Exam 2

Question 1

What are defining features of the cell membrane?

Answer 1

1. selectively permeable–>allow specific molecules in and out
2. responsive to the environment–>able to perceive signals from the environment
3. capacity to change shape–> can grow, shrink, or reshape

Question 2

What are cell membranes mostly made up of and what are two traits about these?

Answer 2

lipid molecules, which are amphipathic, and phospholipids are the most abundant type

Question 3

What is the role of bilayers and proteins in cell membrane structure?

Answer 3

-phospholipids spontaneously assemble into bilayers
-proteins are inserted into the membrane after the bilayer has formed

Question 4

What are characteristics of the bilayer?

Answer 4

1. it is fluid, so the lipids can change places within the layer(rarely flip between layers, however)
2. many different types of lipids exist in a bilayer

Question 5

What affects the fluidity of the bilayer?

Answer 5

1. length of the tail
2. number of double bonds in the tail
3. presence of additional lipids
4. temperature
5. composition

Question 6

What affects fluidity?

Answer 6

-the MORE tightly packed the lipids are, the LESS fluid the membrane
-double bonds=unsaturated, no double bonds=saturated
-high temperature increases fluidity, low temperature decrease fluidity
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Question 7

What is the role of cholesterol in the membrane?

Answer 7

-animal cells add cholesterol in order to control membrane fluidity
-helps fill spaces in the bilayer and gives structure
-acts as a fluidity buffer(helps stiffen the bilayer in high temps and create space between lipids in low temperature)

Question 8

Where and how are phospholipids assembled?

Answer 8

-synthesized by enzymes associated with the ER
-synthesized as a single layer that is uneven, and so enzymes called scramblases redistribute the lips to make things even