2B Cell Membranes Flashcards
Give 5 roles of a membrane
- Partially permeable barrier
- Has binding sites
- Confers antigenic properties to the cell
- Site of certain reaction
- Compartmentalises different cell reactions in organelles
What is the main constituent of the cell membrane?
Phospholipids
What is the structure of phospholipids like?
It is similar to the structure of other lipids
What is the role of phospholipids in the cell membrane?
- Allow lipid soluble substances to enter + leave the cell
- Prevents water soluble substances from moving
How do phospholipids affect the structure of the membrane?
It makes the membrane flexible and self-sealing
What is the model called to describe the arrangement of the phospholipids in the membrane?
Fluid mosaic model
What is cholesterol?
A fatty substance
What role does cholesterol have in a cell membrane?
- It is hydrophobic - therefore it pulls the tails together
- This adds strength + rigidity to the membrane
What reduces the movement of other molecules in the membrane?
Cholesterol
Why is the structure of membrane called a fluid mosaic model?
- Phospholipids bilayer has proteins embedded in it
- Phospholipids can move freely through the bilayer
What is a glycolipid?
A carbohydrate bound to a lipid
What is a glycolipid like?
The lipid portion is embedded in phospholipid bilayer
Carb portion extends outside cell
What is the role of a glycolipid?
Act as recognition + binding sites
What are the two types of protein in the membrane?
- Intrinsic proteins
- Extrinsic proteins
What is an intrinsic protein?
Span the membrane and act as channel + carrier proteins
What are intrinsic proteins made of?
Protein only
What are extrinsic proteins?
On the surface of the membrane (internal or external)
Act as receptors/enzymes
What are extrinsic proteins made of?
Many have carbohydrates attached, forming a glycoprotein
What is diffusion?
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
What sort of molecules can diffuse across the membrane?
Small, non-polar molecules i.e. oxygen and CO2
Is diffusion passive?
Yes - no energy is required for this process
Is facilitated diffusion passive?
Yes
Where does the energy for facilitated diffusion come from?
The process relies on the kinetic energy of diffusion molecules
Does facilitated diffusion occur up of down a conc. gradient?
down
How does facilitated diffusion occur?
- Through transmembrane channels + carriers
- It has to happen at these specific points
What are protein channels?
Water filled hydrophilic channels
Protein channels are selective, what does this mean for the tendencies of the channel?
The channel will remain closed unless the specific ion is present
What do protein channels let through?
Specific water soluble ions
How does a carrier protein work?
Molecule binds to protein, which causes it to change shape + is then released
What energy do carrier proteins use for the required process?
Only use the kinetic energy of the molecules
Do molecules have to be specific to the carrier protein?
Yes they only let certain molecules through
What is osmosis?
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
What water potential does pure water have?
0
What is water potential measured in?
Units of pressure - kPa
What are the units for water potential?
Psi
What is water potential?
A measure of how pure water is
What reduces the water potential?
The addition of solutes
Water diffuses to _____ water potentials
Lower
What happens when water is going into a cell faster than water is leaving?
The cell becomes turgid
What does turgid mean?
Cell is about to burst
What does flaccid mean?
The cell is how it should be
What does plasmolyzed mean?
The cell has shrunk, there is a lack of water
What are the 3 words to describe the different water potentials in plants?
- Turgid
- Flaccid
- Plasmolyzed
What are the 3 words used to describe the osmosis in animal cells?
- Isotonic
- Hypotonic
- Hypertonic
What does Isotonic mean?
Movements of water are equal
What does hypotonic mean?
More water going in than out
What does hypertonic mean?
More water leaving than going in
Isotonic = ?
Flaccid
Hypotonic = ?
Lysis (the cell bursts)
Hypertonic =?
Crenation
What are all the components of the cell membrane?
- Intrinsic proteins
- Glycolipids
- Phospholipids
- Extrinsic proteins
- Cholesterol
- Carbohydrate branches
- Glycoproteins
What is active transport?
Movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
What supplies the energy for active transport?
ATP
What is an example of active transport?
The sodium/potassium pump found in all animal cell membranes
How does the sodium/potassium pump work?
- Continually uses ATP to actively pump sodium out of the cell and potassium into the cell
- This creates a conc. gradient across the membrane
In the sodium/potassium pump, which in pumped into the cell and which is pumped out?
- Sodium = out
- Potassium = in
In cotransport what are the two directions substances can be moved in?
