Section 3: Membrane Structure

Question 1

Membrane Functions

Answer 1

• Separates & maintains living properties of cell: defines the cell
• Internal membranes compartmentalizes the eukaryotic cell
  forms organelles
• Maintains ion and chemical gradients
• Controls material exchange between cell and its environment
• Senses and controls communication between cells
• Malleable: able to change shape

Question 2

What makes a membrane a bilayer

Answer 2

Contains two leaflets (outer and inner)

Question 3

What are biological membranes composed of?

Answer 3

Lipids and proteins

Question 4

Outer leaflet

Answer 4

Part with head groups pointed up.

Question 5

Inner leaflet

Answer 5

Part with head groups pointed down

Question 6

Main membrane lipids:

Answer 6

Phospholipids and sterols

Question 7

Two types of phospholipids:

Answer 7

Glycerophospholipids and Sphingophospholipids

Question 8

Glycerophospholipids

Answer 8

Use glycerol for backbone.

Question 9

Sphingophospholipids

Answer 9

Use sphingosine for backbone.

Question 10

Head structure of Glycerophospholipids

Answer 10

• Glycerol backbone part of hydrophilic head.
• One of three carbons of glycerol is covalently attached to a phosphate which is attached to something else.
• Components of head group are polar sometimes charged.
• Phosphate group has negative charge on it.
• Phospho-head group linked to position 3 of glycerol (hydrophilic)

Question 11

Tail structure of Glycerophospholipids

Answer 11

• Two fatty acid chains esterified to positions 1 and 2 of glycerol (hydrophobic).
• One fatty acid chain is typically cis-unsaturated, forms kink, reduces packing and rigidity

Question 12

Phosphatidylcholine

Answer 12

Head group attached to phosphate (-) is a choline (+) molecule (overall uncharged).

Question 13

Phosphatidylethanolamine

Answer 13

Head group attached to phospahte (-) is ethanolamine (+) molecule (overall uncharged).

Question 14

Phosphatidylserine

Answer 14

Head group attached to phosphate is serine amino acid has - and + parts (overall negative charge).

Question 15

Cholesterol Structure

Answer 15

Major component of membranes (30%).
Has planar ring structure.
* Polar head group, hydrophobic steroid 4 rings, & nonpolar hydrocarbon hydrophobic tail.

Question 16

Cholesterol functions in the phospholipid

Answer 16

• Creates barrier to movement of lipids.
• Creates density in membrane that decreases permeability to water.
  If density increases, less water escapes through.
• increases packing of phospholipids.

Question 17

What drives the bilayer formation nature of phospholipids?

Answer 17

Shape/amphiphilic nature of phospholipid drive bilayer formation.
Shape: size of hydrophobic components is same as head.
Only way to pack them is in two sheets.
Amphiphilic: Exclusion of hydrophobic tails from water is driving force.

Question 18

Why is spherical bilayer most energetically favorable?

Answer 18

• Flat Membrane bilayer has minimum of hydrophobic molecules exposed to water -Except at edges
• Sphere of membrane bilayer has no edges where hydrophobic molecules are exposed to water.

Question 19

Liposomes

Answer 19

Spherical bilayers