyses
What is caveolae?
Special type of lipid raft - small invaginations of the plasma membrane
What is ‘invaginate’?
Turn inside out or folded back on itself to form a cavity
