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Bio 209 > Lecture 7 - Membrane Structure and Transport > Flashcards

Lecture 7 - Membrane Structure and Transport Flashcards

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1
Q

General features of the Fluid Mosaic Model: thermodynamic considerations for bilayers, favorability/unfavorability of lateral vs transverse diffusion of phospholipids

A

Fluid: lipids and proteins in membrane can move laterally

Mosaic: comprised of different lipids and proteins

Thermodynamic considerations: phospholipids are amphipathic (polar head, nonpolar tails) => polar heads face water, nonpolar tails face each other

Lateral > transverse diffusion of phospholipids b/c eliminates need for amphipathic parts to flip (otherwise need an enzyme)

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2
Q

Membrane function: Compartmentalization

A

Membranes form continuous sheets that enclose intracellular compartments

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3
Q

Membrane function: Scaffold for biochemical activities

A

Membranes provide a framework (resulting from physical positioning of protein complexes) that organizes enzymes for effective interaction - also creates protective/”reductive” environment that protects proteins + DNA from oxidative stress

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4
Q

Membrane function: Selectively permeable barrier

A

Membranes allow regulated exchange of substances b/t compartments

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5
Q

Membrane function: Transporting solutes

A

Membrane proteins facilitate the movement of substances b/t compartments

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6
Q

Membrane function: Responding to external signals

A

Membrane receptors transduce signals from outside the cell in response to specific ligands

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7
Q

Membrane function: Intracellular interaction

A

Membranes mediate recognition and interaction b/t adjacent cells => important for formation of larger cell-based structures like tissues and organs

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8
Q

Membrane function: Energy transduction

A

Membranes transduce photosynthetic energy, convert chemical energy to ATP, and store energy

Ex: mitochondria and chloroplasts are double membrane

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9
Q

Membrane lipid function and examples

A

For formation of membrane; Ex: Phospholipids, specifically glycerophospholipids

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10
Q

Storage lipid example

A

For energy storage; Ex: Triglycerides (dietary lipids)

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11
Q

Phospholipid structure:

A

Glycerol backbone + (phosphate + head group) + fatty acid tails (saturated/unsaturated)

Head group in glycerophospholipids is alcohol

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12
Q

Fatty acid structure:

A

Carboxyl group attached to hydrocarbon tail (can be saturated or unsaturated)

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13
Q

Effects of temperature on membrane fluidity; compensation mechanism for unicellular organisms

A
  • Less heat => ordered => lower fluidity
  • More heat => disordered => more fluidity

More important for unicellular organisms than multicellular b/c latter have thermal regulation

Unicellular compensation mechanism via enzymes:
If hot -> increase saturated fatty acids, decrease unsaturated fatty acids
If cold -> decrease saturated fatty acids, increase unsaturated fatty acids

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14
Q

Effects of fatty acid saturation on membrane fluidity

A
  • Saturated => straight => ordered => lower fluidity
  • Unsaturated -=> bent/kinks => disordered => more fluidity
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15
Q

Effects of sterols (cholesterol) on membrane fluidity

A
  • More cholesterol insertion => more fluidity
  • Less cholesterol insertion => lower fluidity
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16
Q

Triglyceride structure:

A

Glycerol backbone + 3 fatty acids

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17
Q

Steroid/sterol structure:

A

Polar head + 4 carbon ring steroid nucleus + alkyl side chain

18
Q

Asymmetry of membranes

A

The differences in lipid composition on each layer of the cell membrane bilayer

19
Q

3 membrane proteins:

A
  1. Peripheral proteins
  2. Integral/transmembrane proteins
  3. Lipid anchor proteins (GPI-linked protein)
20
Q

What are lipidation rxns of proteins?

A
  • Specific AA on protein is covalently modified through attachment of various kinds of lipids
  • Attached lipid can insert into bilayer => draws protein to cell membrane => protein localize to membranes via lipidation (or also GPI anchors)
21
Q

What are isoprenylation rxns of proteins?

A
  • Attachment of different sized isoprenyl group
22
Q

Structural features of peripheral proteins

A
  • Can be lipidated
  • Can interact directly w/ phospholipid head group
  • Can interact w/ other proteins (integral proteins)
  • Can be covalently linked to specific lipids (GPI Anchor)
23
Q

Structural features of integral/transmembrane proteins

A
  • Can be alpha helices or beta-sheets/barrels
  • Alpha helices can cross bilayer either once or multiple times
    => if once, usually act as receptor, R groups must have stretches of nonpolar AA (amphipathic alpha-helix)
    => if more than once, usually act as transporter, outer alpha helices must be nonpolar and inner alpha helices must be polar for hydrophilic molecule transport (amphipathic alpha-helix)
24
Q

What is a lipid raft?

