Cell membrane Flashcards
What is diffusion?
Molecules move down their concentration gradient passively
What affects diffusion rate? What quantifies this?
Surface area
Concentration gradient
Distance
Temperature
Fick’s Law
What is osmosis?
Water moves down its water potential gradient across a partially permeable membrane
What is solubility?
The ability of a substance to dissolve in a solvent
What is the difference between a channel and a carrier?
Channel:
Passive diffusion.
No binding site, open to both environments at the same time.
Can be gated and only open under certain conditions.
Can also be selective with selectivity filters.
Carriers:
Passive or active.
Have binding site, undergo a conformational shape change to present the solute on the other side of the membrane.
Carriers are saturable.
What makes a carrier work actively?
Require ATP hydrolysis to undergo the conformational shape change
What is the main constituent of a cell membrane?
Phospholipids
What arrangement do phospholipids form in the membrane?
Bilayer
What property of phospholipids allows them to form a bilayer?
Amphipathic
What does amphipathic mean?
Hydrophilic and hydrophobic properties
What are the 3 parts of a phospholipid?
Phosphate head
Glycerol
Two fatty acid tails
Which part of the phospholipid is hydrophilic and what part is hydrophobic?
Hydrophobic head
Hydrophilic tail
What are the three most prevalent lipids in the cell membrane?
Phosphatidylserine: Head contains serine residue (PS)
Phosphatidylcholine: Head contains choline residue (PC)
Sphingomyelin (SM), is a type of sphingolipid
Where is sphingomyelin especially present?
Membranous myelin sheath that surrounds some nerve cell axons
What does sphingomyelin consist of?
Phosphocholine head group, a sphingosine, and a fatty acid
Is sphingomyelin synthesised from glycerol?
No
How are the 3 lipid constituents arranged on the inside and outside?
Inside layer containing more PS and the outside layer containing more PC and SM
What is cholesterol?
Unsaturated alcohol (sterol)
What does cholesterol’s interaction with phospholipids result in?
Cholesterol increases membrane packing, which both alters membrane fluidity and maintains membrane integrity so that animal cells do not need to build cell walls
What is the glycocalyx?
A glycoprotein and glycolipid covering that surrounds the cell membranes
What conjugation results in the formation of the glycocalyx?
Glycosylation of the proteins and lipids
What does the fluid mosaic model refer to?
The fluidity and dynamic nature of the membrane
What are three ways a protein can be positioned in a membrane?
Surface proteins
Transmembrane proteins: integral membrane protein that spans the entirety of the cell membrane.
Anchored proteins: proteins located on the surface of the cell membrane that are covalently attached to lipids embedded within the cell membrane.
What do surface proteins often contribute to?
Often are glycosylated and make up glycoproteins in the glycocalyx.
What is a uniporter, symporter and antiporter?
Carrier proteins
Uniporters (move one substance in one direction)
Symporters (move two substances in the same direction)
Antiporters (move two substances in opposite directions) .
