Membranes

Question 1

Biomembranes

Answer 1

components – lipids, sterols, proteins

amphipathicity –> phospholipid form lipid bilayers

Question 2

Fatty Acids

Answer 2

• long hydrocarbon chain with polar carboxyl head
• Cx:y (double bond = unsaturated)
• increase MP = longer chains
• decrease MP = more unsaturation
• sterols btwn fatty acid chains change MP

Question 3

4 Properties of Biomechanics

Answer 3

1) Fluid
2) Closed Compartments
3) Semi-permeable
4) Asymmetric

Question 4

Fluid

Answer 4

Two Dimensional Fluids

• rapid lateral diffusion
• slow transverse movement

Fluidity

• fatty acid length (cis double bonds)
• steroids
• proteins
• temperature

Question 5

Fluorescent Recovery After Photobleaching (FRAP)

Answer 5

• fluorescent membrane proteins + bleach area

Recovery of fluorescence

• proteins laterally diffuse in/out of bleached area
• no recovery = protein immobile

Question 6

Cytosolic vs Exoplasmic

Answer 6

Plasma membrane

• cytosolic face = internal
• exoplasmic face = external

Vesicle membrane

• cytosolic face = external
• exoplasmic face = internal

Question 7

Passage of Molecules

Answer 7

Small, uncharged, hydrophobic molecules pass freely
- carbon dioxide, oxygen, ethanol, water

Large, charged, hydrophilic molecules can NOT pass
- glucose, potassium, calcium, ATP, proteins

Question 8

Asymmetry

Answer 8

• phospholipid composition differs btwn leaflets
• carbohydrates ONLY on exoplasmic face
• proteins embedded fixed orientation OR on one side

Question 9

3 Types of Proteins

Answer 9

Integral
Lipid-linked
Peripheral

Question 10

Integral Proteins

Answer 10

Cytoplasmic
- Arg+Lys (charged aa anchor protein to bilayer)

Transmembrane
- hydrophobic secondary/tertiary span bilayer

Exoplasmic
- glycosylation (anchors proteins to bilayer)

Question 11

Lipid-linked

Answer 11

Glycosylphosphatidylinositol Anchor – exoplasmic with sugar residues

Acylation of Gly residue – attaches through N-terminal

Prenylation of Cys residue – attaches through C-terminal

Question 12

Peripheral

Answer 12

• bound to other proteins on membrane
• attached through non-covalent interactions
• cytoskeleton filaments can associate with bilayer

Question 13

Insertion of Proteins into Membanes

Answer 13

Topogenic Sequences

• N-terminal signal sequence
• Stop-transfer membrane anchor sequence
• Signal-anchor sequence
• Hydrophobic C-terminus

Question 14

Tail-Anchored Protein

Answer 14

• Get3 recognition of hydrophobic C-terminal tail
• binds to membrane embedded Get1 + Get2
• ATP hydrolysis
• hydrophobic tail insert into PM (no extracellular domain)

Question 15

Type I Protein

Answer 15

N-terminal sequence

• SRP recognizes + brings protein to translocon
• N-terminal remain in ER —> translation

Stop-transfer membrane anchor sequence

• stop transfer + anchors protein
• becomes transmembrane domain

Question 16

GPI-Anchored Proteins

Answer 16

• begin as Type I Proteins (N-terminal in lumen)
• aa sequence near membrane recognized by GPI-transamidase
• cleaves + transfers luminal portion to adjacent GPI

Question 17

Type II Protein

Answer 17

Signal Anchor Sequence

• take protein to lumen + anchors protein
• becomes transmembrane domain
• positively charged aa don’t want go through bilayer
• NH3+ stay in cytosol

Question 18

Type III Protein

Answer 18

Signal Anchor Sequence

• take protein to lumen + anchors protein
• becomes transmembrane domain
• no charged aa –> go through bilayer
• NH3+ enter lumen

Question 19

Type IV Proteins

Answer 19

• positively charged aa next to signal-anchor sequence determines orientation of initial helix
• alternating signal-anchor and stop transfer sequences