Topic 2 - B Flashcards
What is the fluid mosaic model?
- Arrangement of molecules in the cell membrane
- Phospholipid bilayer is fluid because it is constantly moving.
- Because the fatty acids are hydrophobic and unsaturated.
What is the role of cholesterol in cell membranes ?
- Gives membranes stability
- Fits between phospholipids and binds to hydrophobic tail which causes them to pack more closely
- Without it cells would burst as it would be too fluid
Why is fluidity needed in cell membranes?
- Diffusion of substances across the cell membrane
- Membrane moves to change shape e.g. phagocytosis
What is the role of extrinsic (peripheral) proteins in cell membranes?
- Don’t span the entire membrane
- Can attach onto an intrinsic (integral) protein
- Communication and cell signalling
- Transfer molecules within the membrane
The difference between cholesterol in hot and cold temperature?
- When HOT it interacts with fatty acid tails to decrease fluidity
- When COLD it prevents membrane from solidifying to maintain fluidity
What are the roles of glycoproteins in cell membranes?
- Proteins with carbohydrates attached
- Important in cell recognition and immunity
- Structural support (found in collagen)
Describe the roles of carrier proteins in cell membranes?
- Used for active transport and facilitated diffusion of molecules
Describe the roles of channel proteins in cell membranes?
- Used as a pathway for facilitated diffusion of large (sugars) or charged (ions) molecules
Why can’t ions diffuse through cell membranes?
Why can’t large molecules diffuse through cell membranes?
- LIMITATIONS OF PHOSPHOLIPID BILAYER
- Charges are repelled by hydrophobic tails in the interior of the phospholipid bilayer
- They are too big as the membrane is selectively permeable and they would be considered impermeable
What are intrinsic proteins?
- Do span the entire membrane
- Carrier and Channel proteins
What is the definition of simple diffusion?
The passive, net movement of molecules or ions from an area of high concentration to an area of low concentration down a concentration gradient until dynamic equilibrium is reached.
What is Fick’s Law?
rate of diffusion = surface area x difference
in conc.
/
diffusion pathway
(membrane thickness)
How does surface area affect rate of diffusion?
- More membrane means more opportunity for net movement
- Increases rate of diffusion
How does diffusion pathway (membrane thickness) affect rate of diffusion?
- The thinner the pathway the shorter distance the molecules have to travel
- Increases rate of diffusion
How does the difference in conc. affect rate of diffusion?
- The greater the difference
- The faster the rate of diffusion
What is the definition of facilitated diffusion?
The passive, net movement of large molecules or ions through a carrier or channel protein from an an area of high concentration to an area of low concentration until dynamic equilibrium is reached.
What are the similarities of facilitated diffusion and simple diffusion?
- Passive process
- Polar molecules move down a concentration gradient from an area of high concentration to an area of low concentration
- Dynamic equilibrium is reached
State the differences of facilitated diffusion and simple diffusion?
- Facilitated occurs at specific points of membrane which has channel or carrier proteins whereas simple diffusion occurs all over the membrane.
- Simple diffusion involves small, non-charged molecules whereas facilitated diffusion involves large (sugars) and charged (ions) molecules.
- Channel proteins only allow water soluble molecules through
- Carrier proteins only allow specific targeted molecules through
What is the definition of Osmosis?
The net movement of water from a region of high water potential to a region of low water potential through a partially permeable membrane until dynamic equilibrium is reached.
Explain water potential?
- Water potential is the liklihood of water molecules moving in or out of a cell
- It is measured in kiloPascals
- Pure water has the highest water potential value at 0 kPa
- Solutions that have a lower water potential than water are negative
- The greater the number of water molecules, the higher the water potential
What is the definition of active transport?
The movement of molecules or ions from an area of low concentration to an area of high concentration, against a concentration gradient - energy in the form of ATP is required.
How does active transport happen?
- A phosphate group from the molecule of ATP attaches itself onto the carrier protein
- Causing it to change shape
- As the protein changes shape the phosphate group pumps the molecule or ion into the cell
What is endocytosis?
- The process which moves macro molecules or large particles into a cell
- E.G. phagocytosis of pathogens and large particles
- E.G. pinocytosis of water and solutes in the water
What is exocytosis?
- The process which moves macro molecules and large particles out of a cell
- E.G. (reverse of endocytosis) materials inside a cell are packed in a vesicle which fuses to the plasma membrane
Explain the roles of guard cells?
- They control the stomata being opened and closed
- Allow diffusion of gases in and out the cell
- E.G if a cell is filled with water it is turgid and the stomata are opened to lose water and make the cell flaccid
What is a protoplast?
- The nucleus and cytoplasm of a plant cells including the organelles it contains
Explain the concept of incipient plasmolysis?
- Midpoint whereby no water is moving in or out of cell by osmosis
- Plants cells have a turgo pressure of 0
Describe plasmolysis?
- When the cytoplasm shrinks away from the cell wall as a result of osmosis
- Protoplast lost contact with the cell wall and loss of water makes cell plasmolysed
Explain a hypotonic solution?
- When a solution has a higher water potential than the cell immersed in it
- A tissue placed in their would gain mass
Explain a hypertonic solution?
- A solution with low water potential than the cell immersed it in
- A tissue placed their would lose mass
Describe the relationship between surface area and volume ratio?
- As organisms get larger their surface area: volume ratio get smaller
- A large surface is needed for specialised exchanges surface and circulatory
What are co-transporters?
- They are a type of carrier proteins that can move 2 molecules at the same time
- They can use the concentration gradient of one molecule to move the other against its concentration gradient
- Very important for the absorption of glucose and amino acids
Explain the process of glucose re-absorption?
- Sodium ions actively transported out of epithelia cells into blood stream (NA+/K+ pump are used)
- This creates a concentration gradient
- Sodium ions diffuse down a concentration gradient from lumen to epithelia via Sodium-Glucose symporter
- Glucose is transported across into the epithelial cell
- High concentration of glucose in epithelial cell so glucose will move into blood stream by facilitated diffusion using a glucose transporter
What is the ratio of the sodium - potassium pump?
- Pump moves sodium in one direction ad potassium in the other at a 3:2 respective ratio
Explain the functions of ATP the sodium - potassium pump regarding sodium?
- ATP is bound to the protein which has a high affinity for sodium and binds to 3
- ATP is hydrolysed into ADP and the protein is phosphorylated by a phosphate changing its tertiary structure
- Now the sodium is in the other side of the membrane
Explain the functions of ATP the sodium - potassium pump regarding potassium?
- Protein now has a low affinity sodium and releases them
- But has a high affinity for potassium and binds with 2
- Causes dephosphorylation of the protein so it revert to its original shape
- Now the potassium is on the other side of the membrane
