Chapter 12

Question 1

What are the common features of biological membranes?

Answer 1

Fluid, semi-permeable, asymmetric, non-covalent structures

Membranes are formed by lipid bilayers and include proteins such as pumps, channels, and receptors

Question 2

What defines eukaryotic cells?

Answer 2

Multiple membrane systems

Eukaryotic cells contain various organelles, each surrounded by membranes

Question 3

What do proteins confer?

Answer 3

selective permeability

Question 4

What makes membranes hydrophobic?

Answer 4

Fatty acids

Fatty acids are carboxylic acids with long hydrophobic tails

Question 5

What are the four different nomenclatures for fatty acids?

Answer 5

• Saturated: dodecanoic acid (12:0)
• One double bond: dodecenoic acid (12:1)
• Two double bonds: dodecadienoic acid (12:2)
• Position of the double bond: Δ#

These nomenclatures help in identifying the structure and characteristics of fatty acids

Question 6

Lipids are amphiphilic, meaning they…

Answer 6

have both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region within the same molecule

Question 7

What are the three types of lipids important for membrane formation?

Answer 7

• Phospholipids
• Glycolipids
• Cholesterol

Lipids have both hydrophobic parts (fatty acids) and hydrophilic parts (head groups)

Question 8

What is the basic structure of phosphoglycerides?

Answer 8

Glycerol-based phospholipid with C1 and C2 esterified with fatty acids, and C3 esterified with phosphate

Phosphatidate is the simplest phosphoglyceride

Question 9

What is the structure of Phosphatidate?

Answer 9

has a structure consisting of a glycerol backbone with two fatty acid chains attached at the 1 and 2 positions, and a phosphate group attached at the 3 position

Question 10

What characterizes sphingolipids?

Answer 10

Sphingolipids are a class of lipids that are characterized by a long-chain amino alcohol backbone, a fatty acid chain, and a polar head group

Uses sphingosine instead of glycerol and has a second tail attached to an amine

Question 11

What are glycolipids?

Answer 11

Sugar-containing lipids

Sugars are always on the extracellular side of the membrane and are derived from sphingosine. They usually have one or more sugars attached to the primary hydroxyl group of sphingosine

Question 12

What is the structure of cholesterol?

Answer 12

Cholesterol is composed of a central sterol nucleus made up of four interconnected hydrocarbon rings, a non-polar hydrocarbon tail, and a hydroxyl group attached to one of the rings

Question 13

What is the role of cholesterol in membranes?

Answer 13

Interferes with close packing of fatty acids and contributes to the formation of lipid rafts

Cholesterol provides rigidity to the membrane

Question 14

What do the lipids of archaea function for?

Answer 14

Membranes are built to protect from environments

Ether bonds resist hydrolysis
Branched chains resist oxidation

Question 15

Fatty acids form ________, lipids form ________

Answer 15

micelles, liposomes

Question 16

What is the structure of a micelle?

Answer 16

A micelle is a spherical structure with a hydrophobic core formed by the nonpolar tails of amphiphilic molecules (like surfactants), surrounded by a hydrophilic shell composed of the polar head groups

Question 17

What are the function of liposomes?

Answer 17

Liposomes are used to deliver drugs, nutrients, and other substances to cells and tissues

Question 18

What are the three types of membrane proteins?

Answer 18

The three main types of membrane proteins are: integral (transmembrane) proteins, peripheral membrane proteins, and lipid-anchored proteins

Question 19

How do fatty acids self-assemble in solution?

Answer 19

Form micelles and liposomes

Spontaneous self-assembly occurs due to hydrophobic interactions

Question 20

What stabilizes the bilayer of membranes?

Answer 20

• Hydrophobic interactions
• Van der Waals forces
• Electrostatic interactions
• Hydrogen bonds

These interactions help maintain membrane integrity

Question 21

What is the fluid mosaic model?

Answer 21

Describes the lateral movement of lipids and proteins within the membrane

Lateral diffusion is fast, while flip-flop is slow

Question 22

What factors affect membrane fluidity?

Answer 22

• Temperature
• Lipid composition
• Unsaturation of fatty acids
• Chain length
• Cholesterol concentration

Fluidity is crucial for membrane function and can change with environmental conditions

Question 23

What are lipid rafts?

Answer 23

Areas of the membrane made by sphingosine-containing glycolipids and cholesterol that are more rigid than the surrounding membrane

Lipid rafts serve as scaffolds for receptor clustering

Question 24

What is the function of Clathrin?

Answer 24

primarily functions as a structural scaffold, forming a lattice-like coat around membranes to facilitate the formation of small vesicles used for intracellular trafficking

Question 25

How are biological membranes asymmetric?

Answer 25

Different lipid compositions and enzymatic activities on each layer ## Footnote Membrane proteins are inserted asymmetrically, contributing to membrane function

Question 26

What is the significance of the transferrin receptor cycle?

Answer 26

It demonstrates the dynamic nature of membrane proteins and their roles in cellular uptake ## Footnote Understanding receptor cycling is crucial for knowledge of cellular processes

Question 27

What is the function of SNARE proteins

Answer 27

SNARE proteins (Soluble NSF Attachment Protein Receptors) function as the primary mechanism for mediating the fusion of vesicles with target membranes