Lecture 3: Membrane fluidity and membrane proteins

Question 1

Compartmentalization

Answer 1

Membrane compartments in the cell allow specialized activities to occur without impacting one another

Question 2

Increasing percentage of saturated fatty acids in a membrane —- fluidity

Answer 2

decrease

Question 3

What is the maximium number of possible double bonds in a fatty acid?

Answer 3

Seems to be 6

Question 4

Cis double bonds and reactivity

Answer 4

• Cis double bonds are more reactive than trans. Reactions that occur in the cell (e.g. oxidation) are important in metabolism and cell signaling.

Question 5

Fluidity determines the physical state of the membrane and is influenced by —

No double bonds*

Answer 5

temperature

Question 6

Transition temperature (3)

What it is + the states

Answer 6

• Below the transition temperature is a cyrstalline gel
• Above the transition temperature is a liquid crystalline phase
• the temperature required to induce a change in the lipid physical state from the ordered gel phase, where the hydrocarbon chains are fully extended and closely packed, to the disordered liquid crystalline phase, where the hydrocarbon chains are randomly oriented and fluid.

Question 7

Transition temperature (and thus fluidity) is influenced by (3)

Answer 7

1. Fatty acid chain saturation (cis- unsaturated fatty acids increase membrane fluidity)
2. Cholesterol Content (Flat rigid, hydrophobic rings impair the movement of the phospholipid fatty acid tails)
3. Fatty acid chain length (shorter fatty acid chains: fewer interactions= less energy to break them apart.)

Question 8

Explain to me the relationship between cholesterol and membrane fluidity (2)

Transition+ the scenario

Answer 8

• Cholesterol eliminates a sharp transition temperature and creates intermediate fluidity
• Cholesterol makes membrane more fluid at lower temperatures (ring interferes with tight packing) and less fluid at higher temperatures (rigid cholesterol impair movement)

Question 9

A balance of membrane fluidity/rigidity is important for (3)

Answer 9

• maintaining structural organization (cell shape) and mechanical support
• Enabling interactions (clusters of proteins) fluid nature allows proteins to move
• Cell movemet, secretion, and endocyctosis (New phospholipid gets inserted into membrane so it can grow/expand)

Question 10

Cells in some organisms can alter their lipid composition in response to changing envrionmental conditions. In response to colder temperatures: (3)

enzyme+shuffle+type

Answer 10

1. Desaturate single bonds in fatty acid chains to double bonds (enzyme desaturase)
2. Reshuffle chains between phospholipids to create those with two unsaturated fatty acids (phosphate head with 2 bent tails as it is usually only one bent)
3. Change the types of phospholipids that it synthesizes (more fatty acids with unsaturated bonds and shorter chain lengths)

Question 11

Proteins are distributed —- across the two leaflets of the membrane bilayer

Answer 11

asymmetrically

Question 12

Three classes of membrane proteins:

Answer 12

1. integral proteins
2. peripheral proteins
3. lipid-anchored proteins

Question 13

Integral membrane proteins

Answer 13

Permanently anchored to or are part of the membrane

Question 14

Transmembrane proteins (3)

What it is+ subset+ includes

Answer 14

• Pass through the lipid bilayer and contain one or more transmembrane domain
• subset of integral membrane
• contains bitopic proteins and polytopic proteins

Question 15

Monotopic protein

Answer 15

Only spans one of the leaflet

Question 16

bitopic proteins

Answer 16

Spans across both leaflets

Question 17

Polytopic proteins

Answer 17

Multiple part of the protein that spans across the bilayer

Question 18

What does transmembrane proteins do? (3)

Answer 18

Act as receptors, channels and roles in electron transport

Question 19

Transmembrane proteins are

Answer 19

amphipathic

Question 20

Tell me about the transmembrane domains (4)

Answer 20

• Transmembrane domains tend to be hydrophobic (form vanderwaals interactions with the fatty acids in the bilayer to keep tight seal)
• Portions of the protein at the surface tend to be hydrophillic
• Interior of channels might also be hydrophilic for polar substances
• takes around 20 (mostly non-polar) amino acids to span both layer of phospholipid membrane

Question 21

Glycophorin A (3)

Answer 21

• single transmembrane domain
• Red blood cell plasma membrane
• bear the antigenic determinants for the MNS blood groups.

Question 22

Pheripheral membrane proteins (4)

bond+trait+how it gets here?+roles

Answer 22

• Associated to the membrane by weak non-covalent bonds (eg: ionic interactions, H-bond)
• Mostly hydrophillic
• Can be recruited to/released from the membrane
• Roles in signal transduction, mechanical support for the membrane, anchor for integral membrane proteins, ezymes

Question 23

Spectrin (2)

Where it is+what it is

Answer 23

• filamentous network required for red blood cells to maintain their shape and elasticity
• on internal surface of the membrane

Question 24

Lipid-anchored proteins (3)

location+bond type+types

Answer 24

• outside the bilayer on either the extracellular or cytoplasmic side
• covalently linked to a lipid molecule in the bilayer
• 2 types: GPI-anchored proteins and hydrocarbon chains embedded in the lipid bilayer

Question 25

GPI-anchored proteins (3)

linkage+ full name+ roles

Answer 25

• Proteins attached to the membrane by a small complex oligosaccharide linked to PI in the membrane
• Glycosyl-PhosphatidylInositol Linkage
• Roles in cell adhesion and as receptors