Lecture 16 - Mem. I

Question 1

Biological membranes are easily dissociable due to______

Answer 1

Non-covalent bonding between phospholipids.

Question 2

What is meant by the “fluid structure” of a membrane?

Answer 2

Lipids readily diffuse LATERALLY, but do not flip from inner to outer leaflets (or vice versa).

Question 3

Describe how micelles are important to biological f(x).

Answer 3

Polar head groups face aqueous environment. The fatty acid tails produce an environment that can “dissolve,” or surround, hydrophobic molecules, like fats.

Question 4

Most phospholipids form a bilayer instead of a micelle. Why?

Answer 4

Though both are driven by hydrophobic forces, most phospholipid fatty acid tails are too bulky to fit in a micelle interior (most micelles

Question 5

Between FA tails, there are _______ interactions.

Answer 5

van der Walls

Question 6

There are _____ and _____ forces between water and polar heads.

Answer 6

Hydrogen bonding; electrostatic

Question 7

Hydrophobic interactions lead to these three “major consequences” in membrane formation.

Answer 7

1) lipid membranes are extensive
2) membranes close on themselves
3) membranes are self sealing (E* favorable)

Question 8

The cholesterol ring structure produces (increased fluidity/stiffness) in a plasma membrane.

Answer 8

Stiffness

Question 9

The hydrocarbon tail associated with a cholesterol molecule produces (fluidity/stiffness) of a membrane.

Answer 9

Fluidity (hydrophobic interactions)

Question 10

In plasma membrane permeability (w/o any channels/transporters), what molecules readily diffuse?

Answer 10

Water (small, no net charge, high [ECF])

Question 11

In plasma membrane permeability (w/o any channels/transporters), what molecules do not readily diffuse?

Answer 11

Large, charged molecules

Question 12

Integral membrane proteins 1* interact with the PM by _______.

Answer 12

Hydrophobic interactions.

Question 13

Integral membrane proteins can be removed from the PM by _______.

Answer 13

Dissociation of the membrane through detergents (disrupts Hydrophobic interactions).

Question 14

Peripheral proteins are bound to the membrane by _____ and ______ interactions.

Answer 14

Electrostatic; hydrogen-bond

Question 15

Peripheral proteins are dissociated from the membrane by ____ and _____.

Answer 15

• pH changes (changes the side chains of the AAs interacting with polar heads)
• salts (interact with the water in solution, causing dissociation and “salting out”)

Question 16

Why are alpha helices the most common membrane spanning motif?

Answer 16

Alpha helices are very flexible (important in the fluid/pliable PM) and have OUTWARD facing hydrophobic R groups due to the helix

Question 17

These proteins are covalently linked to the PM.

Answer 17

Lipid linked proteins

Question 18

Phospholipids that are bound to proteins via sugar linkages.

Answer 18

GPI (glycosyl phosphotidylinositol) linked proteins

Question 19

What critical membrane proteins are found attached by GPI linkages?

Answer 19

Cell adhesion molecules

Question 20

Location of oxidative phosphorylation in the mitochondria.

Answer 20

Inner mitochondrial membrane

Question 21

Site of TCA cycle and fatty acid oxidation

Answer 21

Mitochondrial matrix

Question 22

Which mitochondrial membrane is highly permeable to most ions? Why is this important?

Answer 22

Outer membrane. Important for substrates to be able to readily diffuse.

Question 23

Explain the driving force behind lipid bilayer formation.

Answer 23

The amphipathic nature of phospholipids (polar head, non-polar tail) promotes formation. The polar heads face themselves toward the aqueous environment, and fatty acid tails form a hydrophobic area.