A1CC1 Chapter 3 - Cell Membranes and Transport Flashcards
(53 cards)
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.
