Cytoplasmic Membrane and Transport

Question 1

Describe the basic functions of the cytoplasmic membrane.

Answer 1

• It is essentially a barrier separating the inside of the cell (the cytoplasm) from its environment.
• If the membrane breaks, the integrity of the cell is destroyed, cytoplasm leaks into the environment, and the cell dies.
• It is also a highly selective permeability barrier; can concentrate specific metabolites and excrete waste material

Question 2

What happens if the cytoplasmic membrane breaks?

Answer 2

• If the membrane breaks, the integrity of the cell is destroyed, cytoplasm leaks into the environment, and the cell dies.

Question 3

Describe the structure of the bacteria cytoplasmic membrane.

Answer 3

• The cytoplasmic membrane is a thin structure that surrounds the cell.
• Phospholipid bilayer
o Proteins embedded in it
o Stabilized by hydrogen bonds and hydrophobic interactions
• Phospholipid
o Hydrophobic fatty acid linked to glycerol backbone by ester bond
 Ester bonds are highly reactive (easy to form, easy to break)
o Phosphate component is hydrophilic and interacts with aqueous cytosol or exterior
• Integral membrane proteins

Question 4

What are the functions of the integral membrane proteins?

Answer 4

o Transport in and out
o Chemotaxic
o Enzymes

Question 5

What is the major feature that prokaryotic cell membranes lack compared to eukaryotic cytoplasmic membrane?

Answer 5

• Prokaryotic cell membrane lacks cholesterol and sterols

* The presence of sterols in a membrane strengthens and stabilizes it, making it less flexible

Question 6

What are the membrane-strengthening agents found in prokaryotic cytoplasmic membranes

Answer 6

• Hopanoids (molecules similar to sterols) are found in the membranes of many bacteria
o Likely play a role similar to that of sterols in eukaryotic cells
• Exception: sterols found in mycoplasma (no cell wall) and methanotrophic cells
• Hopanoids not present in archaea

Question 7

What are the major differences between bacterial and archaeal membranes?

Answer 7

• Archaeal lipids lack fatty acids  made up of terpenes instead
o Terpene: long, branched carbon chain composed of repeating units of isoprene (5-carbon hydrocarbon)
• The lipids of Archaea contain ether bonds between glycerol and the terpenes
o Ether bonds are unreactive

Question 8

How do arcaheal membranes ressemble bacterial and eukaryotic membranes?

Answer 8

and outer hydrophilic surfaces and a hydrophobic interior: like Bacteria and Eukarya

Question 9

What are the lipids found in archaeal cell membrane?

Answer 9

1) Glycerol diether
a. 2 terpenes attached to glycerol backbone through ether bond
b. C20 terpene (4 isoprene units) called phytanyl
2) Diglycerol tetraether
a. 2 phytanyl linked tail-to-tail
b. Glycerol backbone and phosphate head
c. Forms a lipid monolayer instead of a lipid bilayer membrane