1. More on Cell Membranes - the basics Flashcards
What are the 2 membrane components ?
Phospholipids.
Cholesterol.
Overall what do phospholipids do?
Form a barrier to dissolved substances.
Describe the structure of phospholipids.
Have a head and tail.
Head is hydrophilic - attracts water.
Tail is hydrophobic - repels water.
Molecules automatically arrange them selves in a bilayer.
Heads face out towards water on either side of membrane.
Why does the membrane not allow water-soluble substances to diffuse through it?
As centre of bilayer is hydrophobic.
What can diffuse through the membrane?
Small, non-polar substances and water.
Overall what does cholesterol do?
Gives stability to membrane.
Fits between the phospholipids.
What is cholesterol?
Type of lipid present in all cell membranes bar bacterial cell membranes.
How does cholesterol help make membrane more stable?
It binds to hydrophobic tails of phospholipids, causing them to pack together closely.
Restricts movement of phosholipids , making membranes less fluid and more rigid.
Why is cholesterol important?
Helps maintain shape of animal cells.
Important for cells not supported by other cells eg red blood cells - float free in blood.
What feature does cholesterol also have?
Hydrophobic regions.
Creates further barrier to polar substances moving through membrane.
What does a polar molecules have?
One end with slightly positive charge.
One end with slightly negative charge.
Not as strong as charges on an ion.
Help molecules dissolve in water.
