A1CC1 Chapter 3 - Cell Membranes and Transport Flashcards
What forms the phospholipid bilayer?
Phosphate head (Hydrophillic)
Fatty Acid Tail (Hydrophobic)
Within the cell membrane proteins can be either…
Extrinsic or Intrinsic.
What is the difference between extrinsic and intrinsic proteins? Give some functionalities too.
Extrinsic = Found on the surface of the bilayer. They act as receptors for hormones and recognition sites.
Intrinsic = Extend across both layers. These act as channels and carrier proteins for the transport of molecules.
Name 8 structures found in the phospholipid bilayer.
Glycolipids
Glycoproteins
Extrinsic Proteins
Phosphate Head
Fatty Acid Tails
Channel Protein
Carrier Protein
Cholesterol
In the fluid mosaic model, state and explain the role of cholesterol, glygoproteins and glycolipids.
Cholesterol = Stabilisation
Glycoproteins = Antigens
Glycolipids = Receptor sites for molecules like hormones
What does the term ‘Fluid Mosaic Model’ actually mean?
Fluid because phospholipids are free to move, and mosaic due to the random assortment of protein molecules.
What affects the molecules ability to cross membranes?
Their properties.
What is the difference between polar vs non-polar molecules and their ability to cross membranes?
Non-polar molecules (like Vitamin A) and smaller molecules (like oxgyen) are able to dissolve directly into the fatty acid tails and diffuse across the membrane.
Polar molecules (like glucose) require active transport via a transport protein as they cannot dissolve directly into the fatty acid tails. (This requires ATP).
What is simple diffusion?
An example of passive transport where molecules move from a high concentration to a lower concentration until equally distributed.
What are the two factors affecting the rate of diffusion?
- Energy (either increasing or decreasing)
- Distance of diffusion
State and explain what factors affect diffusion (5)
- The concentration gradient
- Diffusion distance = takes less time for molecules to diffuse a shorter distance
- Surface area of membrane = The larger the area, the more molecules can diffuse in a given time.
- Thickness of exchange surface = Takes less time for the molecules to diffuse a shorter distance.
- Temperature = An increase in temperature results in molecules having more kinetic energy. This means they move faster and collide with the membrane more frequently.
What is facilitated diffusion?
Facilitated diffusion is a passive process requiring no ATP where it relies instead on the kinetic energy of the molecules involved. It occurs via transport proteins found within the membrane that assist the movement of polar molecules across the membrane.
What are the two types of transport protein?
- Channel proteins = Pores with hydrophillic lining allowing charged ions and polar molecules to pass through. They are specific, and can be opened or closed to regulate the movement of particular molecules.
- Carrier proteins = Allow diffusion across the membrane of larger polar molecules such as sugars and amino acids.
Where do the ions bind to on the carrier protein?
Binding site.
What is active transport?
A form of transport requiring ATP to transport molecules against the concentration gradient.
What affects the rate of active transport?
Anything affecting the respiratory rate as this is what produces ATP. Eg: Cyanide is a respiratory inhibitor hence inhibiting aerobic respiration therefore the production of ATP.
Active transport uses carrier proteins that span the membrane.
From your knowledge, what affects the rate of active transport?
- Anything affecting respiratory rates.
- The number of carrier proteins along a membrane
What does a graph with the rate of uptake against the concentration difference across the membrane look like for a process involving active transport.
Steady incline, then a peak is reached as another variable like the number of carrier proteins is saturated. However, when a respiratory inhibitor is added, the rate falls of rapidly.
What is cotransport?
The transportation of two molecules together. Eg: Glucose and Sodium Ions.
Where is cotransport used for?
The mechanism for glucose is absorbed in the ileum of mammals.
Explain this entire process for glucose absorption in the ileum.
- Sodium Ions are actively transported out of epithelial cells lining the ilium into the blood, creating a low concentration of sodium ions within the cells.
- The higher concentration of sodium ions in the lumen of the gut, compared to the epithelium cells, causes sodium ions to diffuse into the epithelial cells via a co-transport protein. As they do so they couple with glucose molecules carrying them with them.
- Finally, glucose molecules pass via facilitated diffusion into blood capillaries and sodium ions by active transport.
What is a solute?
