Cell membranes and transport Flashcards
- Why is the accepted model of membrane structure termed “fluid-mosaic”?
It is fluid because the phospholipids can move around freely within the membrane and the proteins form a mosaic pattern within the bilayer
- What do the terms hydrophilic and hydrophobic mean?
Hydrophilic: Attracted to water and polar molecules
Hydrophobic: Repels water and polar molecules
- Explain why phospholipids form a bilayer.
The hydrophobic fatty acid tails orient inwards towards each other, the hydrophobic head remains on the outside to act as a barrier between the fluid around and in the cell.
- What is an intrinsic protein?
A protein that passes through from the internal membrane to the external surface.
Some are transport, some are enzymes.
- What is a channel protein?
A tube intrinsic protein which has a hydrophilic lining, which facilitates polar molecules to pass across the plasma membrane. Some channel proteins are like gates and close. Some carrier proteins spin to facilitate polar molecules. Pumps take part in active transport
- What is an extrinsic protein?
A protein that is embedded on the surface and does not pass through the entirety of the phospholipid bilayer.
Some are cell receptors for binding to insoluble hormones or form recognition sites (antigens)
- What determines the position of a protein in the membrane?
The polarity of the protein determines if it sits through (intrinsic) or on (extrinsic) the phospholipid bilayer.
- What is a glycolipid?
A phosphate head with a short branched carbohydrate chain chemically bonded to it facing out. They act as receptors of certain molecules such as hormones for cell interactions.
- What is a glycoprotein?
It is a short branches carbohydrate chain attached which acts as an antigen for cell recognition.
- What is the collective name for glycolipids and glycoproteins on the outer surface of a membrane?
The glycocalyx layer
- Define “diffusion”.
The passive transport of molecules or ions across a selectively permeable membrane down the diffusion gradient (high conc region to low conc region).
- What feature of the phospholipid bilayer prevents polar and charge particles crossing a membrane?
The inner fatty acid tails (hydrophobic) repel polar molecules, making it difficult for the particles to cross.
- Name two gases and two vitamins that can cross the membrane by simple diffusion.
- CO2 and O2
- Vitamin A, Vitamin K (All vitamins can except B and C)
- Explain how lipid solubility and the size of the molecule affect the rate of diffusion.
- More lipid-soluble molecules can dissolve more easily into the phospholipid bilayer and diffuse faster.
- Smaller molecules diffuse faster because they have more energy.
- Explain how the surface area of a cell membrane affects the rate of diffusion.
Increasing the surface area increases the rate of diffusion of water molecules and non-polar molecules.
- What adaptation of the cell membrane increases surface area?
Folds/projections like microvilli
- How does diffusion path affect the rate of diffusion?
Shorter diffusion pathway = faster rate of diffusion
- How does concentration gradient affect the rate of diffusion?
Larger concentration gradient increases the rate of diffusion.
- Explain how temperature affects the rate of diffusion.
Temperature increases the kinetic energy of both the phospholipids, which increases permeability, and the kinetic energy of molecules. This increases the rate of diffusion.
- Give a BRIEF (no more than 5 bullet points) account of the investigation into the effect of temperature on permeability of beetroot membranes.
- Bathe beetroot discs in different temperatures, 5 ml of distilled water, controlled in a thermostatically controlled water bath.
- Leave for 30 minutes and take samples into cuvettes.
- Using a colourimeter, measure the absorbance of the solution and record results.
- Beetroot cells contain red pigments called betalains.
- The rate is determined by the concentration of betalains released, which can be found using a calibration curve.
- Sketch a graph of the investigation results and explain them.
Sigmoid-like curve (levels off at 100% absorbance).
1) As temp increases, phospholipids gain more kinetic energy and vibrate so that the temporary spaces between increase => which increases the permeability.
2) As temperatures increase past the optimum of the extrinsic and intrinsic proteins, they denature, causing large gaps to form in the membrane => increasing permeability.
3) As temperatures become very very high the absorbance will level off once all the betalain has been released.
- State two differences and two similarities between simple and facilitated diffusion.
Differences:
- Simple does not require channel or carrier proteins, but facilitated does.
- Facilitated diffusion levels off at higher concentrations as only so many can diffuse through the proteins but simple rate is only limited by the surface area of the membrane as it goes through the phospholipid bilayer.
Similarities:
- Both are passive processes
- Respiratory inhibitors thus have no effect on rate
- Give the names of two substances that could be transported by facilitated diffusion.
Small charge particles through channel proteins: Calcium ions
Large polar molecules through carrier proteins: Glucose and Amino Acids
- What is co-transport? Give an example.
Sodium-Glucose cotransport at the ileum.
1) Glucose and sodium are deposited into the cell via symport carrier proteins. High to low
2) To maintain Na+ gradient, Na+ is actively transported out cell into the Blood to keep it low so that S-G are continually deposited in from the extracellular fluid.
3) Passive transport of Glucose and Sodium into the cell, Glucose conc is higher inside the cell than it is in the constantly flowing blood. Thus, Glucose is facilitated and diffuses into the blood.
