Cell Membranes - B6 Flashcards
True or false: all cells are surrounded by a membrane.
true
What is the cell membrane a barrier between? (for cell surface membranes)
It is a barrier between the cell and the environment
Is the cell surface membrane partially permeable?
Yes
What are the 3 transportation methods for cell surface membranes?
diffusion, osmosis, and active transport
What does the organelle membrane do?
It divides the cell into different compartments. They act as a barrier between the organelle and the cytoplasm. It’s partially permeable
What are the different parts of a phospholipid and are they hydrophilic or hydrophobic?
-phosphate head > hydrophilic > polar(charged)
-fatty acids> hydrophobic> not polar
Are the phosphate heads on the outside or inside of the phospholipid blayer?
One is on the outside of the cell, one is on the inside, so the fatty acids are facing each other.
Why are cell membranes described as being a fluid mosaic?
-mosaic: membrane is made up from a variety of different molecules arranged into a mosaic(these molecules vary between cell to cell)
-fluid: the position of these molecules within the membrane is fluid - they are able to move around within the cell
What structures make up a cell membrane?
-phospholipid bilayer
-channel protein
-carrier protein
-glycolipids and glycoproteins
-cholesterol
-receptors
-enzymes
What types of molecules go straight through the phospholipid bilayer?
small and non-carged molecules
What type of molecules go through channel proteins?
-small or big water-soluble ions
-can’t get through the bilayer as they’re repelled by phosphates
What type of molecule travels thorugh channel proteins?
glucose, amino acids
How does a carrier protein work?
bind to substrate > change tertiary structure > allows molecule to pass through
What is a glycolipid made from?
made of sugars and lipids
What is a glycoprotein?
protein with sugars on
How does cholesterol aid cell membranes?
-add rigidity/strength
-keeps molecules in place i.e. channel proteins
What do enzymes do for cell membrane structures?
-hydrolyse disaccharides
-uses induced fit
-the disaccharides become monosaccharides and then go through the carrier protein
How do the small, non-charged travel through the phospholipid bilayer?
-move by simple diffusion - doesn’t rely on proteins.
-high conc. on the outside of the cell and a low conc. on the inside of the cell
-simple diffusion is passive - rate increases as conc. difference increases
How do molecules travel through channel and carrier proteins?
-facilitated diffusion(proteins help the diffusion)
-high to low > passive
-rate of diffusion is limited by the no. of proteins - channel or carrier
-some carrier proteins also carry out active transport - low to high, requires energy, have lots of mitochondria
What is the definition of osmosis?
Osmosis is the movement of water molecules from a high water potential to a low water potential across a partially permeable membrane
What is water potential?
the pressure of water on a membrane
What is the water potential of pure water?
-PURE wp is 0(the biggest)
-solutions have a -ve wp (lower wp)
How is water potential created?
-water molecules in constant motion
-some hit the membrane as they move randomly
-the collision of the molecules with the membrane causes a pressure on it. This pressure is known as water potential and is measured in units.
-more water molecules = greater water potential
What does it mean if a solution is isotonic?
no difference in wp - solutions of equal solute conc.
What does it mean if a solution is hypertonic?
-lots of solutes in solution
-RBC shrinks
-osmosis from high to low
What does it mean if a solution is hypotonic?
-solution has higher wp than molecule
-water diffuses via osmosis into molecule
-molecule swells and bursts
Describe the process of facilitated diffusion.
-from high to low conc.
-through protein channel or using a specific carrier protein
-passive
-rate is limited by no. of proteins
Describe the process of active transport.
-from low to high conc.
-uses a specific carrier protein
-requires ATP
-rate limited by ATP availability
-cells which actively transport require many mitochondria to produce ATP via cellular respiration
