Cell Membrane Structure 1.3

State the molecule that regulates the fluidity of cell membranes.

Cholesterol

Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes (7 marks).

Construct a paragraph explaining these concepts - Hydrophilic is attracted to water and hydrophobic is not. Hydrophilic heads and hydrophobic tails are found in phospholipids. Hydrophilic heads face outwards. Hydrophobic tails face inwards. Cholesterol, which is amphipathic, is embedded between the phospholipids. Integral proteins are embedded in membranes because of hydrophobic properties. Peripheral proteins are on the membrane surface due to being hydrophilic.

Cell membranes separate aqueous environments in cells. Explain how the properties of phospholipids help to maintain the structure of cell membranes (8 marks).

Construct a paragraph explaining these concepts - What does a phospholipid contain? The head is made up of? The tail is made up of? The head is hydro? and the tail is hydro? Hydrophilic molecules are attracted to? Hydrophobic molecules are attracted to? Why is the bilayer fluid/flexible in nature? How does fluidity membranes to change shape?

Name an essential feature of the Davson-Danielli model for membrane structure.

Davson-Danielli define the layer as a lipid sandwiched between 2 layers of protein.

Describe the functions of proteins in cell membranes (4 marks).

Describe means to give a detailed account. A description is not an explanation. This means pick 4 cell membrane proteins and describe their functions. Integral and peripheral do not count - you need specific examples.

Be able to distinguish between the Davson-Danielli and Singer-Nicholson model via a diagrammatic picture.

Study pics of both models.

Explain how electron micrographs have helped to falsify the Davson-Danielli model of membrane structure (2 marks).

What was the Davson-Danielli model proposed of? What did the Davson-Danielli micrographs illustrate?

State the property of amphipathic phospholipids that enables them to form a bilayer.

Amphipathic is defined as having both a hydrophobic and hydrophilic region.

State one technological improvement, other than enzymatic digestion, that led to the falsification of previous models to determine model of membrane structure.

Freeze-fracturing

The cell membrane model proposed by Davson-Danielli was a phospholipid bilayer sandwiched between 2 layers of globular proteins. Which evidence led to the acceptance of the Singer-Nicholson model?

Placement of integral and peripheral proteins

List evidence that falsifies the Davson-Danielli model.

Presence of globular proteins within the phospholipid bilayer. Non-polar amino acids cause proteins to remain embedded in membrane. Remember, Davson-Danielli indicated that membrane proteins remained stationary.