Cell Membranes Flashcards
(23 cards)
Substances move across by either…
Diffusion facilitated diffusion and active transport
What do membranes around organelles do?
Divide the cell into compartments and act as a barrier between organelle and cytoplasm
What is the fluid Mosaic model used for
To describe the arrangement of molecules in the membrane
Describe the fluid Mosaic model
Phospholipid bilayer - fluid - constantly moving
Cholesterol molecules present in bilayer
Protein scattered throughout the bilayer like a mosaic
- channel proteins - allow large mol & ions to pass through
-carrier proteins - allow large mol & ions to pass through
-receptor proteins - detect chemical signals
What is the difference between a glycoprotein and a glycolipid
Protein w polysaccharide attached
Lipid w polysaccharide attached
What is the role of a phospholipid in the cell membrane
Head = hydrophilic
Tail = hydrophobic
Molecules automatically arrange themselves into a bilayer
Centre of the bilayer is hydrophobic - membrane doesn’t allow water soluble substances through = barrier
What is the role of cholesterol in the cell membrane
Fit between phospholipids, binding to the hydrophobic tails of the phospholipids
make them pack closer together
restricts the movement = membrane more rigid and less fluid cholesterol helps to maintain the shape of animal cells - important in unsupported cells e.g. RBCs
What affect does temperatures below 0° have on membrane permeability?
Phospholipids have little energy = membrane rigid
C & C proteins deform = more permeable membrane
ice crystals may form and pierce membrane = more permeable
What affects does temperature between 0 and 45° have on membrane permeability
Phospholipids can move around/ not packed as tightly = membrane partially permeable
as temperature ^phospholipids move more as they have more energy = ^ permeability
What effect does temperature above 45° have on membrane permeability
Bilayer starts to melt and membrane becomes more permeable
Water inside cell expands putting pressure on the membrane channel and carrier proteins deform so they can’t control what enters/leaves - ^ membrane permeability
What is diffusion
The net movement of particles from an area of higher concentration to an area of lower concentration
What is facilitated diffusion
Larger molecules so big = diffuses very slowly
Same for charged particles as they are water-soluble
To speed it up like they diffuse via carrier proteins & channel proteins
passive process = goes down concentration gradient
How do carrier proteins work
Large molecule attaches to carrier protein in membrane
Protein then changes shape
This release is molecule on opposite side of the membrane
Different channel proteins facilitate different molecules
How do channel proteins work
Form pores in the membrane for charged particles to diffuse through
different channel proteins facilitate different charge particles
What is the rate of simple diffusion affected by
Concentration gradient
Thickness of exchange surface
Surface area - ^ means more particles can be exchanged in the same amount of time e.g. microvilli
What is the rate of facilitated diffusion affected by
Concentration gradient
Number of channel or carrier proteins
What is osmosis
Fusion of water molecules across a partially permeable membrane
from an area of high water potential to an area of low water potential
What is water potential
The potential of water molecules to diffuse in/out of a solution
Pure water has the highest WP - all solution have a lower WP than PW
If two solutions have the same WP they are isotonic
What is the rate of osmosis affected by
WP gradient
Thickness of exchange surface
Surface area of the exchange surface
What is the difference between active transport and facilitated diffusion
AT move solutes from a low concentration to high concentration
AT requires energy =source of energy ATP
ATP can be hydrolysed (ATP->ADP+Pi) - releasing energy
What are co-transporters
A type of carrier protein
Binds 2 molecules at a time
Concentration gradient of one molecule is used to move the other molecule against its own concentration gradient
What affects the rate of active transport
Speed of individual carrier proteins
The number of carrier proteins present
The rate of respiration and the availability of ATP
How does the sodium potassium pump reabsorbe glucose
Sodium ions ATd out of ileum epithelial cells and into blood via sodium potassium pump creating CG
higher conc of sodium ions in blood than in cell
causes sodium ions to diffuse out of lumen (gut) into cell down CG
via sodium glucose transporter proteins
the co transporter carries glucose into the cell with sodium
concentration of glucose in cell increases
glucose then diffuses out of cell into blood down CG
through a protein channel via Facilitated diffusion