A substance that is dissolved in a solvent.
What is water potential?
Represents the tendency for water to move into or out of a system and the pressure is created by water molecules.
What is osmosis?
The net passive diffusion of water molecules across a selectively permeable membrane from a region of higher water potential to an area of lower water potential.
What is pressure potential?
This represents the pressure exerted by the cell contents on the cell wall. It can be 0kPa or higher.
What does Turgid mean?
This means the plant cell can hold no more water, as the cell wall cannot expand further.
What is a hypertonic solution?
This has a lower water potential relative to the solution inside the cell, due to the presence of solutes.
What is a hypotonic solution?
This has a higher water potential relative to the solution inside the cell, due to the abscence of solutes.
What is an isotonic solution?
This has the same water potential relative to the solution inside the cell.
What happens to the water potential when you add solutes to a solution?
The water potential decreases.
What is the equation for water potential?
Water potential = solute potential + pressure potential
If a cell is hypotonic then which direction does water flow?
Water flows into the cell because the solution has a higher water potential.
If a cell is hypertonic then which direction does water flow?
The water flows out of the cell because the solution has a lower water potential than the cell.
If a cell is isotonic what does this mean?
There will be no net water movement into or out of the cell due to the water potential of both solutions to be the same.
What are the three stages of plasmolysis?
- Turgid
- Incipient Plasmolysis
- Plasmolysed
What does a turgid plant cell look like?
The cytoplasm is pushed against the cell wall.
This is the highest turgor pressure.
What does incipient plasmolysis look like?
The cytoplasm has just started pulling away from the cell wall.
What does plasmolysed look like?
The cytoplasm has now completely pulled away from the cell wall.
Why is the concept of turgor important for a plant cell?
Turgor is important to plants, especially young seedlings, because it provides support, maintains their shape and holds them upright.
How can we measure incipient plasmolysis (experiment)?
We place plant cells into solutions with varying solute potentials, then look at the cells under a microscope.
When plasmolysis has reached 50%, incipient plasmolysis has been reached, and the external sucrose solution concentration must be equal to the internal solute concentration of the onion tissue (as there is no net movement of water overall).
What is the definition of solute potential?
This represents the osmotic strength of a solution. It is the reduction in water potential due to the presence of solute molecules. It is 0kPa or negative.
What do we consider when talking about animal cells and osmosis?
Osmosis affects the cell wall but the animal cells do not have a cell wall meaning that the water potential must equal the solute potential.
What is it called when a red blood cell is placed into a hypotonic solution?
Water enters by osmosis and they burst.
This process is called haemolysis.
What is is called when a red blood cell is placed into a hypertonic solution?
Water leaves the cells via osmosis.
The red blood cell is said to be crenated.
How can we investigate the permeability of membranes?
Beetroot. They contain vacuoles containing a red pigment called betacyanin.
What affects the rate of betacyanin diffusing out of the vacuole?
Temperature
Presence of organic solvents
What is the method of this beetroot experiment?
- Beetroot discs are cut of equal size and volume using a borer, then washed and blotted dry.
- Discs are placed into water, and the quantity of betacyanin that leaked through the membrane was measured using a colorimeter.
- This experiment is then repeated at different temperatures.
How do colorimeters work?
They measure the % transmission of a specific wavelength of light, eg: 450nm, through a sample of liquid. The darker the sample, the lower the transmission.
What are the results of the effect of temperature on the permeability of membranes?
As temperature increases, the %transmission of light decreases linearly.
What is bulk transport?
This is where the cell transports materials in bulk into the cell (endocytosis) or out of the cell (exocytosis).
What is endocytosis?
The engulfing of the material by infolding of the plasma membrane bringing it into the cell enclosed within a vesicle.
State and explain the two types of endocytosis?
- Phagocytosis = The process of where a cell can obtain solid materials that are too large to be taken by other methods. Eg: Phagocytes (white blood cells) destroy bacteria and remove cell debris by phagocytosis.
- Pinocytosis = The process by which the cell obtains liquid materials. It is similar to phagocytosis but the vesicles produced are smaller.
What is exocytosis?
This is the reference to substances leaving a cell after being transported through the cytoplasm in a vesicle. Digestive enzymes are often secreted this way.