Symport - same
Antiport - opposite
What is cotransport?
- Carrier proteins can sometimes transport two particles at once
- Both must be present for transport to take place
Is cotransport active or passive?
Often it’s both active and passive as one particle is moved with conc. gradient and the other is moved against it
Give an example of cotransport
The cotransport of a glucose molecule
What is osmosis ?
The diffusion of water molecules across partially permeable membrane,from an area of higher water potential to an area of lower water potential
What is water potential?
The potential of water molecules to diffuse out of or into a solution
What factors affect the rate of osmosis?
- Water potential gradient
- Thickness of the exchange surface
- The SA of the exchange surface
What is the investigation that can be used to investigate water potential?
You can use potato cylinders to measure water potential of a plants tissue.
Firs, make up several solutions of different, known concs. to test the cylinders in.
For this you can use serial dilution technique.
What is the serial dilution technique?
1- Start with initial sucrose conc. of 2m an dilute each solution by a factor of 2 (eg. 1, 0.5 etc)
2- Line up 5 test tube in a rack
3- Add 10cm^3 of initial 2M sucrose solution to first test tube & add 5 cm^3 of distilled water to the four other test tubes.
4- Then, use a pipette & draw 5 cm^3 of solution from the first test tube, add it to distilled water in second test tube & mix solution thoroughly. You now have 10 cm^3 of solution that’s half as conc. as the solution in first test tube.
5- Repeat process three more times to create solutions of 0.5 M, 0.25 M & 0.125 M
What factors affect simple diffusion?
- Concentration gradient
- Thickness of exchange surface
- The surface area
How does the concentration gradient affect the rate of diffusion?
The higher it is the faster rate of diffusion - diffusion becomes slower over time as it reaches an equilibrium
How are epithelial cells adapted for faster diffusion?
Microvilli - projection formed on surface that increase the surface area and therefore increases rate of diffusion
What factors affect facilitated diffusion?
- Concentration gradient
- Number of channel or carrier proteins
How does increasing the number of channel or carrier proteins affect the rate of facilitated diffusion?
Once all proteins are in use diffusion cant take place any faster even if increased concentration gradient so it increases the rate of facilitated diffusion
What are aquaporins?
- Channel proteins that allow facilitated diffusion of water through membranes
- Found in kidneys and reabsorb water that would have been excreted by body
What is active transport?
Movement of molecules from a low to high concentration (against concentration gradient)
What do carrier proteins do in active transport?
- Molecule attaches to carrier protein
- Proteins changes shape
- Molecules moves across membrane
(same as diffusion)
How to carrier proteins in facilitated diffusion and active transport differ?
- Active transport is from low to high concentration
- Active transport requires energy
Where does active transport gain its energy from?
ATP from respiration (hydrolysis into ADP + inorganic phosphate)
What are cotransporters?
Type of carrier protein
What do cotransporters do?
They bind 2 molecules at same time and concentration gradient of q is used to move other molecules against concentration gradient
When active transport takes place does a decreasing concentration gradient affect the rate of active transport?
It is not affected
What is active transport affected by?
- Speed of individual carrier proteins
- Number of carrier proteins present
- Availability of ATP (rate of respiration)
What is an example of co-transport?
Glucose and sodium in the mammalian ileum
How is glucose absorbed into the blood using the sodium potassium pump?
1) Sodium ions actively transport out of epithelial cells into the blood by sodium potassium pump (this creates a a low concentration of sodium inside the cell)
2) Sodium ions can then diffuse from the lumen into the cell using sodium-glucose co-transport proteins
3) This means glucose inside the cell increases where is can then diffuse into the blood through a protein channel by facilitated diffusion
Why cant glucose diffuse into the blood in the first place?
Concentration is to low for diffusion to take place
Which sort of water has the highest water potential?
Pure water
All solutions have a lower water potential than pure water
What is it called if two solutions have the same water potential?
They’re said to be isotonic
How can water potential gradient affect the rate of osmosis?
The higher the water potential gradient, the faster the rate of osmosis
As osmosis takes place, the difference in water potential on either side of the membrane decreases so osmosis levels off over time
How can the SA of the exchange surface affect the rate of osmosis?
The larger the SA, the faster the rate of osmosis
How can the thickness of the exchange surface affect the rate of osmosis?
The thinner the exchange surface, the faster the rate of osmosis
Which practical can you use to investigate water potential?
Serial dilutions (using potato slices)
