Module 3: Cells and Membranes

Question 1

Membranes are…

Answer 1

continuous, unbroken sheets, enclosing compartments
- structure allows fusion without losing continuity

Question 2

Eukaryotic cells internal membranes define organelles…

Answer 2

• Nuclear envelope
• Mitochondrial membranes
• Chloroplast membranes
• Lysosomal membrane
• Endoplasmic membrane

Question 3

Membrane Functions

Answer 3

1. Compartmentalization (compartments have different contents and activities)
2. Provide a selectively permeable barrier (prevent unrestricted exchange of molecules)
3. Transporting solutes (exchange of molecules across membrane)
4. Scaffold for biochemical activities
5. Responding to external signals (signal transduction)
6. Intercellular interaction (mediates interaction between cell and neighbors)
7. Energy transduction (conversion of one form of energy into another)

Question 4

Cell membrane is made of the following components…

Answer 4

Lipids
Proteins
Carbohydrates
- composed of two layers of lipids and the major type, phospholipids

Question 5

Phospholipid arrangement

Answer 5

• can arrange themselves spontaneously
• arrangement depends on size of the polar head groups
• if head is large and bulky with 1 hydrophobic tail that is buried, spheres called MICELLES
• if contain smaller heads and have two hydrophobic tails, form BILAYER with a closed structure and inner space
• if added to water form enclosed bilayers called LIPOSOMES
• membranes are self healing and spontaneously rearrange

Question 6

Membranes are dynamic because…

Answer 6

they are continually moving, forming and reforming, said to be fluid

Question 7

Lipids can move…

Answer 7

laterally within the membrane

Question 8

Following features of lipids affect fluidity…

Answer 8

1. length of fatty acid tail, longer = less fluid
2. presence of carbon-carbon double bonds, fewer = less fluid
3. cholesterol, inserts into lipid bilayer of animal cell membranes, can increase or decrease fluidity depending on temperature

Question 9

Lipids are found in the membrane in…

Answer 9

lipid rafts
- move in the plane of membrane but don’t flip flop

Question 10

Several functions of membrane proteins…

Answer 10

1. Transporters that move ions and molecules
2. Receptors that allow cells to receive signals
3. Enzymes that catalyze chemical reactions
4. Anchors that attach to other proteins

Question 11

Two types of Membrane proteins

Answer 11

1. Integral: permanently associated with the membrane and can span entire lipid bilayer (transmembrane)
2. Peripheral: temporarily associated with lipid bilayer or with integral proteins via non covalent bonds, can be in or outside the cell

Question 12

Membrane Carbohydrates

Answer 12

Attached from outside of cell
- covalently linked together
– Protein (glycoprotein)
– Lipid (glycolipid)

Question 13

The membrane is a fluid…

Answer 13

mosaic model
- core of membrane is lipid bilayer
- its a fluid structure that allows molecules to move laterally within the membrane
- contains mixture of different molecules
- dynamic structure, components are mobile and can engage in different interactions