Cell membranes Flashcards
(40 cards)
What is the primary function of biological membranes?
To separate the cell’s internal environment from the external environment.
What are cell membranes made of?
Phospholipids, proteins, and carbohydrates.
Why are biological membranes considered selectively permeable?
They allow some substances to pass while blocking others.
What is the role of phospholipids in membranes?
They form a bilayer with hydrophilic heads facing out and hydrophobic tails
facing in.
Why is compartmentalization important in cells?
It allows organelles to perform specialized functions.
What type of molecules can pass freely through the membrane?
Small nonpolar molecules (e.g., O₂, CO₂).
What is the role of cholesterol in the membrane?
It stabilizes fluidity and adds rigidity.
Why can’t ions pass freely through the bilayer?
The hydrophobic core repels charged particles.
How do cells maintain different environments inside vs. outside?
Through selective permeability and transport proteins.
Why are membranes described as “fluid”?
Phospholipids and proteins move within the bilayer.
Why don’t lipids spontaneously flip between layers?
The hydrophilic head cannot pass through the hydrophobic core.
Why is membrane fluidity important?
It allows flexibility, mobility of proteins and relates to permeability.
What factors affect membrane fluidity?
Temperature, lipid composition, and cholesterol.
Why are membrane proteins important?
They perform transport, signaling, and enzymatic functions.
How does temperature affect membrane fluidity?
Higher temperatures increase fluidity, while lower temperatures decrease it.
What happens when cholesterol is added to membranes?
It stabilizes fluidity, preventing extreme changes.
How do unsaturated fatty acids affect fluidity?
They increase fluidity due to kinks in the tails.
How do saturated fatty acids affect fluidity?
They make the membrane more rigid.
What is membrane permeability?
The ability of molecules to cross the membrane.
What type of molecules have high permeability?
Small, nonpolar molecules like oxygen and carbon dioxide.
What type of molecules have low permeability?
Large polar molecules and ions.
How do cells regulate permeability?
By using protein channels and carriers.
What are lipid rafts?
Clusters of lipids and proteins that move together.
What are the two main types of membrane proteins?
Integral and peripheral proteins.
