Membrane Structure

Question 1

What are cell membranes made of?

Answer 1

a phospholipid bilayer with proteins moving freely within it

Question 2

What are Phospholipids?

Answer 2

basic component of membranes that consist of a polar hydrophilic head (composed of a glycerol and a phosphate molecule) and two non-polar hydrophobic fatty acid tails

Question 3

Why are Phospholipids Amphipathic?

Answer 3

because they have both a hydrophilic region and a hydrophobic region

Question 4

List 2 properties of the Phospholipid Bilayer?

Answer 4

1. fluidity of the bilayer allows for the spontaneous breaking and reforming of membranes (endocytosis/exocytosis)
2. Hydrophilic / hydrophobic layers restrict the passage of many substances

Question 5

What is the role of Cholesterol in the Phospholipid Bilayer?

Answer 5

Cholesterol is an amphipathic molecule found only in animal cell membranes.

Cholesterol controls and maintains the fluidity and rigidity of the membrane. It often works to reduce fluidity and permeability of the membrane to restrict hydrophilic particles

Question 6

Describe Integral and Peripheral Proteins

Answer 6

Peripheral Proteins —- are proteins that are temporarily attached to the outer surface of the membrane which also only. only partially go through the membrane. They serve to allow materials to pass from one side of the membrane to another.

Integral Proteins — are proteins permanently embedded in the membrane which also go all the way through the membrane. They allow ions or molecules to move from one side of the plasma membrane to the other

Question 7

What are channel proteins?

Answer 7

Proteins that allow materials to diffuse in and out of a cell

Question 8

What is the role of the carbohydrate on the Glycoprotein on the phospholipid bilayer?

Answer 8

Give the cell its identity

Question 9

State the 7 functions of Membrane Proteins

Acronym: (Jet Rat)

Answer 9

Functions of Membrane Proteins

Membrane proteins can serve a variety of key functions:

1. Junctions – Serve to connect and join two cells together
   (e. g Intercellular joining)
2. Enzymes – a membrane protein that is embedded into the membrane can sometimes be an enzyme involved in several metabolic processes
   (e. g of protein — Cytochrome oxidase)
3. Transport – Responsible for facilitated diffusion and active transport
   (e. g of protein — Calcium pump used in active transport of calcium ions)
   (e. g another example of Protein — Cytochrome C used in electron transport)
4. Recognition – May function as markers for cellular identification (cell recognition)
   (e.g Glycoprotein – used to allow our immune system to recognize our cells. However, also disadvantageous cause
   Viruses can recognize glcyoprotein)
5. Anchorage – Attachment points for cytoskeleton and extracellular matrix (the network of macromolecules found outside of cells — Place where protein molecules attach to give support to the cell)
6. Transduction – Functions as receptors for peptide hormones
   (e. g Insulin receptor)

Question 10

What does the Fluid Mosaic Model Indicate?

Answer 10

It indicates:

1. That Phospholipid bilayers are fluid, in that the phospholipids are in constant motion relative to one another
2. Proteins are embedded within the membrane

Question 11

Describe what the Davson Danielli Model showed?

Answer 11

• Developed by Davson and Danielli in 1935 in an attempt to describe the position of proteins, the phospholipid bilayer model showed phospholipids in the center of the membrane with layers of protein on either side. The two reasoned that since chemical analysis of membranes showed that they were composed of phospholipid and protein and that evidence regarding red blood cells pointed to the prospect of plasma membranes being in the form of a phospholipid bilayer, this model must be accurate.

Question 12

Describe how the Davson and Danelli Model was falsified

Answer 12

Though high magnification electron micrographs in the 1950s seemed to support Davson and Danellis model, the accumulating of evidence in the 1950s and 1960s falsified it. This was done, most notably, through the emergence of evidence from freeze fracturing, a method in which scientists pulled the two phospholipid layers apart. Freeze fracturing electron micrographs showed that there are proteins embedded in the membrane and that the bilayers sometimes extended from one side to another. The falsification of the Davson Danelli model led to the creation of a new model in 1966, the Singer and Nicolson model today referred to as the fluid mosaic model.

Question 13

State 3 assumptions of the Davson and Danneli model were flawed

Answer 13

1. It assumed all membranes were of a uniform thickness and would have a constant lipid-protein ratio
2. It assumed all membranes would have symmetrical internal and external surfaces
3. It did not account for the permeability of certain substances