2B - Cell Membranes Flashcards
What are the different types of membrane?
- Cell membranes
* Organelle membranes
Do all cells have a cell membrane?
Yes
What type of cells also contains organelle membranes?
Eukaryotic cells
What is the function of cell surface membranes?
Control what goes in and out of cells.
What term is used to describe the way in which cell membranes control what goes in and out of cells?
Partially permeable
What are the types of molecule in cell membranes?
- Lipids (mainly phospholipids)
- Proteins
- Carbohydrates
How do carbohydrates fit in the cell membrane?
They attach to proteins or lipids (glycoproteins and glycolipids).
What is the model used to describe cell membranes?
Fluid mosaic model
Describe the fluid mosaic model.
- Continuous phospholipid bilayer -> These are constantly moving (thus “fluid”)
- Cholesterol molecules are inside the bilayer
- Channel, carrier and receptor proteins are either fixed or can move through the bilayer
- Polysaccharides attach to some proteins and lipids to form glycoproteins and glycolipids
Name all of the individual components of a cell membrane.
- Phospholipids
- Cholesterol
- Proteins -> Channel, Carrier and Receptor
- Glycoproteins
- Glycolipids
What is the role of receptor proteins in the cell-surface membrane?
- Allow the cell to detect chemicals released from other cells.
- These chemicals signal for the cell to respond in some way.
Give an example of how receptor proteins work.
Insulin binds to receptor proteins on liver cells, which tells them to absorb glucose.
Explain why the cell-surface membrane can be described as having a fluid mosaic structure.
- “Fluid” -> The phospholipids (and some other molecules) in the bilayer can move around freely.
- “Mosaic” -> The phospholipids, proteins and other molecules are arranged in a mosaic-like pattern.
What is the role of phospholipids in cell-surface membranes?
Arrange themselves in a bilayer, which acts as a barrier for water-soluble substances.
Why do phospholipids arrange themselves in a bilayer in cell-surface membranes?
- Have a hydrophilic head and hydrophobic tail
* In water, a bilayer forms with the heads facing out and the tails facing in
Why does the phospholipid bilayer in cell-surface membranes not allow water-soluble substances to pass through it?
The centre of the bilayer is hydrophobic (that’s where the hydrophobic tails are).
Which parts of a phospholipid molecule are hydrophobic and hydrophilic?
- Hydrophobic - Tail
* Hydrophilic - Head
What type of molecule is cholesterol?
Lipid
In what type of cell membrane is cholesterol found?
All types, except bacterial cell membranes.
Where in the cell-surface membrane is cholesterol found and what does this do?
- Between phospholipid molecules
* This restricts the movements of the phospholipids, making the membrane less fluid and more rigid
What is the role of cholesterol in cell-surface membranes?
- The cholesterol between phospholipids restricts their movement and makes the membrane more rigid
- This maintains the shape of cells
In which cells is cholesterol in the membrane especially important?
Cells that aren’t supported by other cells (e.g. RBCs floating freely in the blood)
What experiment can be used to investigate how temperature affects cell membrane permeability?
Beetroot in water experiment
Describe an experiment to investigate the effect of temperature on cell membrane permeability (beetroot).
1) Cut 5 equal sized pieces of beetroot and rinse.
2) Add the pieces to 5 test tubes and add 5cm3 of water to each.
3) Place each tube in a water bath at a different temperature (e.g. 10C, 20C, 30*C, etc.) and for the same length of time.
4) Remove the beetroot and keep only the coloured water.
5) Use a colorimeter to measure the absorption of each sample - The higher the absorbance, the more pigment is released, so the higher the membrane permeability.
6) Draw a graph of the results.