A
  • Microdomains in plasma membrane that diffuse laterally
  • Contain clusters of specialized proteins (ex: signal transduction), high cholesterol content, and lipidated proteins
  • Structural and functional unit of various proteins important for certain things
  • Idea of localized signal transduction modules
25
Q

What are hydrophobicity/hydropathy plots?

A

Predict location of transmembrane domains in proteins

26
Q

What is simple diffusion? Effect of polarity and size? Why does this effect exist?

A

Solute diffuses through bilayer down its concentration gradient depending on polarity and size

Polarity and size in increasing diffusion rate (ions < large uncharged polar < small uncharged polar < nonpolar molecules)

Polar/charged molecules often form hydration shell, and removal of such shell is endergonic => high Ea for diffusion

27
Q

What are the types of membrane transport proteins?

A

Transporters (conformational change after solute binds) and channels (aqueous pore)

28
Q

Movement of electrically neutral solutes vs charged solutes

A

Neutral: down concentration gradient until equilibrium reached

Charged: combo of electrical and chemical potential difference

Equilibrium w/o electrical potential across membrane has equal particles and charge on both sides

Equilibrium w/ electrical potential across membrane has unequal number of particles and charges on each side

29
Q

What is passive transport? How do proteins deal with hydration shell?

A

AKA facilitated diffusion; transport of molecules down concentration gradient via transporters or channels w/o ATP

Hydration shell: protein form noncovalent bonds w/ dehydrated solute to replace H-bonding with water or by creating a hydrophilic transmembrane passageway/pore

30
Q

What is active transport? What are the associated forms of energy?

A

Transport of molecules via transport proteins that use a form of energy

Energies: ATP, light, or coupled/cotransport

31
Q

How does coupled/cotransport work?

A

Relies on electrochemical gradient established by a pump

32
Q

3 types of transporter-mediated movement

A
  1. Uniport
  2. Symport
  3. Antiport

Symport and antiport are cotransport

33
Q

3 examples of transporters

A
  1. Glucose transporters
  2. Na+/K+ ATPase
  3. ATP synthase
34
Q

Elaborate on glucose transporter (Glut1)

A
  • Glut1 uniporter
  • Facilitated diffusion (works w/ [glucose] gradient) or cotransport
  • Multi transmembrane domains
  • Amphipathic alpha helices
35
Q

What regulates Glut1 expression?

A

insulin hormone

36
Q

How do amphipathic alpha helices work in transporters?

A

Some residue stretches of alpha helix are polar, others nonpolar

When clustered to higher order, polar residues face transported molecule and nonpolar residues face hydrophobic membrane

37
Q

Elaborate on Na+/K+ ATPase

A
  • Electrogenic pump, primary active transport
  • 3 Na+ pumped out, 2 K+ pumped in => net negative charge inside cell
  • Phosphorylated during transport
  • Kind of like antiport, except both Na and K are pumped against gradients
38
Q

How does Na+/K+ ATPase pump drive glucose uptake into bloodstream? What are the sources of energy for glucose to be transported into bloodstream?

A
  • Cell has negative charge, low sodium, and high glucose
  • Na+-glucose symporter in intestinal lumen is a symporter => sodium enters cell down gradient, glucose against gradient
  • Glucose uniporter (ex: Glut2) facilitates glucose export down gradient into blood

Two sources of energy:
1. [Na+] outside&raquo_space;» [Na+] inside
2. Transmembrane potential (inside negative, draws Na+ inward
=> glucose inside cell&raquo_space;» glucose outside cell

(Refer to slides 58 and 59 lec 7)

39
Q

Elaborate on ATP Synthase

A
  • How eukaryotes make ATP in mitochondria
  • Last step in ETC
  • Fo unit is water insoluble transmembrane proton pore
    -F1 unit is water soluble peripheral membrane protein complex
  • Couples ATP synthesis (endergonic) with passive diffusion of protons through inner mitochondrial membrane (exergonic)
40
Q

Uncoupling of ETC from ATP synthesis generates ________ via pore protein ______ which allows protons to flow down gradient like the ________ of ATP synthase

A

Heat; thermogenin; Fo unit

Bio 209 (10 decks)

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