Chapter 4 Flashcards
What are the primary functions of cellular membranes?
- Compartmentalization 2. Scaffold for biochemical acivities 3. Providing selectively permeable barrier 4. Transporting solute 5. Responding to external stimuli 6. Intervellular interaction 7. Energy transduction
What is the benefit of membrane Compartmentalization within the cell?
Enables different cellular processes to occur without external interference (can be regulated independently)
How do cell membranes act as a scaffold for biochemical activities
Basically, molecules can be kept inside membranes to increase the chances of certain biochemical interactions occurring (anchoring them)
How do plasma membranes in cells transport solutes
Often membranes are barriers between areas of high and low solute concentration. Transport machinery in the membrane allow the space inside the membrane to accumulate materials without them floating away
How do cellular plasma membranes respond to external stimuli
In a process known as signal transduction. Receptors on the membrane can react to environment factors (or molecules), causing an internal response (ex cell lysing)
How do cellular plasma membranes take part in Intercellular interaction
Allows cells to recognize one another, adhere or exchange materials.
How do cellular plasma membranes take part in energy transducton
The membranes of mitochondria and chloroplasts hold all the enzymes that break down carbs/fats and sunlight energy!
Which type of human cells are most advantageous for studying plasma membranes and why?
Red blood cells because they are anucleate and do not contain organelles. They are also very easy to obtain
What did Gorter and Grendel do in 1925 when they measured the surface area of the lipids in red blood cells? What conclusion could that lead to?
When extracting the lipids and measuring the surface area covered by the lipids they realized it was double the surface area of the cell itself. One can infer that there must then be two lipid layers.
Why must the plasma membrane of the cell be dynamic?
Movement could not occur otherwise. As well, the cell wouldn’t be able to divide.
What type of molecule is this? Name the components labelled.

Membrane lipid.
A- Hydrophylic head
B - Hydrophobic tail
C - Choline group
D - Phosphate group
E - Glycerol
F - Fatty acid “legs”
Why is it assumed that the lipid bi-layer must have polar and non-polar ends?
Because simple non-polar fatty acids wouldn’t bond to the aqueous environment of the cell (they are hydrophobic). Therefore, the two hydrophobic fatty acid layers face each other with the hydrophilic ends (phosphate ends) facing out
TRUE OR FALSE: Phosphate is non polar
FALSE. it is polar
What gives the lipid bi-layers it’s polar ends?
The presence of the polar molecule Phosphate
How does the cohesion of bilayers help with the functions of the cell
Fatty acids naturally want to stick together in an aqueous environment, and therefore cells can easily mould and shape themselves to their environment, fuse together, and put themselves back together after breaking
If plasma membranes are so good at cohesion, how do the membranes allow molecules through
Through pores/channels lined with polar proteins, preventing the fatty acids on either side from joining together
What is the “unit membrane” concept?
The idea that all membranes have the same basic structure: made of phospholipids with proteins lining them (though ratios/compositions may change)
What is the evidence to suggest that the proteins of plasma membranes are EMBEDDED in the membrane as opposed to lining it. How was that information acquired?
- Proteins isolated have hydrophobic regions
- Some proteins have been found to have portions that stick through BOTH sides of the lipid bilayer (transmembrane proteins)
- Some proteins have been shown to be mobile in the membrane - Images of the membrane show transmembrane proteins This research was performed by analyzing the individual proteins (and amino acids) present in the plasma membrane, identifying things such as hydrophobic amino acid sequences
What is the “fluid mosaic model”
The idea that the core lipid bilayer exists in the fluid state, capable of movement, with proteins penetrating the lipids
Lipid and protein components of the plasma membrane are bound by _____ bonds
non-covalent bonds
What does it mean to say that membranes are amphipathic?
Have hydrophilic AND hydrophobic elements
Describe the three main types of membrane lipids
Phosphoglycerides - Diacylglycerides with small functional head groups linked to the glycerol backbone by phosphate ester bonds
Sphingolipids - ceramides formed by the attachment of sphingosine to fatty acids
Cholesterol - smaller and less amphipathic lipid (only found in animals)
What is the function of cholesterol in the membrane? Where are they found?
Embedded in lipid bilayer, provide structural integrity to the cell
If a lipid bilayer is present (isolated) in an aqueous solution, it will form a ____ called a _____
Sphere called a liposome

