Y12 MS - Transport Across Membranes (Complete) Flashcards
What is shown by A?
Phospholipid
A1 - Hydrophilic phosphate head
A2 - Hydrophobic fatty acid tails
What is shown by B?
Glycolipid
What is shown by C?
Glycoprotein
What is shown by D?
Carbohydrate
What is shown by E?
Cholesterol
What is shown by G?
Channel protein (intrinsic)
What is shown by F?
Extrinsic protein
How are the phospholipids arranged in the cell membrane?
In a bilayer
- Hydrophilic phosphate heads face outwards
- Hydrophobic fatty acid tails face inwards
Are the phosphate heads and fatty acid tails or phospholipids polar or non-polar?
Phosphate heads - polar
Fatty acid tails - non-polar
Why are the fatty acid tails in the cell membrane important?
The fatty acid tails are hydrophobic so prevent water soluble molecules from crossing the membrane
Therefore, a barrier is created between the cytoplasm and the fluid outside of the cell
True or false? The membrane is fluid
The membrane IS fluid
The phospholipids move laterally meaning that the cell membrane can is fluid
What is the function of channel proteins?
Channel proteins span the membrane (intrinsic) and form water filled channels
This means that small, water soluble molecules are able to diffuse across the channel proteins and into or out of the cell
What is the function of carrier proteins
Carrier proteins have a binding site for a specific chemical and transport them across the membrane
The cell membrane is ———— —————. What does this mean?
The cell membrane is selectively permeable so only allows some chemicals to cross the membrane
The cell membrane is modelled by the fluid mosaic model. What does this mean?
Fluid - the phospholipids are able to move around laterally
Mosaic - the proteins within the phospholipid bilayer form a scattered, mosaic pattern when viewed from above
Phospholipids can form a bilayer. What is the other arrangement of phospholipids which can be formed?
A micelle
This is formed when phospholipids are shaken / mixed with water
What is the function of glycolipids and glycoproteins?
They are used as cell recognition sites
The pattern of the carbohydrate units act as antigens on the surface of the cell
What is the function of cholesterol in the cell surface membrane
Cholesterol decreases the fluidity of the membrane by linking phospholipids together, making the structure more stable so it doesn’t split apart
What is diffusion
The net movement of a substance down a concentration gradient
What is Ficks Law?
The rate of diffusion is proportional to
(Surface area x concentration gradient) / diffusion distance
What are the common adaptations for to increase the rate of diffusion
Large surface area
Short diffusion distance
Maintained diffusion gradient
What is simple diffusion in the cell membrane
Where small, non-polar molecules pass across the cell membrane by diffusion (intrinsic proteins not required)
What type of molecules can move across the cell membrane by simple diffusion
Small and non-polar e.g oxygen, fatty acids, carbon dioxide, fat-soluble vitamins
Where does facilitated diffusion occur in the cell membrane
Intrinsic proteins in the cell membrane facilitate (help) the movement of polar molecules across the membrane
- Uses channel / carrier proteins
What are the similarities and differences between simple and facilitated diffusion
Similarities:
- Require a concentration gradient
- Do not need energy (passive processes)
- Result in the movement of a substance across the cell membrane
Differences:
- Simple diffusion involves non-polar molecules whereas …
- Facilitated diffusion requires gated / permanent protein channels whereas …
- Facilitated diffusion is specific whereas …
- Simple diffusion is slower whereas …
- Facilitated diffusion has a maximum rate due to the limited number of proteins whereas …
What is osmosis
The passive movement of water from a high water potential to a lower water potential across a selectively permeable membrane
True or false? A high water potential means the solution is concentrated
False - high water potential means it is dilute
What does an isotonic solution mean
It has the same water potential
What happens when animal cells are placed in distilled water and why does this occur
Distilled water has a water potential of 0 so water moves into the cells by osmosis. This results in them swelling and bursting as animal cells do not have a cell wall to keep them rigid
What happens to animal cells when they are placed in a concentrated salt solution and why does this happen
The concentrated salt solution will have a lower water potential than inside the cells so water will move out of the cells by osmosis. This will result in the cells shrinking and shrivelling because animal cells do not have a cell wall to keep them rigid
What happens when a plant cell is placed in distilled water and why is this
Distilled water has a water potential of 0 so water will move into the cell by osmosis. This will result in the cell stiffening but overall maintaining its shape as plant cells have a cell wall to keep them rigid and prevent them from bursting
What will occur when a plant cell is place in a concentrated salt solution and why is this
The concentrated salt solution will have a lower water potential so water will move out of the cell by osmosis. This will result in a process called plasmolysis where the cell body shrinks and pulls away from the cell wall, leaving spaces between the cell membrane and cell wall. This is because the cell wall remains rigid and does not allow the cell to shrink
What is active transport
The movement of molecules against a concentration gradient from an area of low to high concentration. This requires energy in the form of ATP made by cell respiration in the mitochondria
What does is mean that channel proteins don’t have a fixed shape (unlike channel proteins)
The carrier protein can switch between two shapes, allowing it to open on either side of the membrane
How does active transport work
Active transport requires carrier proteins
Carrier proteins are specific to particular molecules or ions
When these molecules or ions bind to the carrier protein, ATP is needed to make the carrier protein change shape to allow the transfer of these substances across the cell membrane
The ATP is hydrolysed (producing ADP, an inorganic phosphate and energy) to release energy in order for this to occur
What is co-transport
The coupled movement of substances across a cell membrane by a carrier protein (involving a combination of facilitated diffusion and active transport)
What is an example of co-transport
The co-transport of sodium ions and glucose on the cell surface membrane of epithelium cells lining the ileum
