1.3 Cell membrane structure

1.3  Cell Membrane structure 

Lesson one: The Phospho-lipid bilayer.

Objectives: Understand what is meant by the ampiphatic phospholipid bi-layer. Understand the role of membrane proteins and cholesterol. Understand that the Singer-Nicholson model for membrane structure has replaced the Davson-Danielli model.

Keywords:

  • Ampiphatic: having a hydrophilic (water-loving) and a hydrophobic end (water-hating)
  • Phospholipid: the backbone molecule of the cell membrane. Made from a phosphate group and two fatty acid chains, joined through glycerol.
  • Integral proteins: proteins which span the cell membrane
  • Peripheral proteins: proteins which are embedded in the surface of a cell membrane

Cell membranes surround all cells, as explained in cell theory. Cell membranes also enclose many eukaryotic organelles, e.g. lysosomes. Some organelles have a double membrane eg. chloroplast, mitochondria, nucleus. Perhaps surprisingly, they all have much the same structure.

image credit: cronodon

image credit: cronodon

  • A: Phospholipid A1 phosphate, A2 fatty acid chains
  • B: Glycolipids
  • C: Glycoproteins
  • D: Carbohydrate group
  • E: Cholesterol
  • F: Peripheral protein
  • G: Integral protein

 

 

 

 

 

Follow slides Slides 1-7 in the powerpoint below

 

[slideshare id=52257087&doc=c-150831160046-lva1-app6891]

Task: Model the cell membrane with plasticine. This is an example from an IB Biology class at the Lincoln school. Can you interpret it?

IMG_0031

Task: Draw the cell membrane, using the Singer-Nicolson fluid mosaic model.

[slideshare id=52022804&doc=c-150824214449-lva1-app6891]

 

Task: Draw the cell membrane from memory. Be careful to use sharp, unbroken lines to show outlines. Label clearly, and indicate the size of the cell membrane (7.5nm thick)

Just for fun: A class challenge! image


Lesson two: Consider the evidence behind the Davson Danielli model (protein sandwich), and the Singer Nicholson (Fluid-Mosaic)

 

Keywords:

  • Ampiphatic: having a hydrophilic (water-loving) and a hydrophobic end (water-hating)
  • Phospholipid: the backbone molecule of the cell membrane. Made from a phosphate group and two fatty acid chains, joined through glycerol.
  • Integral proteins: proteins which span the cell membrane
  • Peripheral proteins: proteins which are embedded in the surface of a cell membrane
  • Fluid-mosaic: term applied to the Singer-Nicholson model, that claims that the phospholipids are free to move, hence fluid. Also that the proteins are interspersed with the phospho-lipids, hence the mosaic. 

Task: Watch the video about the development of the Davson-Danielli model. Summarise the key evidence supporting the Davson-Danielli model.

 

Now watch the second video on the development of the Singer-Nicholson ‘fluid mosaic’ model. Summarise the evidence in support of the this model.

 Discussion Question: What is the purpose of a scientific model like the Davson-Danielli or Singer-Nicholson model?

 

Lesson 3: Transport Across membranes

Objective: Predict how a sodium ion, oxygen, water and a bacteria cross a cell membrane.

Keywords:

  • Diffusion: The spreading out of particles from a high concentration to a low concentration, not requiring energy
  • Faciliated diffusion: Diffusion, that happens through a protein channel (and so can be controlled by gates.
  • Osmosis: The movement of water from a high water potential (low salt concentration) to a low water potential (high salt concentration), across a semi-permeable membrane.
  • Active transport: The movement of particles from a low concentration to a high concentration, against the concentration gradient, requiring energy.

We will use slides 8-22.

 

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