Transport across CM Flashcards
(35 cards)
structure of the phospholipid bilayer
phospholipid molecules have a hydrophilic head and hydrophobic tails. They form a phospholipid bilayer in which the hydrophilic heads point outwards and interact with the aqueous solutions either side of the bilayer/ attracted to water.
Hydrophobic tails are repelled by water so point inwards.
function of cholesterol in the CSM
restricts the movement of phospholipids in the bilayer, so making the membrane less fluid and more rigid.
Structure related to function of the phospholipid bilayer
Allows for control of movement of substances across the membrane.
the centre of the bilayer is hydrophobic, so only small, non-polar lipid soluble substances (like oxygen) are able to pass through it.
Other substances are only able to cross where there are specific transport proteins.
The membrane is strong, flexible and self-sealing.
glycoprotein structure
protein attached to carbohydrate
glycolipid structure
lipid attached to carbohydrate
CSM glycoprotein function
cell-surface receptors for hormones and neurotransmitters, allow cells to attach to one another, cell recognition
CSM glycolipid function
allows cells to join together to form tissues, cell recognition, carbohydrate extends and is a receptor for specific molecules.
Fluid-mosaic model
Why are plasma membranes described as each of these 3 things?
FLUID: Phospholipid molecules move relative to one another so the membrane changes shape and is flexible.
MOSAIC: Proteins embedded in the phospholipid bilayer have different sizes and shapes, and are arranged randomly like mosaic tiles.
MODEL: The accepted structure is based on experimental and chemical evidence so is a model.
simple diffusion definition
The net movement of particles from a region in which they are highly concentrated to a region in which their concentration is lower until they are evenly distributed.
limitations of the phospholipid bilayer in simple diffusion
simple diffusion occurs through the phospholipid portion of the bilayer - only small, non-polar, lipid-soluble molecules are able to diffuse in this way as the centre of the bilayer is non-polar and hydrophobic.
adaptations of cells for rapid transport across their membranes
large surface area, large number of protein channels or carrier proteins in their membranes.
Importance of membranes within cells
plasma membranes around organelles
- Control passage of materials in or out of organelles.
- Separate organelles from cytoplasm (dif conditions)
- Form an internal transport system - ER/vesicles
- Lysosomes have a membrane to isolate the enzymes in they which would damage other parts of the cell.
- They are surfaces for reactions to happen on - e.g. protein synthesis in RER.
is diffusion an active or passive process?
passive
Which types of proteins are involved in facilitated diffusion?
protein channels and carrier proteins
What is facilitated diffusion?
The passage of molecules or ions down a concentration gradient across a plasma membrane, via specific protein channels or carrier proteins.
Role of protein channels in facilitated diffusion.
Form water-filled (hydrophilic) channels across the membrane.
Specific water-soluble ions can pass through the membrane.
Selective: each opens in the presence of a specific ion. Entry + exit can be controlled.
Role of carrier proteins in facilitated diffusion
Bind to specific molecules, change shape and release the molecule on the other side of the membrane. No extra energy is needed.
Osmosis definition
The passage of water from a region of higher to lower water potential across a selectively permeable membrane.
Where does water move in osmosis?
from areas of higher WP to areas of lower WP
What is the WP of pure water?
0
How can the water potential of cells/ tissues be found?
by placing them in a series of solutions of dif WPs. (serial dilution) When external WP = that of sample there will be no net movement of water.
Make a calibration curve and find the concentration when net movement is 0.
What happens when water potential on either side of a cell membrane are not equal?
water will move across the membrane from the side of higher to lower WP. Cells can burst/ lyse or shrivel due to osmotic gain or loss of water.
Differences between facilitated diffusion and active transport
- facilitated diffusion is a passive process but active transport requires ATP
- facilitated diffusion occurs along a concentration gradient but active transport occurs against.
- facilitated diffusion uses both channel and carrier proteins but active transport only used carrier proteins
role of carrier proteins in active transport
- molecule to be transported binds to the carrier protein and ATP binds on the inside of the cell/ organelle
- ATP is hydrolysed, releasing energy required to change the protein’s shape and move the molecule across the membrane, against its concentration gradient.
